DESIGN, DIMENSIONS AND MONITORINGNS AANNDANDAAA D MMMOONMONMMM NG

FISH PASSESPAAASSSSSSSEEEEEEEES PAAAA

Published by theFood and Agriculture Organization of the United Nations

in arrangement withDeutscher Verband für Wasserwirtschaft und Kulturbau e.V. (DVWK)

Rome, 2002

Fish passes – Design, dimensions and monitoring

This book was originally published byDeutscher Verband für Wasserwirtschaft und Kulturbau e.V., DVWK(German Association for Water Resources and Land Improvement)

as DVWK-Merkblatt 232/1996:Fischaufstiegsanlagen – Bemessung, Gestaltung, Funktionskontrolle.

The designations employed and the presentation of material inthis publication do not imply the expression of any

opinion whatsoever on the part of the Food and AgricultureOrganization of the United Nations concerning the legal status of

any country, territory, city or area or of its authorities, orconcerning the delimitation of its frontiers or boundaries.

The designations ‘developed’ and ‘developing’ economiesare intended for statistical convenience

and do not necessarily express a judgementabout the stage reached by a particular country, territory

or area in the development process.

The views expressed herein are those of the authorsand do not necessarily represent those of the

Food and Agriculture Organization of the United Nations.

All rights reserved. Reproduction and dissemination of material in thisinformation product for educational or other non-commercial purposes areauthorized without any prior written permission from the copyright holdersprovided the source is fully acknowledged. Reproduction of material in thisinformation product for resale or other commercial purposes is prohibitedwithout written permission of the copyright holders. Applications for suchpermission should be addressed to the Chief, Publishing Management

Service, Information Division, FAO, Viale delle Terme di Caracalla,00100 Rome, Italy or by e-mail to copyright@fao.org

FAO ISBN: 92-5-104894-0DVWK ISBN: 3-89554-027-7

DVWK ISSN: 0722-7167

English version copyright 2002 by FAOGerman version copyright 1996 by DVWK

Preparation of this publication

This co-publication by FAO and DVWK (German Association For Water Resources and Land Improvement)is a translation of a book that was first published by DVWK in German in 1996.The FAO Fisheries Departmenthas decided to produce the English edition to make available the valuable information contained in thistechnical document on a world-wide scale as no comparable work was so far available, especially as regardsthe close-to-nature types of fish passes.

This document was translated into English by Mr. D. d’Enno, Translator, United Kingdom, and Mr. G. Marmulla,Fishery Resources Officer, FAO, Rome. It was edited by G. Marmulla and Dr. R. Welcomme, FAO Consultantand former staff member of FAO’s Fisheries Department.

The German edition “Fischaufstiegsanlagen – Bemessung, Gestaltung, Funktionskontrolle” was prepared bythe Technical Committee on “Fishways” of the DVWK and published in the DVWK “Guidelines for WaterManagement” that are the professional result of voluntary technical-scientific co-operative work, available foranyone to use. The German edition was financially supported by the German Federal Inter-State WorkingGroup on Water (LAWA).

The recommendations published in these Guidelines represent a standard for correct technical conduct andare therefore an important source of information for specialist work in normal conditions. However, theseGuidelines cannot cover all special cases in which further, or restricting, measures are required. Use of theseGuidelines does not absolve anyone from responsibility for their own actions. Everyone acts at his or her ownrisk.

Acknowledgments

We express our best thanks to Dr. Alex Haro, Ecologist, S.O. Conte Anadromous Fish Research Center,Turners Falls, USA, and Dipl.-Ing., Ulrich Dumont, Floecksmühle Consulting Engineers, Aachen, Germany,who kindly assisted with the revision of the translation. We also acknowledge with thanks the kind support byMr. D. Barion, DVWK, and Mr. W. Schaa, State Agency for Water and Waste Management – District ofCologne, Branch Office Bonn, as well as Drs B. Adam and U. Schwevers, Institute for Applied Ecology, Kirtorf-Wahlen (all Germany).

The most particular thanks are due to Mr. G. Ellis, Rome, who patiently prepared the layout in a veryprofessional manner.

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FAO/DVWK.Fish passes – Design, dimensions and monitoring.Rome, FAO. 2002. 119p.

Abstract

Key words: fish pass; fishway; fish ladder; technical fish passes; close-to-nature types; hydraulic calculation;upstream migration; free passage; river rehabilitation; restoration; longitudinal connectivity; monitoring

Many fish species undertake more or less extended migrations as part of their basic behaviour. Amongst thebest known examples in Europe are salmon (Salmo salar) and sturgeon (Acipenser sturio), which often swimseveral thousands of kilometres when returning from the sea to their spawning grounds in rivers. In additionto these long-distance migratory species other fish and invertebrates undertake more or less short-term orsmall-scale migrations from one part of the river to another at certain phases of their life cycles.

Fish passes are of increasing importance for the restoration of free passage for fish and other aquatic speciesin rivers as such devices are often the only way to make it possible for aquatic fauna to pass obstacles thatblock their up-river journey. The fish passes thus become key elements for the ecological improvement ofrunning waters. Their efficient functioning is a prerequisite for the restoration of free passage in rivers.However, studies of existing devices have shown that many of them do not function correctly. Therefore,various stakeholders, e.g. engineers, biologists and administrators, have declared great interest in generallyvalid design criteria and instructions that correspond to the present state-of-the-art of experience andknowledge.

The present Guidelines first refer to the underlying ecological basics and discuss the general requirementsthat must be understood for sensible application of the complex interdisciplinary matters. These generalconsiderations are followed by technical recommendations and advice for the design and evaluation of fishpasses as well as by proposals for choosing their hydraulic dimensions correctly and testing the functioning.Fishways can be constructed in a technically utilitarian way or in a manner meant to emulate nature. Bypasschannels and fish ramps are among the more natural solutions, while the more technical solutions includeconventional pool-type passes, slot passes, fish lifts, hydraulic fish locks and eel ladders. All these types aredealt with in this book. Furthermore, particular emphasis is laid on the importance of comprehensivemonitoring.

These Guidelines deal with mitigation of the upstream migration only as data on improvement of downstreampassage was scarce at the time of the preparation of the first edition, published in German in 1996. Therefore,the complex theme of downstream migration is only touched on but not developed in depth.

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Foreword by FAO

In many countries of the world inland capture fisheries, in their various facets, play an important role insecuring food availability and income and in improving livelihoods either through food or recreational fisheries.Since years, the Food and Agriculture Organization of the United Nations (FAO) does not relent to promotethe concept of sustainability in the use of resources and sustainable development continues to be a highlydesirable goal in all fisheries and aquaculture activities. However, to achieve this objective in capture fisheries,especially, not only improved fisheries management but also sound ecosystem management is needed.

Freshwater is becoming a more and more precious resource and there is increased competition for its use bythe various sectors, e.g. agriculture, fishery, hydropower production, navigation etc., of which fishery isgenerally not the most important one economically. The responsibility for the protection of the aquaticecosystem usually lies outside the fishery and in many cases, the fishery has to be managed within theconstraints imposed by the external sectors. Activities such as dam construction for water supply and powergeneration, channelization for navigation and flood control, land drainage and wetland reclamation foragricultural and urban use all have a profound impact on the aquatic ecosystem and thus on the natural fishpopulations. One of the worst effects of dams and weirs is the interruption of the longitudinal connectivity ofthe river which means that fish cannot migrate freely anymore. This does not only concern the long-distancemigratory species but all fish that depend on longitudinal movements during a certain phase of their life cycle.

The Fisheries Department’s Regular Programme and field-based activities are tailored to providemanagement advise on best practices and help implementing the Code of Conduct for Responsible Fisheriesand the relevant Technical Guidelines. In the framework of the Department’s Major Programme, the InlandWater Resources and Aquaculture Service (FIRI) implements, inter alia, an activity on prevention of habitatdegradation and rehabilitation of inland fisheries, including considerations regarding fish migration andmitigation measures. As normative work under this activity, FIRI gathers, reviews, analyzes and disseminatesinformation in relation to dams and weirs and their interactions with fish and fisheries and promotes therehabilitation of the aquatic environment as an appropriate tool for the management of inland waters.

In the attempt of making aquatic resources more sustainable, FIRI pays special attention to improved fishpassage and restoration of the free longitudinal connectivity as these are important issues on a worldwidescale that attract growing interest. This book “Fish passes – design, dimensions and monitoring” which hasoriginally been published in German by Deutscher Verband für Wasserwirtschaft und Kulturbau e.V., DVWK(German Association For Water Resources and Land Improvement) is an extremely valuable contribution tothe mitigation of obstructed fish passage. It first refers to the underlying ecological basics and discusses thegeneral requirements, that must be understood for the sensible application of the complex interdisciplinarymatters, before it gives technical recommendations and advice for the design of fish passes, the correctchoice of their hydraulic dimensions and the evaluation of their effectiveness. Based on knowledge andexperience from mainly Europe and North America, the book describes the various types of fish passes, withspecial emphasis on “close-to-nature” solutions. Monitoring is dealt with as a key element for success.

The FAO Fisheries Department decided to co-publish the English edition to make widely available thevaluable information contained in this technical document. This is the more important as no comparable bookexisted so far in the Anglophone literature, especially as regards the close-to-nature types of fish passes. It ishoped that this book contributes largely to increase the awareness of the need for unobstructed fish passageand to multiply the number of well-designed and well-dimensioned fish passes around the globe to restorelost migration routes.

Jiansan JIAChief, Inland Water Resources andAquaculture Service (FIRI)Fishery Resources DivisionFisheries Department, FAO

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Great efforts have been undertaken in Germany in the past decades to bring the water quality of surfacewaters back to an acceptable state, defined as “slightly to moderately loaded” according to the Germanbiological water quality classification. Improvements were mainly achieved through the construction of sewagetreatment plants for purifying domestic and industrial sewage. Today efforts in water protection managementare more and more directed towards the restoration of the natural ecosystem functions of the river channel,its banks and the former floodplains. Changes in channel morphology should therefore be reversed as far aspossible, and obstructions that cannot be overcome by migratory fish be eliminated.

In 1986, the responsible Ministers of the five riparian countries of the river Rhine, the third largest river inEurope, and the relevant Directorate of the European Commission set a political agenda for the restoration ofthe Rhine and agreed to undertake actions to enable the return of salmon and other migratory fish to theRhine and its tributaries by the year 2000. To achieve this objective, fish passes were, and still are, requiredin many places, but generally valid design criteria were lacking for the construction of fully functional fishways,particularly for solutions that look natural and blend well with the landscape. To satisfy this demand theGerman Association for Water Resources and Land Improvement, DVWK (Deutscher Verband fürWasserwirtschaft und Kulturbau e.V.), the professional, non-governmental and non-profit body representingGerman experts engaged in water and landscape management, prepared and published these Guidelines in1996. In the meantime the salmon has already been detected again in the river Rhine and some of itstributaries. What a progress!

An interdisciplinary working group of biologists and engineers compiled research results and experiencesfrom Germany and other countries that reflect the current state-of-the-art of technology in this field. With thepublication of these Guidelines in English, the DVWK hopes to contribute to making the experience andguidance on restoring the longitudinal connectivity of flowing surface waters available to hydro-engineers andfishery specialists in other countries. With this book we hope to make a contribution to the transfer ofknowledge across national boundaries, and will be pleased if it gives useful suggestions for the forward-looking management of waters in Europe and world-wide.

Bonn, October 2002Dr. Eiko Lübbe,Chairman of the DVWK’s Standing Committee on International Cooperation.

Foreword to the English edition by DVWK

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1 to the original German publication

Foreword1

Fish passes are of increasing importance for the restoration of free passage for fish and other aquatic speciesin rivers. Such devices are often the only way to make it possible for aquatic fauna to pass obstacles that blocktheir up-river journey. They thus become key elements for the ecological improvement of running waters.

The efficient functioning of fish passes is a prerequisite for the restoration of free passage in rivers. Studiesof existing devices have shown that many of them do not function correctly. Many specialists have thereforedeclared great interest in generally valid design criteria and instructions that correspond to the present state-of-the-art of experience and knowledge.

A specialized Technical Committee set up by the German Association for Water Resources and LandImprovement has determined the current state-of-the-art technology for construction and operation of fishpasses, through interdisciplinary co-operation between biologists and engineers. Research results andreports from other countries have been taken into account.

The present Guidelines first refer to the underlying ecological basics and discuss the general requirementsthat must be understood for sensible application of the complex interdisciplinary matters. These generalconsiderations are followed by technical recommendations and advice for the design and evaluation of fishpasses as well as by proposals for choosing their hydraulic dimensions correctly and testing the functioning.

In preparing these Guidelines it became clear that some questions, particularly those related to the designand integration of fish passes at dams used for hydroelectric power production, could not be answered tocomplete satisfaction. The reasons are, firstly that there is little reliable data on the functioning of fishways andthat the behaviour of fish in the vicinity of fish passes needs further study. Secondly, defining the dimensionsof close-to-nature constructions by applying the present hydraulic calculation models can only provide roughapproximations. There is thus still a considerable need for research that would fill such gaps in our knowledge.For the same reason, it is, unfortunately, not possible to respond immediately to the wish for recommendingstandards for fish guiding devices and downstream passage devices that many professionals concerned withthe subject have expressed.

The Technical Committee was composed of the following representatives of consulting firms, engineeringconsultants, energy supply companies, universities and specialized administrations:

ADAM, Beate Dr., Dipl.-Biol., Institut für angewandte Ökologie (Institute for Applied Ecology),Kirtorf-Wahlen

BOSSE, Rainer Dipl.-Ing., RWE Energie AG, Bereich Regenerative Stromerzeugung (KR)(Rhenish-Westphalian Electricity Board, Department for Regenerative ElectricPower Generation (KR)), Essen

DUMONT, Ulrich Dipl.-Ing., Ingenieurbüro Floecksmühle (Floecksmühle Consulting Engineers),Aachen

GEBLER, Rolf-Jürgen Dr.-Ing., Ingenieurbüro Wasserbau und Umwelt (Hydraulic Engineering andEnvironment Consulting Engineers), Walzbachtal

GEITNER, Verena Dipl.-Ing., Ingenieurbüro Prein-Geitner (Prein-Geitner Consulting Engineers),Hildesheim

HASS, Harro Dipl.-Biol., Fischereidirektor, Niedersächsisches Landesamt für Ökologie, DezernatBinnenfischerei (Lower Saxony Regional Authority for Ecology, Department forFreshwater Fishery), Hildesheim

KRÜGER, Frank Dr.-Ing., Landesumweltamt Brandenburg, Referat Gewässergestaltung, Wasserbauund Hochwasserschutz (Brandenburg Regional Environmental Authority,Department for River Design, Hydraulic Engineering and Flood Protection),Frankfurt/Oder

RAPP, Robert Dr.-Ing., Abteilungsdirektor, Bayerische Wasserkraftwerke AG BAWAG (BavarianHydroelectric Company BAWAG), Munich

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SANZIN, Wolf-Dieter Dr., Dipl.-Biol., Regierungsdirektor, Bayerisches Landesamt für Wasserwirtschaft(Bavarian Regional Authority for Water Management), Munich

SCHAA, Werner Dipl.-Ing., Regierungsbaudirektor, Staatliches Umweltamt Köln, Außenstelle Bonn(State Agency for Water and Waste Management – District of Cologne, BranchOffice Bonn), Bonn, (President of this Technical Committee)

SCHWEVERS, Ulrich Dr., Dipl.-Biol., Institut für angewandte Ökologie (Institute for Applied Ecology),Kirtorf-Wahlen

STEINBERG, Ludwig Dipl.-Biol., Oberregierungsrat, Landesanstalt für Ökologie, Bodenordnung undForsten/Landesamt für Agrarordnung Nordrhein-Westfalen, Dezernat für Fischerei(North Rhine-Westphalian Agency for Ecology, Land and Forestry/North Rhine-Westphalian Office for Agricultural Development in Recklinghausen (LÖBF),Department for Fisheries at Kirchhundem-Albaum), Kirchhundem-Albaum (Vice-President of this Technical Committee).

Herewith the Technical Committee wishes to thank the representatives of fishery associations, angling clubs,the Society of German Fishery Administrators and Fishery Scientists, the dam operating companies andexperts from public authorities and administrative bodies who have supported the work of the TechnicalCommittee through special contributions and advice. All those who sent in constructive suggestions at thereviewing stage are also thanked.

Bonn, November 1995 Werner Schaa

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Contents

page1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

2 Ecological principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 2.1 Running water ecosystems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 2.1.1 Geology and climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 2.1.2 Water velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 2.1.3 Shear stress and substrate distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 2.1.4 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 2.1.5 Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 2.2 River continuum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 2.3 Biological zoning of running waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 2.4 Potentially natural species composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 2.5 Migration behaviour of aquatic organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 2.6 Hazards to aquatic fauna caused by dams and weirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

3 General requirements for fish passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .213.1 Optimal position for a fish pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 3.2 Fish pass entrance and attraction flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24 3.3 Fish pass exit and exit conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26 3.4 Discharge and current conditions in fish pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 3.5 Lengths, slopes, resting pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 3.6 Design of the bottom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 3.7 Operating times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 3.8 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 3.9 Measures to avoid disturbances and to protect the fish pass . . . . . . . . . . . . . . . . . . . . . . . . .30 3.10 Integration into the landscape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

4 Close-to-nature types of fish passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .314.1 Bottom ramps and slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 4.1.1 Functional principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31 4.1.2 Design and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 4.1.2.1 Construction styles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 4.1.2.2 Plan view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 4.1.2.3 Longitudinal section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 4.1.3 Remodelling of drops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35 4.1.4 Conversion of regulable weirs into dispersed or cascaded ramps . . . . . . . . . . . . . . . . . . . . .35 4.1.5 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36 4.1.6 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37 4.2 Bypass channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41 4.2.1 Principle of functioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41 4.2.2 Design and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41 4.2.2.1 Plan view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42 4.2.2.2 Longitudinal section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42 4.2.2.3 Channel cross-section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 4.2.2.4 Big boulders and boulder sills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43 4.2.2.5 Design of the water inlet and outlet areas of the bypass channel . . . . . . . . . . . . . . . . . . . . . .44 4.2.2.6 Crossings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 4.2.3 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 4.2.4 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47 4.3 Fish ramps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 4.3.1 Functional principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 4.3.2 Design and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 4.3.2.1 Plan view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 4.3.2.2 Longitudinal section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51 4.3.2.3 Body of the ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51

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4.3.2.4 Big boulders and boulder sills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 4.3.2.5 Bank protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 4.3.2.6 Stabilized zone downstream of the fish ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 4.3.3 Special cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53 4.3.3.1 Rough-channel pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53 4.3.3.2 Pile pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53 4.3.4 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54 4.3.5 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55 4.4 Hydraulic design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61 4.4.1 Flow formulae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61 4.4.2 Flow resistance of perturbation boulders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61 4.4.3 Design calculation of boulder sills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64 4.4.4 Critical discharge over bottom ramps and slopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67 4.4.5 Trial runs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68

5 Technical fish passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69 5.1 Pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69 5.1.1 Functional principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69 5.1.2 Design and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69 5.1.2.1 Plan view . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69 5.1.2.2 Longitudinal section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70 5.1.2.3 Pool dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70 5.1.2.4 Cross-wall structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71 5.1.2.4.1 Conventional pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71 5.1.2.4.2 Rhomboid pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 5.1.2.4.3 Humped fish pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73 5.1.3 Hydraulic design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73 5.1.4 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75 5.1.5 Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76 5.2 Slot passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78 5.2.1 Principle of functioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78 5.2.2 Design and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78 5.2.2.1 Top-view plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78 5.2.2.2 Longitudinal section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78 5.2.2.3 Pool dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78 5.2.2.4 Structural characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79 5.2.2.5 Bottom substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80 5.2.3 Hydraulic calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80 5.2.4 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84 5.2.5 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86 5.3 Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87 5.3.1 Functional principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87 5.3.2 Design and dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88 5.3.2.1 Top-view plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88 5.3.2.2 Longitudinal section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88 5.3.2.3 Channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89 5.3.2.4 Cross-channel structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89 5.3.2.5 Water inlet and water outlet of the pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89 5.3.3 Hydraulic calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90 5.3.4 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 925.3.5 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93 5.4 Eel ladders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95 5.4.1 Peculiarities of eel migration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95 5.4.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95 5.4.3 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96 5.5 Fish lock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96 5.5.1 Functional principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96

5.5.2 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97 5.5.3 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97 5.5.4 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98 5.6 Fish lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100 5.6.1 Functional principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100 5.6.2 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100 5.6.3 Overall assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100 5.6.4 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101

6 Monitoring of fish passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103 6.1 Objective of monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103 6.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .103 6.2.1 Fish traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104 6.2.2 Blocking method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104 6.2.3 Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .104 6.2.4 Electro-fishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1066.2.5 Automatic counting equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1066.3 Assessment of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .106

7 Legal requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1097.1 New installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1097.2 Existing installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109

8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .111

9 Table of symbols and signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .115

10 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

Photo credit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118

Appendix: Overview of the most frequently used construction types of fish passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119

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xv

List of Figures and Tables

Fig. 2.1: Adaptations of body forms of fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3Fig. 2.2: Body posture of mayfly larvae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4Fig. 2.3: Changes in flow characteristics in a river at different discharge conditions . . . . . . . . . . . . . . . .5Fig. 2.4: Substrate distribution depending on flow velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5Fig. 2.5: River Continuum Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8Fig. 2.6: Trout zone of the River Felda (Hesse) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10Fig. 2.7: Grayling zone of the River Ilz (Bavaria) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Fig. 2.8: Barbel zone of the River Lahn (Hesse) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Fig. 2.9: Bream zone of the River Oder (Brandenburg) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11Fig. 2.10: Determination of indicator fish zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14Fig. 2.11: Larvae of the caddis fly Anabolia nervosa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15Fig. 2.12: Bullhead (Cottus gobio) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Fig. 2.13: Nase (Chondrostoma nasus) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Fig. 2.14: Salmon (Salmo salar) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16Fig. 2.15: Huchen (Hucho hucho) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18Fig. 2.16: Life cycle of catadromous migratory fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19Fig. 2.17: Life cycle of anadromous migratory fish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19Fig. 3.1: Impassable sudden drop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Fig. 3.2: Culvert under a road . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21Fig. 3.3: Aerial view of the Neef dam on the Moselle River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22Fig. 3.4: Flow pattern in a river . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23Fig. 3.5: Optimum position of a bypass channel and a technical fish pass . . . . . . . . . . . . . . . . . . . . .23Fig. 3.6: Location for the construction of a fish pass at oblique-angled obstacles . . . . . . . . . . . . . . . . .23Fig. 3.7: Position of fish passes at bypass hydroelectric power stations . . . . . . . . . . . . . . . . . . . . . . . .24Fig. 3.8: Fish pass with antechamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Fig. 3.9: Fish pass entrance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25Fig. 3.10: Hydroelectric power station with collection gallery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26Fig. 3.11: Cross-section through a collection gallery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26Fig. 3.12: Different water inlets (fish pass exits) for varying headwater levels . . . . . . . . . . . . . . . . . . . .27Fig. 3.13: Bent fish pass with resting pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29Fig. 3.14: Coarse bottom substrate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29Fig. 4.1: Definitions of types of natural-looking fish passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31Fig. 4.2: River stretch with close-to-nature features as an example to be followed

in the design of natural-looking bottom sills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32Fig. 4.3: Examples of construction types of bottom ramps and slopes . . . . . . . . . . . . . . . . . . . . . . . . .33Fig. 4.4: Bottom slope as rockfill construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33Fig. 4.5: Bottom step as boulder bar construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Fig. 4.6: Plan view of a curved bottom ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34Fig. 4.7: Conversion of an artificial drop into a rough bottom slope . . . . . . . . . . . . . . . . . . . . . . . . . . . .35Fig. 4.8: Conversion of a regulable weir into a supporting sill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35Fig. 4.9: Grossweil/Loisach bottom ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37Fig. 4.10: Bischofswerder plank dam before modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Fig. 4.11: Bischofswerder supporting sill after modification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38Fig. 4.12: Longitudinal section of a bottom step in the Mangfall River . . . . . . . . . . . . . . . . . . . . . . . . . . .39Fig. 4.13: Bottom step in the Mangfall River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39Fig. 4.14: Plan view showing the position of the Mühlenhagen/Goldbach bottom ramp . . . . . . . . . . . . .40Fig. 4.15: Mühlenhagen/Goldbach bottom ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40Fig. 4.16: Bypass channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41Fig. 4.17: Bypass channel at Lapnow Mill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42Fig. 4.18: Examples for securing bottom and banks of bypass channels . . . . . . . . . . . . . . . . . . . . . . . .43Fig. 4.19: A bypass channel with perturbation boulders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Fig. 4.20: Boulder sills for breaking the slope in a bypass channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44Fig. 4.21: Control device at the water inlet of the bypass at Kinsau Lech dam . . . . . . . . . . . . . . . . . . .45Fig. 4.22: Bypass channel in the Varrel Bäke stream near the Varrel Estate . . . . . . . . . . . . . . . . . . . . . .47

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Fig. 4.23: Sketch of position of Seifert’s Mill Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Fig. 4.24: Bypass channel at Seifert’s Mill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48Fig. 4.25: Sketch of position of the Kinsau bypass channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Fig. 4.26: Kinsau bypass channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49Fig. 4.27: Positioning of fish ramps at dams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50Fig. 4.28: Fish ramp at the Krewelin weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Fig. 4.29: Fish ramp at the Eitorf weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51Fig. 4.30: Rough-channel pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Fig. 4.31: Rough-channel pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53Fig. 4.32: Pile pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54Fig. 4.33: Eselsbrücke fish ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55Fig. 4.34: Dattenfeld fish ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56Fig. 4.35: Dattenfeld fish ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56Fig. 4.36: Delmenhorst fish ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57Fig. 4.37: Uhingen rough-channel pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58Fig. 4.38: Fish ramp at the Spillenburg weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59Fig. 4.39: Fish ramp at the Spillenburg weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59Fig. 4.40: Fish ramp at the Spillenburg weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60Fig. 4.41: Fish ramp at the Spillenburg weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60Fig. 4.42: Bypass channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62Fig. 4.43: Sketch to illustrate the example of calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63Fig. 4.44: Hydraulic design calculation of boulder sills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64Fig. 4.45: Fish stream at the Kinsau Lech dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64Fig. 4.46: Drowned-flow reduction factor � . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65Fig. 4.47: Flow at a boulder sill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66Fig. 4.48: Sketch to illustrate the example of calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66Fig. 4.49: Test run at the Eitorf-Unkelmühle fish ramp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67Fig. 5.1: Conventional pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69Fig. 5.2: Pool passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69Fig. 5.3: Pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70Fig. 5.4: Pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71Fig. 5.5: Pool-pass terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71Fig. 5.6: Cross-wall design of a rhomboid pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72Fig. 5.7: Rhomboid pass of the Moselle weir at Lehmen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73Fig. 5.8: Humped fish pass at the Geesthacht dam on the river Elbe . . . . . . . . . . . . . . . . . . . . . . . . . .73Fig. 5.9: Cross-section through the pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75Fig. 5.10: Longitudinal section through pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75Fig. 5.11: The Coblenz/Moselle pool pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76Fig. 5.12: Pool pass at Dahl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77Fig. 5.13: Pool pass at Dahl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77Fig. 5.14: Slot pass with two slots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Fig. 5.15: Slot pass at the Bergerac weir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78Fig. 5.16: Dimensions and terminology for slot passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79Fig. 5.17: Flow velocity distribution in the slot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80Fig. 5.18: Longitudinal section through a slot pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81Fig. 5.19: Detail of slot pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81Fig. 5.20: Slot current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82Fig. 5.21: Water discharge in the slot pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82Fig. 5.22: Discharge coefficient for sharp-edged slot boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82Fig. 5.23: Sketch illustrating the example of calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83Fig. 5.24: Cross-walls of a slot pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84Fig. 5.25: Slot pass at the Spree dam of Neu Lübbenau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86Fig. 5.26: Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Fig. 5.27: Baffles in a Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Fig. 5.28: Characteristic velocity distribution in a Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87Fig. 5.29: Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88Fig. 5.30: Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88

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Fig. 5.31: Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90Fig. 5.32: Relation of h* = f(ho) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90Fig. 5.33: Dimensions of the baffles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91Fig. 5.34: Longitudinal section of a Denil pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91Fig. 5.35: Sketch of the Denil pass at the Unkelmühle hydroelectric power station . . . . . . . . . . . . . . . .93Fig. 5.36: Lower Denil channel with resting pool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94Fig. 5.37: Lower Denil channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94Fig. 5.38: Sea lamprey (Petromyzon marinus) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94Fig. 5.39: Eel (Anguilla anguilla) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95Fig. 5.40: Rhomboid pass with eel ladder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95Fig. 5.41: Eel ladder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96Fig. 5.42: Principle of how a fish lock functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97Fig. 5.43: Fish lock at Schoden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98Fig. 5.44: Fish lock at Schoden . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99Fig. 5.45: Principle of how a fish lift functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100Fig. 5.46: Tuilières fish lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101Fig. 5.47: Entrance to the Tuilières fish lift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101Fig. 6.1: Fish trapping for monitoring purposes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105Fig. 6.2: Marked Salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105Fig. 6.3: Electro-fishing for monitoring purposes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105

Tab. 2.1: Distribution of selected fish species of the indicator fish zones of the water systems of the Rhine, Weser and Elbe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Tab. 2.2: River zoning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Tab. 2.3: Slope classification of the river zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13Tab. 3.1: Average body lengths of adults of some larger fish species . . . . . . . . . . . . . . . . . . . . . . . . . .28Tab. 5.1: Recommended dimensions for pool passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72Tab. 5.2: Minimum dimensions for slot passes with only one slot . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79Tab. 5.3: Water levels and flow velocities at high headwater level . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84Tab. 5.4: Guide values for channel widths and channel slopes in Denil passes . . . . . . . . . . . . . . . . . . .89Tab. 5.5: Guide values for the design of baffles in Denil passes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89

constructing fish passes does not eliminate thebasic ecological damage caused by the dams,such as loss of river habitat or loss of longitudinalconnectivity, this measure attenuates the negativeecological impact of these obstructions to a certainextent and thereby increases their ecologicalcompatibility. For instance, the success of theprogramme begun in the mid 1980s to reintroducesalmon and sea trout in rivers of North Rhine-Westphalia should not be attributed exclusively tothe improved water quality due to the constructionof sewage treatment plants but also to the re-linking of potential spawning waters (the Sieg riversystem) to the main river (Rhine) by building fishpasses at critical obstacles (STEINBERG &LUBIENIECKI, 1991). Moreover, this re-linking ofaquatic ecosystems is an important contribution toefforts to facilitate the recolonization of rivers byendangered fish species and, more generally, tospecies and habitat conservation. Today, therestoration of the longitudinal connectivity of riversis a declared sociopolitical goal. This can beachieved by either decommissioning (i.e. thedemolition) barriers that are no longer required, byreplacing them with bottom slopes or throughconstruction of fish passes.

Fish passes are structures that facilitate theupstream or downstream migration of aquaticorganisms over obstructions to migration such asdams and weirs. While the objective of re-linkingwaterbodies is by no means limited to benefitingfish but rather aims at suiting all aquatic organisms,such terms as “fish ladders”, “fishways”, “fishpasses” and “fish stairs” will be used throughoutthese Guidelines in the absence of a moreappropriate general term that would encompassother aquatic organisms as well as fish. Thisterminology is also to be seen against the historicalbackground since in the past emphasis was laid onhelping fish to ascend rivers. Today, the term“fishway” is used in a broader sense to refer notonly to the fish fauna but to all aquatic organismsthat perform migrations. It further broadens itsmeaning to also include downstream migration - anaspect which is becoming increasingly important.

Fish ladders can be constructed in a technicallyutilitarian way or in a manner meant to emulatenature. Bypass channels and fish ramps are amongthe more natural solutions, while the more technicalsolutions include conventional pool-type passesand slot passes. Apart from the conventional types,special forms such as eel ladders, fish lifts andhydraulic fish locks are also used. TheseGuidelines present the current state of knowledgeon fish passes for upstream migration only and giveadvice on, and instructions for, their construction,

1 Introduction

Many fish species undertake more or lessextended migrations as part of their basicbehaviour. Amongst the best known examples aresalmon (Salmo salar) and sturgeon (Acipensersturio), which often swim several thousands ofkilometres when returning from the sea to theirspawning grounds in rivers. In addition to theselong-distance migratory species other fish andinvertebrates undertake more or less short-term orsmall-scale migrations from one part of the river toanother at certain phases of their life cycles.

Weirs had already been installed during theMiddle Ages in many streams and rivers inEurope to exploit their water power potential.These historical features still constitute anessential component of our cultural landscape.Rivers continue to be subject to further wideranging and intensive anthropogenic uses as aresult of industrialisation and increasing humanpopulations.

Besides such purposes as flood control, navigationand production of drinking water, hydropowerproduction plays an important role in theconstruction of new dams today, especially underthe aspect of the increased promotion of the use ofrenewable energy. Hydro-electric energy istherefore vigorously promoted as a means ofreducing CO2 emission from fossil energy sources.The character and quality of river ecosystems aredeeply affected when obstacles such as dams andweirs are placed across a river. The construction ofdams and weirs results in the flooding of entiresections of rivers that are thus transformed intowater storage impoundments and lose their riverinecharacter. Moreover, these obstacles interrupt thelongitudinal connectivity of a river so thatunhindered passage for aquatic organisms is nolonger ensured. This, together with other factorssuch as water pollution, leads to a decrease in thepopulation size of some fish species (e.g. salmon,sturgeon, allis shad), sometimes to levels close toextinction.

The negative effects of man-made barriers such asdams and weirs on migratory fishes were knownearly on. For instance, in the thirteenth century theCount of Jülich delivered a writ for the Rur (tributaryof the Maas in North Rhine-Westphalia) orderingthat all weirs should be opened for salmonmigrations (TICHELBÄCKER, 1986). Certainlysuch radical solutions are no longer practical today,but present-day obstacles can be made passableby the construction of fish passes. Although

1

operation and maintenance as well as on testingtheir functioning.

Currently there is also a need by management forinformation on the design and construction ofbehavioural barriers for fish (e.g. screens of airbubbles, light, electric current, etc. to prevent fishfrom being sucked into turbines or waterabstraction points#) and devices to help fishdescend (i.e. bypass systems to ensuredownstream migration#). Since there is aconsiderable lack of information on these themesat present, the DVWK has initiated research in thisarea and launched an initiative to prepare otherspecific Guidelines in relation to these issues.Therefore, the theme of downstream migration willonly be touched on in the present booklet but notdeveloped in depth.

2

# explanation added by the editor

3

2 Ecological principles

2.1 Running water ecosystems

Running waters naturally interlink different eco-regions, and are of essential ecologicalsignificance. They are, therefore, rightly called the“vital lines of communication in nature”. Hardly anyother ecosystem exhibits such great structuraldiversity and, as a consequence, features such richand diverse colonization by different species ofplants and animals. But probably also no otherecosystem is used to the same extent for humanactivities or is as highly impacted by pollution orstructural alterations.

The character of an unimpaired running waterecosystem is determined naturally by a complexand extraordinarily complicated structure involvingnumerous abiotic (non-living) and biotic (living)factors. Thus a change in only one of theparameters provokes a chain of very differenteffects on the living communities of running waters(biocoenoses). At present we have little knowledgeof the mechanisms by which such effects areproduced.

The combination of different geophysical, climaticand other abiotic factors has a decisive influenceon the structure as well as on the quality of thedifferent habitats within a river. The followingtherefore describes some of these fundamentalparameters.

2.1.1 Geology and Climate

Different eco-regions, e.g. the lowlands near thecoasts, the highlands and the alpine region,differ fundamentally in their geological andclimatic properties, and therefore, notsurprisingly, the character of the running watersof such regions differs correspondingly. Thehydrological characteristics of rivers as well asthe hydrochemical properties of the water itselfare determined by such factors as altitude,precipitation and the composition of theoutcropping rocks. The slope of the terrain isalso an orographic factor and has a decisiveeffect on the character of other abiotic factors,e.g. water velocity and bottom substratecomposition as well as on the processes oferosion and sedimentation.

2.1.2 Water velocity

Water velocity is the most important determiningfactor in running waters ecologically. The fauna of

running waters live in constant danger of beingswept away by the current, consequently,permanent colonization of running waters is onlypossible for such organisms that have eitherdeveloped mechanisms to withstand the drift or arein a position to move against the current.

In adapting to the various flow characteristics inrunning waters, aquatic fauna have developeddifferent biological strategies for avoiding the lossof territory from downstream drift:

Adaptation of body form

The body shapes of both fish and benthic (bottom-dwelling) invertebrates are optimally adapted to theflow regimes of their respective habitats. Fish in fastflowing upper reaches of streams have torpedo-shaped bodies and thus only offer low resistance tothe current (e.g. brown trout, Salmo trutta f. fario, orminnow, Phoxinus phoxinus), while high-backedfish such as bream, Abramis brama, and carp,Cyprinus carpio, colonize waters with more gentlecurrents (Figure 2.1).

Fig. 2.1: Adaptations of body forms of fish to differentflow velocities (from SCHUA, 1970)(a) Species occurring in the fast flowing

upper reaches of streams: browntrout, minnow, bullhead;

(b) Species occurring in slow flowingriver regions: bream, carp, rudd.

4

primarily by drifting. For example, young bullheadsswim up to 2 km upstream after having beentransported downstream with the current as youngfry when their swimming ability was not yet welldeveloped (BLESS, 1990). The imagoes of someinsect species fly upstream to compensate for theloss of terrain that they had incurred as a result oflarval drift (PECHLANER, 1986). Similarcompensatory migrations are known withfreshwater hoppers (Gammaridae) (HUGHES,1970; MEIJERING, 1972).

Slope is the dominant factor that determines watervelocity (and the current) of morphologicallyunimpaired rivers and hence the general structureof the river channel. Water velocity can also changeconsiderably under the influence of localdifferences in channel width. These dynamicchanges of the river structure are accompanied bythe formation of different current patterns, whichare at the basis of the multiform mosaic-likecharacter of aquatic habitats. Variations in flowregime also alter the living conditions in runningwaters. There are for example areas where gentlecurrents prevail at normal water level but which areexposed to high current velocity during times offlood (Figure 2.3). During the flood aquaticorganisms are swept downstream more easily andthe fauna must balance the loss of terrain bycompensatory movements after flooding abates.

2.1.3 Shear stress and substrate distribution

The energy of running water dynamically remodelsthe channel of natural watercourses by erosion andsedimentation. The shear stress of the watercauses solids to be transported (bed load) andshifted on a large scale. This leads to the formationof different bottom and bank structures as well asdiffering current patterns:

m In meandering and braided rivers, steep cutbanks form at the outer edge of a bend throughremoval of bottom and bank material by erosion,while flat bank deposits are formed at the inneredge by deposition of materials.

m Deposition of gravel, sand and silt locallyreduces the water depth, thus forming shallows.

m Removal of solid materials causes greater waterdepths (deep pools, holes).

m Sections with gentle current alternate with rapidcurrent sections (pool and riffle structures) overrelatively short distances.

m Dynamic shifts in the course of the river channelform bays, blind side arms and backwaters.

Adaptation of behaviour

Many aquatic organisms use active behaviouraladaptations to avoid being carried downstream. Aclear example is mayflies of the genus Baetis thatpress their bodies onto the substrate when thecurrent flows faster and thus only offer slightresistance (Figure 2.2).

Attachment strategies

Many benthic invertebrates attach themselves tothe substrate by means of suckers (leeches andblackfly larvae Simulium spp.), by secretion of spunthreads (midge larvae), or by means of hooks,claws or bristles on their limbs.

Organisms living in areas with gentle current

Areas of gentle current form behind and underlarger stones; the bullhead (Cottus gobio), forexample, uses these areas as shelter. The bullheadseeks direct contact with the substrate and, as itgrows, favours shelters of different sizes dependingon its body size. Fish and numerous invertebrateorganisms find shelter against high water velocityand predators in the rivers’ interstitial space, i.e. inthe gaps between the bottom substrate particles.Thus for example, yolk-sac larvae of the grayling(Thymallus thymallus), protect themselves frompredators by penetrating as deep as 30 cm into theinterstices.

Compensatory migrations

Compensatory migrations are directional movementsthat serve to balance losses of position caused

Fig. 2.2: Body posture of mayfly larvae of thegenus Baetis (from SCHUA, 1970)(a) in weak currents(b) in strong currents

5

Running waters transport solids depending on theirgrain size (Figure 2.4). At high water velocities andcorrespondingly high shear stress at the bottom,even large substrate particles are carried along bythe current. When there is a decrease in the shearstress, the coarse substrates are the first tosediment out while finer fractions are carried onuntil even these are deposited in zones of reducedcurrents. Accordingly, in natural or nearly naturalrivers the substrate shows a mosaic distributioncorresponding to the different currents and iscolonized by different living communities(biocoenoses), each with their own specific habitatrequirements. Because the habitat requirements formany species can alter considerably during theirlife cycles, this differentiated substrate is anessential precondition for a rich variety of speciesto populate running waters:

m Many fish species, e.g. brown trout (Salmo truttaf. fario), grayling (Thymallus thymallus), barbel(Barbus barbus), and riffle minnow (Alburnoidesbipunctatus) require gravel beds composed ofspecific substrate particle sizes to spawn on.

m The larvae (ammocoetes) of brook, river andsea lampreys (Lampetra planeri, Lampetrafluviatilis, Petromyzon marinus) need, inaddition, fine sedimentary deposits where theyare burrowed and develop over many yearswhile feeding by filtering organic material fromwaters flowing over them.

m The nase (Chondrostoma nasus) feeds bygrazing on algae growing on stones; it thereforeneeds stones and boulders while feeding and agravel substrate for spawning.

fine and middle grade sands

gravel, stones d > 6 cm

alderroots

y32

0.740.700.600.50

0.400.30

0.20

0.10

glacial sands and gravel

1

z

0

0.3

0.2

0.1

detritus layer isotachs, v in m/s

Fig.2.3: Changes in flow characteristics in a river at different discharge conditions(a) at low water level: slow velocities; the water flows round obstacles (b) at high water level: high velocities; the water flows over obstacles

Fig. 2.4: Substrate distribution depending on flow velocity

6

frequently not due to toxic substances (cyanide,pesticides, etc.) but rather to a lack of oxygenarising from the oxygen-consuming breakdown oforganic matter such as sewage or liquid manure.The oxygen content of the water, which in turn isclosely linked to the water velocity and current,exerts a considerable influence on the colonizationof running waters by aquatic organisms:

m Invertebrates that are adapted to high oxygenlevels in the headwaters of streams, meet theirtotal oxygen demand by diffusion over the bodysurface. Due to the rapid current, an intensivesupply with oxygen-rich water is guaranteed tosatisfy breathing needs, so that differentstonefly larvae for example, have not developedany special organs (gills) for absorbing oxygen.

m Species such as, for example, mussels (bivalves),the larvae of mayflies (Ephemeroptera) andcaddis flies (Trichoptera) that live in riverstretches with more gentle currents have gillsas breathing organs that facilitate theexchange of oxygen.

m Some benthic organisms such as, for example,midge larvae (Chironomidae) and tube worms(Tubifex tubifex) have haemoglobin in their bodyfluids as a special adaptation to habitats withchronic oxygen deficiency. Haemoglobin has ahigh capacity to bind oxygen, so that thoseorganisms endowed with it are able to meettheir oxygen demand even in a low-oxygenenvironment.

m Also some fish species have developedadaptations to different oxygen levels in thewater. Species such as brown trout (Salmotrutta f. fario) and minnow (Phoxinus phoxinus)that live in the upper reaches of streams(rhithron), where the water remains cool even insummer, have at their disposal sufficient oxygenall year round if the waters are natural andunpolluted. Therefore, these species havecomparatively low-performance gills and thushave to rely on a good oxygen supply from thewater: brown trout cannot tolerate oxygenconcentrations significantly below 9 mg/l forlong periods.

m However, species of the lower reaches of slow-flowing rivers (potamon) are adapted tonaturally occurring oxygen deficits. Forinstance, carp (Cyprinus carpio) can survivein oxygen concentrations of 2 to 3 mg/l.Some indigenous species from loach family(Cobitidae), for example spined loach (Cobitistaenia), weather-fish or bougfish (Misgurnusfossilis) and stoneloach (Noemacheilus

2.1.4 Temperature

The temperature of running water is of specialimportance to the limnetic biocoenosis. Manyspecies are adapted to a narrow temperature rangefor their metabolic functions and normal behaviour.Such species can only tolerate a limited degree ofdeviation from their temperature optimum. Even aslight warming of running waters through thermalpollution (input of water warmed up in ponds,cooling water from thermal power stations, etc.) orwarming of impounded waters through intensesolar radiation can limit their colonization by suchtemperature sensitive organisms. Conversely, thereproduction of fish is linked to a minimumtemperature that differs for each species. Whilebrown trout (Salmo trutta f. fario) spawns attemperatures below 5ºC, the reproduction of thenase (Chondrostoma nasus) is only triggered at8ºC, and the reproduction of the minnow (Phoxinusphoxinus) starts at 11ºC. Species typical of thelower river reaches (potamon) such as carp(Cyprinus carpio) and tench (Tinca tinca) onlyspawn at temperatures well over 20ºC. Watertemperatures and temperature variations also playa fundamental role in the migratory behaviour offish (JONSSON, 1991). Thus the smolts of salmonand sea trout in the Norwegian river Imsa prefer tomigrate downstream at temperatures over 10ºC,whereas most adult eels swim down the river attemperatures between 9º and 12ºC. Increasingwater temperatures also trigger upstream migrationof fish. However, too high a water temperaturehinders upstream migration because, when thetemperature exceeds a species specific limit, themetabolism of the fish may be taxed and the fish’sphysical strength may be limited.

2.1.5 Oxygen

Dissolved oxygen plays a significant role in theaquatic environment. Uptake of oxygen throughthe surface of the water under turbulent flowconditions in running waters (i.e. the physicalintake of oxygen) is significant but oxygen is alsoproduced by planktonic and epiphytic algae aswell as higher aquatic plants, through the processof photosynthesis (biological oxygen supply). Thesolubility of oxygen is largely dependent on watertemperature as much less oxygen dissolves inwater at higher temperatures than at lowertemperatures. Organic pollution, which iseliminated by oxygen-consuming microbialdecomposition in the process of self-purificationof rivers, can reduce oxygen levels in the waterconsiderably. In extreme cases this can cause thedeath of aquatic organisms. Fish mortalities are

m In the upper reaches of a stream the oxygencontent is characterized by saturation orsupersaturation. Because of the strong turbulentflow, there is a permanent uptake ofatmospheric oxygen. The oxygen content of thewater in a river drops with the length of itscourse, not least because of the higher watertemperature and slower flow velocity. In thelower reaches, aquatic plants, and especiallyphytoplankton, increasingly influence theoxygen content of the water.

Special cases, e.g. the effects of discontinuousslope development, a rapid increase in dischargebecause of inflowing larger tributaries, or theenergy intake while flowing through lakes, are notconsidered in this generalized model.

The River Continuum Concept illustrates the factthat there is likewise the formation of acharacteristic biological gradient, corresponding tothe alteration of different abiotic factors in thecourse of a river. This gradient can also beunderstood in terms of the biological energy flow inthe river and is the expression of a set pattern ofinput, transport, use and storage of organic matterin the river and its biocoenoses. The biologicalgradient is recognisable as certain species or typesof organisms are replaced by others in acharacteristic sequence along the river course. Thebiocoenoses of a particular reach of a river or evenof the whole river system are thus typicallyinterlinked in a set pattern, and follow, according tothe River Continuum Theory, the common strategyof minimising energy losses within the wholesystem. Thus the biocoenoses of lower reachestake advantage of the incomplete energytransformation of organic material by the upstreambiocoenoses, whereby mainly the organic materialthat is transported downstream is further brokendown (Figure 2.5).

This theory is supported by the fact thatinvertebrates in different parts of the river (upper,middle and lower reaches) utilize different foodelements and exhibit different nutrition strategies.The fundamental bioenergetic influences along theriver continuum consist of both local influxes ofallochthonous materials including organic matterand light as well as the drift of organic material fromthe upper reaches and from tributaries discharginginto the middle and lower reaches:

m The upper reaches are strongly influenced byvegetation on the banks. On one hand this reducesautotrophic production in the river itself throughshading, but on the other provides the river with alarge amount of allochthonous dead organicmatter, particularly in the form of fallen leaves.

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barbatulus) have the ability of intestinalbreathing as an adaptation to habitats withchronic oxygen deficiency. When the oxygencontent of the water is low, these species canswallow air from which oxygen is extracted intheir intestines by a special breathing organ.

2.2 River continuum

The “River Continuum Concept” by VANNOTE et al.(1980) describes the ecological function of riversas linear ecosystems and the effects ofinterruptions of their connectivity. This energy-flowmodel provides a theoretical basis for claiming theintegrity of the linear connectivity of river systemsand is based on the characteristic alteration ofabiotic factors in the course of a river as describedin section 2.1. Aquatic species show adaptations tothe specific living conditions prevailing in anyparticular river reach and form characteristicbiocoenoses that change in a natural successionalong the watercourse as the abiotic factors vary.An idealised model, based on the fundamentalrelations between the gradients of the physicalfactors and the biological mechanisms thatinfluence the composition of living communities inrivers, can be constructed according to thefollowing assumptions:

m The discharge of the river increases constantlyfrom source to mouth.

m The steepness of the slope usually decreaseswith increasing distance from the source.

m The velocity of the current is very high in theupper reaches and decreases steadily towardsthe estuary, where there is a regular tidalreversal of the direction of the current.

m The substrate is graded along the course of theriver in a characteristic manner determined bythe velocity of the current. While the substrate ofthe upper reaches mainly consists of boulders,pebbles and coarse gravel, fine gravel and sanddominate in the middle reaches, and theestuary area is characterized by fine sand, siltand clay substrate.

m The average annual temperature of well under10ºC in the upper reaches of temperate streamsis comparatively low but increases along thecourse of the river. Also the range oftemperature variation continually increasesalong the course of the river. While thetemperature near the source is usually quasi-constant throughout the year, it may varybetween 0ºC in winter and 20ºC in summer inthe lower reaches.

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brown trout

bullhead

grayling

barbel

bream

ruffe

flounder

coarse detritus

P : R < 1

epilithic growth

macrophytes

+

epiphytic growth

P : R > 1

filter feeders and collectors

scrapers

shredders

predators

micro-organisms

relative width of the river

zooplankton

P : R < 1

coarse detritus

phytoplankton

fine detritus

fine

detrit

us

fine detritus

Figure. 2.5 River Continuum Concept: Alteration of structural and functional characteristics of running waterbiocoenoses as a function of the width of the river (From: Bavarian Regional Office for Water Management, 1987)P = primary production; R = respiratory activity; P/R = ratio of primary production to respiratory activity

9

m The significance of the influx from the terrestrialzones decreases with increasing river width. Atthe same time both the autotrophic primaryproduction in the water itself as well as thedownstream transport of organic material fromthe upper reaches increase significantly.

m The physiological differences betweenbiocoenoses of different river reaches arereflected in the ratio of the primary production(P) to the respiratory activity (R) of thebiocoenosis (P/R). In the upper reachesrespiratory activity dominates while in themiddle reaches primary production is moreimportant. In the lower reaches, however, theprimary production is strongly reduced throughincreased water turbidity and greater waterdepth. At the same time, a large amount of fineorganic material, which comes originally fromfallen leaves in the upper reaches, is importedby the flow, so that here again respiratoryactivity predominates over primary production.

The different morphological and physiologicalstrategies of aquatic organisms can be understoodas an expression of their adaptation to the basicfood elements that are present and the prevailingnutritional conditions in the different river stretches.The following feeder types can be distinguished:

m “Shredders”, that use coarse organic material(> 1 mm), such as fallen leaves, and that arereliant on the supporting activity of micro-organisms.

m “Collectors”, that filter small (50 mm – 1 mm)or very small (0.5 – 50 mm) particles from theflowing water or take them up from thesubstrate. Like the shredders, the collectors arealso reliant on the microbial organisms and theirmetabolic products, which they ingest togetherwith the food particles.

m “Scrapers”, that are specialized in grazing onthe algal growth on the substrate.

m “Predators”, that feed on other functional typesof feeders.

In accordance with the specific nutritionalconditions (P/R < 1), both shredders and collectorstogether dominate the invertebrate biocoenoses ofthe upper reaches. Scrapers are mainly to be foundin the middle reaches (P/R > 1). As the river widthincreases and as the food particle size decreasessignificantly, the collectors again gain importance inthe biocoenoses of larger rivers. The proportion ofpredators only changes slightly in the course of theriver, but the species composition differs. We thushave:

Upper reaches: shredders and collectors

Middle reaches: scrapers

Lower reaches: collectors

Fish communities also show a characteristicsequence along the course of the river. Cold-waterfish communities of the upper reaches, which arecomposed of few species, are successivelyreplaced by warm water communities with highspecies diversity. The species in the upper reachesmainly feed on invertebrates (are invertivores),while the fish communities of the middle reachesconsist of both invertivores and piscivores (eatingother fishes). Plankton-eating (planktivore) speciesare limited to the lower reaches of large rivers. Wethus have:

Upper reaches: invertivore fish

Middle reaches: invertivore and piscivore fish

Lower reaches: planktivore fish

The basic prerequisite for the functioning of thismodel is that the animal communities can alter andadapt to local conditions without problems inaccordance with the dynamics of the system. Forexample individual species should be free tosearch for suitable feeding grounds in accordancewith their life cycle and the seasonal conditions.This requires unhindered upstream anddownstream passage for organisms in the relevantriver stretches. Disturbances of the biologicalenergy influx, for example through lack of shrubson the banks, or disturbancies of the energy andmaterial flows due to damming, as well asdisturbances in the formation of biocoenoses, thatare typical of a certain ecosystem, undoubtedlyhave a negative influence on the colonization of thewhole river system. Interruptions of the rivercontinuum, and thus of the circulation of materialsin the river, lead to changes in the energy balance.

2.3 Biological zoning of running waters

Knowledge of the interactions between abiotic andbiotic factors in rivers, allows the demarcation ofthe habitats of typical biocoenoses from oneanother within the river continuum, thus permittingthe division of the river into distinct individualzones. This zoning has quite practical implications;for example it provides an essential basis for anecologically oriented fishery and allows thenegative effects of human interventions in a river tobe clearly demonstrated. For fishery purposes, thedifferent river stretches are traditionally classifiedby main indicator fish species that arecommercially significant and that characterise thefish composition of a particular section. Experience

10

shows that fish communities in the upperreaches are mainly composed of brown trout(Salmo trutta f. fario) and grayling (Thymallusthymallus), while the middle reaches are mainlypopulated by barbel (Barbus barbus) and thelower reaches by bream (Abramis brama). Ineach section typical “associated fish species”can be related to these indicator species. Thislongitudinal succession of fish communities (i.e.zonation#), that follows a distinct pattern, wasexemplarily documented by MÜLLER (1950) forthe river Fulda and the same sequence of fishcommunities is present in the Rhine and Elbesystems with, however, some slight differencesin the species composition (see Table 2.1):

m The upper trout zone## is populated by threefish species, i.e. apart from the indicator speciesbrown trout (Salmo trutta f. fario), only the brooklamprey (Lampetra planeri) and the bullhead(Cottus gobio) are found as “associatedspecies”.

m In the lower trout zone (Figure 2.6) the loach(Noemacheilus barbatulus) and the minnow(Phoxinus phoxinus) occur in addition to theabove-mentioned species.

m The grayling zone (Figure 2.7) is alsopopulated by all the species of the trout zonebut the grayling (Thymallus thymallus)dominates over brown trout. Furthermore,numerous other species, such as the chub(Leuciscus cephalus), roach (Rutilus rutilus)and gudgeon (Gobio gobio) are also present.

m In the barbel zone (Figure 2.8) the species ofthe upper trout zone may still occur but not as

breeding populations, while altogetherCyprinidae, such as barbel (Barbus barbus),bleak (Alburnus alburnus), whitebream (Bliccabjoerkna) and nase (Chondrostoma nasus), andthe predators pike (Esox lucius) and perch(Perca fluviatilis) dominate. The range ofspecies in this zone is considerably larger thanthat of the grayling zone.

m The fish coenosis of the bream zone (Figure 2.9)lacks those “associated species” of the graylingand barbel zones that prefer fast currents suchas the riffle minnow (Alburnoides bipunctatus)and minnow (Phoxinus phoxinus). The barbel(Barbus barbus), too, is also only found locallyin stretches of stronger current. Instead, bream(Abramis brama) and other typical still waterspecies such as tench (Tinca tinca), carp(Cyprinus carpio) and rudd (Scardiniuserythrophthalmus) dominate.

m The estuarine zone at the river mouth is calledthe ruffe-flounder zone. This zone is alreadysubject to the influence of the tides. Both,limnetic species such as the ruffe(Gymnocephalus cernua) and the species ofthe bream zone, can be observedsimultaneously with marine species such asthe flounder (Platichthys flesus) and theherring (Clupea harengus).

The biocoenoses of rivers are thus characterisedboth by indicator fish species and associatedspecies. This zonation applies not only to fishbut also to aquatic invertebrates. Thus, even ifthe indicator fish species are absent, as mightbe the case in severely polluted or heavilyanthropologically modified waters, the fish zonecan be identified correctly on the basis of theassociated fish species and invertebrates. For

Figure 2.6Trout zone of the River Felda(Hesse)

# remark by the editor ## remark by the editor: nomenclature of the zones according to Huet, 1949

11

Figure 2.9Bream zone of the RiverOder (Brandenburg)

Figure 2.8Barbel zone of the RiverLahn (Hesse)

Figure 2.7Grayling zone of the RiverIlz (Bavaria)

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Upper Lower Grayling Barbel Bream Ruffe-trout trout zone zone zone flounderzone zone zone

Brown trout (Salmo trutta f. fario) ■■■■■ ■■■■■ ■■■■■Bullhead (Cottus gobio) ■■■■■ ■■■■■ ■■■■■Brook lamprey (Lampetra planeri) ■■■■■ ■■■■■ ■■■■■Stone loach (Noemach. barbatulus) ■■■■■ ■■■■■ ■■■■■ ■■■■■Minnow (Phoxinus phoxinus) ■■■■■ ■■■■■ ■■■■■Stickleback (Gasterosteus aculeatus) ■■■■■ ■■■■■ ■■■■■ ■■■■■ ■■■■■Grayling (Thymallus thymallus) ■■■■■ ■■■■■Riffle minnow (Alburnoides bipunct.) ■■■■■ ■■■■■Dace (Leuciscus leuciscus) ■■■■■ ■■■■■ ■■■■■ ■■■■■Gudgeon (Gobio gobio) ■■■■■ ■■■■■ ■■■■■ ■■■■■Chub (Leuciscus cephalus) ■■■■■ ■■■■■ ■■■■■ ■■■■■Roach (Rutilus rutilus) ■■■■■ ■■■■■ ■■■■■ ■■■■■Barbel (Barbus barbus) ■■■■■ ■■■■■Nase (Chondrostoma nasus) ■■■■■ ■■■■■Bleak (Alburnus alburnus) ■■■■■ ■■■■■ ■■■■■White bream (Blicca bjoerkna) ■■■■■ ■■■■■ ■■■■■Perch fluviatilis) ■■■■■ ■■■■■ ■■■■■Pike (Esox lucius) ■■■■■ ■■■■■ ■■■■■Bream (Abramis brama) ■■■■■ ■■■■■ ■■■■■Ruffe (Gymnoceph. cernua) ■■■■■ ■■■■■ ■■■■■Orfe (Leuciscus idus) ■■■■■ ■■■■■ ■■■■■Rudd (Scardinius erythrophthalamus) ■■■■■ ■■■■■Carp (Cyprinus carpio) ■■■■■ ■■■■■Tench (Tinca tinca) ■■■■■ ■■■■■Anadromous species

Sea trout (Salmo trutta f. trutta) ■■■■■ ■■■■■ ■■■■■ ■■■■■ ■■■■■Salmon (Salmo salar) ■■■■■ ■■■■■ ■■■■■ ■■■■■ ■■■■■River lamprey (Lampetra fluviatilis) ■■■■■ ■■■■■ ■■■■■ ■■■■■Sea lamprey (Petromyzon marinus) ■■■■■ ■■■■■ ■■■■■ ■■■■■Allis shad (Alosa alosa) ■■■■■ ■■■■■ ■■■■■Twaite shad (Alosa fallax) ■■■■■ ■■■■■ ■■■■■Sturgeon (Acipenser sturio) ■■■■■ ■■■■■ ■■■■■Catadromous species

Eel (Anguilla anguilla) ■■■■■ ■■■■■ ■■■■■ ■■■■■Flounder (Platichthys flesus) ■■■■■ ■■■■■ ■■■■■■■■■■ Main distribution area of reproductive populations

■■■■■ Secondary distribution area of reproductive populations

Table 2.1: Distribution of selected fish species in the major fish zones of the water systems of the Rhine,Weser and Elbe (modified after SCHWEVERS & ADAM, 1993)

13

therefore occupy comparable ecological niches.Therefore, the River Continuum model, and thusthe biological zoning of rivers, may in principle beregarded as having world-wide validity.

HUET (1949) showed through systematic studiesof physico-chemical parameters and fishdistribution in numerous rivers, mainly in Francebut also in Belgium, Luxembourg and Germany,that the formation of river zones is primarilydetermined by the current. HUET used both slopeand, as an approximation of discharge, the width ofrivers as a measure of current. The relationshipbetween these two parameters and river zonationare shown in TABLE 2.3. In this table HUET’soriginal data are complemented by differentiatingbetween epi- and meta-rhithron based onexperience from the Weser and the Rhine systems.Figure 2.10 provides a simple means forclassification of river zones based on slope andriver width. This classification is valid for themoderate climates in Central Europe, and thus alsofor all the river systems in Germany (HUET, 1949).

2.4 Potentially natural species composition

In considering the whole spectrum of Europeanfreshwater fish species, it is clear that at presentcertain fish species do not find suitable habitatconditions in many rivers. Thus 51 of the total 70indigenous fish species that could theoretically be

example the barbel zone, which is characterized bya high proportion of isopods (slaters), dipteralarvae (flies) and hirudinids (leeches), by a lowpopulation density of sand-hoppers (amphipods)and caddis flies (trichoptera) and by the absence ofcertain plecoptera species (stoneflies), can bereliably distinguished from the grayling zone(ILLIES, 1958).

In order to emphasize this fact, ILLIES (1961)introduced a generally accepted internationalnomenclature for running waters to replace thezonation based on indicator fish species. He firstdivided running waters into two major categories,brooks (rhithron) and rivers (potamon), which areeach further subdivided into three. For the watersof Central Europe, ILLIES’ nomenclature issynonymous with the classification by indicator fishzones (TABLE 2.2).

ILLIES (1961) showed that sequences ofbiocoenoses comparable to that of the river Fulda,which is typical for Central European waters, alsoexist in the Amazon basin as well as in Peruvianand South African waters. But not surprisingly, thecomponent species are different. However, theindigenous indicator and associated fish species ofthose waters have developed similar strategies tosurvive within the currents to those that haveevolved in the homologous species of the CentralEuropean rivers. They also exhibit the samefeeding habits as do the European fish and

upper reaches upper trout zone epi-rhithron

brook middle reaches lower trout zone meta-rhithron

lower reaches grayling zone hypo-rhithron

upper reaches barbel zone epi-potamon

river middle reaches bream zone meta-potamon

lower reaches ruffe-flounder zone hypo-potamon

Slope [%] for widths of rivers of

< 1 m 1 – 5 m 5 – 25 m 25 – 100 m > 100 m

epi-rhithron 10.00 – 1.65 5.00 – 1.50 2.00 – 1.45

meta-rhithron 1.65 – 1.25 1.50 – 0.75 1.45 – 0.60 1.250 – 0.450

hypo-rhithron 0.75 – 0.30 0.60 – 0.20 0.450 – 0.125 – 0.075

epi-potamon 0.30 – 0.10 0.20 – 0.05 0.125 – 0.033 0.075 – 0.025

meta-potamon 0.10 – 0.00 0.05 – 0.00 0.033 – 0.000 0.025 – 0.000

hypo-potamon Estuary areas influenced by the tides

Table 2.3: Slope classification of the river zones (modified after HUET, 1949)

Table 2.2: River zoning (after ILLIES, 1961)

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present in Germany appear on the Red List ofExtinct or Endangered Species for the FederalRepublic of Germany (BLESS et al, 1994). Becauseof the continuing improvements in water quality andthe extensive efforts in ecological upgrading ofaquatic biotopes, the number of fish species thatare able to recolonize lost terrain is increasing.

For some years now, there have been an increasingnumber of reports of the return of migratory fishspecies to various river systems from which theyhad been absent for decades. The assumption thatthe positive development of stocks of even severelyendangered species progresses steadily is justifiedby the fact that populations of sea trout (Salmotrutta f. trutta), flounder (Platichthys flesus) and riverlamprey (Lampetra fluviatilis) have been shown tobe steadily increasing. Furthermore spawning sealampreys (Petromyzon marinus) have beenreported from the Sieg river and sturgeons(Acipenser sturio) have been caught in the Dutchestuary of the Rhine (VOLZ & DE GROOT, 1992).Thus, the hope that once barren waters can berecolonized, even with “ecologically demanding”fish species, appears to be realistic.

Both the fauna actually present and those speciesthat could potentially recolonize a certain riversector within a reasonable time have to be takeninto account to ensure that sufficient considerationis given to ecological interests in planning watermanagement and hydraulic engineering measures.The concept of a “potential natural fish speciescomposition” of a certain ichthocoenosis can beused, to facilitate such planning. Here all speciesshould be included that were originally indigenousin a certain river sector and that find there atpresent, or will be able to find there in theforeseeable future, a suitable habitat. The re-creation of suitable habitats can be achievedthrough improvements in water quality, structuralrehabilitation of the river and the restoration of thelongitudinal connectivity of a river system.

Different aspects should be considered indetermining the potentially natural fish speciescomposition. Since the accurate determination ofthe potentially natural fish fauna is an essentialprecondition for correct ecological evaluation of ariver, it should generally be performed by fisheryexperts according to the following criteria:

m River zoning: The first requirement fordetermining the potentially natural fish speciescomposition is the exact identification of theriver zone (cf. chapter 2.3). A first approximationof the potentially natural species spectrum canbe derived by assigning both indicator andassociated fish species to the selected zone.

m Biogeographical aspects: The specific speciescomposition of the fish communities in thecatchment basin, which depends on both thetypically regional characteristics and the specificproperties of the river, has to be taken intoconsideration in determining the species of thepotential natural fish fauna of any river. Forinstance, the nase (Chondrostoma nasus) isfound in the Central European river systems(from the Loire to the Vistula), but is completelyabsent from both the Weser and Elbe systems aswell as from the rivers in Schleswig-Holstein. Onthe other hand, the distribution of the huchen(Hucho hucho) (Figure 2.15) and several speciesof percidae, such as the little chop (Asprostreber) and the striped ruffe (Acerinaschraetzer), are exclusive to the Danube system.

m Topographical particularities: Aquaticbiocoenoses reflect special topographicconditions, which must be considered indetermining the potential natural fish fauna. Forexample, no indicator fish zones can be definedfor rivers that flow through lakes, or take theirorigin from lakes, as under these conditions

slope in %

width of the river in meters

5 20 25 40 60 80 100 120 140 160 180 200

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

trout zonetrout zone

grayling zonegrayling zone

barbel zonebarbel zone

bream zonebream zone

small stream river large river

Fig. 2.10 Graphical representation of the relationsbetween slope, river width and river zoningfor determination of indicator fish zones(modified from HUET, 1959). The typicalcore zones are shown in grey; the zoneslying between the grey fields are transitionalzones. However, these transitions take placegradually in rivers.

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their different life stages. Migrations are undertakenboth by fish and by the less mobile benthicinvertebrates (Figure 2.11). Migrations may beeither longitudinal in the main channel, or lateralbetween the main channel and side waters. Whererivers repeatedly form lakes along their course,as for example in the North German lowlands,there is a need for the interlinking of thesedifferent ecosystems to allow the organisms tomigrate so as to satisfy their migration andhabitat requirements. Longitudinal connectivity ofrivers thus has an extremely important role toplay with regard to reproductive exchange as wellas to the spreading of populations and therecolonization of depopulated stretches of river.

Compensatory upstream migration

Terrain losses caused by drifting can be activelybalanced by upstream movements.

Moving between different habitats

Some fish undertake intra-annual migrationsbetween their feeding and resting habitats, orinhabit in the course of their life cycle different partsof a river that offer specific conditions that satisfythe requirements of their different developmentphases. This becomes particularly clear whenlooking at the life cycle of the bullhead (Cottusgobio; Figure 2.12) (BLESS, 1982). The bullhead,being active at night, rests under cover during theday. It therefore seeks hollows in the substrate thatcorrespond exactly to its size. While the adult fishhave a preference for river reaches with rapidcurrent and correspondingly coarse substrate,

mixed biocoenoses occur that are characterisedby stagnant water fish species in the still waterareas of the river and by riverine species in theareas at the lake outlets.

m Quality of the habitats: Additions or absencesfrom the potential natural species spectrum maybe caused by massive human interventions andanthropogenic changes in the river morphology.For example, many rivers of the barbel zone,e.g. the Moselle and the Main, are impoundedfor almost their entire course with cascades ofdams. Similarly, if there is also no possibility oflateral migration into the tributaries of the barbeland grayling zone, the habitats of current-dwelling species are damaged to such a degreethat recolonization by these species appearsunrealistic for the foreseeable future. On theother hand, still-water species such as carp,which were not indigenous, usually find suitablespawning conditions in dammed rivers andcolonize these waters with permanent andreproductive populations.

m Historical evidence: Indications of thepotential natural fish fauna are usually obtainedfrom historical sources (v. SIEBOLD, 1863;WITTMACK, 1876; LEUTHNER, 1877; v. d.BORNE, 1883 and others), or from analyses ofhistorical catch reports. Typical examples of thelatter are the one carried out for thereconstruction of the former area of distributionof sturgeon in the Rhine system byKINZELBACH (1987), or the investigations ofKLAUSEWITZ (1974a, 1974b, 1975) of theoriginal fish fauna of the Main by scrutinizing oldfish collections. Some caution is needed ininterpreting such historical records as thespecies mentioned are usually those mostexploited by fisheries, while such small fish asbitterling (Rhodeus sericeus amarus),bougfish (Misgurnus fossilis) and white asp(Leucaspius delineatus), although ecologicallyimportant, are rarely mentioned. Furthermore,the lack of a standard German nomenclatureacross the different regions of the countryinvolving the same name being used fordifferent species causes considerabledifficulties in the interpretation of historicalsources. For example the German words“Schneider” [cutter] and “Weißfisch” [whitefish] have each been used to designatedifferent fish species in different regions.

2.5 Migration behaviour of aquatic organisms

Fish rely on migrations to satisfy their requirementswith regard to the structure of the biotope during

Fig. 2.11: Larvae of the caddis fly Anabolia nervosa ina fish pass in the Dölln river (Brandenburg)

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Figure 2.14:Salmon (Salmo salar)

Figure 2.13:Nase (Chondrostoma nasus)

Figure 2.12:Bullhead (Cottus gobio)

17

young fish, during their growing phase, find theiroptimal habitat in areas with gentle currents andfine grained substrates. Such differing substrateconditions do not often exist very close to eachother, particularly in waters that have beeninfluenced by anthropogenic activities, so thatmoving between habitats at different stages duringthe life cycle may involve migrations over longdistances. A range of activity of up to 300 km hasbeen proven for nase (Chondrostoma nasus)(Figure 2.13) and barbel (Barbus barbus)(STEINMANN, 1937).

At the end of summer different fish species moveinto winter habitats. These are usually located inthe lower reaches of rivers and thus in deeperstretches with more gentle currents. There fishmove down to the bottom of the river where theystay for hibernation while reducing theirmetabolism.

Spawning migration:

Spawning migrations are a special type of migrationbetween different parts of a species’ range. Theyare undertaken by most indigenous fish specieswithin the river system in which they live. Knownexamples are the barbel (Barbus barbus) and browntrout (Salmo trutta f. fario). If spawning migrationsare blocked by impassable obstructions, the fishmay spawn in parts of the river where conditions areless suitable (emergency spawning). This results inlower recruitment or complete failure ofreproduction with subsequent extirpation of thespecies from the habitat.

Diadromous migration behaviour:

The life cycle of diadromous migratory fish speciesincludes obligatory movement between marine andfreshwater ecosystems. The necessity ofunhindered passage through the river system canbe well demonstrated on the basis of the biologicalrequirements of such diadromous migratory fish.Interruption of the migratory routes inevitably leadsto extinction of the populations. With regard to thedirection of migration, two groups of migrants canbe distinguished:

m Catadromous species, such as the eel (Anguillaanguilla), migrate downstream as adults toreproduce in the open sea. With eels,reproduction takes place exclusively in theSargasso Sea, and the willow-leaf-shaped larvae(leptocephali) drift passively with the sea currentsinto coastal regions. After metamorphosis, the asyet unpigmented young fish (“glass eels”) migrateupstream, where they develop until they aresexually mature (Figure 2.16).

m Anadromous species, such as salmon (Salmosalar) (Figure 2.14), sea trout (Salmo trutta f.trutta), sturgeon (Acipenser sturio), allis shad(Alosa alosa), sea lamprey (Petromyzonmarinus) and the river lamprey (Lampetrafluviatilis) migrate from the sea into rivers whenthey are sexually mature in order to spawn inthe upper river reaches. In turn, the young fishmigrate back to the sea after a certain timewhere they then grow until they are sexuallymature (Figure 2.17).

Population exchanges:

The balancing of differing population densities inneighbouring river stretches takes place throughupstream or downstream migrations and leads togenetic exchange between populations.

Downstream migrations:

Downstream migrations fulfil yet another essentialbiological function in addition to that of spawningmigrations of eels or the downstream migration ofsalmon and sea trout smolts. For example whenecological catastrophes happen, such as severefloods or discharges of pollutants, benthicinvertebrates in particular can drift downstream(i.e. a so-called “catastrophic drift”). In all casesirrespective of whether migrations are activelyundertaken (i.e. escape) or passively endured, theaquatic organisms thus depend on adequate freelongitudinal connectivity.

Propagation:

The mobility of aquatic organisms plays a criticalrole in the recolonization of whole waterbodies andwater courses, or of portions of them that arechronically barren or which were depopulated in asingle catastrophic event. Thus only a short timeafter the Sandoz accident recolonization of thebarren stretches of the Rhine occurred (MÜLLER &MENG, 1990), so that only two years after theaccident the fish populations had recovered and nolonger showed signs of damage (LELEK &KÖHLER, 1990). This rapid regeneration isparticularly attributed to immigration from thetributaries into the river Rhine.

Large freshwater mussels of the family najadae arepeculiar in the way they propagate as they spreadthrough their larval stage (glochidium larvae).These larvae parasitize the gill epithelia or the finsof indigenous fish, and can thus be transported bytheir hosts over long distances in the water systembefore they fall onto the sediment and develop intosexually mature mussels.

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2.6 Hazards to aquatic fauna caused by dams and weirs

The indigenous fish fauna of Germany is subjectedto many threats that have resulted in a severereduction in the stocks of many species. Theprincipal sources of danger of hazards forindigenous fish are the following humaninterventions in aquatic biotopes:

m Water pollution through domestic and industrialsewage discharges, as well as run-off fromagriculture (fertilisers, pesticides, erosion), andatmospheric emissions (SO2, acid rain, etc.).

m Changes in channel morphology that lead toecological degradation or destruction of habitats.

m Disruption of longitudinal connectivity causedby impassable obstacles.

m Effects of fishing activities on fish stocks.

BLESS et al. (1994) found that, due to thesehazards, of the 70 indigenous German freshwaterfish species:

4 species were extinct or missing;

9 species were threatened with extinction;

21 species were severely endangered;

17 species were endangered.

Of the fish species that are extinct, missing orthreatened with extinction, 82% are migratoryspecies, or species with a high oxygen demandrequiring clean gravel for spawning and that canonly live in biotopes with rapid currents (BLESSet al., 1994). Thus, one of the most critical threatsto these species is the damming of rivers. Theextinction of these populations can be blamed on

the interruption of free passage caused byobstacles as well as the formation of artificiallyimpounded waters behind dams and weirs. Theseobstacles undoubtedly alter the hydraulic andmorphological properties of the river to a degreewhich depends on the size and extent of thereservoir. Further threats to aquatic biocoenoses(LWA, 1992) are:

m The increased cross-sections of theimpoundments behind dams and weirssignificantly reduce flow velocity and thevariability of the current.

m Increased sedimentation of fine sediments inthe impoundment that covers the coarsesubstrate so that the original mosaic of differinggrain sizes is altered.

m Many aquatic organisms lose their hyporheicinterstitial habitat as a result of the failure torearrange sediments by the current.

m Flow-through through the interstices of thesubstrate, and thus the availability of oxygen, isreduced. Sedimenting organic matter isincreasingly broken down anaerobically so thatsapropel (i.e. putrefying sludge) builds up,particularly in eutrophic waters.

m The water temperature increases due to thereduced flow velocity and the longer retentiontime of the water in the impoundment.

m Oxygen deficiency can occur in theimpoundment because the water’s capacity tobind oxygen decreases as it warms up andbecause the intake of atmospheric oxygen atthe air/water interface is reduced due to thereduced turbulence.

Figure 2.15:Huchen (Hucho hucho)

19

(Chondrostoma nasus) among fishes, lose theirfeeding grounds.

m The food supply for fish is reduced becauseof an altered and/or reduced range ofinvertebrates.

m The loss of important parts of the habitat leadsto disturbance of the age structure of the fishpopulations thus endangering species.

m The biocoenosis is reduced to those adaptablespecies that have no problem to tolerate thealtered abiotic conditions.

Channel reaches below dams (i.e. the originalnatural main channel#) that fall dry due to theabstraction of water by bypass power stationsconstitute a further problem for aquatic organisms.As at bypass power stations the water is usually re-injected into the channel only at some distancefurther downstream, only little water remains in theoriginal natural channel or the channel might evendry out completely over prolonged periods. Incomparison to intact river sections, these dried-outreaches are extremely impaired with the followingthreats for the biocoenoses:

m A severely reduced flow regime minimizes thevariability of the current, so that only the bottomof the river channel is wetted and pools ofstagnating water are formed (so-called trapeffect). Riverine species can no longer find anadequate habitat.

m Reduced current in the impoundment coupledwith increased nutrient inflow into the watersfavour the growth of aquatic plants oftenresulting in algal blooms or excessive weedgrowth. The photosynthetic production from anexcessive biomass of plants can lead to aconsiderable increase in pH, and thus bears therisk of fish mortality particularly under strongsolar radiation. Furthermore, the massive decayof aquatic plants in autumn can lead to fishmortality through oxygen deficiency or depletion.

m Light penetration to the river bottom isconsiderably reduced at greater water depths;thus growth of periphytic algae is impaired.

m Energy flow, as described in the river continuumconcept, is interrupted by increasedsedimentation of organic matter. This results indisturbances in the metabolic processes in rivers.

These alterations to the habitats in rivers caused bydamming and impoundment have lasting negativeinfluences on the biocoenoses:

m Especially the current-dwelling (rheophilic)species and organisms with high oxygendemand lose their habitat, particularly in largerimpoundments.

m Species that need clean gravel for spawning donot find appropriate spawning grounds, andorganisms living in the interstices, as well asbottom-living fish, lose their shelter.

m Species that feed on periphytic algae, such asthe grazers among invertebrates or the nase

HYPO-RHITRON

Fig. 2.16: Life cycle of catadromous migratory fish:example of the eel (Anguilla anguilla)

Fig. 2.17: Life cycle of anadromous migratory fish:example of the salmon (Salmo salar)

# remark by the editor

m The water in the impacted river reach (i.e. inthe original natural main channel#) is severelywarmed in summer, so that there is a dangerof the reach drying-out completely with aconsequent dehydration of the aquaticorganisms.

m Furthermore, the formation of ground ice(anchor ice) in winter can kill organisms.

m Other physical-chemical parameters also alterdue to the absence of the current, which is thenormal determinant in rivers. This causesfurther changes such as, for example, algalbloom and increased oxygen consumption.

m When the maximum turbine flow-throughcapacity of the hydroelectric power station is

exceeded, i.e. when more water is in the riverthan can pass through the turbines, the rapidlyincreased discharge into the original naturalmain channel that was then almost dry can leadto increased drifting of aquatic fauna.

Establishing minimum flow requirements for theimpaired channel stretch downstream of a damattempts to counter these problems (DVWK, 1995).There are different approaches and regionallydifferent processes for the setting of minimum flowswhich, however, are not further dealt with in theseGuidelines.

20

# remark by the editor

water quality or the interests of current users.Numerous examples show that the degree ofpollution and the use that is made of a waterbodycan change within a very short time, and thatanthropogenic interests can be forced into thebackground. Thus, the restoration of longitudinalconnectivity becomes important even for riverreaches whose present ecological condition allowsonly limited colonization by aquatic organisms. Onthis basis the elaboration of concepts that supportthe interlinking of river systems makes a realcontribution towards sounder river management.However, even individual mitigation measures canfit effectively into the overall, ecologically orientedconcept of the restoration of longitudinalconnectivity (SCHWEVERS & ADAM, 1991).

Free longitudinal passage through rivers is mainlyimpeded, or made impossible, by sudden artificial

3 General requirements for fish passes

Longitudinal connectivity in rivers is criticalecologically to satisfy the diverse migratory needsof aquatic species (Chapter 2.5). It is, therefore, anessential requirement for all waters to whichmigratory species are native. When restoringlongitudinal and lateral connectivity to a riversystem it is ecologically sound practice to link themain channel with backwaters and secondarybiotopes such as waterbodies that were createdafter the extraction of solids (e.g. flooded quarries,gravel pits, peat workings etc.). Longitudinalconnectivity must be conserved or restoredregardless of the size of river, the extent ofstructural modification of the channel, the present

21

Figure 3.1:Even if not very high, suddendrops like the one shownpresent impassable obstaclesto migration for small fish.Lauge stream at Gardelegen(Saxony-Anhalt)

Figure 3.2:Culverts with detached jetsscouring the adjacent streambottom are an impassableobstacle to migration for aquaticorganisms. Pritzhagener Mill inthe Stöbber (Brandenburg)

drops (Figure 3.1), weirs or dams that cannot bepassed by aquatic organisms. Apart from suchstructures, culverts (Figure 3.2) or stretches of riverthat have been intensively modified by concrete-lined channels, paved river bottoms orprefabricated concrete half-shell elements can alsoact as obstructions to migration. Before planning afish pass, the first step must be to question theneed to maintain the existing cross-riverobstruction, since the construction of a fish pass isalways only the “second best solution” for restoringunhindered passage through a river. In smallerrivers, particularly, there are numerous weirs anddams, such as mill and melioration weirs, whoseoriginal purpose has been abandoned but whichstill stop migration of aquatic organisms. Theremoval of such obstacles should be givenpreference over the insertion of a fish pass whenattempting restoration of longitudinal connectivity.Exceptions to this principle may occur whereconflicts arise with other ecological requirements,such as the preservation of a valued wetland by thehigher level of the impounded waters, or withregional socio-cultural needs.

The following basic considerations pertain tofundamental features, such as the optimal locationand design criteria of fishways in a river, which areindependent of the particular type of fish pass. Thegeneral criteria that fish passes should meetinclude the biological requirements and thebehaviour of migrating aquatic organisms and thusconstitute important aspects in planning fishways.However, it has to be pointed out that present-dayknowledge of the biological mechanisms thattrigger or influence migrations of such organisms isstill sketchy and there is a great need for furtherresearch to serve as a basis for criteria for fish passconstruction.

General standards for fish passes include differentindividual aspects that must be taken into accountin planning for the construction of a new dam, inassessing an existing fish pass or in planning forthe fitting of fishways to an existing dam. Theserequirements should take priority over economicconsiderations. Depending on local circumstances,it might well be necessary to build several fishpasses at one dam to ensure satisfactory passageof all species. Statements that are generally validare given preference here over specific solutionsfor individual cases, since each dam has its ownpeculiarities that derive from its configuration andintegration into the river.

3.1 Optimal position for a fish pass

While in rivers, that have not been dammed, thewhole width of the channel is available for themigration of aquatic organisms, fish passes atweirs and dams usually confine migratingorganisms to a small part of the cross section of thechannel. Fish passes are usually only relativelysmall structures and therefore have thecharacteristics of the eye of a needle, particularly inrivers and large rivers (Figure 3.3). In practice, thepossible dimensions of any fishway are usuallyseverely limited by engineering, hydraulic andeconomic constraints, particularly in larger rivers.Thus the position of a fishway at the dam is ofcritical importance.

Fish and aquatic invertebrates usually migrateupstream in, or along, the main current (Figure 3.4and Figure 3.5). For the entrance of a fishway to bedetected by the majority of upstream migratingorganisms, it must be positioned at the bank of theriver where the current is highest. This has theadded advantage that, with a position near the

22

Figure 3.3Aerial view of the Neef dam inthe Moselle River (Rhineland-Palatinate) to show the sizeof the fish pass (see whitearrow) in comparison to thetotal size of the dam.

➡

or turbine outlet. Placing the outflow of the fish pass(and thus its entrance) in the immediate vicinity ofthe dam or weir minimizes the formation of a deadzone between the obstruction and the fish passentrance. This is important, as fish swimmingupstream can easily miss the entrance and remaintrapped in the dead zone. A fish pass that extendsfar into the tailwaters below the dam considerablylimits the possibility that fish find the entrance, adesign fault that has been responsible for thefailure of many fish passes.

Where dams or weirs are placed diagonally acrossthe river and overflow along their entire crest,upstream migrating fish usually concentrate at theupstream, narrow angle between weir and bank(Figure 3.6). Therefore, the fish pass should clearlybe sited in this area.

As regards bypass hydroelectric power stations,there are two options for positioning the fish pass toensure longitudinal connectivity. Firstly the fishpass can be built at the power station, providing alink between the tailwater channel and theheadwater channel. Secondly it can be constructedat the weir, acting as a link between the originalnatural main channel and the headwater of theimpoundment. Usually a fish pass is constructed atonly one of these locations. Since the fish generallyfollow the strongest current, they tend to swim upthe tailwater channel to the turbine outlet ratherthan entering the old main channel through whichthe discharge is usually lower. Construction of a

bank, the fish pass can be more easily linked to thebottom or bank substrate.

The most suitable position for a fish pass athydroelectric power stations is also usually on thesame side of the river as the powerhouse. Thewater outlet of (i.e. the entrance# to) the fish passshould be placed as close as possible to the dam

23

weir

undercutbank

point bar bank

undercutbankpoint bar

bank

main current

Fig. 3.4: Diagram showing the flow pattern in ariver with undercut banks and point barbanks. Fish swimming in or along themain current will arrive at the weir alongthe side of the undercut bank.Consequently, a fish pass should bepositioned as closely as possible to thepoint where the fish meet the obstacle(modified after JENS, 1982).

headwater

tailwater

b) fish pass(technical

construction)

a) bypass channel(close-to-nature

construction)

dam construction

turbulent zone

Fig. 3.5: a) Optimum position of a bypass channeland b) optimum position of a technical fish pass:

Fish migrating upstream are guided bythe main current and swim up to thezone of highest turbulence in thetailwater directly below the dam or theturbine outlet. In the vicinity of the bank,fish seek a way to continue to moveupstream. Most importantly, it must beensured that fish can pass the bottom sillof the stilling basin (modified afterLARINIER, 1992d).

headwater

tailwater

fixed weir

fishway

water outlet(fish pass entrance)

water inlet(fish pass exit)

turbulent zone

Fig. 3.6: Fish moving upstream gather in thenarrow angle between the weir and thebank. This is the most suitable locationfor the construction of a fish pass (afterLARINIER, 1992d).

# remark by the editor

fish pass from the tailwater channel to theheadwater channel is therefore needed in suchcases. However, when the turbine capacity of thepower plant is exceeded, excess water is spillingover the dam into the old main channel, so it is alsoadvisable to install a fish pass at the barrage. Thewater from this second fish pass can also be usedto provide minimum environmental flows in the oldchannel so that running water conditions aremaintained there, provided that the discharge issufficiently high. From an ecological point of view, itis therefore highly advisable in such cases toconstruct two fish passes, one at the hydropowerplant and one at the barrage (Figure 3.7).

3.2 Fish pass entrance and attraction flow

The perception of the current by aquatic organismsplays a decisive role in their orientation in rivers.Fish that migrate upstream as adults usually swimagainst the main current (positive rheotaxis).However, they do not necessarily migrate within themaximum flow but, depending on their swimmingabilities, they may swim along its edge. If migrationis blocked by an obstruction, the fish seek onwardpassage by trying to escape laterally at one of thedam’s sides. In so doing they continue to react withpositive rheotaxis and, in perceiving the currentcoming out of a fishway, are guided into the fishpass.

The properties of the tailrace below a dam (watervelocity and degree of turbulence) influence theattracting current that forms at the entrance to thefish pass. The attraction exercised by the current is

also influenced by the velocity and angle of theemergent flow, as well as by the ratio of riverdischarge to discharge by the fish pass. Theattracting current must be perceptible, particularlyin those areas of the tailrace that are favoured bythe target species or to which the fish are forced toswim due to the tailwater characteristics. Thevelocity at which the attracting current exits the fishpass should be within the range of 0.8 to 2.0 m s-1

(SNiP, 1987).

Particularly where the tailwater level fluctuates, aspecial bypass can be used to channel additionalflow directly from the headwater to the entrance ofthe pass in order to boost the intensity of theattracting current. Using a bypass avoids that theflow characteristics in the pass are negativelyinfluenced by an increased flow within the pass thatis, in fact, only needed at the fish pass entrance.The bypass can be in the form of a pressure pipe,but it is usually better to have an open channel.Under no circumstances should the velocity of thisadditional water, that comes out of the bypass,hinder fish to swimming into the pass. Except forspecial cases flow velocity should not exceed2 m s-1. The addition of an antechamber at the fishpass entrance is described by the RussianStandard Work on fish passes (SNiP, 1987). Suchchambers, that receive water from both the fishpass and the bypass, are now part of manyinstallations in France and the USA. Flows from thedischarge of the fishway and that of the bypass mixin this antechamber to form the attraction current thatejects into the river (Figure 3.8). In this case, the

24

original river bedfish pass(e.g. fish ramp)

fish pass(e.g. vertical slot pass)

powerhouse

impoundment headwater

weir

trailwater

artificial island

Figure 3.7: Ensuring longitudinal connectivity at a bypass hydroelectric power station through constructionof two fish passes, i.e. one directly at the hydropower plant and the other at the weir.

that function well provide the basis for the followingremarks. Theoretical approaches using calculationsto determine the propagation characteristics of theattracting current are provided by the RussianStandard Work (SNiP 1987) and by KRAATZ(1989).

The entrance of the fish pass must be positionedwhere fish concentrate while moving upstream.The characteristics of the tailwater currents andthe structural details of the hydropower stationdetermine the area of concentration. In many casesthis is directly below the weir or dam, at the foot ofthe barrage or at the turbine outlets. Therefore, anycurrent to attract fish must be directed from theentrance to the pass towards the area ofconcentration in such a way that fish, in following

velocity at the water outlet (i.e. the fish passentrance#) must not exceed 2 m s-1 even at low water.

There is an unproved assumption that either theincreased influx of atmospheric oxygen into thewater or the splashing sounds from the water in thefish pass exert a “luring effect” that can be used inoptimising fish pass design. Unfortunately this hasnot yet been substantiated. Technical devices forguiding fish in a certain direction, such asbehavioural barriers or mechanical guidingdevices, are not dealt with in these Guidelines,since no reliable data on the efficiency of suchdevices is yet available. Laboratory experiments onthe effects of lateral inflows into rivers as well asobservations on the behaviour of fish at fish passes

25

powerhouse

fishway withrelatively low

dischargeweir

trash rack

bypass as open channel or closed pipe(can also be used to help fish move downstream)

antechamber turbine outlets

attraction currentwater outlet

(fish pass entrance)

Figure 3.8:Additional discharge is sentthrough a bypass into anantechamber downstream ofthe first pool of the fish passto increase the attractioncurrent at the fish entrance

powerhouse

fish pass(e.g. pool pass)

rough bottom

rough bottomclose to the bank

tailwater

partition pillar

embankment

rock filling to form a ramp

ca.1:1,5 Figure 3.9:Underwater rockfill rampconnecting the fish passentrance with the riverbottom

# remark by the editor

the current, will be drawn to the entrance of thepass and thus enter the fishway.

If possible, the entrance of the fish pass should beat the bank, parallel to the main direction of flow, sothat fish can swim in without altering direction. If theentrance to the fish pass is located too fardownstream of the obstruction the fish will havedifficulty finding it.

The further downstream of the dam that theattracting current flows into the river, the moreimportant it is that this current is clearly perceptibleto fish moving upstream. An adequate attractingcurrent can be obtained by increasing the watervelocity at the entrance to the fishway or by passinga high discharge through the pass itself or byputting additional attraction water through abypass. Model experiments showed that anattracting current that leaves the fish pass entranceat a maximum angle of 45º is most effective for thefish, provided that enough water is available toallow a high discharge through the fishway at a

sufficiently swift velocity. A wider angle projects thejet further towards mid-river but is accompanied bythe risk that the attracting current does notanymore follow the bank and that fish swimmingnear the bank only notice this attracting currentwhen they are right by the entrance.

A critical problem is how to construct the fish passentrance so that fish can swim into the fishwayeven at low water levels. Entry into the fishpass canbe eased, even for bottom-living fish species andmacrozoobenthos, by linking the fish pass to thenatural river bottom. This can be done with a rampwith a maximum slope of 1:2 (Figure 3.9). Someexisting fish passes have their entrances orientedtowards the weir and thus at an angle of 180ºrelative to the river current. In such cases theentrance is unsuitable in that it can not establish anattracting current to enable the fish to find theentrance to the fishway.

A collection gallery has been incorporated into thedesign of American hydroelectric power stations toserve as a special type of fish pass entrance(CLAY, 1961). This type of construction is inspiredby the fact that many fish swim upstream throughthe turbulent zone at the outlet of the powerstation’s turbines and thus arrive directly at theobstacle. A gallery located over the turbine outletsstretches over the whole width of the obstacle atexactly this point. This gallery has various outlets,one next to each other, through which the attractingcurrent is discharged. Fish entering the gallery areled through it into the actual fish pass, which alsohas its own direct entrance (Figures 3.10 and3.11). This type of construction is, however, notsuitable for bottom-living fish.

Since diurnal fish avoid swimming into darkchannels the fish pass should be in daylight andthus not covered over. If this is not possible thefishway should be lit artificially in such a way thatthe lighting is as close as possible to natural light.

3.3 Fish pass exit and exit conditions

Where the fish pass is installed at a hydroelectricpower station, its water inlet (exit into theheadwater#) must be located far enough from theweir or turbine intake so that fish coming out of thepass are not swept into the turbine by the current.A minimum distance of 5 m should be maintainedbetween the fish pass exit and the turbine intake orthe trash rack. If the current velocity of theheadwater is greater than 0.5 m s-1, the exit area of

26

headwater

water outlets from(fish entrances into)collection gallery

water outlet(fish pass entrance)

weir

powerhouse

fish pass

water outlet(fish pass entrance)

area of highturbulence

trash rack

water inlet(fish pass exit)

tailwater

powerhouse collection channel

max. tailwater level

min. tailwater level

draft tube

area with gentle,reversed current

Fig. 3.10: Diagram of an American hydroelectricpower station with a collection gallery(after LARINIER, 1992d)

Fig. 3.11: Cross-section through a collectiongallery (after LARINIER, 1992d)

# remark by the editor

The water intake of the fishway should be protectedfrom debris by a floating beam.

Structural provisions should be made so that acontrol device (e.g. a trap) can be installed at theexit of the fishway to monitor its effectiveness.These could be footings for a fish trap and anadjacent lifting device for instance. It should also bepossible to shut down the flow through thefishpass, e.g. for control and maintenance work.

3.4 Discharge and current conditions in the fish pass

The discharge required to ensure optimumhydraulic conditions for fish within the pass isgenerally less than that needed to form anattracting current. However, the total dischargeavailable should be put through the fish pass toallow unhindered passage of migrants, especiallyduring periods of low water. This is particularlyadvisable for dams that are not used forhydropower generation. If more water is available tosupply the fishway than is needed for thehydraulically-sound functioning of the existing orplanned fish pass, alternative designs should beenvisaged, e.g. the construction of a rocky rampthat should be as wide as possible. In some casesa structural adaptation of the fishway’s exit areamay be necessary to limit the discharge throughthe fish pass, e.g. during floods, in the interest ofefficient functioning.

Using supplementary water to increase flows thatdoes not originate from the river on which the fishpass is situated, such as discharge from waterdiversions or sewage treatment plants, should beavoided. The mixing of waters of different physical-chemical properties disturbs the sensitive olfactory

the fish pass has to be prolonged into theheadwater by a partition wall.

In general, if the headwater level of theimpoundment is constant, the design of the waterinlet does not present a problem. However, specialprovisions have to be made at dams where theheadwater level varies. Here the fish pass eitherhas to be of such a type that it’s functioning is onlyslightly affected by varying headwater levels, orrelevant structural adaptations of its water inletarea must be incorporated. A vertical slot exit hasproved appropriate for technical fish passes if thevariations in headwater level are at maximumbetween 0.5 to 1.0 m. Where variations in levelexceed one metre, several exits must beconstructed at different levels for the fishway toremain functional (Figure 3.12).

With certain types of fish pass, mechanicalregulation of the flow-through discharge may benecessary for the pass to continue to function.Simple aperture controls at the exit (i.e. the waterintake) may be suitable. When the impoundmentshows greater variations in level, more complexstructures with control systems or barrier devicesmay be necessary. Unfortunately such devices areliable to malfunction or, alternatively, the staff mayoperate the control systems improperly causing alessening in the efficiency of the fish pass.

Strong turbulence and current velocities over2.0 m s-1 must be avoided at the exit area of the fishpass so that fish leave the pass for the headwatersmore easily. Furthermore, linking the exit of thefishway with the natural bottom or bank substrateby means of a ramp facilitates the movement ofmigrant benthic organisms from the fish pass intothe headwater.

27

Max. headwater level

Fish passwater inlet at maximum filling level of the impoundment

(maximum headwater level)

water inlet at minimum filling level of the impoundment (min. headwater level), with regulable sluice gate

Min.headwater

level

Figure 3.12:At the side of the impound-ment, several water inlets (fishexits#) at different levelsguarantee that fish can leavethe fish pass even at varying(lower) headwater levels.

# Remark by the editor

orientation capability of the fish and thus reducestheir urge to continue migration.

The turbulence of the flow through the fishwayshould be as low as possible so that all aquaticorganisms can migrate through the passindependently of their swimming ability. LARINIER(1992b) recommends that the volumetric energydissipation in each pool of a pool pass should notexceed 150 to 200 W per cubic meter of poolvolume.

In general, current velocity in fishways should notexceed 2.0 m s-1 at any narrow point such as inorifices or slots and this limit to velocity should beassured by the appropriate design of the pass. Theaverage current velocity in the fishway must besignificantly lower than this value, however. Thepass should incorporate structures that formsufficient resting zones to allow weak swimmingfish to rest during their upstream migration.Furthermore, the current velocity near the bottom isreduced if the bottom of the fish pass is rough. Asa rule, there should be laminar flow through the fishpass as plunging (turbulent) flow can only beaccepted under specific local conditions, such asover boulder sills.

3.5 Lengths, slopes, resting pools

Instructions for the correct dimensions of fishwaysinclude information on such features as slope,width, length and water depth as well as thedimensions of orifices and resting pools. Theseinstructions depend mainly on the particular type offish pass to be built as well as on the availabledischarge. Type-specific instructions are to befound in the relevant sections of these Guidelinesthat deal with the different types of fish passes. Allinstructions given in these Guidelines are minimumrequirements.

The body length of the biggest fish species thatoccurs or could be expected to occur (inaccordance with the concept of the potentialnatural fish fauna) is an important consideration indetermining the dimensions of fish passes. The factthat fish can grow throughout their whole lives mustbe taken into account when gathering informationon the potential fish sizes. The body lengths shownin Table 3.1 are average sizes. Maximum sizes,such as that of the sturgeon that can grow to 6.0 min length, are not provided.

The average body length of the largest fish speciesexpected in the river as well as the permissibledifference in water level must be considered indefining the dimensions of a fish pass, (cf.Chapters 4 and 5). Since a difference in water level

of only �h = 0.2 m entails a maximum currentvelocity of 2.0 m s-1 for instance at orifices andcrosswalls, it is recommended that the water leveldifference between pools in a fishway be also keptbelow 0.2 m (Figure 5.4). Such a maximumdifference in water level leads to a current velocityin the layer just above the rough bottom that allowseven fish that have a weak swimming performanceto pass. Waterfalls and drops where aerated jetswould form must be avoided.

For more technical constructions the maximumpermissible slope ranges from 1:5 to 1:10,depending on the construction principle chosen,while close-to-nature constructions should showmaximum slopes less than 1:15 corresponding tothe natural form of rapids (cf. Chapter 4). It is,however, acceptable for the slope of a natural-looking fish pass to not correspond to the naturalslope of the river at this very location.

The swimming ability of the fish species of thepotential natural fish fauna and all its life stages hasto be considered in setting the length of a fishway.However, data on the swimming velocity of fish is

28

Table 3.1: Average body lengths of adults of somelarger fish species

Fish Bodyspecies length [m]

Sturgeon Acipenser sturio 3.0

European catfish Silurus glanis 2.0

Pike Esox lucius 1.2

Salmon Salmo salar 1.2

Huchen Hucho hucho 1.2

Sea lamprey Petromyzon marinus 0.8

Sea trout Salmo trutta f. trutta 0.8

Allis shad Alosa alosa 0.8

Barbel Barbus barbus 0.8

Lake trout Salmo trutta f. lacustris 0.8

Bream Abramis brama 0.7

Orfe Leuciscus idus 0.7

Carp Cyprinus carpio 0.7

Chub Leuciscus cephalus 0.6

Grayling Thymallus thymallus 0.5

Twaite shad Alosa fallax 0.4

River lamprey Lampetra fluviatilis 0.4

Brown trout Salmo trutta fario 0.4

resting pool should be set so that the volumetricpower dissipation must not exceed 50 W m-3 of poolvolume. Valid data on the maximum permissiblelength of fish passes are not generally available.However, for types of pass without rest zones andof a length that is excessive for fish to negotiate ina single effort, it is recommended that resting poolsare placed at intervals of such lengths as definedby the difference in level of not more than 2.0 mbetween pools. Denil passes must be broken up byresting pools at least after every 10-m-stretch oflinear distance for salmonids, and at least afterevery 6 to 8 m for cyprinids.

3.6 Design of the bottom

The bottom of a fish pass should be covered alongits whole length with a layer at least 0.2 m thick of acoarse substrate (Figure 3.14). Ideally the substrateshould be typical for the river. From the hydraulicengineering point of view, a coarse substrate isnecessary for the creation of an erosion-resistantbottom. However, the bottom material used for thisshould be as close to natural as possible andshould form a mosaic of interstices with a variety ofdifferently sized and shaped gaps due to the variedgrain size. Small fish, young fish, and particularlybenthic invertebrates can retreat into such gapswhere the current is low and can then ascendalmost completely protected from the current. Thecreation of a rough bottom usually presents fewproblems in close-to-nature types of fishways.

The rough bottom must be continuous up to andincluding the exit area of the fish pass, as well as atthe slots and orifices. In some more technical typesof construction, such as Denil passes, the creationof a rough bottom is not possible. This means thatbenthic invertebrates cannot pass through themand thus these constructions do not fulfil one of theessential ecological requirements for fish passes.

3.7 Operating times

The migrations of our indigenous fishes take placeat different times of the year. While many cyprinidspecies (Cyprinidae) migrate mainly in spring andsummer, the spawning migrations of salmonidspecies (Salmonidae) occur mainly in autumn andwinter. The migratory movements of benthicinvertebrates probably occur during the entirevegetative period. The time of the day at whichaquatic organisms move in rivers also differs for thedifferent groups. Thus, numerous benthicinvertebrates are mainly active at twilight and atnight, while the time of maximum activity of thedifferent fish species varies considerably and can in

not listed here since the values determined indifferent investigations differ markedly from oneanother or is even contradictory (JENS, 1982;STAHLBERG & PECKMANN, 1986; PAVLOV,1989; GEITNER & DREWES, 1990). In any case,the requirements of the weakest species, or of theweakest life stages, must be considered whendefining the dimensions of a pass.

Resting zones or resting pools should be providedin fishways. Here fish can interrupt their ascent andrecover from the effort. In some types of pass, suchas slot or pool passes, resting zones are inherentto the design. In others, such as rock ramps, theycan easily be created. Resting pools whereturbulence is minimal should be inserted atintermediate locations (Figure 3.13) into types offishways that have normally no provision for restingzones due to their design. The dimensions of a

29

dam wall

resting pools

area ofturbulent water

Fig. 3.13: Technical fish pass with resting pools,bypassing the obstacle in a bent design(modified from TENT, 1987)

Fig. 3.14: Coarse bottom substrate in a slotpass; Lower Puhlstrom weir in theUnterspreewald (Brandenburg)

fact even alter during the year (MÜLLER, 1968).Because of this variability in the timing ofmigrations fish passes must operate throughout theyear. Limited operation can be tolerated only duringextreme low- and high water periods (i.e. for the 30lowest days and the 30 highest days in one year),since at such times fish usually show a decrease inmigratory activity.

Continuous 24-hour operation must be guaranteedsince, once they have entered the fishpass,invertebrates that are little mobile would be unable toescape even a short drying out of the pass andinevitably die if the pass is only operating periodically.

3.8 Maintenance

The need for regular maintenance must beconsidered from the start of planning a fish pass aspoor maintenance is the chief cause of functionalfailure in fishways. Obstruction of the exit of thepass (i.e. the water inlet) and of the orifices,damage to the fish pass structure or defective flowcontrol devices are not rare but can be overcomethrough regular maintenance. There must beunhindered and safe access to the pass so thatmaintenance can be assured. Close-to-naturetypes of construction such as rock ramps areeasier to maintain than highly technical structuresbecause obstruction with debris of the water inletarea or the boulder bars is rarely total and does notimmediately halt operations. Highly technicalstructures therefore require more frequentmaintenance. A maintenance schedule can bedrawn up or adjusted on the basis of operationalexperience of the type and frequency ofmalfunction of the fish pass in question.Maintenance must always be carried out afterfloods, however.

3.9 Measures to avoid disturbancesand to protect the fish pass

The competent authorities should establish zonesclosed to fishing above and below fishways in orderto protect migrating fish from any disturbance. Suchregulations can be made on the basis of thefisheries law of the administrative entity in whichthe fish pass is installed. Leisure activities such asswimming and boating should also be kept awayfrom the immediate neighbourhood of fish passes.Only in exceptional and well-justified cases, fishpasses can be built close to boating lanes, boatslips or shipping locks. Furthermore, access to fishpasses should be limited to maintenance workers,control personnel or scientists to carry out scientificstudies.

When viewing windows are built in fishways, as inmonitoring stations for observing migrations, one-way glass should be used and the observationchamber darkened.

The functioning of the fish pass must not beimpacted negatively if the barrage or any nearbystretches of water are altered, for example bydeepening the channel, raising the elevation of thedam, or by the construction of a hydropower station.

3.10 Integration into the landscape

Every effort should be made to integrate the fishpass into the landscape as harmoniously aspossible, although the correct functioning of thefishway must take priority over landscaping. Underthis aspect, particularly close-to-nature types ofconstruction link functional and landscapingconsiderations in the best possible way and mayalso play an important role as substitute biotopesfor rheophilic organisms.

Natural building materials or construction materialsthat are typical of the local conditions should beused in the construction of fishways in aconsequent manner. The wood used should not bechemically treated. Vegetation should be allowed toproliferate naturally as far as possible to createpossible cover for migratory fish and shade thefishway, although it might be necessary to initiallyplant suitably adapted local plants and shrubs toget the vegetation started.

30

There are similarities in the design of the varioustypes of close-to-nature constructions and hybridforms exist. For example, bottom slopes, fish rampsand bypass channels can be constructed incascades, using boulder sills or single boulders toincrease the roughness of the bottom substrate.Hydraulic calculations related to the hydraulics ofclose-to-nature constructions will be dealt with insummary form in section 4.4.

4.1 Bottom ramps and slopes

4.1.1 Principle

A bottom ramp or slope is a mechanism to dispersethe hydraulic head (i.e. the difference in water levelbetween the impoundment and the water surfacedownstream#) over a certain distance by keepingthe hydraulic gradient of the slope as gentle aspossible.

Bottom ramps and slopes were originally developedwith the aim of stabilising river bottoms. They areincluded here, together with fish passes, especiallybecause gently inclined, low-gradient rocky rampsor slopes exhibiting a rich mosaic of structuraldiversity represent the most advantageous method

4 Close-to-nature types of fish passes

The “close-to-nature style” of construction of sillsand fish passes, such as rock ramps, imitates asclosely as possible natural river rapids or brookswith steep gradients (Fig. 4.2). Also theconstruction material chosen corresponds to whatis usually present in rivers under natural conditions.

The constructions described below are usually site-specific and thus cannot be applied generally.However, they meet biological requirements moresatisfactorily than the technical constructionsdescribed in Chapter 5 with regard to theconnectivity of rivers. Furthermore, the close-to-nature design enables new running-water biotopesto be created in a watercourse, while blendingpleasantly into the landscape.

For the purpose of these Guidelines the followingconstructions are defined as “close-to-naturetypes” of fish passes (Fig. 4.1):

m Bottom ramps and slopes,

m Bypass channels and

m Fish ramps.

31

Figure 4.1: The three types of natural-looking fish passes

a) Bottom ramp and slope:

A sill having a rough surface andextending over the entire riverwidth with as shallow a slope aspossible, to overcome a leveldifference of the river bottom.This category also includesstabilizing structures (e.g.stabilizing weirs), if the body ofthe weir has a shallow slopesimilar to the slope of a ramp orslide and is of loose construction.

b) Bypass channel:

A fish pass with features similar tothose of a natural stream,bypassing a dam. As the dam ispreserved unchanged, itsfunctions are not negativelyaffected. The whole impoundedsection of the river can thus bebypassed.

c) Fish ramp:

A construction that is integratedinto the weir and covers only apart of the river width, with asgentle a slope as possible toensure that fish can ascend.Independently of their slope, theyare all called ramps; in general theincorporation of perturbationboulders or boulder sills isrequired to reduce flow velocity.

# text in brackets added by the editor

for the restoration of a river continuum as they bestimitate the conditions of a river stretch naturally richin structural diversity and gradient (Fig. 4.2).

The conventional construction of sills must usuallybe modified to allow fish passage, in order torespond to the demand for longitudinal connectivityin rivers. Smooth concrete bottom ramps and steephydraulic drops are unsuitable as they do not allowthe upstream migration of fish and will therefore notbe dealt with in these Guidelines.

According to DIN# 4047, Part 5, the distinctionbetween a bottom ramp and a bottom slope isbased solely on the gradient of the slope: Artificialstructures that have gradients of 1:3 to 1:10 aredefined as being “ramps” while those exhibitinggentler slopes of 1:20 to 1:30 are called “bottomslopes”. Constructions that have gradients of 1:15or less are therefore generally included amongstbottom slopes in these Guidelines.

Bottom ramps and slopes are especially useful assubstitutes for vertical or very steeply inclineddrops in the river. They are also being used, to anincreasing extent, as substitutes for regulable weirsif a flow control system is no longer required, inwhich case they operate as protection structure orsills that maintain the headwater level. From ageneral ecological point of view, this method hasthe important advantage that natural flowconditions will even be restored in theimpoundment upstream of the weir due to silting-upof the area in the medium to long term.

4.1.2 Design and dimensions

4.1.2.1 Construction styles

Bottom ramp and slope constructions (Fig. 4.3) canbe classified as follows:

m Set or embedded-boulder constructions (conventionalramps in dressed and ordered construction mode)

m Rockfill constructions (loose rock construction)

m Dispersed or cascaded constructions (embeddedrocky sills construction)

Conventional boulder ramps with slopes of 1:8 to1:10 and with correspondingly high flow velocitiesshould be adopted only where there is very heavyhydraulic stress. From an ecological point of view,loose rockfill constructions, and in particular rockysill constructions, are to be preferred.

Embedded-boulder constructions (Fig. 4.3, a)are generally limited to ramps with gradients ofapproximately 1:10. The ramp is constructed bysetting on edge individual boulders that are 0.6 to1.2 m in size and are often attached to one another.The structure generally stands on a base layer(base course) which, depending on theoutcropping stratum, consists of a layer (course) ofcrushed stones or a multistage gravel base layer(course). The base layer is dimensioned inaccordance with conventional rules. The extremeupstream and downstream boulders of such aramp are usually kept in place by sheet-pile walls,rows of piles or securing steel elements (rammed-in railway rails, steel girders or the like).

32

Figure 4.2:A river stretch with close-to-nature features, e.g. rich invaried slopes, provides apattern for the design ofnatural-looking bottom sills.

Uneven slopes, often dividedup into cascades, arecharacteristic of such riverstretches. Low drops overboulder sills are followed bypools in which fish find shelterand can survive periods oflow-water. Aschach (Bavaria).

# DIN (Deutsche Industrie-Norm[en]): German Industrial Standards(remark by the Editor)

Incorporating individual large boulders canincrease roughness. A cascaded design using rocksills is also possible, whose main purposes are tokeep an appropriate water level on the ramp underlow-water conditions and to enhance structuraldiversity. The rock filling can also be secured byrows of wooden piles or elements consisting ofsectional steel reinforcing bars. A naturally erosion-resistant river bottom requires no furtherstabilisation at the transition to the tail water. In thiscase the rockfill is extended with a constant slopeto below the level of the tail water river bottom andthe secured zone downstream is kept short, i.e.only approximately 3 to 5 m. A continuous transitionwith a trough-shaped pool, as shown in Fig. 4.4,should be created in rivers in low-lying areas withsubstrates that are not resistant to erosion or are

The area of stabilized bottom downstream of thedownward securing element is kept quiteshort, being only 3 to 5 m in length. Howeverfurther bottom-securing elements are requireddownstream where there is a danger of poolformation through erosion. These usually take theform of rockfills. Construction usually requires dryexcavation. The structure thus formed is relativelyrigid but can withstand very heavy hydraulic stressdue to the bonding effect of the boulders.

From an ecological point of view, rockfillconstructions (Fig. 4.4) are to be rated moresatisfactory than embedded-boulder constructions.Their main body consists of a multi-layered rockfillwhere the thickness of the layers is at least twicethe maximum diameter of the biggest stones used.

33

a) Embedded-boulder construction (dressedconstruction):Single layer structure on a base layer (base course);boulders set evenly and often clamped to one another;uniform roughness; rigid structure; resists to highdischarges; downstream river bottom must be stabilized.

b) Rockfill construction (loose construction):Loose multilayer rockfill; downstream river bottom mustbe stabilized; a base layer (base course) is necessary ifthe natural bottom substrate is sandy; resilient structure;divers roughness; low costs.

c) Dispersed/cascaded construction (boulder barconstruction):Slopes broken by boulder bars forming basins; basinscan be left to their own dynamics to form pools; greatstructural variety; low costs.

Figure 4.3: Construction of bottom ramps and slopes (altered from GEBLER, 1991)

Figure 4.4:Bottom slope as rockfill construction(modified from GEBLER, 1990)

HW

MW

bottom slope: Ι < 1:15

hr

row ofpiles

MW

HW

perturbation boulders

or boulder sillsho

secured downstream river bottoml = 7 to 10 hr

depth of pool:h = 1/3 to1/2 hr

base layer (base course) coarse gravel/pebbles

or geotextiles

embankment secured by rockfill to above MHW (mean high water)

continuous row of piles

Longitudinal section

Cross-section

sandy or silty, and the adjacent downstreambottom-securing part should be prolonged accordingly.

The embankments along the ramp and theimmediate downstream bottom zone must also besecured with rockfill that reaches above the meanhigh-water line. Planting the embankments withappropriate vegetation enhances their resistanceto erosion and keeps the main flow axis in thecentre of the river during floods.

Works to build loose rockfill ramps can generallybe carried out without diverting the river. However,the greater overall length of the ramp as comparedto boulder constructions offsets any savings incosts.

All elements of the river fauna can negotiate rockfillramps.

Embedded rocky sills constructions (steppedpools or dispersed/cascaded ramps) (Fig. 4.5)mainly consist of a number of boulder barscomposed of large field boulders or river bouldershaving diameters of ds = 0.6 to 1.2 m. To enhancestability the boulder bars can be arranged in anarch (in top view) so that the boulders lean againstone another keeping themselves in place. With anerosion-resistant, stony or coarse-gravel bottom,as is the case in mountain streams, the boulderbars are embedded as deeply as 2.5 m (cf. alsoFig. 4.3.c) and are secured by rows of piles or steelelements. In another variant a base layer is built upfrom rockfill and the boulder bars are bonded intothe river bottom. In these cases, the boulder barsneed not be so deeply embedded. The result is aconstruction comparable with that shown inFig. 4 .4. The transition to a rockfill constructionwith additional boulder sills is smooth.

Boulder bars form basins that are filled with graveland large cobble material and can be left to naturaldynamics. Even sandy substrates typical of riversin lowland areas normally remain in the basins.Although the substrate may be removed at highdischarges, it quickly re-accumulates when flowvelocities are again reduced.

The distances between bars, and the arrangementof the boulders, should be chosen in such a wayas to ensure that differences in water level of�h = 0.2 m are not exceeded.

It has to be emphasised that the structural diversityof the embedded rocky sills constructions issometimes so high that the slopes can hardly berecognized as artificial structures. The planningand construction of such ramps calls for greaterexperience than do the other types of close-to-nature passes.

River fauna can negotiate bottom slopes carriedout as boulder bar constructions in both directionswithout limitation.

4.1.2.2 Plan viewBottom ramps are constructed with a spatialcurvature as shown in Fig. 4.6 in large rivers withbottom widths of bbot >15 m. The crest profile has apitch of 0.3 to 0.6 m in cross-section. Ramps insmaller rivers do not generally include any spatialcurvature and a rectilinear crest is constructedinstead. The adjacent downstream zone ofstabilized bottom protects the construction againstretrogressive erosion. A low water channel shouldbe incorporated to protect the ramp from drying outor from having too shallow a water depth during lowdischarges.

4.1.2.3 Longitudinal sectionAs a rule, bottom ramps using boulder constructionare designed with slopes of 1:8 to 1:10 (dressedconstruction). Sills carried out as rockfill and barconstructions are designed with flatter slopes of1:15 to 1:30.

34

basins filled with locally available bottom material

boulder bars embedded deep into the bank

embankments must be secured by biological engineering and technical constructional measures

boulder bars embedded up to 2.5 m deep,possibly additionally secured by steel elements

Fig. 4.5: Bottom step in boulder bar construction(plan view)

b 'o r = 1,25 b 'o

r = 1,25 bu

ub

bo ramp

immediate downstream river bottom zone

Fig. 4.6: Plan view of a curved bottom ramp(after SCHAUBERGER, 1975)

undesired lowering of the ground water levels in theriverine low lands. However, the water levels can nolonger be regulated. Nor is it any longer possible toincrease the discharge cross-section by loweringthe weir during flooding; as a consequence, waterlevels can rise when there are heavy flows.Widening the ramp crest can improve theperformance of the sills. The substitution of a weirby a dispersed or cascaded ramp is particularlysuitable if the intensity of agricultural utilization ofthe low lands has been reduced, or if other usessuch as hydropower generation or navigation havebeen abandoned.

One advantage of this method is that theimpounded area above the sill is allowed to silt upand free-flowing conditions can be re-establishedin the medium to long term. In any case,investigations should always be made to determinewhether the ground water levels need to bemaintained or whether local conditions would allowfor lowering of the head, thereby rehabilitatingmore of the former impoundment.

As far as possible, the ramp structure shouldtake the form of a simple rockfill; the top layercan also incorporate large boulders or boulderbars (Fig. 4.8). The gaps between rocks can be

The flow velocities that occur when boulder rampshave slopes of 1:10 must certainly be regarded asexcessive for many fish and benthic species. Thissituation can be improved by adopting a profile thatrises towards the riverbanks, producing zones ofcalmer flow in the marginal areas.

Even at low discharges the mean depth of watershould not be less than h = 0.30 to 0.40 m. Bigboulders and fairly deep basins forming restingpools make it easier for fish to ascend and give avery varied and also optically attractive flowpattern. Bar-type bottom constructions fulfil thesecriteria best.

The maximum permissible flow velocity in fishpasses is vmax = 2.0 m/s.

4.1.3 Remodelling of dropsSteep drops that are impassable by aquatic faunacan often be converted to a bottom slope withrelatively little effort. In the case of small drops(Fig. 4.7), all that is needed is a heap of field rocksor river stones at a shallow inclination into whichlarger boulders or boulder bars can be embedded.Such slopes should be about 1:20. The edge of thedrop should either be bevelled or covered withstones to ensure continuity with the bottomsubstrate.

4.1.4 Conversion of regulable weirs into dispersed or cascaded ramps

If water management requirements allow, theconversion of weirs into a dispersed or cascadedramp should be preferred to the construction of aseparate fish pass.

A dispersed or cascaded ramp allows the waterlevel to be maintained upstream and avoids any

35

mean water level

high water level

upper edge of terrain

mean water level

high water level

row of piles:wooden piles,steel sections

or rod irons

perturbation boulders, d = 0.6 -1.2mbody of the sill as rockfill construction, Ι < 1:20,to be "sealed" by the flushing-in of gravel and sand

incorporated sand or clay as "sealing"

old weir

securing the downstream bottom,

minimum 3 to 5 m

h r

demolish weirsuperstructures

oldberm

silting-up

Figure 4.8 Conversion of a regulable weirinto a protection sill

boulders must bear against end sills

Fig. 4.7: Conversion of an artificial drop into arough bottom slope.

substantially filled by washing in gravel and sand(alternatively these can be incorporatedcontinuously during construction), thus reducingwater losses at low discharges and preventing theramp from drying-out. An initial pouring ofsandy/clayey material has also proved effective asa sealant. Both the sill crest and the connection tothe riverbed downstream can be secured by rowsof piles.

The superstructures (flow regulation elements) ofregulatable weirs must be demolished and thesubstructure (stilling basin) covered over.

4.1.5 Overall assessment

From the ecological point of view, the constructionof rough bottom ramps with a low inclination angleis the best way to restore fish passage in rivers

where the obstacle cannot be completely removed.Loose constructions (rock fills) and barconstructions are to be preferred to moreconventional boulder ramps. The use of concreteshould be minimal consistent with stableconstructions.

Rockfill or bar-type bottom sills can also be used tomodify both drops in rivers and regulatable weirs.

Maintenance is relatively low and can be limited tothe occasional removal of floating debris andwaste, as well as periodic checks for possibledamage, in particular after flooding.

The entire aquatic fauna can freely pass theseconstructions in both upstream and downstreamdirections.

36

37

GROSSWEIL BOTTOM RAMP

Details of the river Details of the bottom ramp

River: Loisach, Bavaria Construction: Boulders

Discharge: MNQ = 8.68 m3/s Width: b = 72 m

MQ = 23.1 m3/s Difference of head: h = 2.7 m

HQ100 = 400 m3/s Slope: 1 : 10, marginal zones 1 : 15

Responsible: WWA Weilheim Year of construction: 1973/74

Constructional design:

The construction is in the form of a rough boulder ramp (weight of boulders 3-5 t) in dressed and orderedmode with an upstream and downstream sheet-pile wall. The adjacent downstream zone of stabilizedbottom is short. Since experience was slight at the time of construction as to whether or not fish couldascend such ramps, a 4 m wide fish pass, constructed from boulders of different heights to form pools,was incorporated in the right-hand third alongside the boat slide.

The ramp becomes very shallow towards the left bank, which leads to highly differentiated flow patternswith lower water depth and lower flow velocities in this marginal zone. This allows even fish that are weakswimmers to ascend. In contrast, it is difficult for fish to find the actual fish pass due to the highly turbulentflow conditions at the fish pass entrance where there is almost no attraction current. The shallow marginalzones are therefore substantially more effective and completely adequate to sustain fish passage. Basedon the positive experience collected here, the Water Management Authority (WWA) of Weilheim hasconstructed other bottom ramps without separate fish passes in their area with excellent results.

The fishery lessees of this river could observe a positive development of the fish stock.

4.1.6 Examples

Figure 4.9:Grossweil/Loisach bottomramp (view from downstream)The considerably reducedflow velocities and thedifferentiated flow pattern inthe shallower marginal zoneensure that even weakerswimmers amongst the fishspecies, as well as benthicfauna, can negotiate theramp, so that othermitigation facilities (i.e. aseparate fish pass) are notneeded.

38

BISCHOFSWERDER PROTECTION SILL

Details of the river Details of the protection sill

River: Dölln Stream, Brandenburg Construction: Rockfill sill

Discharge: MNQ = 0.44 m3/s Width: b = 4.0 to 6.0 m

MQ = 0.9 m3/s Slope: � = 1 : 20

HQ25 = 5.1 m3/s Length l = 20 m

Height of sill h = 1.0 m Depth of water h = 0.3 to 0.6 m at MQ

Responsible: LUA Brandenburg Max. flow velocity vmax = 1.3 to 2.2 m/s

Year of construction: 1992

Description of construction:This protection sill replaced a plank dam (culture dam) and was constructed as a rockfill ramp. The bodyof the ramp consists of river stones (d = 25 cm) and was “sealed” by clayey-sand that was poured-in atthe start of construction. Large boulders (d = 50 to 100 cm) reduce the flow velocity and give the fishshelter as they ascend.

Monitoring of the upstreammigration has confirmed thatthe ramp can be negotiated. Adense ichthyocoenosis, rich inspecies, has developed due toimmigration from the RiverHavel in those sections of theDölln stream situated abovethe ramp that previously had animpoverished aquatic fauna.

Figure 4.10:Plank dam beforemodification - an impassableobstacle for the aquatic fauna

Figure 4.11:Bischofswerder protection sillafter modification

39

MAXLMÜHLE BOTTOM SILL

Details of the river Details of the bottom ramp

River: Mangfall, Bavaria Construction: Bar construction

Discharge: MNQ = 1.16 m3/s Width: b = approx. 15 m

MQ = 4.83 m3/s Height of step h = 1.7 m

HQ100 = 270 m3/s Slope: � = 1 : 26

Responsible: Free State of Bavaria/ Year of construction: 1989

WWA Rosenheim

Description of construction:

A number of constructions with steep drops that could not be negotiated by the aquatic fauna werereplaced by bottom ramps of the close-to-nature design in the restored part of the Mangfall River atMaxlmühle (near the Weyarn motorway bridge).

The ramp shown below is of the bar construction type; the body of the ramp consists of individual,transverse bars embedded to adepth of 2.5 to 3 m.The transversebars are curved and offset, so thatthey lean against one another. Theresulting basins are filled withindigenous bottom material and leftto their natural dynamics (poolformation, silting-up). Bottom rampsdesigned in this way blend very wellinto the river landscape and canhardly be recognized as artificialconstructions.They are passable bythe entire aquatic fauna.

0,00 6,50 12,50 18,50 22,0 30,00 45,00

589,20588,70

590,91:3

593,5

row ofrails class V river boulders, laid on bedding concrete

and with the gaps sealed between the boulders

bottom step prior to modification

589,20

590,9

593,5

bottom step after modification

row of railswas retained

transverse bar, boulders d = 1 to 1.2 m and embedded to a depth of 2.5 to 3 m, boulders only loosely trimmed

basins at different levels, disposed laterally offset and filled with natural

bottom material

Figure 4.12:Longitudinal section of a bottomstep in the Mangfall River, boulderbar construction (diagrammatic).

Figure 4.13:Bottom step in the Mangfall RiverThe bar construction used in thiscase creates an extraordinarystructural variety. In order to restoremigrations, the transformation of adrop in the river bottom over theentire width of the river must alwaysbe regarded as the best possiblesolution, being preferable to anyseparate fish ladder.

40

MÜHLENHAGEN BOTTOM SILL

Details of the river Details of the bottom ramp

River: Goldbach near Mühlenhagen Construction: Rockfill construction

Mecklenburg/West Pomerania Width: b = 3.4 m

Discharge: MQ = 0.38 m3/s Slope: � = 1 : 20

HHQ = 2.8 m3/s Length l = 38 m

Height: htot = 1.70 m Year of construction: 1992

Responsible: Altentreptow District

Goldbach

Goldbach

layer of willow branchesbase secured

with fascines and gabions

bottom width: b = 3.40 m� = 1:20, h = 1.7 m17 boulder sills

dual-layer rockfill on geotextiles

demolish weir superstructures and fill up the canal

to equalize with terrain

island

Figure 4.14:Plan view showingthe posit ion of theMühlenhagen/Goldbachbottom ramp

Figure 4.15:Mühlenhagen/Goldbachbottom rampNo right of use existsany longer at theabandoned mill weir. Thebypassed millpond issilted up but representsan aquatic biotope thatis worth protection.Simply demolishing theweir installation wouldhave led to considerablebottom erosion and thelowering of the watertable in the headwaterarea. The weir wastherefore replaced by arough bottom slope with

a shallow gradient, in order to maintain the actual headwater level to which nature got accustomedover the last centuries.The ramp has a total height of 1.7 m and a slope of 1:20. Boulder bars form cascaded basins to keep flowvelocities within permissible limits. The water depths in the pools are 30 to 40 cm. The channel cross-section was secured by a layer of stones on a geotextile base. Field boulders of 40 to 50 cm in diameterwere used to create the bars.

rheophilic river species are particularly adverselyaffected.

Moreover, bypass channels maintain or restore theriver continuum as they provide flow conditionssimilar to those of an undisturbed river and thusallow migrants to by-pass the entire impoundedarea, sometimes up to the limit of the backwater,without incurring any sudden changes in the abioticcharacteristics.

4.2.2 Design and dimensionsThe principles of “close-to-nature” river restorationshould be applied in the design of a bypasschannel, (DVWK 1984, LANGE & LECHER, 1993et al). However, because of the steeper slopes it isoften essential that the bottom and the banks bestabilised and that measures are taken to reduceflow velocities.

A natural brook rich in steep slopes, such as thatshown in Fig. 4.2, can be taken as a model fordesigning a bypass channel.

From this model, the following design criteria forbypass channels can be derived, where thedimensions given are minimal suitable requirements:

Slope:

� = 1:100 to max. 1:20,in accordance with the nature of the river;

bottom width:

bbot > 0.80 m;

mean depth of water:

h > 0.2 m;

4.2 Bypass channels

4.2.1 PrincipleThe term ‘bypass channel’ is used for fish passesthat bypass an obstacle and that are in the form ofa natural-looking channel that mimics a naturalriver. The channel can be of considerable length.Bypass channels are particularly suitable for theretrofitting of already existing dams wheremigration is to be restored by inserting a fish pass,since it generally requires no structural alterationsof the dam itself.

As a rule, only a proportion of the discharge isdiverted through the bypass channel. However, inthe case of abandoned culture weirs, protectionsills or dam installations on smaller rivers, the totaldischarge up to a predetermined value (usuallymean water level), can be sent through the bypasschannel; the dam itself remains functional, but thenserves exclusively to pass floods.

The main disadvantage of a bypass channel is therelatively large surface area required for theconstruction. Whether or not such type of fish passcan be used, therefore depends much on theparticular local conditions. On the other hand, theextended length of such a channel offers an idealopportunity for a close-to-nature construction thatblends pleasantly into the landscape.

Constructing a bypass channel does not only meanproviding a passage for migratory fish but alsomeans creating the prerequisite for rheophilic(current-loving) species to use the channel ashabitat. This aspect deserves even closer attentionin the restoration of those impounded rivers whereconditions for living and reproduction of stenotypic,

41

power-house

weir

turbulent zone

bypass channel

limit of backwater

steep slopeattraction current!cut in terrain!

gentle slope,as far as possible

without reinforcement

solid constructionsat the water inlet

bridge,road

Figure 4.16:Bypass channel.Bypass around a dam:example of common design

mean flow velocity:

vm = 0.4 to 0.6 m/s

(predominant water depth and mean flowvelocity depending on the size and nature ofthe river);

maximum flow velocity:

vmax = 1.6 to 2.0 m/s, locally limited;

bottom:

rough, continuous, connectivity with theinterstitial spaces; if possible use should bemade of the natural, locally availablesubstrate, without further sealing oradditional securing of the bottom;

shape:

sinuous or straight, possibly meandering,with pools and rapids;

cross-section

variable, preferably banks protected usingbiological engineering methods, big boulders,boulder sills to break the slope;

width-related discharge:

q > 0.1 m3/s · m

4.2.2.1 Plan viewThe shape adopted should be selected inaccordance with local spatial circumstances, andthe geological and slope characteristics. Thechannel can be straight or sinuous or even bent.The positioning of the entrance to the bypass belowthe dam is ruled by the same principles as thosethat apply to more technical passes. The bypasschannel must sometimes be turned back on itself

by 180° to ensure that the entrance from thetailwater is placed directly beneath the weir orthe turbine house. Due to the considerablelength of some bypass channels, the outlet into theheadwater must often be placed quite farupstream.

A special form of bypass channel is the so-calledpond pass that consists of a succession of pond-shaped widened sections, which are connected toone another via drops in the artificial river (bouldersills) or via short steep channels (JENS, 1982,JÄGER, 1994).

Bypass channels can also be combined with otherconstructions. For example, technical fish passes(pool, Denil or vertical slot passes, cf. Chapter 5)may be used to overcome locally difficult sectionsin the channel or to make the connection to thetailwater.

4.2.2.2 Longitudinal sectionThe slope of the bypass channel should be asgentle as possible. A guide value for the upper limitof the slope is �bot = 1:20. A steep slope can bebroken up by incorporating rock sills. Areas ofcalmer flow, pools or pond-like widenings enablefish to ascend more easily, particularly when theyfollow longer sections with steep slopes, and alsoserve as refuges.

If sufficient space is available for the bypasschannel, only a few sections with a steeper slopeshould be incorporated (Figure 4.16). A sectionwith steeper slope is useful at the connection tothe tailwater in order to produce a satisfactoryattraction current. The other sections can then beconstructed following the natural slope of the rivers

42

Figure 4.17:Bypass channels make itpossible to follow a designclose to nature and to blendin well with the locality. In thisexample, the contour waschosen as a function of theexisting tree cover.Lapnow Mill (Brandenburg).

plantings using willow sticks and combinationsthereof.

If the indigenous bottom substrate is sufficientlyresistant to erosion and if there is no risk toadjacent properties, the bypass channel can be leftto its own natural dynamics and the bottom doesn’tneed to be artificially secured.

Slight shading of the channel by plantations oftrees or bushes has a favourable effect on fishmigration (since fish can hide and can find shelter),while at the same time they blend pleasantly intothe landscape and contribute towards bankstabilization.

4.2.2.4 Big boulders and boulder sillsWith slopes of between 1:20 to 1:30, it is generallynot possible to maintain the permissible mean flowvelocity of 0.4 to 0.6 m/s in the bypass channelwithout additional controlling structures. Largeboulders are the natural and visually mostattractive material for such additions.

The following methods can be used:

m The incorporation of big boulders in an offset,irregular arrangement that leads to increasedroughness. During medium and low discharge,the water flows around or only slightly over suchboulders. The boulders also increase the waterdepth and reduce flow velocity. Ascending fishfind refuges in the flow shadow of the boulders.Local alternations in the flow regime may occurin the narrowed cross-section (Fig 4.19). Guidevalues for the setting of the boulders are:

in that particular region and require no extensivereinforcements.

The critical water depth must be based on thepotential natural fish fauna and its swimmingperformance (depending on the fish zone) butshould not be less than h = 0.2 m.

4.2.2.3 Channel cross-sectionThe width of the cross-sections, the water depthand the current should be as diverse as possible.However, the bottom width should not be less than0.80 m. Narrowing and widening the channelcontributes towards a natural-looking design.Reinforcement of the cross-section will normally beneeded and is essential in stretches of particularlysteep slope. Guidelines for methods for riverrestoration that give characteristics close to naturalfeatures should be used in deciding the type ofreinforcement to be adopted. Generally it issufficient to secure the bottom with coarse gravel orwith river stones placed on a gravel or geotextileunderlay. The interstitial spaces thus created alsooffer satisfactory possibilities for colonisation by,and migration of, benthic invertebrate fauna.Furthermore, the coarse stones hold back the finerparticles of sediment so that the natural bottomsubstrate can accumulate in the interstices.

It is preferable to use combined constructionmethods to secure the base of the slope and thebanks, for example by using living plants incombination with rocks, fascines (bundles of sticks)and the like. Fig. 4.18 shows some examples ofconsolidation with fascine sheeting, set blocks,layers of willow branches, copse planting or

43

min

max

rockfill or coarse gravel, possibly on a mineral base layer or a layer of geotextiles

willow cuttings

max

min layer ofwillow branches

fascine sheeting

pile to keep fascines in place

max

min

set boulders

planting, e.g. ofyoung alder

slopes left to natural succession

a) Rockfill with planting b) Fascine sheeting c) Set boulders of tree cuttings with a layer of willow branches and tree planting

Figure 4.18: Examples for securing bottom and banks of bypass channels

ax = ay = 2 to 3 ds

(for the definition of ax, ay and ds see Fig. 4.19)

The clear distance between these big bouldersshould be at least 0.3 to 0.4 m.

They should be embedded into the bottom byup to one third or one half of their depth. Theboulders must be big enough to prevent anyunauthorised displacement, for example, bychildren at play.

m The incorporation of transverse bars can narrowthe flow cross-section to such an extent that apool is formed between the bars where water isheld back. The transverse bars are formed fromlarge boulders embedded into the reinforcedbottom at varying depths. This method is inprinciple illustrated in Fig 4.20, the bouldershere being staggered in the bars. As a rule,large rectangular-sided rocks (square stones)are required, set on edge.

m The incorporation of submersible boulder sills(cascades). These sills, which are totally or onlypartially submerged, are formed from largeboulders embedded in the bottom. As water is

slowed down by the damming effect, pools areformed, in which a water depth of betweenh = 0.3 and 0.6 m should be aimed at(depending on the nature of the stream). Thedistance between the bars (clear pool length)should not be less than 1.5 m in rhithronicreaches, where, because of the bottom slope,the individual bars are stepped in relation to oneanother, forming a cascade (stepped poolpass). The height of drop at each sill must notexceed �hmax = 0.20 m. In potamonic reachessmaller drops of �h = 0.10 to 0.15 m should beadopted to allow inter alia for inaccuracies inconstruction, minor clogging with debris, etc.The distance between the bars must be suchthat no detached free overflow jet is producedand the sill always remains in the backwash ofthe next sill downstream. In addition, individuallarge boulders can also be incorporated in thepools (Fig. 4.20). The spacing between the sillsand the water depths must be sufficient to formresting zones in the basins. It is thereforerecommended that the volumetric powerdissipation should be limited to E = 150 W/m3 inthe potamon and to E = 200 W/m3 in the rhithron(for energy conversions in the basins see alsosection 4.4).

This construction pattern allows even finesediment to be retained in the basins, thuscreating substrate conditions closely resemblingnatural conditions.

4.2.2.5 Design of the water inlet and outlet areas of the bypass channel

Particularly where the headwater levels fluctuate orwhere there is a risk of the banks flooding, solid

44

b

dsa

x

ay

Fig 4.19: A bypass channel in which perturbationboulders have been placed

bb

smax

min

h > 0,2 m

Δh = 0.1 to 0.2 mΔh

l = Δh / Ι

boulder sills

in general bottom must be secured

cross-section longitudinal section

plan view

boulder size:0.5 to 0.8 m

tree cuttingsor young alder

low-water cross-section

sp

w

hweirhead

Fig 4.20:Boulder sills for breaking theslope in a bypass channel

a technical fish pass, particularly when connectingto a massively consolidated tailwater channel of ahydroelectric power station or when there arewidely fluctuating tailwater levels.

4.2.2.6 CrossingsThe length of bypass channels means that someform of crossing is usually needed for traffic orother purposes. Such crossings should bedesigned to ensure that no new obstacles tomigration are created and a bridge is usually thebest solution. A (dry) berm under the bridgefacilitates the migration of other animals (amphibia,otters, etc.).

Crossings must be designed in such a way that thecross-section of the bypass channel is notnarrowed. A rough, continuous bottom is alsoindispensable under the bridge or in the tunnel toensure that small fish and benthic fauna can passthrough. If it is impossible to use the natural bottomsubstrate, a 0.20 to 0.30 m thick layer of coarsegravel or pebbles will suffice. The length of thecrossing should not exceed 10 times the width ofthe opening.

4.2.3 Overall assessmentThe most important advantages of bypasschannels are as follows:

m They blend pleasantly into the landscape.

m They can be negotiated by small fish andbenthic invertebrates.

constructions and flow control mechanisms arerequired at the water inlet of the bypass channel(i.e. fish pass outlet#). The flow through the channelcan be limited and the channel can even beblocked off for maintenance working this way. Sucha mechanism can be created satisfactorily bysimple supporting concrete or quarry-stone wallsequipped with a suitably dimensioned controldevice. The height of the opening must ensure thatthe fish pass does not run dry even at low-water –something that must be avoided in a bypasschannel because it would not only stop fishascending but also have adverse effects on thebenthic fauna present in the channel. The fish passoutlet should also be designed in such a way as toallow for the use of a fish trap during monitoringoperations.

The design of the water outlet (entrance to the fishpass#) must ensure that there is an adequateattraction current in all operational situations. Inorder to achieve this the connection to the tailwatershould be as steep as possible, so that the flowvelocities create an adequate guiding effect. Wheretailwater levels fluctuate, the discharge cross-section can be narrowed by a solid constructionthat opens through a slot (cf. section 5.2 on slotpasses), thus increasing the flow velocity at thewater outlet.

The bottom of the fish pass should be connecteddirectly to the river bottom, if ever possible.

Adequate reinforcements are needed round thewater outlet (fish pass entrance#) to counteract theincreased stress on the riverbanks and bottom thatusually occurs below dams. The first part of thebypass channel (i.e. the part just following theentrance to the pass#) may have to take the form of

45

# remark by the editor

Figure 4.21:Control device at the waterinlet of a bypass channel in aretention dam (shortly beforecompletion). The constructionlimits the inflow and can beclosed when floods occur orfor maintenance work on thechannel. It is essential thatthe opening extends rightdown to the bottom and doesnot interrupt the continuity ofthe bottom substrate.Lech dam at Kinsau (Bavaria).

These advantages are counterbalanced by thefollowing disadvantages:

m The large surface area required.

m The great length of the channel.

m The sensitivity to fluctuations in the headwaterlevel, which may possibly make necessary anadditional construction at the water inlet (fishpass exit).

m Connection to the tailwater is often onlypossible by including a technical fish pass.

m Deep cuts into the surrounding terrain may beneeded.

46

m They create new habitats, particularly as asecondary biotope for rheophilic species.

m They have a reduced tendency to clogging andare therefore more reliable to operate, withreduced maintenance efforts.

m They by-pass an obstacle usually in a long bendand are therefore particularly suitable forretrofitting to existing dams, that have no fishpass, as normally no constructional alterationsto the dam are required.

m They make it possible for migratory species toavoid the entire impounded area, from the footof the dam to the limit of the backwater.

47

4.2.4 Examples

VARREL BÄKE STREAM BYPASS CHANNEL

Details of the river Details of bypass channel

River: Varrel Bäke Stream, Length: l = 130 m

Lower Saxony Width: bbot = 2.50 m

Function: Mill dam Slope: � = 1 : 45

Discharge: MNQ = 0.35 m3/s Discharge: Q = 0.25 to 0.50 m3/s

MQ = 0.96 m3/s Depth of water: h = 0.30 to 0.80 m

MHQ = 8.14 m3/s Flow velocity: vmax = 1.3 to 1.4 m/s

Height of fall: htot = 2.9 m Distance between rock sills: 3.35 m

Year of construction: 1992

Responsible: Ochtumverband

Figure 4.22:Bypass channel in the Varrel Bäke stream nearthe Varrel Estate (Lower Saxony)

Although the abandoned mill dam is no longerused for hydropower generation, it had to bepreserved for reasons of bottom stabilisationand the maintenance of the ground waterlevels. Water for feeding the fishponds isdiverted at a location upstream of the mill dam.With discharges up to MNQ (mean low waterlevel), the portion of discharge not required forfeeding the fish ponds is sent through the fishpass.

Although the slope is relatively gentle,structural elements had to be incorporated toincrease the water depth and reduce flowvelocity. The crossbars consist of boulders seton edge and embedded in bottom sills. Due totheir height, the boulders remain fully effectiveto positively influence the hydraulics, even withfairly high discharges.The banks are secured toabove the mean water level with a rockfillcovered by a carpet of vegetation.

48

SEIFERT’S MILL BYPASS CHANNELDetails of the river Details of bypass channel

River: Stöbber, Brandenburg Length: l = 120 m

Discharge: MNQ = 0.15 m3/s Width: bbot = 2.4 m

MQ = 0.37 m3/s Slope: � = 1 : 25

MHQ = 0.88 m3/s Water depth: h = 0.20 to 0.50 m

Function: Mill dam Flow velocity: vmax = 1.8 m/s

Height of fall: htot = 3.30 m Year of construction: 1993

Although the former mill damis no longer used to generatepower, the millpond had tobe preserved as a retentionbasin and for the reason ofprotecting the wetlandbiotope that had developed.A bypass channel of 120 min length, through which thetotal discharge is sent up to aMHQ (mean high-waterdischarge), has beenconstructed next to the milldam. The total difference inheight of 3.30 m meant thatthe bed of the channel had tobe secured in parts, withboulder sills incorporated.Other stretches exhibit zerogradient and have noreinforcements, so thatnatural dynamics were ableto develop pools, steepbanks and silting.

spring waterbiotope

fish pass

water inlet device

old concrete pipe, NW 1200,with frost-proof fillingand adapted as biotopefor bats

boulder sills� = 1:25channel secured with rockfill

sections that are not reinforced:� = 0, pools and resting zones

destroyed dam has been repaired

(road to) Buckow

riverStöbber

N

(road to) Waldsieversdorf

mill dammin Q = 20 l/s

mill pond,progressivelysilting up

max. impounding head 36.50ca.44.00

33.0

33.20

monkdecommissioned

old mill race retained for flod relief,a minimum of Q = 20 liters per secondis always allowed to flow through

mill

dwelling

Figure 4.24:Bypass channel at Seifert'sMill

The alternation of reinforcedstretches with boulder sillsand unreinforced stretchesproduces a highly variableflow regime. The areas withzero gradient can be left totheir natural dynamics. Theforeground of the photographshows a cutting of thesloping bank, but this doesnot endanger the installation.

Figure 4.23:Sketch of position of Seifert's Mill Dam

49

KINSAU BYPASS CHANNEL

Details of the river Details of bypass channel

River: Lech, Bavaria Length: l = approx. 800 m

Discharge: MQ = 85 m3/s Discharge: Q = 0.8 m3/s

HQ100 = 1400 m3/s Width: variable, bbot = 2.5 - 4.0 m

Utilisation: Hydroelectric power production Slope: variable, on average

Height of fall: htot = 6.5 m � = 1 : 100 max. about 1 : 30

Responsible: BAWAG Year of construction: 1992

Figure 4.26:Below the main weir the bypass channel isconnected to the old river bed, which foroperational reasons is given a minimumdischarge of 20 m3/sec. The photographshows the upstream section of the bypasschannel of the Lech dam at Kinsau. This zonewas constructed with a gentle slope so that anundulating design could be achieved withoutreinforcement of the channel cross-section.The maximum difference in height is overcomein the lower section, which is constructed incascade form and has a slope of � = 1:20 to1:30. The discharge is controlled by an inletconstruction that also protects the bypasschannel against floods.

The situation at this weir would be significantlyimproved by a second fish ladder at the mainpower station.

N

central dam

ecological protection area

gravel bank

stretch

of free flo

wpower station tailwater

fish stream (without connection to headwater)

cascades, slopeapprox. 1:30

main weir with small power station

eastern side dam

slope approx. 1:1000

bypass channel

inlet construction

biotope for batswestern side dam

main power stationwith subsidery weir

Lech [river]

Figure 4.25: Sketch of position

4.3 Fish rampsA weir can only be converted to a bottom ramp orslide over its whole width (cf. section 4.1) if thewater levels do not need to be controlled andadequate discharge is available. This is often notthe case because of the water requirements forhydroelectric power generation, flood protection,agriculture or fish farms. In these cases, a roughramp of reduced width (a so-called fish ramp) canbe integrated into at least a portion of the weirinstallation to ensure that the aquatic fauna canmigrate (Fig. 4.27). Fish ramps are also suitable forretrofitting to existing weirs that don’t have a fishpass.

The model for designing a fish ramp is againderived from Nature. The primary objective of fishramp design is to mimic the structural variety ofnatural river rapids or streams with more or lesssteep slopes, similar to that shown in Fig. 4.2.

4.3.1 PrincipleA fish ramp is normally integrated directly in theweir construction, and concentrates, as far aspossible, the total discharge available at low andmean water level (Fig. 4.27). At by-pass powerstations, for example, the necessary residualdischarge can be sent through the fish ramp andwater only spills over the weir crest during floods.

Big boulders or boulder sills are arranged to formcascades on the fish ramp to ensure the waterdepths and flow velocities required to allowupstream migration of fish.

The width of the ramp is mainly defined by thedischarge at times of upstream fish migration. Theefficiency of ramps for facilitating upstreammigration might be reduced when discharges are

50

heavy, as in the case of flooding. The need forstructural stability is an essential element incalculating the size of a fish ramp that mustwithstand floods.

4.3.2 Design and dimensions

4.3.2.1 Plan viewAs a rule, fish ramps are set by riverbanks and thebank that receives the greater portion of the currentis the most favourable. The upper, acute angleshould be selected for the construction of the fishramp at submerged weirs standing obliquely in theriver. An existing empty evacuation channel orabandoned sluiceway can often be used for theconstruction of a fish ramp.

Fish ramps installed at fixed weirs with very steepslopes, at obstacles with vertical drops or at weirsequipped with movable shutters often have to beconfined on one side by a solid wall (partition wall inFig. 4.27); cf. also Fig. 4.28. Fish ramps at gentlysloping weirs can be given a inclined lateral filling, toprevent the formation of dead corners (cf. Fig. 4.27).

If the entire discharge passes through the fishramp, the guide current is always clearly directed. Itis therefore possible to place the entrance to theramp further downstream. Fish ramps usually jointhe headwater at the weir crest, which hastechnical advantages, for diverting water duringconstruction for example. The upstream water inlet(i.e. the fish pass exit#) may need to be designedwith a narrowed cross-section to limit dischargesthrough the ramp, particularly during flooding.

The width of the ramp should be a function of theavailable discharge, but should not be less thanb = 2.0 m.

Figure 4.27:Positioning of fish ramps atdamsWeir with movable shutters fixed weir

# remark by the editor

described in section 4.3.2.7, which can have aslope up to 1:10.

Longer sections with gentle slopes and with deeperresting pools are recommended, particularly in thecase of ramps longer than 30 m.

4.3.2.3 Body of the ramp

The construction types usually used for the bottomsills are:

m rockfill construction (loose construction);

m block-stone construction (conventional Schaubergerramp in dressed and ordered construction); or

m dispersed construction (bar construction).

4.3.2.2 Longitudinal sectionThe general requirements of fish ramp design canbe defined as follows:

m mean depth of water: h = 30 to 40 cm;

m slope: Ι < 1:20 to 1:30;

m flow velocity: vmax = 1.6 to 2.0 m/s;

m bottom substrate: many interstitial gaps, rough, continuous, connection to the bottomof the river bed;

m shelters, deep zones and resting pools tofacilitate upstream migration.

Fish ramps require slopes of 1:20 or less. Oneexception is the rough-channel pool pass

51

Figure 4.29:Position of a fish ramp at themain weir of a bypass powerstation. The total minimumdischarge is normally sentthrough the fish ramp, so thatwater only flows over theweir at higher discharges.

Eitorf fish ramp on the Sieg(North Rhine Westphalia).

Figure 4.28:In this example, the fishramp takes the place of theleft-hand weir bay, the totaldischarge up to MQ (meandischarge) being sentthrough the fish ramp. Theramp is designed in theform of a rough channelwith perturbation bouldersarranged offset. The body ofthe ramp is a rockfillconstruction. A low wall madeof stones separates the fishramp from the unobstructedweir area. Krewelin weir,Dölln Stream (Brandenburg).

These can also be transposed to fish ramps, withoccasional slight modifications; cf. section 4.1 andFigure 4.3.

For fish ramps, dressed stone is only used inexceptional cases. Generally, the substructureconsists of crushed rockfill, which is put in layers inaccordance with the rules for base layers or is builtup on geotextile material or possibly a sealinglayer. Building the entire ramp body from solidmaterial increases costs but may be necessary forconstructional or stability reasons. In this case, thesurface layer of the concrete ramp body should beroughened by embedding a layer of gravel or rubbleinto the concrete before it sets.

Ramps of the bar construction type are veryfrequent. Individual deeply embedded boulder barsare arranged to form cascades. The basinsbetween the boulder bars can be filled withavailable indigenous bottom material and left tonatural dynamics for pool formation and silting. Insandy-bottomed rivers, the basins must be coveredwith riprap (a filling of rocks), since otherwise thepools would become too deep after scouring duringheavy discharges. The resulting ramp correspondsto a rockfill ramp with boulder sills.

Problems can arise with rockfill ramp bodies whenthe river carries little water, as water may be lostthrough seepage through the rockfill. In extremecases this may lead to the ramp crest running dry,so that the ramp is unable to function as a fishpass. In rivers that carry a lot of sedimentarymaterial, and where the ramp crest is at the level ofthe headwater bottom, self-sealing takes placerelatively quickly through washed-in sediments.Self sealing may take a very long time if the rampcrest is high and no sedimentary material is carriedby the water, in which case sand and gravel can beartificially washed-in to fill the gaps.

A wedge-shaped or parabolic cross-section isrecommended for ramps where there are varyingdischarges. This cross section concentrates thesmall discharges during low-water periods, whileallowing, at times of high discharges, shallowerregions to form at the sides where flow velocitiesare then correspondingly lower.

4.3.2.4 Big boulders and boulder sills

With the usual gentle ramp slopes of 1:20 and 1:30,and despite a rough bottom, it is not possible tokeep flow velocities below the maximumpermissible limits. For this reason, additionalelements that reduce flow velocity and increasewater depth are incorporated into the slopes of the

fish ramps. Again, large boulders are the mostsuitable for this purpose.

As for bypass channels, the following may be usedwith fish ramps, too:

m Single, large, perturbation boulders aroundwhich the water flows, increasing the roughnessof the ramp and providing resting places andshelters for fish (cf. Figure 4.19), or

m Irregular boulder bars that extend transverselyover the entire ramp width. The water can floweither through or over these bars, which formpool structures (cf. Figure 4.20).

The design corresponds to that given insection 4.2.2.4 for bypass channels. Boulder barshave the advantage of providing adequate waterdepths in the basins even at low discharges, and ofretaining fine sediments.

The hydraulic calculation is described in section 4.4.

4.3.2.5 Bank protectionThe banks of fish ramps must be protected in acompetent manner to withstand the high flowvelocities to which they are continuously exposed.Boulder sills and perturbation boulders requirespecial measures to secure them and preventerosion by the flow, which would otherwiseendanger the functional efficiency and stability ofthe installation. The banks must be stabilized byriprap or set blocks and the protection must extendabove the mean water line. Above this line, theslopes can be secured with live plants. Examplesare given in Fig. 4.18, combinations of these alsobeing possible.

4.3.2.6 Stabilized zone downstream of the fish ramp

The stability of a fish ramp is endangered byscouring, where pools form at the base of the rampand initiate retrogressive erosion. This must becounteracted by securing the river bottom justdownstream of the ramp. The most convenient wayto do this is to use multi-layered rock fills, possiblywith a base layer substructure.

The length of the downstream zone that must besecured corresponds to that for bottom ramps orslides (GEBLER, 1990, KNAUSS, 1979, PATZNER,1982, WHITTAKER & JÄGGI, 1986). Whereriverbeds are resistant to erosion, the minimumlength of the secured bottom zone is between 3 to5 m. In the case of sandy river bottoms endangeredby erosion GEBLER (1990) recommends that thedownstream zone be secured for distancescorresponding to 7 to 10 times the ramp height,

52

The width of the channel should not be less than1.5 m and the clear distance between the boulderbars should be 1.5 to 2.5 m. The minimum waterdepth required is h = 0.4 m.

The bottom of the channel should only beconstructed in concrete if heavy flood dischargesare expected. A rockfill bottom is better.

Large, slender boulders (quarry-stones), embeddedin the bottom layer of the pass, are used to build thetransverse bars (Figure 4.31). Depending on theexpected discharges the boulders are embeddedapproximately 0.4 m in the rockfill bottom,embedded into the channel concrete before it setsor set on a concrete sill. The boulders must beembedded in such a way that water only flowsaround them, and not over them. The clear width ofthe opening between the boulders should not beless than 0.20 m, to enable larger fish to ascendand to reduce the risk of clogging with debris.

The boulders must be offset in both the longitudinaland the transverse directions to allow the dischargeto better fan-out and for better dissipation of energyin the pools. The discharge jets should alwaysimpinge on a boulder of the next transverse bardownstream and should not shoot through the nextbar in order not to form a short-circuit current.

The characteristics of such irregular structurescannot be calculated exactly beforehand and thereis a risk that the fish pass would probably notimmediately function well without testing andmodifying. It is therefore all the more important tocarry out intensive testing during the constructionphase as a result of which the arrangement of theboulders in the transverse bars can be improved.

4.3.3.2 Pile passAnother special form of fish ramp is the so-called“pile pass” (Fig. 4.32) in which wooden piles reduceflow velocity sufficiently to allow for the upstreammigration of fish (GEITNER & DREWES, 1990).This variant is particularly recommended if largerocks are not to be used because they would notmatch the natural characteristics of the river.

In a pile pass piles are arranged, either in rows oroffset at intervals of 5 to 10 times the pile diameter,and rammed into the ramp body or embedded inthe concrete in the case of a solid substructure.Thepiles should be 10 to 30 cm in diameter. The lengthof the piles must be such that water only flowsaround, and not over, them at normal water levels.To improve their self-cleaning, it is recommendedthat the piles should be inclined slightly in the

with the grain size of the rockfill material beinggraded downstream (cf. Fig. 4.4). It is alsorecommended that a pool should be constructed atthe base of the ramp as a calming basin.

4.3.3 Special cases

4.3.3.1 Rough-channel pool passA rough-channel pool pass is a combination of atechnical fish pass and a fish ramp, in which thepool cross-walls are substituted by columnar rocksset on edge. This arrangement allows appreciablygreater water depths to be obtained and a steeperslope (up to maximum 1:10) to be used than withconventional fish ramps. A decisive feature in thiscase is that the differences in water level betweenthe pools must not exceed �h = 0.2 m, to maintainthe maximum permissible flow velocities ofvmax = 2.0 m/s. As a rule, a rough-channel poolpass requires a solid masonry or concrete partitionwall that separates it from the body of the weir (cf.Fig. 4.30).

This type of fish pass is particularly useful forrhithronic streams where there is little spaceavailable for the construction.

53

weir partition wall

weir crest

cross bars of slender bouldersh = 1.0 to 1.2 mgap widths bs = 0.15 to 0.3 m,the boulders are embedded in the bottom.

partition wall

wall, or set blocks,to stalilize the bank

b

If neccessary, correct gaps during test run.

h > 0.4 m

bottom substrate d > 0.2 mcross-section

longitudinal section

Δh < 0.2m

l

Figure 4.30: Rough-channel pool pass (plan)

Fig. 4.31: Rough-channel pool pass (channelcross-section and longitudinal section)

direction of flow, so that they are overflowed for ashort time during flooding.

In contrast with other constructions, pile passes arerelatively insensitive to fluctuating headwaterlevels, if the piles are long enough. In accordancewith the law of linear resistance, flow velocitiesremain identical with different water depths on theramp.

4.3.4 Overall assessmentFish ramps are “close-to-nature” constructions andcharacterised by the following features:

m They are suitable for retrofitting of low fixed-weirinstallations.

m They can be passed even by small fish and fryand by the benthic invertebrates.

m They are also suitable for downstream migrationof fish.

m They have a natural-looking, visually attractivedesign.

m They require little maintenance in comparisonwith other constructions.

m They are not easily clogged; deposits of flotsamand flood debris do not immediately affect theefficiency of the installation.

m Their guide currents are satisfactory and easilylocated by fish.

m They offer habitat for rheophilic species.

Their disadvantages are:

m Sensitivity to fluctuating headwater levels.

m The large discharges necessary for theiroperation.

m The large amount of space they occupy.

54

ramp

row of piles

rough bottom

Fig. 4.32: Pile pass (diagrammatic longitudinal section)

55

4.3.5 Examples

ESELSBRÜCKE FISH RAMPDetails of the river Details of the fish ramp

River: Elz, Baden-Württemberg, Width: b = 2.5 to 3.5 m

carries sedimentary material Slope: � = 1 : 20

Discharge: MQ = 2.0 m3/s Length: l = 30 m

HQ100 = 147 m3/s Water depth: h = 0.2 to 0.4 m

Height of fall: h = 1.20 m Max. flow velocity: vmax = 1.5 m/s

Dam: Fixed oblique weir Discharge: Q = 0.3 to 0.4 m3/s

Function: Protection sill Year of construction: 1993

Figure 4.33:Eselsbrücke fish ramp on the Elz (view from tailwater)

The inclined ramp, that is shallow, blends well into the embankment and the existingweir construction.

Description of the construction:

The fish ramp at the Eselsbrücke weir on the Elz River was incorporated in the upstream area of the weirthat is oblique to the river axis. The ramp was well blended into the landscape and the existing weirconstruction by placing it between the existing bank slope and the body of the weir.

An incision approximately 4 m wide was made in the weir crest to connect the ramp with the headwater.The skeleton of the ramp body consists of ten crossbars made of boulders (h = 1.0 to 1.5 m) arranged ingroups. The area between the crossbars was filled with a mixture of river stones and gravel. Limiteddynamic activity resulting in pool formation and gravel deposits is allowed in the intermediate basins.

56

DATTENFELD FISH RAMP

Details of the river Ramp data

Watercourse: Sieg, NRW Width: b = 10 m

Discharge: MNQ = 3.0 m3/s Slope: � = 1 : 20

MQ = 21.0 m3/s Length: l = 50 m

HHQ = 612 m3/s Discharge: Q = 2.0 m3/s

Barrage: Solid weir sill Max. flow velocity: vmax = 1.5 – 2.0 m/s

Height: h = 1.80 m Year of construction: 1987

Width: b = 90 m Responsible: StAWA# Bonn

Figure 4.35:View from tailwater

Figure 4.34:Dattenfeld/Sieg fish ramp(general view of the bottomsill with incorporated fishramp)

Description of the construction:The fish ramp has been integrated into the angle between the right riverbank and the existing solid weirsill. The body of the ramp was erected as a solid concrete structure with embedded quarry-stones androughened with a layer of coarse gravel embedded in the wet top layer of concrete before it set. Inaddition, large perturbation boulders (diameter up to 80 cm, spaced in such a way as to leave a clear

distance of approx. 1.5 mbetween them) reduce theflow velocity and createshelters for fish as theyascend the ramp. The ramphas rather shallow watertowards the bank that allowseven the weaker fish speciesand benthic fauna to ascend.

# StAWA: Staatliche Ämter für Wasser-und Abfallwirtschaft [GovernmentOffices for Water and WasteManagement] (remark by the editor)

57

DELMENHORST FISH RAMP

Details of the river Ramp data

Watercourse: Delme, Lower Saxony Width: b = 2.4 to 4.5 m

Discharge: MNQ = 0.3 m3/s Slope: � = 1 : 41.5

MQ = 1.0 m3/s Length: l = 27 m

MHQ = 5 m3/s Water depth: h = 0.30 – 0.7 m

Fall head: h � 0.6 m Max. flow velocity: vmax = 1.3 – 1.4 m/s

Use: Formerly for water abstraction Year of construction: 1993

Responsible: Ochtumverband

Figure 4.36:Delmenhorst fish ramp.

View of the headwater endshortly before completion.The gently sloped ramp iscovered with an uninterruptedsubstrate layer of graveland stones. With the rampbuilt in the headwater areaof the weir and the outlet(fish entrance#) situatedimmediately adjacent tothe weir, the formation of"dead corners" is avoided.Rough-surfaced, gentlysloped ramps of this typecan be negotiated by theentire river fauna withoutrestriction.

Details of constructionOne of three existing evacuation gates of the weir was replaced with a gently sloped fish ramp. The fulldischarge runs through the ramp up to mean low-water flow, and water spills over the weir only at greaterdischarges.

The ramp is installed in the headwater area of the weir so that the outlet into (i.e. fish entrance from#) thetailwater lays immediately at the weir foot, adjacent to the overflow. A concrete wall was constructed toconfine the ramp on the mid-river side upstream of the weir. The ramp consists of crossbars formed oflarge boulders, arranged at intervals of 4 to 5.5 m. The boulders lie on gabions. Differences in water levelof ca. 10 cm occur at the crossbars. Trough-shaped pools form between the crossbars. Both the pools andthe passages between the boulders are covered with a continuous layer of coarse gravel and stones,about 25 cm thick, which form interstitial spaces.

The ramp can be closed off for maintenance by means of a sluice gate in the intake area through whichthe water flows onto the ramp and which, at the same time, keeps out debris.

# remark by the editor

58

UHINGEN ROUGH-CHANNEL POOL PASS

Details of the river Fish pass data

Watercourse: Fils, Baden-Württemberg Discharge: Q = 0.34 m3/s

Construction type: Tube weir Width: b = 1.90 m

Height: htot = 3.6 m Slope: � = 1 : 9

Discharge: MQ = 9.8 m3/s Length: l = 32 m

HQ100 = 284 m3/s Water depth: h = 0.6 to 0.8 m

Use: Water power Year of construction: 1989

Figure 4.37:Uhingen/Fils rough-channelpool pass

View from tailwater end.

Details of constructionThe Fils is a hydraulically modified, rubble-carrying upland stream, with a slope of � = 2 ‰, a bottom widthof b = 10 to 15 m, and a stony to gravely bottom.

The fish pass was connected to the existing left-bank wall and separated from the weir body by a lowconcrete partition wall. The boulders, placed on edge, are embedded into the concrete foundation, uponwhich was laid a substrate layer of coarse gravel, ca. 0.20 m thick and containing a few larger rocks. Theboulder bars are spaced at between 1.65 and 3.15 m. The initial concern that widely varying water depths(and flow velocities) would appear at the individual cross-bars due to the irregular discharge cross-sections was not confirmed in the trial run. Although some extra work on the installation, involvingenlarging or plugging of slots, was necessary, the water depths and the differences in water levels laidfrom the beginning within the specified limits.

59

FISH RAMP AT THE SPILLENBURG WEIR

Details of the river Fish pass data

Watercourse: Ruhr, NRW Discharge: Q = 1 m3/s

Discharge: MNQ = 20 m3/s Width: b = 10 m

MQ = 70 m3/s Slope: � = 1 : 25

HHQ = 2300 m3/s Length: l = ca. 102 m

Construction type: Two-stepped, fixed weir Water depth: h = 0.6 to 1.0 m

Height: h = 2.6 m Year of construction: 1993

Use: Water power, drinking water Responsible: StAWA# Herten

Details of constructionThe fish ramp was built at the left flank of the Spillenburg Weir with a difference in level of ca. 2.60 m atlow water. Steel berms provide the lateral boundary of the installation; they also served as floodwaterprotection during the period of construction. The berms were covered with coarse rubble and are nolonger visible.

The fish ramp is divided into 17 pools (length l = 3 to 4 m) formed of boulder bars consisting of largeboulders (each weighing up to 1.5 t). The boulders are placed directly on the ramp body and lean againstone another. The pools are filled with a 20 cm thick layer of gravel and stones. Concrete was not useddeliberately. The discharge is controlled by a regulatable intake structure.

island

old ship lock

weir

Ruhr

Spillenburg

fishpass

cross-section

geotextile leveling layer

outcropping bottom

rock fill

lateralberm

longitudinal section

OW Ruhrintake structure

UWΔh < 0.2 m h < 0,6 m

3 to 4 m

bouldersbottom substrate

# StAWA: Staatliche Ämter für Wasser- und Abfallwirtschaft[Government Offices for Water and Waste Management] (remark bythe editor)

Figure 4.39: Layout and ramp design

Figure 4.38: Setting the boulder bars

60

FISH RAMP AT THE SPILLENBURG WEIR

Figure 4.41: Spillenburg weir; fish ramp after completion

The Department for Fisheries of the LÖBF/LAfAO NRW confirmed the functioning of theconstruction in May 1994. Already a few months after completion, a rich variety of benthicspecies including mussels, snails, caddis fly and dragon fly larvae had colonized the ramp.

Figure 4.40: Spillenburg weir; fish ramp under construction

The crossbars were laid from the intake structure to the tailwater. During the trial run, thewater depths in the pools were corrected by plugging or enlarging gaps in the boulder sillsand it was paid attention to not exceed a maximum water-level difference of Δh = 20 cm.

SCHEUERLEIN (1968) gives a function for theresistance coefficient for turbulent discharge inrough channels and on block stone ramps with adressed and ordered stone base, which,disregarding the air content of the water and anassumed packing factor of 0.5 for the dressed andordered stones, can be written in the followingform:

1 = -3.2 log ⎧⎩(0.425 + 1.01 �) k ⎫

⎭ (4.3)��� hm

Validity range: � = 1:8 to 1:15,ds = 0.6 to 1.2 m

The roughness k of the dressed and orderedstones can be estimated as

k � 13 to 12 ds

From the mean flow velocity vm and the flowsurface area A, the discharge Q is obtained as

Q = vm · A (4.4)

4.4.2 Flow resistance of perturbation boulders

In bypass channels and fish ramps with embeddedperturbation boulders set as shown in Figure 4.42,the influence of the bottom roughness is masked bythe flow resistance of the boulders. The resistancecoefficient �tot in Equation (4.1) can then becalculated from the following formula, cf. ROUVÉ(1987):

�tot = �s + �o (1 – o) (4.5)

(1 – v)

in which is

v = Vs =

immersed vol. of perturbation boulders(4.5a)

Vtot total volume A . I

o = Ao,s =

surface area of perturbation boulders(4.5b)

Ao,tot total basal area Iu . I

�s = 4 cwAs (4.5c)Ao,tot

where cw � 1.5 is the form drag coefficientand As = dsh* the wetted area of theperturbation boulders (4.5d)

where the variable h* becomes theaverage water depth hm if the water flowsonly around the boulders

or becomes the boulders height hs for boulders that are completely submerged.

4.4 Hydraulic designA distinction must be made between the two basictypes of discharge in the hydraulic design of fishpasses:

a) Service discharges: These are understood toinclude the normal discharge range, which isexceeded, or may not be not reached at all, ononly a few days in the year and for which thefunctioning of the fish pass has to beguaranteed. The fish pass must be designed insuch a way that the water depths that fish needfor ascending are respected and that thepermissible flow velocities are not exceeded forthese service discharges.

b) Critical discharge: This is a flooding dischargethat only recurs at intervals of several yearsflooding, but for which the fish pass must bedesigned so that its stability is maintained. Asfish can anyhow not ascend during these heavydischarges, this factor does not need to betaken into consideration for the fish migration.The critical discharge for the fish pass can belimited or adjusted with appropriate water intake(fish pass exit#) structures or regulatory devices.

4.4.1 Flow formulaeThe methods currently recommended for hydraulicdesign calculations of running waters have beencompiled in the DVWK-Guidelines 220/1991“Hydraulic calculations of running waters”.

The calculation of mean flow velocity in openchannels is based upon the Darcy-Weisbach flowformula:

vm = 1 ��������� (4.1)��� 8 g rhy �

where rhy = A (4.1a)lu

The resistance coefficient � is calculated for runningwaters with a rough bottom and under steady,uniform flows (normal flow) according to the formula

1 = -2 log ks /rhy (4.2)

��� 14.84

(Validity range: ks < 0.45 rhy),

in which the equivalent sand roughness diameter ks

is replaced for calculation by the average rockdiameter ds, in the case of a rockfill bottom, and bygrain size diameter d90 in the case of a mixedbottom substrate.

61

# remark by the editor

The resistance coefficient of the bottom �o can bedetermined approximately from the hydraulic radiusrhy of the total cross-section according to Equation(4.2). It is low in comparison with the resistancecoefficient of the perturbation boulders.

For practical applications, it is usually sufficient todisregard v and o in Equation (4.5) and calculatethe overall resistance coefficient from thesuperposition of the individual resistances from

�tot = �s + �o (4.6)

where �s = cW4 As (resistance coefficient of ax ay perturbation boulders) (4.6a)

and As � ds · h* (4.6b)

with ds, ax, ay as in Figure 4.42.

ax and ay represent the average spacing betweenthe boulders in the direction of flow (ax) and acrossthe flow (ay), while, in small rough channels withonly one boulder for each cross-section, ay must bereplaced by the channel width b.

For pile passes, cw can be put to cw = 1.0(GEITNER & DREWES, 1990).

The mean flow velocity is again obtained fromEquation (4.1) and the discharge from Equation (4.4).

The maximum flow velocities in the cross-sectionsbetween the boulders are decisive in allowing fishto pass, and can be calculated approximately fromthe formula

vmax = vm (4.7)

1– AsAtot

where A tot = unobstructed flow cross-section(without perturbation boulders)

and As = sum of the wetted areas of all theboulders within an extremelyconstricted cross-section

The selected slopes, boulder spacing and boulderdiameters should be such that, on average,subcritical flow appears. Changes in the flowpattern must only be allowed in the narrow gapsbetween the boulders if at all.

Given the present state of knowledge the validity ofthese calculations, and particularly of the above-mentioned value for cw � 1.5, has to be limited tothe following ranges:

Boulder spacing ax = ay = 1.5 to 3 ds,

ay - ds > 0.3 m,

Water depth hm/hs < 1.5,

Slope � = 1:20.

RemarksApart from the shape of the boulders, the form dragcoefficient cw in Equations (4.5c) and (4.6a) isdecisively influenced by the effect of the flowpatterns that occur behind the boulders that lie justupstream. The resistance coefficient also changesif the boulders are submerged. The few availabledata on these problems show values both largerand smaller than cw = 1.5. However, generalcalculation methods, such as those that dittodetermine the resistance coefficients of woodaround which water flows, cannot yet be specified.A considerable need for research exists here. A trialrun is, therefore, always required.

An example of calculation

At the main weir of a bypass power station, a fishramp is to be built over which the required minimumflow is Q = 1.2 m3/s. The ramp is to have a slope of1:25 (� = 0.04) and a water depth of h = 0.40 m.Thebody of the ramp is to be built of quarry-stones,whose roughness is estimated at ks = 0.12 m. Theflow velocity should be reduced and fish shelterscreated by perturbation boulders that have an edgelength of ds = 0.6 m. The ramp will have atrapezoidal cross-section as shown in Figure 4.43.Therefore, the following characteristic baselinedata are:

Flow area: A = 2.6 · 0.4 + 2 · 0.42 = 1.36 m2

Wettedperimeter: lu = 2.60 + 2 . 0.4 ������1 + 22 = 4.39 m

Hydraulic radius: rhy = Alu = 1.36

4.39 = 0.31 m

Ramp width at water level:

bsp = 2.6 + 2 · 2 · 0.4 = 4.20 m

62

ax

ay

plan view

hAs

luperturbation boulders

ay

cross-section

m

bm

ds

hs

l

Fig. 4.42: Bypass channel with perturbation boulders

1___ = -2 log 0.12/0.31________ = 3.16 → �o = 0.10.���o 14.84

Hence the overall resistance coefficient is �tot

according to Equation (4.5)

�tot = �s+ �o (1 – o) ___________

1 – v =

0.92 + 0.1(1– 0.18) _______________ 1 – 0.233 = 1.31.

The mean flow velocity is obtained from Equation(4.1) as

vm =����������� 8 g rhy �______�tot

= �������������������8 . 9.81 . 0.31 . 0.04 ________________1.31 = 0.86 m/s

and hence the discharge:

Q = vm · A = 0.86 · 1.36 = 1.17 m3/s � 1.20 m3/s.

Hence, as shown here, the ramp can cope with thedischarge as required in the exercise statement.

The maximum flow velocity will appear in the mostconstricted flow cross-sections where threeperturbation boulders are imbedded in a line. FromEquation (4.7) is obtained:

vmax = vm______As

= 0.86____________

3 . 0.4 . 0.6= 1.83 m/s

1 –Ages

___ 1 – 1.36

_________

vmax < vperm = 2.0m/s (vperm = hightestpermissible water velocity#).

To predict the type of flow that occurs on the ramp(in the unobstructed cross-section), the Froudenumber is calculated:

Fr2 = vm

2 bsp______g Atot

= 0.862 4.20________9.81 .1.36

= 0.233

→ Fr = 0.48 (4.8)

As the Froude number is Fr < 1, the status is that ofsubcritical flow.

In the most constricted cross-section, where

be = bsp – 3·ds = 4.2 – 3 · 0.6 = 2.4 m

Ae = Atot – As = 1.36 – 3 · 0.24 = 0.64 m2

the Froude number becomes:

Fre2 =

vmax2 be_______

g Ae =

1.832 . 2.4________9.81 . 0.64

= 1.28

→ Fre = 1.13. (4.8a)

The perturbation boulders should be placed withaverage axial distances of ax = ay = 1.0 m as shownin Figure 4.43. For a channel section l = 10 m long,about 28 boulders are needed.

Each individual perturbation boulder has a wettedsurface of

As � 0.6 · 0.4 = 0.24 m2

As the calculation is made for a section l = 10 mlong, the volume ratios and surface area ratios are:

28 �4 ds2 h 28 �4 0.62 0.4

v = I A

= 10 . 1.36

= 0.233

28 �4 ds2 28 �4 0.62

o = I . lu

= 10 . 4.36

= 0.18.

Based on As = 28 · 0.24 = 6.72 m2

and Ao,tot = l · lu = 10 · 4.39 = 43.9 m2

the resistance coefficient of the perturbationboulders is calculated as

�s = 4 cwAs____Ao,tot

= 4 . 1.5 6.72____43.9

= 0.92.

Taking into account the bottom roughness, theresistance coefficient is calculated according toEquation (4.2) as follows:

63

a = 1.0 mx

a = 1.0 m y

perturbation bouldersd = 0.6 m

2.60 m

1:2 0.4 m

s

0.6

plan view

cross-section

Fig. 4.43: Sketch to illustrate the example ofcalculation

# remark by the editor

This means that supercritcal flow already appears.But since the Froude number is Fre < 1.7, nopronounced jump occurs.The energy transformationmust be brought about through the stream jetstriking the next perturbation boulder beneath theconstriction.

For comparison:

The simplified calculation approach according toEquation (4.6) yields quite similar results.

When the resistance coefficient of the bottom is�o = 0.10 as already determined, and

�s = 4 cw As____

ax ay= 4 . 1.5 0.4 . 0.6_______

1.0 .1.0 = 1.44 and

�tot = �s + �o = 1.54

a mean flow velocity follows of

vm =����������� 8 g rhy �______�tot

= �������������������8 . 9.81 . 0.31 . 0.04 ________________1.54 = 0.79 m/s

and a maximum value of vmax = 1.68 m/s as well as

a discharge of Q = 1.08 m3/s.

The differences compared with the first resultamount to only about 8%.

4.4.3 Design calculation of boulder sills

Boulder sills are composed of boulders and form asystem of pools due to their retention effect. Theboulders are placed on gaps in the crossbars, i.e.the flow passes only through the clear sectionsbetween the boulders. Where low discharges occurand where channels are relatively wide, it is oftennecessary to partially close the gaps between thelarger boulders - as sketched in Figure 4.44 - byputting bottom sills formed of flat stones. In this

way, higher retention and a greater water depth canbe achieved during low flows.

In conformity with the hydraulic laws, thecharacteristics of flows that go over or through aboulder sill correspond to those of the flow over afixed weir, whereby the two basic cases of complete(no-drowned condition) and incomplete (drownedcondition) flow have to be distinguished.

The limit between complete and incompleteovertopping flow is determined primarily by theratio h/hhead but also by the shape of the sill, cf.PREISSLER/BOLLRICH (1992), Chapter 9.

For preliminary design calculation, it is sufficient todetermine the flow using the Poleni formula:

Q = 23 � � bs���2g hhead

3/2 (4.9)

where bs − the sum of the unobstructed flowwidths.

64

OW

UWb bs.i s.1 h hü

Δh

Δhhh

l

longitudinal view

cross-sectionw

w

Fig. 4.44: Hydraulic design calculation for bypasschannels and ramps with boulder sills(schematic diagram)

Figure 4.45:Fish stream next to the Lechdam of KinsauThe stsmeep slope is brokenup by crossbars made ofboulders. The bottom of thebasins between the sills is notreinforced, enabling scouredpools to be formed.

The size and depth of pools between the sillsshould guarantee low-turbulence flow so thatmigrating fish find enough shelter and opportunitiesto recover from their swimming efforts. The guidevalue for the volumetric power dissipation isE = 150 to 200 W/m3, and can be calculated fromthe following formula

E = g�hQ______

bhmlw=

g�hQ______Alw

(4.11)

where hm = mean water depth in the pools

b = mean pool width

A = mean pool cross-section

lw = unobstructed pool length, lw � l - ds.

At boulder sills made from columnar rocks placedon edge without a ground sill (cf. Figure 4.47) as inrough-bottomed channel pool passes, flowchanges occur in the narrow cross-sectionsbetween the boulders at times of low tailwaterlevels or when the gaps are quite narrow. In thesecases, the headwater depth that results for eachparticular step can also be determined bycomparing the energy levels:

The minimum energy level necessary to carry thedischarge Q through the clear cross-sectionsamounts to

hE,min = 32

3

����������Q2______gbs

2 (4.12)

From the comparison of the energy level in thenarrows with the energy level in the headwater

hE,o = ho + vo

2__2g

= hE,min + hv (4.13)

and taking into account the head loss hv in relationto the critical depth

hv = �vgr

2__ 2g =

�_3 hE,min (4.14)

it results the energy level in the headwater abovethe weir sill as

hE,o = (1 + �/3) hE,min. (4.15)

For the inlet-loss coefficient �, the value � = 0.5 maybe assumed, which applies in the case of sharp-edged inlets.

In this calculation, the headwater depth isindependent of the water level below the sill.

Where there are clear cross-sections of varyingheights, or where the boulder sill is submergedacross its full width (i.e. including the largeboulders), the flow Q must be determined sectionby section. With regard to the spillway coefficient �,the values known for a sharp-edged, wide-crestedweir, or a rounded weir crest, can be useddepending in each case upon the type of sill andthe stone material used. In any case, the limits ofvalidity of the values or formulae must be strictlytaken into consideration. In general, the followingcan be recommended:

Broad, sharp-edged rocks, crushedmaterial:

� � 0.5 to 0.6

Rounded stones, e.g. fieldstones:

� = 0.6 to 0.8

The drowned-flow reduction factor � takesaccount of the influence of the tailwater level h(i.e. the water level downstream of the overflowedboulder) and can be taken from Figure 4.46.The values are about the same as those for abear-trap weir or for a broad-crested weir, cf.PREISSLER/BOLLRICH (1992). In the case ofcomplete (no-drowned condition) discharge, thiscoefficient is � = 1.0.

The maximum flow velocities appearing at theboulder sills are governed by the difference inwater level �h and amount to

vmax = ������2g�h. (4.10)

65

0.6 0.7 0.8 0.9 1

h / h

0

0.2

0.4

0.6

0.8

1

�

head

hhead h

Figure 4.46: Drowned-flow reduction factor �

# remark by the editor

An example of calculation

A bypass channel at a dam in a potamon reach ofa river can be subjected to a minimum ofQmin = 0.1 m3/s for low-water flows and at most toQmax = 0.31 m3/s. Boulder sills are incorporated inthe channel so that a pool systems forms. At lowflows, a water level between 0.30 and 0.40 m isneeded in the fish pass.

The water-level difference is set to Δh = 0.10 m andthe boulder sill spacing to l = 2.5 m. The slope istherefore calculated as

� = �h__I

= 0.1___2.50

= 1: 25 or 4%.

The maximum flow velocity is obtained from

vmax = ������2g�h = ���������������19.62 . 0.10 = 1.40 m/s

and is thus lower than the permissible flow velocity

vpermissible = 2.0 m/s.

The boulder sills consist of fieldstones of ds = 0.6 min diameter and must be set in such a way as toconcentrate the low-water discharge. The clearcross-sections are partially closed with flat stonesthat should be submerged by a water cushion(nappe) of at least hhead = 0.2 m.

In the clear cross-sections, stones of ds = ca. 0.4 mare embedded in the bottom in such a way as torise about 20 cm above the bottom. This leads to ahead of

hhead = 0.4 - 0.2 = 0.2 m.

Since the h / hhead = 0.10/0.20 = 0.5, according toFigure 4.46 a free-flow discharge with � = 1.0 canbe assumed, so that the necessary width for theopening with a spillway coefficient � = 0.5 (for

relatively sharp-edged boulders) is calculated fromEquation (4.9) as

bs = Qmin =

0.123 � � ����2g ho

3/2 23 0.5 .1.0 ������19.62.0.23/2

� 0.75 m

The spaces between the stones are arrangedalternating left and right in order to provide ameandering pool flow. Division into two openings,each ca. 0.4 m wide is also possible. The largerboulders next to the gap are to be placed in such away that the sill is 0.4 m high and the pools arefilled even at low flows. The large boulders,embedded to a depth of 20 cm in the bottom, musttherefore have a diameter of about 60 cm.

The bottom of the channel has 2.5 times the widthof the clear areas between the stones in order toallow the openings to be arranged in staggeredparallel formation so that no short-circuit flow candevelop in the pools. The bottom width willtherefore be

b = 2.5 · 0.75 � 1.9 m,

from which the overall width of the sill for a slope of1:2 is calculated as

b = 1.9 + 2 · 2 · 0.4 = 3.50 m.

The cross-section of the entire channel resultingfrom the construction is sketched in Figure 4.48.

It is important to know the water level at maximumflow to determine the height of the bank protection.The corresponding head then produced must bedetermined by trials, since no straightforwardsolution can be suggested because of the diversepatterns of the spillway profile.

66

bs

h h

�h

o

�hho h

l

longitudinal section

cross-section

u

u

hE,o

vu2g

h =vEL

hE,min

2

Figure 4.47: Flow at a boulder sill

Fig. 4.48: Sketch to illustrate the example ofcalculation

b = 0.75 ms

3.50 m

1.90 m

l

1:2

0.2

0.1

�h=0.1min h =0.30 m0.2

longitudinalsection

cross-section

while at maximum discharge they increase to

vm,max = Qmax_____

A =

0.31________________ _1.9 .0.45 + 2 .0.452 = 0.25 m/s.

The low mean flow velocities in the pools result ina relatively low-turbulence pool flow and allowfiner sediments to settle at least in the low-flowperipheral areas. Bottom protection is neverthelessnecessary, owing to the much greater stresses thatoccur in the spillway areas.

The turbulence conditions in the pools areestimated according to Equation (4.11). AtQmax = 0.31 m3/s and with

A = b·hm + m·hm2 = 1.90 · 0.45 + 2 · 0.452 = 1.26 m2

and lw = l - ds = 2.50 - 0.60 = 1.90 m

the volumetric power dissipation results as

E = gQ�h______

Alw =

9810 . 0.31 . 0.1 _____________1.26 . 1.90

= 127 W/m3.

< Epermissible = 150 to 200 W/m3

4.4.4 Critical discharge over bottom rampsand slopes

For bottom ramps and slopes of the rockfill-type,WHITTAKER and JÄGGI (1986) consider thefollowing equation as a criterion of stability

qpermissible = 0.257 ��������� g s – w________

w �-7/6 d65

3/2 (4.16)

After several trials, the calculations indicate awater-level increase of about 0.10 m.

Supposing that the head hhead is

hhead = 0.2 + 0.1 = 0.30 m

and the drowned-flow reduction factor is � � 1.0for h/hhead = 0.20/0.30 = 0.66 according to Figure4.46, the discharge Q in the gaps is calculated as

Q = 23 � � bs����2g hhead

3/2

= 23 0.5 .1.0 . 0.75 ������19.62.0.303/2= 0.18 m3/s.

Over the remaining width of the weir sill ofb = 3.50 - 0.75 = 2.75 m, where hhead = 0.10 m and� = 0.5 (no flow reduction by submerge, sinceh = 0) a discharge of

Q = 23

. 0.5 . 2.75 ������19.62 . 0.103/2 = 0.13 m3/s

is carried through, so the total discharge amounts to

Qtot = 0.182 + 0.128 = 0.31 m3/s.

Since the water-level differences in this example donot change, as compared with low discharge, thesame maximal flow velocities of vmax = 1.40 m/soccur even at maximum discharge. Only themean flow velocities in the pools change. Atlow-water and with a mean water depth ofhm = (0.3 + 0.4)/2 = 0.35 m, they amount to

vm,min = Qmin_____

A =

0.1________________ _1.9 . 0.35 + 2 .0.352 = 0.11 m/s

67

Figure 4.49:Test run at the Eitorf-Unkelmühle/Sieg fish ramp Precise design calculation ofirregular boulder sills of thiskind is not possible. Theoptimum arrangement of theboulders was therefore initiallydetermined here with the aid ofsandbags. Only after this test,the boulders were permanentlyembedded. Test runs of thiskind must be considered asbeing an essential part of theconstruction process and theircosts must therefore beaccounted for already at theplanning stage.

Since d65 � dS /1.06 and S = 2700 kg/m3, theformula can be written in the form

qpermissible = 0.307 ���g �-7/6 dS3/2 (4.16a)

Equation (4.16) already contains a safety margin of20%.

Block-stone ramps can be subjected to muchgreater loading stress compared with rockfillbottom steps. According to GEBLER (1990), thereis yet no known validated stability criterion. Theexperiments by WHITTAKER and JÄGGI gave anincrease of the permissible discharge by a factor1.7 to 2.0 for dressed and ordered boulders,compared with Equation (4.16). It must be pointedout, however, that the permissible impingement isgreatly influenced by the quality of the work (e.g.faults in the block paving), particularly for block-stone ramps, and other causes of failure such asscour in the tailwater, slope erosion, etc., alsoinfluence the stability of the structure.

The stable foothold of exposed individual rocks(perturbation boulders, boulder sills) has to beproved separately. Impacting forces, both thehydraulic pressures due to differences of waterlevels �h and the forces due to the maximum flowvelocities, must be taken into account here.

4.4.5 Trial runsHydraulic design calculations of natural-lookingbypass channels and fish ramps can always onlybe considered as preliminary estimates. Thereason lies, firstly in the desired (and also aimed at)diversity of the constructional materials (e.g.boulders) used, the cross-sections, flow conditions,etc., and secondly in the fact that up to now only

incomplete studies and results are available.Hence, there are uncertainties in the selection ofthe coefficients (e.g. roughness, dischargecoefficients, intake losses) in the design formulae.Nevertheless, the hydraulic design calculation(preliminary approximation) must be done in orderto estimate the order of size of the requiredboulders and cross-sections as well as theanticipated flow velocities and discharge volumes.Owing to the imponderables, trial runs are alwaysnecessary in which observance of the thresholdvalues and planning targets regarding discharge,flow velocities and water depths can be checkedand, where applicable, corrected. Trial runs shouldalso be carried out for varying discharges, i.e. onseveral different dates, since the hydraulicconditions, both in the fish pass and in thedevelopment of the guide current in the tailwater,vary very widely. In particular, if inherent dynamicdevelopments are permitted, checks should becarried out and, if necessary, improvements madeeven at later stages, i.e. during the regularoperational period.

During the trial run, the following planning targetsshould be checked in particular:

m Flow patterns and water depths: very shallowsections, areas with very high turbulence, short-circuit flows and detached jets must be avoided.

m The maximum flow velocities must not exceed2.0 m/s, particularly at the critical locations (i.e.narrow cross-sections, submerged bouldersills).

m Differences of water level at drops and sills:�h < 0.2 m.

68

succession of stepped pools. The discharge isusually passed through openings (orifices) in thecross-walls and the potential energy of the water isdissipated, step-by-step, in the pools (Figure 5.1).

Fish migrate from one pool to the next throughopenings in the cross-walls that are situated at thebottom (submerged orifices) or at the top(notches). The migrating fish encounter high flowvelocities only during their passage through thecross-walls, while the pools with their low flowvelocities offer shelter and opportunities to rest. Arough bottom is a prerequisite to make pool passesnegotiable for benthic fauna.

5.1.2 Design and dimensions

5.1.2.1 Plan view

The design of pool passes is usually straight fromheadwater to tailwater. However, curved passes orpasses that are folded so as to wind-back once onthemselves by 180°, or even several times(Figure 5.2), resulting in a shorter structure, are

5 Technical fish passes

Technical fish passes include the following types:

m Pool passes

m Vertical slot passes

m Denil passes (counter flow passes)

m Eel ladders

m Fish locks

m Fish lifts

This section describes only the common types oftechnical fish pass, whose hydraulic and biologicaleffectiveness have been adequately studied.

5.1 Pool pass

5.1.1 Principle

The principle of a pool pass consists in dividing upa channel leading from the headwater to thetailwater by installing cross-walls to form a

69

trash rack

power-house

weirweirweir

turbulentzone

turbulentzone

turbulentzone

fishw

ay

Curved fishway Linear fishway Folded fishway

trash rack trash rack

power-house

power-house

(reversed several times)

fishw

ay

fishw

ay

Figure 5.2: Pool passes (plan view) (modified and supplemented after LARINIER, 1992a)

headwater

tailwater

detail

Figure 5.1:Conventional pool pass(longitudinal section andpool structure) (modified andsupplemented after JENS,1982)

also used. Wherever possible, the water outlet(downstream entrance to the fish pass#) below theweir or turbine outlet must be located in such a waythat dead angles or dead-ends are not formed.Basic principles, similar to those outlined inChapter 3, apply here to regulate the distance ofthe fish pass entrance in relation to the weir or theturbine outlet.

An alternative design and arrangement of the poolsis shown in Figure 5.3.

5.1.2.2 Longitudinal sectionDifferences in water level between individual poolsgovern the maximum flow velocities. They aretherefore a limiting factor for the ease with whichfish can negotiate the pass. In the worst case, thedifference in water level (�h) must not exceed0.2 m; however, differences in level of �h = 0.15 mat the normal filling level of the reservoir are moresuitable. The ideal slope for a pool pass iscalculated from the difference in water level andlength of the pools (lb):

� = �h / lb (5.1)

where lb is as shown in Figure 5.4,

so that values of � = 1:7 to � = 1:15 are obtained forthe slopes if the value lb ranges from 1.0 m to2.25 m. Steeper slopes can only be achieved bymaking the pools shorter if the permissibledifferences in water-level are respected. However,this results in considerable turbulence in the poolsand should be avoided if possible.

The number of pools needed (n) is obtainedfrom the total head to be overcome (htot) and thepermissible difference in water level between twopools (�h) (Figure 5.4):

n = htot � 1 (5.2)�h

where the total height htot is obtained from thedifference between the maximum filling level of thereservoir (maximum height) and the lowesttailwater level upon which the design calculation forthe fish pass is to be based.

5.1.2.3 Pool dimensionsPool pass channels are generally built fromconcrete or natural stone. The partition elements(partition cross-walls) can consist of wood orprefabricated concrete.

The pool dimensions must be selected in such away that the ascending fish have adequate spaceto move and that the energy contained in the wateris dissipated with low turbulence. On the otherhand, the flow velocity must not be reduced to theextent that the pools silt up. A volumetric dissipatedpower of 150 W/m3 should not be exceeded toensure that pool flows are not turbulent. A volumetricdissipated power of 200 W/m3 is permissible in thesalmonid zone (LARINIER 1992a).

The pool size must be chosen as to suit thebehavioural characteristics of the potential naturalfish fauna and should match the size and expectednumber of migrating fish. Table 5.1 gives therecommended minimum dimensions for pool sizesand the design of the cross-walls taken from

70

# remark by the editor

Figure 5.3:A pool pass made of clinkerbricks, with alternating pools,at a mill dam in Hude on theBerne (Lower Saxony). Theconstruction fits in well withthe general picture of thehistorical mill.

which fish can ascend by swimming into the nextpool. The openings reach to the bottom of the pooland allow to create a continuous rough-surfacedbottom when the substrate is put in.

The importance of surface openings (notches) isusually overestimated as ascending fish willinvariably first try to migrate upstream by swimmingand only exceptionally will try to surmount anobstacle by leaping over it. The turbulence arisingfrom the detached jets coming out of surfaceopenings adversely affect the flow conditions in thepools. Moreover, with varying headwater levels,submerged cross-walls cause problems in theoptimisation of discharges. Nevertheless, if surfaceorifices are provided, their lower edge shouldstill be submerged by the water level of thedownstream pool in order to avoid plunging flowsand thus allow fish to swim over the obstacle.

Recommended dimensions for orifices andnotches are given in Table 5.1.

In general, submergence of cross-walls should beavoided wherever possible so that water flowsonly through the orifices (or surface notches).Submerged cross-walls at the water outlet (fishpass entrance#) have a particularly negative effectas thus adequate guide currents rarely form.

various literature sources and adapted to thehydraulic design criteria and empirical values forfunctioning fish passes (see Figure 5.5 fordefinitions of the technical terms). The smaller pooldimensions apply to smaller watercourses and thelarger values to larger watercourses. An alternativetype of fish pass must be considered if therecommended pool lengths and discharges cannotbe achieved.

The bottom of the pools must always have a roughsurface in order to reduce the flow velocity in thevicinity of the bottom and make it easier for thebenthic fauna and small fish to ascend. A roughsurface can be produced by embedding stonesclosely together into the concrete before it sets.

5.1.2.4 Cross-wall structures

5.1.2.4.1 Conventional pool passConventional pool passes are characterised byvertical cross-walls that stand at right angles to thepool axis (cf. Figures 5.1 and 5.5) and that maybe solid (concrete or masonry) or wood. Woodencross-walls facilitate later modification but theyhave to be replaced after a few years.

The cross-walls have submerged openings that arearranged in alternating formation at the bottom ofthe cross-wall (dimensions as in Table 5.1) through

71

ΔhΔh<0.2 m

min h=0.6 m

h + Δh

max. impounding head

bottom

headwateremergency shutter or flowregulating device

floating beams

bottom substrate

tailwater

low-water flow

mean flowemergency shutter

1

23 4

5n = 6

l = n l tot

lb

BrŸcke/ Steg

. b

bottom

Figure 5.4:Longitudinal section througha pool pass (schematic)

hs

b

s

h

hb

l

Δ

ba

ah

h s

Δh

b

submerged orifices

cross-walls

bottom substrate

notches

hü

d

hw

hü = hweirhead

Figure 5.5:Pool-pass terminology

# remark by the editor

5.1.2.4.2 Rhomboid passThe rhomboid pass differs from the conventionalpool pass in that the cross-walls are arrangedobliquely to the pool axis and point downstream(cf. Figures 5.6 and 5.7). Since successive cross-walls alternate in their attachment to the channelwalls (i.e. one from the right channel wall, one fromthe left channel wall), each pool has one long sideand one short side. The length of the shorter sideshould not be less than 0.3 m and that of the longerside should be at least 1.8 m. Submerged orificesare always put at the upstream end of the cross-wall while surface notches are always in thedownstream corner (JENS, 1982).

The angle of inclination of the cross-walls relativeto the bottom of the pass is approximately 60° andthe angle between the cross-walls and the poolaxis is 45 to 60°. This gives the cross-walls a veryirregular shape in the form of a rhomboid, hencethe name “rhomboid pass”. Separate moulds areneed for building the right and left side cross-wallssince they are not mirror images and they areinclined in opposite directions.

Otherwise, the same recommendations apply withregard to the average dimensions of the poolsand orifices and the water depths as for theconventional pool passes shown in Table 5.1.

72

Table 5.1 Recommended dimensions for pool passes

Pool dimensions1) Dimensions of Dimensions of Discharge4) Max.Fish species in m submerged orifices the notches3) through differenceto be water in m in m the in waterconsidered length width depth width height width height fish pass level6)

lb b h bS hS2) ba ha m3/s �h in m

Sturgeon5) 5 – 6 2.5 – 3 1.5 – 2 1.5 1 - - 2.5 0.20

Salmon,Sea trout,Huchen 2.5 – 3 1.6 – 2 0.8 – 1.0 0.4 – 0.5 0.3 – 0.4 0.3 0.3 0.2 – 0.5 0.20

Grayling, Chub,Bream, others 1.4 – 2 1.0 – 1.5 0.6 – 0.8 0.25 – 0.35 0.25 – 0.35 0.25 0.25 0.08 – 0.2 0.20

upper trout zone > 1.0 > 0.8 > 0.6 0.2 0.2 0.2 0.2 0.05 – 0.1 0.20

Remarks1) The larger pool dimensions correspond to larger submerged orifices.2) hs – clear orifice height above bottom substrate.3) If a pass with both top notches and submerged orifices is planned, the larger pool dimensions should be applied.4) The discharge rates were determined for �h = 0.2 m by using the formulae shown in section 5.1.3. The lower value

relates to the smaller dimensions of submerged orifices in pools without top notches; the higher discharge is obtainedfor the larger submerged orifices plus top notches (� = 0.65).

5) Pool dimensions for the sturgeon are taken from SNiP (1987), since there is no other data available with respect tothis fish species.

6) The difference in water level refers to the difference in level between pools.

cross-walls

longitudinal section

Fig. 5.6: Cross-wall design of a rhomboid pass(after JENS, 1982)

Figure 5.8 (HENSEN & SCHIEMENZ, 1960).Unlike other pool passes the orifices are not offsetto one another but are aligned. In hydraulic modelexperiments, the shape of the channels has beenoptimised to the extent that virtually no eddies orrollers form in the pools. The resulting flow in thepool is always directed which makes it easier forthe fish to find their way through the pass.

Humped fish passes require long pools and allowfor only small water-level differences of �h = 0.14 mbetween pools. Therefore, humped fish passes areonly appropriate if:

m low heads have to be overcome and

m sufficient space is available for such longconstructions.

Experience with humped fish passes indicates thatthey are also suitable for fish species that are weakswimmers. If a rough bottom is incorporated, thepass can also ensure passage of benthic fauna.The major disadvantages of this type of fish passare the extensive space required and technicaldemands for the shape of the streamlined channelorifices.

5.1.3 Hydraulic designThe following parameters are crucial and must berespected if pool passes are to function correctly:

m flow velocities in the orifices must not exceedthe threshold value of vmax = 2.0 m/s;

m discharge in the fish pass and

m volumetric power dissipation should not exceedE = 150 W/m3 in general, or E = 200 W/m3

within the salmonid region, in order to ensurelow-turbulence flows in the pools.

The advantages of this design are more favourableflow characteristics in the pools and improved self-cleaning. The inclined cross-walls act as guidesleading the ascending fish to the next orifice.

5.1.2.4.3 Humped fish passThe humped fish pass, developed by Schiemenz, isa special form of the pool pass in which the orificesare designed as widening streamlined channels, cf.

73

50 6.50 50 506.50

1.0 6035

3030

3030

60

20

1.80

20

plan view

longitudinal section

7.0 7.0

2.0

Figure 5.8:Design and dimensions ofthe pools of a humped fishpass at the Geesthacht dam onthe river Elbe (measurements incm or m) (after HENSEN &SCHIEMENZ, 1960)

Another humped fish pass isto be found in Gifhorn on theOberaller, which is smaller,having a width of 0.75 m andonly one central submergedorifice of 25 × 25 cm.

Fig. 5.7: Example of a rhomboid pass (Moselleweir Lehmen, view from tailwater)

Maximum flow velocities occur within the orificesand can be calculated from the formula

vs = ������2g�h (5.3)

Equation (5.3) gives a permissible water-leveldifference at the cross-walls of �h = 0.2 m if theupper threshold value vmax = 2.0 m/s is respected.

The equation

Qs = �As������2g�h (5.4)

where As = hsbs (for terms see Figure 5.5)(5.4a)

should be used to determine the discharge in theorifices. The discharge coefficient is influenced bythe design of the orifices and by the bottom substrateand can be estimated as � = 0.65 to 0.85.

The discharge over the top notches can becalculated from

Qa = 23 � � ba����2g hweirhead

3/2 (5.5)

where

hweirhead is the difference in the water levelbetween headwater and tailwater, cf. Figure 5.5

� is the discharge coefficient (� � 0.6), and

� is the drowned-flow reduction factor.

After LARINIER (1992a), the drowned-flowreduction factor �, by which the influence of thetailwater of the respective downstream pool isexpressed, can be calculated from

� = ⎧⎩1 – ⎧⎩1 – �h__hweirhead

⎫⎭

1.5⎫⎭

0.385(5.6)

which is valid for the range: 0 ≤ �h__hweirhead

≤ 1,

for �h > hweirhead, � = 1

The spillway and outflow coefficients in Equations(5.4) and (5.5) can only be approximate values, asthey depend upon the shape of the orifices. Ifnecessary, they must be determined more precisely.

The maximum velocities of the jet coming from topnotches can likewise be calculated fromEquation (5.3).

To ensure a flow with low turbulence andadequate energy conversion within the pools, thevolumetric dissipated power should not exceedE = 150 to 200 W/m3. The power density can beestimated from

E = g�hQ___________bhm(lb – d) (5.7)

in which the total discharge Q = Qs + Qa must beentered for Q.

Some specific characteristics must be taken intoaccount in the hydraulic design calculations ofhumped fish passes. These are made necessaryby the incomplete energy conversion in the poolsand must be looked up in the specialized literature(HENSEN & SCHIEMENZ, 1960).

Example of calculation for a conventional pool pass

Calculations are to be made for a conventional poolpass at a dam. The water level differences betweenheadwater and tailwater fluctuate betweenhtot = 1.6 m and htot = 1.2 m for the discharges thathave to be used as basis for the design, cf.Figure 5.10. The river is classified as potamon, withthe typical potamonic ichthyofauna (chub, bream,etc.). Large salmonids such as sea trout or salmonare not anticipated.

The pool dimensions are selected from Table 5.1as follows:

Pool width b = 1.4 m

minimum water depth h = 0.6 m.

The surface of the pool bottoms is roughened usingriver boulders as shown in Figure 5.9.

The cross-walls are to have only bottom orifices,with a clear orifice span of bs = hs = 0.3 m, cf.Figure 5.9. Top notches are not planned for.

The maximum water level difference must notexceed �hmax = 0.2 m so that, according toEquation (5.2), the number of pools needed is

n = htot � 1 =

1.6� 1 = 7 pools.

�h 0.2

With higher tailwater levels, the water-leveldifference falls to

�hmin = 1.2___8

= 0.15 m.

According to Equation (5.3), the flow velocity inthe orifices is calculated for a �h = 0.2 m (lowwater conditions) as

vs = ����������������19.62 . 0.2 = 1.98 m/s

and for �h = 0.15 m

vs = �����������������19.62 . 0.15 = 1.71 m/s;

74

➝ lb = 1.89 � 1.90 m

is required in order to create low-turbulence flowthrough the pool. The longitudinal section is shownin Figure 5.10. At a water depth of 1.0 m, a bottomsubstrate layer of 20 cm and �h = 0.15 m, theheight of the downstream cross-wall is

hw = 1.0 + 0.20 + 0.15 = 1.35 m

and the height of the upstream wall

hw = 0.8 + 0.20 = 1.0 m.

The height of the intermediate cross-walls isstepped down by 5 cm each.

5.1.4 Overall assessment

Pool passes are among the oldest types of fishpasses and they have certainly proved their worthwherever the design, layout and maintenance wasappropriate. Pool passes are suitable formaintaining the possibility of migration at dams forboth strongly swimming fish, and for bottom-oriented and small fish. In pool passes acontinuous rough bottom can be constructedwhose spaces offer opportunities for ascent to thebenthic fauna.

The relatively low water requirements of between0.05 and 0.5 m3/s for normal orifice dimensionsand differences in water level are an advantage.

On the other hand, the high maintenancerequirements of pool passes are disadvantageous,as there is a high risk of the orifices beingobstructed by debris. Experience has shown thatmany pool passes are not functional during most ofthe time simply because the orifices are clogged bydebris. Pool passes, therefore, require regular,maintenance and cleaning, at least at weeklyintervals.

the flow velocity is thus always lower than thepermissible maximum of vmax = 2.0 m/s.

According to Equation (5.4), with an assumedcoefficient � = 0.75, the discharges amount to

Qs.max = � As ������2g�h = 0.75 · 0.32 · 1.98

= 0.134 m3/s

at low-water, and drop at higher tailwater levels to

Qs, min = 0.75 · 0.32 · 1.71 = 0.115 m3/s.

Following from Equation (5.7) where E = 150 W/m3

at a minimal mean water depth of

hm = h + �h/2 = 0.6 + 0.2/2 = 0.7 m

and a plank thickness of d = 0.1 m, a pool length of

(lb – d) = g�hQ______

Ebhm=

9.81 .1000 . 0.134 . 0.20_____________________ 150 . 1.40 . 0.7

75

bottom substrate: boulders d = 30 cm,pressed to a depth of 10 cm into concrete before it sets

submerged orifices 30 × 30 cm, arranged alternately

weir planks d = 10 cm

1.40 mfreeboard> 0.30 m

1.0

to 1

.35

m

0.30

0.30

0.20

h

= 0

.7 m

m

Figure 5.9: Cross-section through the pools

max. impounding head + 2.20

river bottom

+1.40

max. water levelmin. water level

�h=0.2min h = 0.6

0.8 m+ 1.0Δh=0.15 m

1.60 7 × 1.90 = 13.30 m 1.40

l = 16.30 m

bottom substrated = 0.20 mramp

1:2

groves for emergency shutter

floating beam

river bottom ± 0.0

tot

NW+0.6

groves for emergency shutter

Figure 5.10: Longitudinal section through pool pass (sketch accompanying example of calculation)

76

5.1.5 Examples

POOL PASS AT KOBLENZ

Details of the dam Details of the fish pass

River: Moselle, Rhineland-Palatinate Pool width: b = 1.80 m

Use: Water power generation, Pool length: lb � 2.60 m

navigation (shipping) Number of pools: n = 24

Flows: NQ1971/80 = 20 m3/s Water depth: h = 1.0 m

MQ1931/90 = 313 m3/s Total length: ltot = 102 m

HQ1993 = 4165 m3/s Slope: � � 1 : 12

Fall head: hF = 5.30 m Cross-walls: Concrete walls with

Year of construction: 1945-54 top notches and

Responsible: Federal Waterway Authorities/ bottom orifices

Moselle Hydroelectric Company 30 × 30 cm

Figure 5.11: The Coblenz/Moselle fish pass (view from tailwater)

The fish pass of this dam, that entered into operation in 1951, is situated at the side of the powerstation on the right bank of the Moselle. The functioning of the pass has been checked byGENNERICH (1957), PELZ (1985) and others. Although a large number of fish were able tonegotiate the pass, many more were caught in the immediate vicinity of the turbine outlets,apparently because they were unable to find the entrance to the pass. Tests showed that thedistance of about 45 m between the fish pass entrance and the turbine outlets, which is due tothe great length of ca. 102 m of the pass, is to be blamed.

77

POOL PASS AT DAHL

Details of the dam Details of the fish pass

River: Lippe, at kilometer 99.0, NRW Width: b = 1.0 m

Flows: MNQ = 12.3 m3/s Total length: ltot = 46.0 m

MQ = 32.3 m3/s Slope: � = 1 : 11 to 1 : 24

MHQ = 179 m3/s Construction

Type: Block stone ramp characteristics: Prefabricated concrete parts

Height of step htot = 2.6 m with bottom orifices

Responsible: Lippeverband, Dortmund and top notches

Year of construction: 1985

Fig. 5.12: Dahl pool pass (shortly before going into operation)

Fig. 5.13: Dahl pool pass in operation (view from tailwater)

Description of construction:The bottom sill has been changed to a rough block stone ramp with berms at the headwater and tailwaterends. The pass was integrated into the ramp that was constructed along the undercut left bank;prefabricated concrete parts with grooves, into which the cross-walls were inserted, were used toconstruct the pool pass. The cross-walls have alternating bottom orifices of 25 × 25 cm and top notches.

Data on functioningMonitoring and fish counts by RUPPERT & SPÄH (1992) proved that fish can negotiate the pass.However, ascent by benthic invertebrates is hardly possible because of the smooth concrete bottom.

5.2 Slot passes

5.2.1 PrincipleThe slot pass, or vertical slot pass, was developedin North America and has been widely used theresince the middle of the twentieth century (CLAY,1961; BELL, 1973; RAJARATNAM et al., 1986).This type of structure has also been usedincreasingly in the Federal Republic of Germanyover the last few years.

The slot pass is a variation of the pool passwhereby the cross-walls are notched by verticalslots extending over the entire height of the cross-wall; see Figure 5.14. The cross-walls may haveone or two slots depending on the size of thewatercourse and the discharge available. In theone-slot design, the slots are always on the sameside (in contrast to the conventional pool passwhere the orifices are arranged on alternate sides).

5.2.2 Design and dimensions

5.2.2.1 Plan viewThe same principles as those outlined forconventional pool passes apply to the correctpositioning of a slot pass and the location of itsentrance at a dam, cf. section 5.1.

5.2.2.2 Longitudinal sectionThe longitudinal section of a slot pass correspondsto that of a conventional pool pass as described insection 5.1; see also Figures 5.18 and 5.23.

The characteristics for bottom height at the fishpass entrance and exit, and the water depth,outlined in section 5.2.3 should be observed.

5.2.2.3 Pool dimensionsIn particular, slot width and the number of slots(one or two), and the resulting discharge,determine the pool dimensions required. As withpool passes, it is only possible to attain low-turbulence flow in the pools if the pool sizeguarantees a volumetric power dissipation ofE < 200 W/m3 (LARINIER, 1992a). The pooldimensions given in Table 5.2 have been shown tobe suitable both in laboratory tests and in practicalexperiments (KATOPODIS, 1990; GEBLER, 1991;LARINIER, 1992a). Readers are referred toFigure 5.16 for the relevant terminology. Thedimensions quoted refer to slot passes with oneslot. Where two slots are planned, the width of thepool should be doubled accordingly, therebymaking the sidewall opposite the slot the axis ofsymmetry.

78

Figure 5.15:Slot pass at the Bergerac weiron the Dordogne (France)

(htot=4.0m, b=6.0m, lb = 4.5 m,ltot = 73 m, Q = 2.2 to 7 m3/s,additional 0 to 6 m3/s througha bypass channel, year ofconstruction 1984).

This type of construction hasproven excellent both forlarge salmonids and theeconomically significant allisshad (Alosa alosa) as well asfor cyprinids.

Fig. 5.14: Example of a slot pass with two slots(diagrammatic)

with correspondingly bigger pool dimensions inaccordance with Table 5.2. However, in individualcases, slot widths of s = 0.20 m might also suffice,if the necessary high discharges were not availablefor example. The possible effects on the flowregime in the pools must be considered if the slotwidths are modified compared to those shown inTable 5.2.

The shape of the cross-walls must be such that noshort-circuit current, that would pass through thepools in a straight line from slot to slot, is formedbut rather a main current is created that curls backon itself so as to utilise the entire pool volume forlow-turbulence energy conversion. Such currentregimes are encouraged by incorporating a hook-shaped projection into the cross-walls that has theeffect of deflecting the flow in the area in front of theslot aperture. The slot boundary on the wall sideconsists of a staggered deflecting block. Thedistance “a” (see Fig. 5.16) by which the deflectingblock is staggered compared to the cross-wallcreates a slot current that is deflected by theangle � to direct the main current towards thecentre of the pool. According to GEBLER (1991),the distance “a” should, be chosen in such away that the resulting angle is at least 20o insmaller fish passes. In passes with larger slotwidths, larger angles of between � = 30o to 45o

are recommended (LARINIER, 1992a, RAJARATNAM,1986).

Table 5.2 shows the recommended values for thedesign of cross-walls. The relevant terminology canbe found in Figure 5.16.

It has been proved from models and field tests thatthe current regime required in the pools cannot be

According to GEBLER (1991), the minimumdimensions for slot passes with slot widths ofs = 0.15 to 0.17 m should be lb = 1.9 m andb = 1.2 m.

5.2.2.4 Structural characteristics The most important characteristic of a slot passis its slot width (s), which has to be chosen onthe basis of the fish fauna present and thedischarge available; see Table 5.2. For browntrout, grayling, cyprinids and small fish, slot widthsof s = 0.15 to 0.17 m are sufficient. Where largesalmonids are to be accommodated (for examplesalmon, sea trout, and huchen), and in larger riverswith correspondingly high discharges, larger slotwidths of s = 0.3 m to 0.6 m are recommended

79

b

s

ac

f

αdeflecting blook

lb

cross-wall withhook-shaped projection

maincurrent

d

Fig. 5.16: Dimensions and terminology for slotpasses with one slot only (plan view)

Table 5.2: Minimum dimensions for slot passes with one slot only (dimensions in m) (According to GEBLER, 1991, and LARINIER, 1992a)

Grayling, bream, chub, others Sturgeon

Fish fauna to be considered Brown trout Salmon, sea trout, huchen

Slot width s 0.15 – 0.17 0.30 0.60

Pool width b 1.20 1.80 3.00

Pool length lb 1.90 2.75 – 3.00 5.00

Length of projection c 0.16 0.18 0.40

Stagger distance a 0.06 – 0.10 0.14 0.30

Width of deflecting block f 0.16 0.40 0.84

Water level difference h 0.20 0.20 0.20

Min. depth of water hmin 0.50 0.75 1.30

Required discharge1 Q in m3/s 0.14 – 0.16 0.41 1.40

1 calculated for �h = 0.20 m and hmin

In addition to facilitating ascent for benthic faunaas described earlier, the bottom substrateconsiderably reduces flow velocities near thebottom and in the slots. Figure 5.17 shows that theconsiderable reduction in flow velocities can belargely attributed to the effect of the bigger stones.These protected areas make it possible for specieswith low swimming performance, such as loach,gudgeon or bullhead, to migrate upwards throughthe pass.

It is important to ensure that the bottom substrateof the fish pass is connected to the bottomsubstrate of the watercourse. If the bottom of thefish pass is higher than the river bottom, it shouldbe connected to the river bottom by rock fill.

5.2.3 Hydraulic calculationThe following should be monitored under alloperating conditions:

m water depths;

m flow velocities in the slot (critical values);

m discharges and

m power density for the volumetric powerdissipation in the pools.

The water depths directly below a cross-wall asdetermined from the average level of the bottomsubstrate, should be large enough to preventflushing discharge in the slot. This can beguaranteed by the following conditions:

hu > hgr or (5.8)

vmax > vgr (5.8a)

where hgr = 3

��������Q2____gs2 (5.8b)

vmax = ������2g�h (5.8c)

vgr = �����ghgr (5.8d)

The minimum water depth (measured directlybelow the slots) at �h = 0.20 m, is approximatelyhu = hmin = 0.5 m. The following procedure issuggested to guarantee this depth under alloperating conditions (cf. Figure 5.18):

m The lowest headwater level is the decisive factorin determining the bottom level at the waterintake (fish pass outlet#). The surface of thesubstrate before the first pool (coming from

80

guaranteed if the recommended values are notrespected.

Prefabricated concrete components or wood areappropriate building materials for the cross-walls.As a constructional requirement with woodencross-walls, frames or steel carriers set in theconcrete bottom are needed as abutments. Thedeflecting block can easily be set in the form of apiece of squared timber, standing on its edge andfastened to the wall. Depending on the constructionmethod chosen, the cross-walls may be installedeither as true verticals or perpendicular to thebottom.

The cross-walls should be sufficiently high so thatat mean discharge the water does not flow overthem.

5.2.2.5 Bottom substrateThe slot pass makes it possible to create acontinuous bottom substrate throughout thewhole fish ladder. The material used for thebottom must have a mean grain diameter of atleast d50 = 60 mm. Where possible the materialshould be the same as the natural bottom substrateof the watercourse. The minimum thickness of thebottom layer is about 0.2 m. It is advisable toembed several large stones, that form a supportstructure, into the bottom concrete before theconcrete sets whereas the finer substrate can thenbe loosely added.

rough bottomsmooth bottom

water level

bottom

bottom substrate

Flow velocity

Dis

tanc

e fr

om th

e so

lid b

otto

m

Fig. 5.17: Flow velocity distribution in the slot,comparison between smooth and roughbottom (after GEBLER, 1991).

# remark by the editor

Figure 5.22. Here the values cover a range froms = 0.12 to 0.30 m, hu = 0.35 to 3.0 m and�h = 0.01 to 0.30 m. If larger slot dimensions areto be used, trials with scale models arerecommended.

Equation 5.9 has been used to constructFigure 5.21 for slot widths s = 17 cm and for�h = 0.20 m and �h = 0.15 m. Therefore thedischarge can be directly read off for these cases.

Discharge calculations are more complex ifdifferent headwater and tailwater levels are beingconsidered, for example, if the lower pools have agreater water depth due to specific tailwaterconditions (e.g. backwater influences from below)or if there are different headwater levels (e.g. onfixed weirs or dams). Very different water depthsthen occur at the cross-walls, leading to varyingdifferences in water level, comparable with a damfilling or draw-down line. Discharge calculation canthen only be attempted by iteration through thefollowing procedure: First, the discharge must beestimated by assuming a mean water leveldifference at the most upstream (first) cross-wall.

upstream) is at a level that is determined by theheadwater level minus (hmin + �h).

m The low-water level (NW), that is the lowest levelfor most of the year (except for maybe a fewdays), determines the tailwater level. The levelof the surface of the bottom substrate of the lastpool downstream (water outlet/fish passentrance) should be set to NW – hmin.

At these headwater and tailwater levels the waterdepth is the same in all pools and the water leveldifferences between two successive pools are thesame throughout the pass. This assumption is theworst-case scenario for those impoundmentswhere the maximum headwater level is constant.The number “n” of pools required is found from theequation

n = htot � 1 (5.2)�h

where again �h ≤ 0.20 m should be used as thethreshold value for the difference in water level.

The maximum flow velocity vmax occurs in the slotsand is related to the maximum difference in waterlevel �h by

vs = ������2g�h. (5.3)

Discharges in slot passes are determined by thehydraulic conditions in the slots and can beestimated using the equation (5.9):

Q = 23 �r s ����2g ho3/2 (5.9)

where �r = f (hu /ho) as shown in Fig. 5.22.

The coefficient �r was established from test resultsfrom laboratory trials (RAJARATNAM, 1986 andGEBLER, 1991) and field measurements (KRÜGER1993). The coefficient can be determined from

81

mean-water level

headwater bottom

min. impounding

head

max. impounding heador

high-waterlevel

h+Δh

0.20

min h =0.5 m

Δh ≤ 0.2 m

l = n l

high-waterlevel1

2 3

4

4 5n = 6

min. water level

emergency shutter

floating beam

b

emergency shutter

bottom

tot.

h minsubstrated = 20 cm

NW

Figure 5.18: Longitudinal section through a slot pass (schematic)

ΔhΔh

h > 0.5 m

≥ 0.20 m

� ≤ 1:10

hu ho

Fig. 5.19: Detail of slot pass (schematic longitudinalsection)

Using this estimated discharge, the headwaterdepth ho can be found step-by-step for each cross-wall, starting the calculation from the last,downstream cross-wall. This calculation can alsoonly be solved by iteration, as �r is a function ofhu /ho. If the estimated value for the discharge wascorrect, the calculated value ho at the first (upper)cross-wall must correspond to the headwater level.If this is not so, the calculation must be repeatedusing a different estimated discharge.

In order to guarantee low-turbulence current in thepools, the power density for the volumetric powerdissipation in the pools should not exceed thethreshold value of E = 200 W/m3 given by LARINIER(1992a). The volumetric power dissipation is givenby the formula:

E � g�hQ___________bhm(lb – d) (5.7)

Example of calculation for a slot pass:A weir is to be fitted with a slot pass.The headwaterlevel varies between 61.95 m (summer headwaterlevel) and 62.10 m (winter headwater level). Therelevant tailwater low-water level is 60.60 m withthe bottom of the watercourse being at 60.00 m; thedownstream fish pass bottom should lie at thesame level as the bottom of the river. There is noneed to consider large salmonids when planningthe fish pass.

The discharge, flow velocity and turbulenceconditions in the pass should be determined for theminimum and maximum headwater level.

82

Figure 5.20: Slot current in aslot pass

The current must emergediagonally from the slot toprevent short-circuit currentin the pool (lower Puhlstromdam/Unterspreewald).

0.6 0.7 0.8 0.9 1 1.1 1.2

h in m

0

0.1

0.2

0.3

0.4Q in m3/s

o

Δh = 0.15 mu

Δh

h ho

Δh = 0.20 m

0.5 0.6 0.7 0.8 0.9 1

h / h

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

RAJARATNAM, s = 30 cmKRÜGER, s = 17 cmKRÜGER, s = 12 cmGEBLER, s = 17 cmGEBLER, s = 15 cmintegrating curve

r

o

μ

u

Fig. 5.21: Water discharge in the slot pass with a slotwidth of s = 17 cm

Fig. 5.22: Discharge coefficient �r = f(hu /ho) inEquation (5.9) for sharp-edged slotboundaries.

The dimensions are selected as follows inaccordance with Table 5.2:

m slot width: s = 0.17 m;

m pool length: lb = 1.90 m;

m pool width: b = 1.40 m.

Figure 5.24 shows one proposal for the design ofthe installations (i.e. cross-walls).

With the maximum difference between headwaterand tailwater being htot = 62.1 – 60.6 = 1.50 m anda permissible water level difference of �h = 0.2 m(Table 5.2), the number of pools to be constructedis calculated from equation (5.2):

n = htot � 1 =

1.5� 1 = 6.5 � 7 pools.

�h 0.2

However, further calculation shows that at least8 pools, i.e. nine cross-walls, are required so as notto exceed the permissible water level difference athigh headwater level (winter level).

Therefore, the overall length of the pass, includingan anterior and a posterior chamber (each oflength 1.0 m), is:

ltot = 8 · 1.90 + 2 · 1.0 = 17.20 m.

The pools contain a 0.2 m thick bottom substratelayer. The minimum water depth is chosen ash = 0.60 m in the fish pass to achieve the sameflow regimes in all pools at lower headwater levels,while the total difference between headwater andtailwater is apportioned equally to all cross-walls.From

min htot = 61.95 – 60.6 = 1.35 m

and �h = 1.35/9 = 0.15 m

the level of the water inlet (fish pass exit) on theheadwater side, related to the upper edge of thesubstrate, becomes:

ze,substrate = 61.95 – (0.6 + 0.15) = 61.2 m

and the level of the solid fish pass bottom in theheadwater inlet (fish pass exit) becomes:

ze,bottom = 61.2 – 0.2 = 61.0 m.

At low headwater levels, the same water leveldifferences and water depths occur at each cross-wall. The maximum flow velocity in the slots is then

vs = ������2g�h = ���������������19.62 . 0.15 = 1.72 m/s

< permissible vs = 2.0 m/s.

From Fig. 5.21 the approximate value Q = 0.16 m3/scan be read off for ho = 0.75 m and �h = 0.15 mand is confirmed by the detailed calculation:

ho = 0.75 m, hu = 0.6 m,

hu/ho = 0.6/0.75 = 0.80

Figure 5.22 gives �r = 0.49

Q = 23 �r s����2g ho3/2

= 23 0.49 . 0.17������19.62 .0.753/2 = 0.16 m3/s.

Calculating the volumetric dissipated powertests the turbulence conditions in the pools.As the calculation shows, the thresholdvalue of E = 200 W/m3 is not exceeded withhm = hu + �h/2 = 0.6 + 0.15/2 = 0.675 and

83

NW 60.6061.0 m

61.20 m

summerheadwater

level61.95 m

winterheadwaterlevel62.10

0.300.15

0.75

0.20

0.60

Δh=0.15

1.0 m 8 x 1.9 m = 15.20 m 1.0 m

17.20 m

12 3

4 5 6 7

water level in the passat min. headwater level

60.0

8 9

MW

Figure 5.23: Sketch accompanying the example of calculation (longitudinal section through the slot pass)

Evorh = g�hQ________bhm(lb - d)

= 1000 .9.81. 0.160 . 0.15_____________________ 1.40 . 0.675 . (1.90 . 0.7)

= 138 W/m3.

The flow calculation must be done by iteration athigh headwater level according to the algorithmgiven:

The test calculation shows that for high headwaterlevels there will be a �h1 = 0.15 m at the first cross-wall, hence with

84

ho,1 = 0.90 m and hu,1 = 0.75 m

hu,1/ho,1 = 0.75/0.9 = 0.833 giving �r = 0.46

a discharge of

Q = 23 0.46 . 0.17 ������19.62 .0.93/2 = 0.197 m3/s

can be calculated. Because the discharge isdependent on ho and the coefficient �r isdependent on hu/ho, no explicit solution is possibleand the water levels corresponding to thisdischarge in the pools can only be found byiteration.To this end, �h is estimated at each cross-wall thereby defining �r; then Equation 5.9 is usedto calculate the headwater depth ho for thedischarge Q. The result of the iteration is shown inTable 5.3.

The turbulence conditions are only determined forthe most downstream pool since this is where thehighest water level difference occurs. Withhm = (0.81 + 0.66)/2 = 0.735, the volumetric powerdissipation in the eighth pool is

Evorh = gQ�h8________

bhm(lb - d)=

1000 .9.81. 0.197 . 0.19_____________________ 1.40 . 0.735 . (1.90 – 0.1)

= 198 W/m3 < Epermissible = 200 W/m3

which is just less than the permissibleE = 200 W/m3.

The calculation shows that for high headwaterlevels there are already critical flow velocities ofv � 2 m/s at the lower cross-wall, which is thereason for inserting eight, rather than seven, pools.Were there only seven pools there would be amaximum flow velocity of vs = 2.17 m/s at the lowercross-wall. This example shows that especiallyvarying headwater levels demand careful testing of

bottom substrate

weir planksd = 10 cm

steel profile U 160 (groove and current deflector)

17

81620

190

14016

15

110

deflecting block,squared timber

Fig. 5.24: Proposed design for cross-walls of a slotpass.

The weir planks are held on both sides inU-profiles whilst the central steel profilesimultaneously assumes the function ofthe hooked projection for diverting thecurrent. The width of the central steelprofile should therefore be greater(b = 16 cm) (according to KRÜGER et al,1994b).

Cross-wall no. 1 2 3 4 5 6 7 8 9

Elevation of the bottom above sea level 61.20 61.05 60.90 60.75 60.60 60.45 60.30 60.15 60.00

hu in m 0.75 0.75 0.75 0.75 0.73 0.72 0.70 0.66 0.60

ho in m 0.90 0.90 0.90 0.90 0.89 0.88 0.87 0.85 0.81

�h in m 0.15 0.15 0.15 0.16 0.16 0.16 0.17 0.19 0.21

vs in m/s 1.72 1.72 1.72 1.77 1.77 1.77 1.83 1.93 2.03critical !!

Water level HW = 61.95 61.80 61.65 61.49 61.33 61.17 61.00 60.81 TW =in pool 62.10 60.60

Table 5.3: Water levels and flow velocities at high headwater level

m Not sensitive to varying tailwater levels.

m Benthic invertebrate fauna can also migrate ifthe bottom substrate has continuous interstitialspaces.

m Because the orifices extend vertically over thetotal height of the cross-walls the slot pass isless susceptible to clogging than traditional fishpass designs. Partial clogging of the dischargecross-section does not cause complete loss offunction.

m This type of construction is suitable both for usein small streams with low discharge and for usein larger rivers.

m Slot passes can cope with discharges from justover 100 l/s to several m3/s.

In view of these advantages slot passes should bepreferred to conventional pool passes. Presentknowledge indicates that slot passes should begiven preference over other technical fish passes.

the hydraulic conditions in slot passes in order toavoid the risk of wrongly dimensioning the pass.

5.2.4 Overall assessmentSlot passes (vertical slot passes) are well suited toguarantee ascent by both fish species that areweak swimmers and small fishes.

Other advantages are:

m Vertical apertures that stretch over the wholeheight of the cross-walls are suited to theswimming behaviour of both bottom-living andopen-water fish.

m Reduction in flow velocities near the bottom ofthe slots also allows low performance fish toascend. A prerequisite for this is the installationof a bottom substrate with some largerperturbation boulders.

m Suitable for use even with varying headwaterlevels.

85

86

NEU LÜBBENAU SLOT PASS

Details of bottom step Details of fish pass

Watercourse: Spree at km 165.3 Dam height: htot = 1.2 to 1.4 m

Unterspreewald, Slot width: s = 0.17 m

Brandenburg Number of pools: n = 9

Flows: MQ = 5.5 m3/s Pool width: b = 1.0 and 1.4 m

MNQ = 1.5 m3/s Length of pool: lb = 1.6 to 1.9 m

Year of construction: 1992 Overall length: ltot = 19.2 m

Function: Weir

5.2.5 Example

Figure 5.25:Slot pass at the Spree dam at Neu Lübbenau/Unterspreewald (view from tailwater)

DesignThe pool dimensions are generous with b = 1.4 m and lb = 1.9 m except that the upper three pools are ofreduced width (b = 1.0 m) for constructional reasons. Analogous to Figure 5.24, the cross-walls are madeof 10 cm thick dam planks held on both sides in vertical steel carriers (U-profiles). The diversion blocksare squared timbers vertically dowel-jointed onto the sidewall.

The fish pass is situated between the weir and the ship lock, almost in the centre of the river, which isgenerally considered a disadvantage. The initial fears that the fish might have difficulties in finding theentrance to the pass have not been substantiated although the narrow width (15 m) of the Spree may bethe true determining factor in avoiding failure. A location on the left bank of the Spree would certainly have

been better. Unfortunately, also only a few largeperturbation boulders have been set into thebottom of the pass and these cannot substitutefor a continuous rough bottom substrate.

Fish counts have confirmed that fish passfunctions well. The numbers of ascending fishwere considerable, i.e. over 10 000 fish in bothperiods April/May 1993 and 1994, and with peaksof more than 1 800 fish/day (KRÜGER et al., 1994b).

The original fish passes designed by Denil hadconcave-shaped baffles. Starting from thisprototype numerous variations were developed insubsequent years (see LARINIER 1992b forcomparisons). Of these the so-called “standardDenil pass”, with U-shaped sections in thebaffles as shown in Figure 5.27, proved to be themost functional. Today, Denil passes are almostexclusively of this standard type so that thedescription that follows can be restricted to thestandard Denil pass.

5.3 Denil pass

5.3.1 PrincipleAround the turn of the nineteenth century theBelgian engineer G. Denil developed a fish passwhich was then named a “counter flow pass”,because of the way it worked, and today is called“Denil pass” after its inventor (DENIL, 1909).

The fish pass consists of a linear channel, in whichbaffles are arranged at regular and relatively shortintervals, angled against the direction of flow(Figure 5.26).The backflows formed between thesebaffles dissipate considerable amounts of energyand, because of their interaction, allow a relativelylow flow velocity in the lower part of the bafflecutouts (Figure 5.28). This allows the Denil pass tohave a steep slope, relative to other types of fishpasses, and to overcome small to medium heightdifferences over relatively short distances.

The compact construction of the Denil pass and thepossibility of prefabricating the pass in dryconditions and installing it once assembled makesthis type of construction particularly suitable forretrofitting of existing dams, that do not have afishway, and for use where there is not muchspace.

87

Fig. 5.26: Denil pass (schematic)(modified after LONNEBJERG, 1980)

Fig. 5.28: Characteristic velocity distribution in a Denil pass (modified after KRÜGER, 1994a).

Fig. 5.27: Baffles in a Denil pass (standard Denil, terminology)(modified after LONNEBJERG, 1980).

lower edge baffle cutout

flow velocity v

dist

ance

from

the

botto

m h

bafflesh*

αc α1· sin

b

b

h

cc

a

a

12

5.3.2 Design and dimensions

5.3.2.1 Plan viewThe channel is always straight in plan. Bends arenot allowed as they have a negative influence onthe current characteristics. Changes of directioncan only be achieved by using intermediate pools.

Fish must ascend a Denil pass in one episode ofcontinued swimming, since they cannot restbetween the baffles. Too great a length of pass will,therefore, select for larger and stronger swimmingspecies. As a result, the channel length must bechosen in accordance with the swimmingperformance of fish with low stamina. A resting pool(cf. Figure 5.29) must be built every 6-8 m forcyprinids or every 10-12 m for salmonids. Thedimensions of such resting pools must be chosenin a way that the imported energy is transformedinto low-turbulence flow, and that adequate resting

zones are formed. A natural-looking design can bearranged for the resting pools, which can mimicsmall, natural, vegetated waterbodies. Thevolumetric power dissipation (power density forconversion of hydraulic energy) of the resting poolsshould be less than E = 25-50 W/m3.

The same principles apply to the positioning of theoutlets of Denil passes as apply to pool passes.

5.3.2.2 Longitudinal sectionThe usual slopes for the channel are between� = 1:5 (20%) and 1:10 (10%). The width andpermissible slope of the channel areinterdependent if the hydraulic conditions thatfavour the ascent of fish are to be guaranteed.According to LARINIER (1983), the guideline valuesas shown in Table 5.4 can be recommended.

88

Figure 5.30:Denil pass made of woodGifhorn/Ise (Lower Saxony)

Figure 5.29:Denil pass with intermediateresting pools. View fromheadwater, Gollmitzer mill/Stromat Prenzlau (Brandenburg)

the baffle cutouts and the distance “a” between thebaffles are dependent on the width of the channeland may only be varied within low tolerance rangesas they have a considerable effect on the currentconditions. Denil passes are very sensitive tochanges in these dimensions, making it advisableto stick to the prescribed geometry. The validity ofthe model calculations given in section 5.3.3 isabsolutely restricted to the dimensions of thestandard Denil pass described here. The values inTable 5.5 can be used as guidelines for designingbaffles.

5.3.2.5 Water inlet# and water outlet##

of the passThe water flow should always reach the inlet (fishpass exit) from the direction that represents anupstream prolongation of the channel axis.Narrows and bends before the inlet have a negativeeffect on the flow conditions. There should be some

5.3.2.3 ChannelThe channel of a Denil pass is either made ofconcrete or wood (Figure 5.30). Its clear width mustbe determined as a function of the dischargeavailable and the fish species expected.

If large salmonids are included in the potentialnatural fish fauna the channel width should bebetween b = 0.8 m and 1.2 m. Channel widths ofbetween b = 0.6 and 0.9 m are sufficient if onlybrown trout and cyprinids are expected. It is alsopossible to lay two or more channels next to oneanother in parallel if adequate discharge isavailable.

5.3.2.4 Cross-channel structuresThe baffles are preferably made of wood and onlyin rare cases of metal. All edges should be wellrounded to avoid injury to the fish as they ascend.

The baffles are inclined in upstream direction at anangle of � = 45o compared to the channel bottomand have a U-shaped section that is triangular in itslower part. The dimensions ba, c1 and c2 that define

Table 5.4: Guide values for channel widths and slopes in Denil passes (LARINIER, 1983)

89

Fish fauna Channel width Recommended slopes � Water discharge1)

to be considered b in m as % 1 : n Q in m3/s

for h*/ba = 1.5

Brown trout, 0.6 20.0 1 : 5 0.26

Cyprinds and 0.7 17.0 1 : 5.88 0.35

others 0.8 15.0 1 : 6.67 0.46

0.9 13.5 1 : 7.4 0.58

Salmon 0.8 20.0 1 : 5 0.53

Sea trout and 0.9 17.5 1 : 5.7 0.66

Huchen 1.0 16.0 1 : 6.25 0.82

1.2 13.0 1 : 7.7 1.17

Note: 1) Calculated according to Equation (5.10) with the recommended dimensions of the cross-walls according to Table 5.5

Table 5.5: Guide values for the design of baffles in a Denil pass depending on the selected channel width,after LONNEBJERG (1980) and LARINIER (1992b)

Tolerance range Recommendedguide values

Baffle width ba/b 0.5 – 0.6 0.58

Baffle spacing a/b 0.5 – 0.9 0.66

Distance between the lowest point of the cutout and the bottom c1/b 0.23 – 0.32 0.25

Depth of the triangular section c2/c1 2 2

# i.e. fish pass exit (remark by the editor)## i.e. fish pass entrance (remark by the editor)

channel bottom, measured from the water surfacedown to the lower edge of the baffle sections, (cf.Figure 5.31). The value of h* should not be lessthan 0.35 m and should ensure that h*/ba = 1.5 to1.8, for maximum discharge, since the velocitypattern according to Figure 5.28 is no longerguaranteed at greater water depths.

The flow characteristics in Denil passes have beeninvestigated by LARINIER (1978), LONNEBJERG(1980), RAJARATNAM (1984) and KRÜGER(1994), to name but a few. The results again showthe susceptibility of Denil passes to changes ingeometry (cf. also KATOPODIS 1990). Thedischarge through a standard Denil passwhich respects the recommended channel andbaffle dimensions shown in Tables 5.4 and 5.5can be calculated by using the KRÜGER’s (1994)equation:

Q = 1.35 ba2.5���g � ⎧⎩

h*__ba

⎫⎭

1.584(5.10)

The discharge required for the Denil pass is shownin Table 5.4 as a function of channel width andslope.

Hydraulic model tests are recommended to findthe optimum design where the geometriccharacteristics to be used differ from the standardDenil pass.

As already mentioned, resting pools must be builtafter every 6 to 8 m of channel length (afterapproximately 10 m for salmonids) where largeheight differences are to be overcome. The poolvolume must be large enough to allow a low-turbulence dissipation of the imported flow energy.The chosen pool size should therefore be such thatthe following condition is fulfilled:

90

means to close off the channel at the water inlet tomake maintenance work on the channel easier.

The Denil channel must project sufficiently far intothe tailwater that the outlet (fish pass entrance) isat least at the level of water in the channel even atlow water. During higher tailwater levels, thebackwater influence is displaced further into thechannel, without having any great effect on thecurrent patterns in the fish pass.

The water outlet of a Denil fish pass should, wherepossible, be connected to the bottom of thewatercourse to help fish species that migrate alongthe bottom to better find the entrance into the pass.In shallow watercourses the bottom must be securedusing gravel or rubble; this is, however, in fact usuallyanyhow required and done by constructing calmingbasins or secured downstream bottom zones.

5.3.3 Hydraulic calculationsHydraulic calculations for Denil passes are onlypossible with the help of empirical approaches.Individual tests show that the correct range ofvalidity of the results must be strictly observed andthat extrapolation into other geometric or slopeconditions is highly uncertain. Therefore, it is hereagain mentioned explicitly that the calculationsbelow are only applicable to the standard Denilpass of given dimensions.

The water depth in the Denil pass is affected by thewater level at the entrance and by entry losses. Inpractice, the diagram (Figure 5.32) given byLONNEBJERG (1980) is sufficiently precise. Hereho refers to the level of the lower edge of the firstbaffle section (first baffle upstream) whilst h*describes the water depth perpendicular to the

Fig. 5.31: Denil pass (longitudinal section, sketchillustrating the construction principle andterminology)(modified after LARINIER, 1992b).

Fig. 5.32: Relation of h* = f(ho)(modified after LONNEBJERG, 1980)

ho

α = 45°

α

hh*

ac α1· sin

0 0.2 0.4 0.6 0.8

h* in m

0

0.2

0.4

0.6

0.8

1h in mo

__2

Qv2

E = _______bmhmlb

< 25 to 50 W/m3 (5.11)

where bm, hm, lb are the mean width, waterdepth and length of the resting pools andv = Q/(h* · ba).

It is difficult to prove the permissible flow speed ina Denil pass. The velocity distribution given inFigure 5.28 must be guaranteed by correct designof the baffles.

Example of calculation:A dam with a maximum difference in water level of3.0 m between headwater and tailwater is to befitted with a Denil pass. The fish pass should be

91

0.80

0.46

0.40

0.20

1.30

Fig. 5.33: Dimensions of the baffles

1 : 6.66

α

α = 45°

headwater+63.0

a

a = 0.53 m

1 pool+62.0

2 pool+61.0

tailwater+ 60.0

6.75 3.0 6.75 3.0 6.75

1.20

1.0

denil section 1denil section 2

denil section 3

st

nd

Figure 5.34: Longitudinal section of the fish pass

tailored to suit both cyprinids and the huchen. Theheadwater level can be held constant at + 63.0 munder all likely operating conditions. The lowesttailwater level is at + 60.0.

The channel width of b = 0.8 m is chosen fromTable 5.4 and the slope of the channel is to be

� = 15% = 1 : 6.66.

The baffle spacing (a) is obtained from:

a = 0.66 · b = 0.66 · 0.8 = 0.53 m.

Two intermediate pools are required to overcome aheight difference of 3 m, thus the total channellength is divided into three channels with a lengthof l = 6.75 m each (cf. Figure 5.34).The water depthin both intermediate pools should be abouthm = 1.20 m.

The dimensions of the baffles are chosen inaccordance with Table 5.5 and are shown inFigure 5.33:

The value of h* is determined by

h* = 1.5 · ba = 1.5 · 0.46 = 0.7 m.

Therefore, the height of the baffles is

ha = 0.7/sin 45° + 0.2 + 0.1 (freeboard) = 1.29 � 1.3 m.

Figure 5.32 gives the inflow water level

ho = 0.83 m

so the bottom height of the first baffle is calculatedfrom

h1 = h0 + c1 · sin(� + arctan �) (5.12)

h1 = 0.83 + 0.2 · sin (45° + 8.53°) = 0.99 � 1.0 m.

m It can easily be used to retrofitted existing dams;

m It is not susceptible to variations in tailwaterlevel;

m It usually forms a good attraction current in thetailwater.

The disadvantages of this type of construction are:

m High susceptibility to variations in theheadwater levels. In practice, only variations ofa few centimetres, with a maximum of about20 cm, are permitted;

m Relatively high discharges needed compared toother construction types;

m Clogging with debris can easily upset itsfunctioning. Denil passes require regularinspection and maintenance.

The success of Denil passes has been adequatelyproven, in particular for salmonids, and cyprinidssuch as the barbel, that have a lower swimmingperformance, by counting numbers of ascendingfish. On the other hand, the monitoring that hasbeen carried out to date shows that small fish andfish of low swimming performance have only arestricted possibility to pass through, especiallywhen the length of the structure is too long. Thereis, therefore, a selection for larger, strongerswimming species and individuals.

Likewise, ascent by microorganisms and invertebratebenthic fauna must be rated impossible.

For these reasons Denil passes should only beused if other structures cannot be built, for exampledue to lack of space.

92

The discharge is calculated by using equation(5.10):

Q = 1.35 ba2.5���g � ⎧⎩

h*__ba

⎫⎭

1.584

= 1.35 . 0.46 2.5���������� 9.81.0.15 ⎧⎩

0.7___0.46

⎫⎭

1.584

Q = 0.457 m3/s.

The dimensions of the resting pools can be foundusing equation (5.11). With E = 35 W/m3 and theflow velocity

v = Q/A � Q_____

ba . h*

= 1.42 m/s

the necessary area “Anec” of the resting pool isthen:

__2

Qv2 1000____2

. 0.457 .1.422

Anec = lb . bm = ______hm

. E = __________________

35 . 1.20

= 10.97 m2.

The pool width of bm = 4.0 m and pool length oflb = 3.0 m give a base area of 12.0 m2. The diagramin Figure 5.34 shows a longitudinal section of thefish pass.

5.3.4 Overall assessmentThe Denil pass is characterized by the followingadvantages:

m It can have steep slopes with resulting lowspace requirements;

m There is the possibility of prefabricating thechannel elements;

93

UNKELMÜHLE DENIL PASS

Details of the dam Details of fish pass

Watercourse: Sieg, NRW, Width: b = 0.64 and 0.74 m

Flows: MNQ = 1.5 m3/s Length: l = 6.60 and 9.50 m

MQ = 22 m3/s Slope: � = 1 : 4.5

HHQ = 700 m3/s Fall Head: hF = 3.2 m

Use: Water power Discharge: Q = 0.3 to 0.38 m3/s

Year of construction: 1930 Responsible: StAWA Bonn

Operator: RWE-Energie AG

5.3.5 Example

DesignAn existing traditional pool pass around the powerhouse of the hydropower station at Unkelmühle, thathad been built in 1930, was replaced by a Denil pass under the control of the StAWA, Bonn, as the formerfish pass was not functioning properly owing to the small dimensions of the pools and the slope being toosteep. The new pass consists of two Denil channels connected by a resting pool, which was built as animpervious, reinforced concrete trough with stone rubble cladding and planted with aquatic vegetation.The upper channel is 6.60 m long and the lower 9.50 m and both have a slope of 1 : 4.5. The channelsare made of reinforced concrete with wooden cladding to which the wooden baffles are fixed. The fishpass is fed by a discharge of 300 to 380 l /s.

Ascending fish can be observed through an under-water viewing window in the observation chamber atthe edge of the resting pool. An installation that can accommodate a fish trap for monitoring purposes hasbeen fitted to the water inlet of the upper channel (fish pass exit#).

Figure 5.35: Fish pass at the hydroelectric power station Unkelmühle/Sieg (NRW)

N

turbineoutflow

6.60

RWE powerhouse

fish trap formonitoring purposes

upper denil channel

head race

resting pool

trash rack

+88.45lowerdenilchannel

+86.80

tail race

9.50

7.60

+ 90.00

water inlet

observationchamber

# remark by the editor

94

Data on efficiency:LUBIENIECKI et al. (1993) tested theefficiency of the fish pass from May1991 to May 1992 using the fish trapto monitor fish migration. Thenumbers of ascending fish were tosome extent surprising. On some200 control days over 1000 ascendingbarbel were found. Monitoring also

showed that other fish species were ascending the pass in only very small numbers. A particular successin 1993 was finding that sea lampreys were ascending the pass. This species died out 40 years ago in theRiver Sieg but new fishways had made it possible to recolonize the Sieg.

Example (continued)

Figure 5.36:View of the lower Denil channel andthe resting pool above.

The attraction current that affects alarge area of the tailrace is clearlyvisible; it is responsible for the easewith which the entrance of the passis detected by fish.

Figure 5.38:Sea lamprey (Petromyzon marinus)from the Sieg.

Figure 5.37:View of the lower Denil channel.

The concrete channel is coveredwith wood to which the baffles arefitted that have a U-shaped cutout.The high turbulence water-airmixture on the surface misleads theobserver as there are much lowerflow velocities near the bottom areaof the channel.

positioned bundles of brushwood etc, have provenunsuccessful. Therefore, mitigation facilitiesspecially attuned to the performance of glass eelscan be useful in addition to existing fish passes,particularly in the estuary area of rivers where theascending eels are still very small. Eels of largerbody lengths also use the more common types offish pass so that separate eel ladders are notrequired there.

5.4.2 DesignTwo principle types of design are common:

1. Pipes are laid through the body of a weir, oftenclose to the river bottom, in which bundles ofbrushwood, fascines or other baffles are placedto lower the flow velocity. The baffles are oftenattached to a chain, so that they can be pulled

5.4 Eel ladders

5.4.1 Peculiarities of eel migrationThe eel, being a catadromous migrant fish, lives inalmost all standing and flowing waters connectedto the sea. It grows in fresh water until sexualmaturity and then migrates down the river to thesea in the silver phase, presumably to spawn in theSargasso Sea.

The post-larval eels (so-called glass eels) reachthe coast of Europe in two to three years andpenetrate from there into inland waters. Theascending eels with a body length of 7 to 25 cm arecertainly in a position to overcome small obstacleswith rough surfaces, small cracks or fissures.However, the ability of young eels to ascend isfrequently overestimated and many weird andwonderful climbing aids, such as vertically

95

Figure 5.39:Eel (Anguilla anguilla)

Figure 5.40:Rhomboid pass and eelladder on the Sauer dam atRosport (Rhineland-Palatinate).

View from headwater.

The eel ladder, in whichbrushwood bundles are placed,is paralleling the bank-side wallof the rhomboid pass.

out and replaced. The eel has to wind its waythrough the built-in devices to overcome theobstacle to migration. This type of device hasnot been found suitable in practice since thetubes become quickly clogged with debris; thisis very difficult to discover (the pipe iscompletely beneath the water) and just asdifficult to remedy.

2. Relatively small and flat open channels, whichpass from tailwater to headwater and are madeof concrete, steel or plastic in which variousfittings are placed that help eel in windingupwards. According to JENS (1982), brush-typestructures have proven to be most suited to thispurpose. However, brushwood, gravel and gridsare also used as built-in devices. Thesechannels should have a cover as protectionagainst predators such as rats and gulls.

The way in which the eel ladders are laid outensures that water only trickles through them, sothey are just moistened. This means that theycannot be used for the ascent of other fish species,nor is this intended.

The exit of an eel ladder must always be at thebank. Connection with the bottom is not required asglass eels migrate in the surface-water layer. Itshould be noted that the small discharges through

an eel ladder are barely sufficient to provide anadequate guide current and, if necessary,additional water supply, e.g. through a bypass, hasto be provided to create sufficient attraction.

Because of the low swimming performance of theyoung eel, the exit of the pass into the headwatermust at all costs be placed in an area with gentlecurrent; under no circumstances it should beplaced just close to the screens of the turbineinlets.

5.4.3 Overall assessmentEel ladders are only suitable for allowing upstreammigration of eels. Due to its selectiveness, an eelladder on its own is not sufficient for mitigation ifalso other fish species have to pass the obstacle asthe eel ladder would not allow them to do so. Eelladders are specially recommended in the estuaryareas of rivers in addition to the other technical fishpasses (pool passes, Denil passes etc) tospecifically allow young eel to migrate upstream.

5.5 Fish lockThe use of fish locks as mitigation devices hasbeen known for quite some time now and has beenapplied especially in the Netherlands, Scotland,Ireland and Russia (van DRIMMELEN, 1966;JENS, 1982). Some fish locks exist on the RiversSaar and Sieg in Germany.

The structure of a fish lock is similar to a ship lock(see Figures 5.42 and 5.43). Both essentiallyconsist of a lock chamber as well as a lower inletand an upper outlet structure with closing devices.However, there are some differences as far as thefunctioning is concerned which also make it clearthat a ship lock, over and above its actual purpose,is not normally sufficient to sustain fish migrationsnor can it replace a fish pass. In particular, the lackof a permanent guide current, the short openingtimes of the sluice gates, the high turbulence in thechamber during filling procedures and the positionof the lock at the dam only exceptionally allowfishes to find their way through a ship lock.

However, it is possible in exceptional cases toconsider whether the operating mode of the shiplock can be modified temporarily (e.g. during themain migration season for glass eels or salmonids)to facilitate the ascent of fish.

5.5.1 PrincipleThe functional principle of a fish lock is shown inFigure 5.42. It is possible to distinguish fouroperating phases:

96

Fig. 5.41: The eel ladder at the Zeltingen dam onthe Moselle (Rhineland-Palatinate) isadapted to the specific migratorybehaviour of the eel. The ladder consistsof a channel in which an endless plasticbrush is laid to help the eel movingupstream by winding its way through thebrush. Also this eel ladder wasconstructed in combination with aconventional pass and parallels the side ofthis pass (after JENS, 1982).

270

230

cover

console

rectangularchannel

"endless" nylon brush

concrete wall

160

do not exceed 1.5 m/s at any time or in any placewithin the chamber and that the water level in thechamber rises or falls at less than 2.5 m/min(SNiP, 1987).

With regard to the position of the fish lock at thedam and the location of the entrance and the exit,the same criteria apply as for other fish passes.Because of their compact structure fish locks can,for example, be housed in partition piers.

5.5.3 Overall assessmentFish locks have an advantage as alternatives totraditional technical fish ladders if

m There is not much space and

m There are very large height differences toovercome.

Equally the fish lock offers structural advantages ifvery large (e.g. sturgeon) or low performance fishspecies have to be taken into consideration.

It is not possible at present to exclude a selectiveeffect with regard to the ease with which they arepassed by invertebrates, bottom-living fish andsmall fish.

The moving parts, drive and control systemsrequire increased maintenance efforts comparedwith traditional fish passes.

1. The lock is idle. The lower gate is open and thewater level in the chamber is at the level of thetailwater. The fish must now be shown the wayfrom the tailwater into the lock chamber by aguide current. To this end either the upper sluicegate is slightly opened or a guide current isproduced by sending water through a bypass(i.e. pipeline) that ends at the entrance to thelock chamber. The fish gather in the chamber.

2. The lock chamber is being filled. The lowersluice gate is closed; the upper one is slowlyopened fully. The flow coming from theheadwater leads the fish in the chamber to theupper exit.

3. The water level in the chamber is equal to thatof the headwater. Water is passed into thetailwater through a slot in the lower sluice gateor a special pipe, whereby an attraction currentis produced at the exit to the headwater.The fishfind their way out of the chamber.

4. The lock chamber is emptied after closing theupper and opening the lower sluice gates. Thelock is again in an idle state.

The timing of the operating modes is doneautomatically. Usually there are half-hourly tohourly operating intervals. The most efficientrhythm and, if applicable, the necessary seasonaladjustments, can only be determined throughmonitoring controls.

5.5.2 DesignThe design of the chambers and closing devices isvariable and largely depends on the specific localconditions. When designing the chamber bottomthere should be measures to prevent fish being leftin areas that become dry. To this end, the chamberbottom can have a stepped design (Figure 5.43) orjust be inclined (Figure 5.42). The chamberdimensions should clearly be larger than the poolsof conventional fish passes as many more fishmust remain in the chamber for a longer time. Theconstruction of a rough bottom is possible inprinciple. Chambers that are open to the top aredesirable.

The guide current may be produced, or intensified,by sending water through a bypass (cf.Figure 5.43). The cross section of the water outletof the anterior chamber should be dimensioned insuch a way that an effective guide current isguaranteed in the range between v = 0.9 andmaximum of 2.0 m/s (on average v = 1.2 m/s).When designing the influxes and discharges for thefilling and emptying phases of the lock chambercare should be taken that the mean flow velocities

97

1

Initial positionupper sluce gate

slot

lower sluce gate

opened

attraction current

closed

opened

Filling the lock2

3

slot

Fish moving out of the lock

4

Empting the lock

slot open

attraction current

attraction current

headwater

headwater

headwater

headwater

tailwater

tailwater

tailwater

tailwater

lock chamber

Fig. 5.42: How a fish lock works (schematiclongitudinal section)

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5.5.4 Example

SCHODEN FISH LOCK

Details of the dam Details of the fish lock

Watercourse: Saar, Rhineland-Palatinate Fall head: hF = 5.70 m

Flows: MNQ = 19 m3/s Chamber width: b = 1.0 m

(from 1946/93 MQ = 80 m3/s Length: I = 34 m

data series) HHQ = 1 230 m3/s Year of construction: 1981

Use: Water power, ship navigation Operator: WSA Saarbrücken

Control flow: Q = 2 � 30 m3/s Responsible: RWE Energie AG

Structural design:During the development of the Saar as a waterway for shipping, a fish lock was constructed on theSchoden dam. This was incorporated in the partition pier between the powerhouse and the weir. Theentrance to the lock is located near to the turbine outlet.The entrance into the fish lock has a cross sectionof 0.65 � 0.80 m and is submerged. On the headwater side, the exit releases fish into the impoundment.

A hydraulically activated rolling gate serves to close off the lock towards the tailwater while towards theheadwater the lock chamber is sealed off by a dam shutter. A fish trap can be installed between the shutterand the exit for monitoring purposes.

Figure 5.43: Longitudinal section and plan view of the Schoden fish lock (Saar)

1.0 4.56 11.26

141.00 HW 142.00

grating bridge grating

bypass

headwater gate

17.47

Saar [river]

1.0A

fish lock

draft tube exit

fishlockentrance

chamber hosting the shutter

A

rolling shutter

tailwater 136.31

134.95

control panel

cross-sectionA-A

weirfish trap partition pier

2 x DN 100

99

SCHODEN FISH LOCK

Example (continued)

Figure 5.44: The Schoden/Saar fish lock (view of the weir installation)

The lock is installed in the partition pier between the weir and the powerhouse (see the arrow).

Data on effectiveness:Fish monitoring in the lock carried out by the district authority in Treves confirm the effectiveness of thefish lock. In all, in the period from 15.4.1992 to 18.7.1992, over 50 000 fish moved through the lock(KROLL, 1992, oral presentation at the symposium on “Long distance migratory fish in rivers regulated bydams”, held at Koblenz on 16 and 17 November 1992). Tests regarding the effects of different turbineoperation modes on the effectiveness of the fish lock showed no significant differences in numbers of fishentering the lock, regardless of whether only the turbine near the lock was in operation, or only the oneon the bank side, or both turbines together.

5.6 Fish lift

5.6.1 PrincipleWhere there are considerable height differences(> 6 to 10 m) and little water available there arerestrictions on the applicability of conventional fishpasses, due to the building costs, the spacerequirement and, not least, the physiologicalabilities and the performance of the fish. Wheregreat heights are to be overcome, solutions havebeen developed to carry fish from the tailwater tothe headwater using a lift.

A trough is used as a conveyor and is eitherequipped with a closable outlet gate or can betilted. When in the lower position, the trough is sunkinto the bottom. Fish have to be attracted towardsthe fish lift by a guide current. In addition, a slidingand collapsible grid gate located in front of the lift,may serve to push the fish into the lift and thusabove the transport trough.The lower gate of the liftcloses on a regular cycle. The fish gathered abovethe trough can no longer escape, are “caught” bythe rising trough and conveyed to the top. Here awatertight connection may be made to the upperwater level or else the trough is simply tipped outabove the headwater level into a funnel. Along withthe water from the trough the fish reach the upperchannel where, once again, there must be a clearattraction current.

The regular cycle is determined according to actualmigratory activity.The operation is usually automatic.

5.6.2 StructureFigure 5.45 shows in a diagrammatic sketch thestructure of a fish lift as constructed both on theeast coast of the United States and in France(LARINIER, 1992c).

The same principles apply to the positioning of afish lift as for conventional fish passes.

5.6.3 Overall assessment

m Little space is required, and large heightdifferences can be overcome with such fish lifts,e.g. even at high dams. However, the structuralexpenditure is considerable.

m Since the fish are conveyed upstream passively,fish lifts are suitable for species with lowswimming performance as well as for thetransportation of large fishes.

m Fish lifts are not suited for the upstreammigration of invertebrates and the downstreammigration of fish.

m Large variations in the tailwater always meandesign problems in providing an adequate guidecurrent.

m The expenditure on maintenance for fish lifts ishigher than for traditional fish passes.

100

headwater

tailwater

bypass (attraction current)

attraction current

attraction current

trough inlower position

trough in upperposition

motor

steel rope

lift, shaft

shutter

outlet, closable

collapsible andsliding grid gate

shutter, sliding down

Figure 5.45:Schematic view of thestructure of a fish lift andfunctional principle (modifiedafter LARINIER, 1992c).

101

TUILIÈRES FISH LIFT

Details of the dam Details of the fish lift

Watercourse: Dordogne, France Lift height: h = 10 m

Use: Water power Transport trough volume: V = 3.5 m3

Flow: Q = 285 m3/s Guide current: Q = 4 m3/s

Fall head: hF = 12 m Link to headwater: Slot pass, l tot = 70 m

Energy production by: EDF h = 2.0 m, Q = 1.0 m3/s

Year of construction: 1990

5.6.4 Example

Functional data:

Proof was obtained by video monitoring that more than 100 000 fishes used the lift in the period 11 Mayto 28 July 1989. The lift is not only accepted by large salmonids and allis shad but also by cyprinids, seaand river lamprey etc. The slot pass link to theheadwater is equipped with an observationwindow from which the fish can be easilyobserved as they swim upstream.

Figure 5.46:Tuilières fish lift. The lift is located on the righthand side directly adjacent to the turbine outletsand conveys fish 10 m high into an intermediatepool whence the last two metres of difference inheight are overcome by a slot pass.

Figure 5.47:The lower entrance to the Tuilières fish lift

The collapsible grid gate is closed and thenpushes the fish, that have gathered in theantechamber, towards the transport troughbefore this trough is lifted. The gate considerablyimproves the efficiency of the installation.

The opening of the canal, through which thewater necessary for operating the slot pass(Q = 1 m3/s) is led, can be seen at the top right ofthe photo. At the same time, this additional waterimproves the attraction towards the lift.

can be invoked as an indicator of the possibility ofupstream migration of invertebrates.

Most fisheries laws prohibit catching fish in fishpasses. If research necessitates the capture of fishfrom a fish pass, an exemption permit must berequested prior to fishing. Granting of this permit isonly possible if the owner of the fishery is inagreement prior to any fishing action. Usually themanagement of monitoring should be entrusted tofisheries experts.

6.2 Methods

The timing and duration of testing are of greatsignificance to the reliability of any control offunctioning. This should preferably take placeduring the main migration periods, which can differregionally due to local particularities and weatherconditions.

The following biological and technical elementsshould be considered when drafting a monitoringstrategy and later when assessing the functioningof the fish pass:

Ú The potential natural fish fauna of thewatercourse and the actual qualitative andquantitative composition of fish stocks in theheadwater and tailwater of each dam. In addition,similar assessments should be made of thebenthic invertebrate fauna.

Ú The unrestricted ascent of all migratorydevelopmental stages of the relevant fishspecies.

Ú The current state of connectivity of the watersystem.

Ú The general requirements for planning andconstruction of the fish pass as set out in theseGuidelines.

Ú If necessary, proposals for optimising the fishpass should be made.

Control of the functioning of the fish pass requiresnot only the obligatory counting of all fish that havenegotiated the fishway but also the assessmentof a number of other parameters and baselineconditions. These data are used to appraise theefficiency of the pass by comparing the monitoringresults with the natural migratory activity of the fishfauna in the stretch of water being investigated.Theadditional data include:

Ú Counting ascending fish, classified by speciesand size groups, data on sexual maturity.

6 Monitoring of fish passes

Provision of structural prerequisites for monitoringthe functioning of fish passes should be made forall new installations that must observe currentwater legislation. Particularly where there isconsiderable divergence from the guidelines in thisbook, approving authorities should have thepossibility to order a control of functioning. Thefollowing presents exclusively the methodology forthe assessment of monitoring of upstreammigrations; monitoring of downstream migration isnot dealt with at this point.

6.1 Objective of monitoring

The objective of monitoring is to prove explicitlythat the fish pass entrance can be found and thefish pass negotiated by fish. Monitoring goesbeyond checking the construction against theplanning directives and construction certification,as well as beyond the obligatory trial run (seeChapter 4.4.5), which is required particularly for themore natural looking constructions. It also goesbeyond routine maintenance (see Chapter 3.8).New fish passes that have been constructed inaccordance with the guidelines in this instructionbooklet, should be assumed to function well inprinciple.

Experience shows that actual constructionsfrequently diverge from the recommendations inthese Guidelines because of local circumstances. Itis then often difficult to fully assess the effects ofany possible impairment of function. In suchcases, possibilities for monitoring and structuralimprovements to the pass should be incorporatedin the project as early as at the approval procedurestage. Monitoring is also recommended for newlybuilt fish passes when there is no, or onlyinadequate, experience with the operation of the(new) type of construction chosen, or if the pass isunique because of its dimensions (e.g. very highwater discharges or fall heads). The methodsdescribed below can also be applied to monitoringof existing fish passes.

While sufficiently tested methods for monitoringupstream migration of fish exist, it is generally verydifficult to prove the efficiency of upstreammigration of benthic invertebrates in fish passes.The invertebrates’ differing colonisation strategiesmean that proof of their migration has usually to berestricted to recording colonisation within the fishpass itself. Present knowledge indicates that theexistence of continuous bottom substrate alone

103

Ú Data on water level and discharge trends(increasing or decreasing water discharges),weather, turbidity of the water or degree oftransparency.

Ú Details of lunar phase with reference to themigratory activity of the fish, particularly duringeel migration.

Ú Measurement of current velocities and dischargein the fish pass.

Ú Measuring oxygen content and water temperature,

Ú Determining fish stocks in the headwater andtailwater taking into account stocking measuresin each of the stretches of water.

Ú Noting other relevant details of the fish such asdisease or injury.

Ú Assessing the overall condition of the fish passand its level of maintenance.

Ú Recording any modifications of theenvironmental conditions of the river andrecording particular events such asmaintenance measures, fish mortalities etc, thatmay have bearings on the migratory activity inthe fish pass.

It is recommended that already during constructionof the pass provision be made for built-in trappingchambers or at least lifting devices for the use ofmobile fish traps to be installed directly at the outletof the pass. This is particularly necessary intechnical passes to test ascent of fish in the pass.The methods for controlling the functioning of thepass should be appropriate to the type of pass. Ifnecessary, several methods may have to becombined to balance out the different disadvantagesof the individual methods. Various traditionalmethods are listed below, which, when used in theappropriate manner, can help to provide reliabledata on the functioning of the fish pass.

6.2.1 Fish traps

The standard method for testing both natural-looking and technical passes is trapping the fish.Traps can be used provided that the cross sectionof the pass can be completely blocked off by thefish trap and that there is a tight connection to thebottom. The fish trap should be installedimmediately at the water intake of the pass (i.e. thefish pass exit#; Figure 6.1) and can be built as abox, pedestal or special fish trap according to localcircumstances. Box traps are the most appropriatefor use in pool or slot passes, their size beingdetermined by the dimension of the pools. Thetraps should be set in the uppermost pool. Control

104

traps, which are, for example, set in resting pools orwhich are not set immediately at the water intakedo not give any definite proof that fish cannegotiate the total length of the pass.

The fish trap should be made of robust, dark,plastic yarn with maximum mesh size of 10 – 12 mm to allow the catch of young fishduring the control. Box traps consist of a lightaluminium frame, whose sides are filled with eitherplastic netting or coated wire mesh.

Control tests with traps require intensive care bytrained staff. Fish may be injured as a result of highdensity in the trap, particularly in times of increasedmigratory activity. Frequent emptying can preventthis. The fish are removed from the trap, measuredand their parameters recorded according to thedefined programme, and released into theheadwater. Since the trap, in the way it is set,prevents migration downstream from theheadwater into the fish pass, this method providesreliable data on upstream movement.

6.2.2 Blocking method

This method involves blocking-off the water intakeof the fish pass (i.e. fish pass exit#) with a net orgrid to prevent fish swimming in from theheadwater. All fish are then removed from thefishway, either by electro-fishing or by drying thepass. Control fishing, which is carried out after acertain time, reveals then the fish that have enteredthe fish pass from the tailwater.

This method can be applied at all passes thatprovide places for the fish to rest. It is, therefore,not suitable for Denil passes. Problems ariseparticularly from clogging of the blocking device bydebris and floating solids.

Test fishing in a fish pass using conventionalmethods or electro-fishing is not suitable as afunction control unless the water intake of the fishpass (i.e. the fish pass exit#) is first blocked off. It isotherwise, impossible to determine from whichdirection the fish migrated into the pass, i.e.whether they came from the tailwater or headwater.

6.2.3 Marking

Marking of fish can be used to control thefunctioning of the more natural fish passes and isoften used to study migrations in aquatic systems.Marking of fish must be reported to, or approved by,the appropriate authorities. There are many

# remark by the editor

105

Figure 6.2:Salmon marked with redtattooing dye and releasedinto the Mühlbach, a tributaryof the Lahn (Rhineland-Palatinate), in the frameworkof a repopulation programme.

Figure 6.1:Fish trapping to monitor thefunctioning of the fish rampat the Pritzhagener Mill onthe Stöbber (Brandenburg)

Figure 6.3:Electro-fishing for monitoringpurposes on the fish ramp at theUnkelmühle weir in the SiegRiver (North Rhine-Westphalia)

different methods for marking fish, such as the useof coded marks (tags) or dye injections(Figure 6.2), each of which has distinct advantagesand disadvantages.

When using this method autochthonous fish, that iscaught in the relevant waterbody, is marked andreleased into the tailwater of the dam beinginvestigated. Control of the functioning of the fishpass then consists of proving the presence ofmarked fish in the water intake area (fish exit area#)of the pass or in the headwater. Information aboutthe recapture of the marked fish can be gainedeither directly by using conventional methods, suchas fish traps or electro-fishing, or through thenotification by anglers of any marked fish caught.Since the recapture rate is generally low, largenumbers of various species and sizes must bemarked for release into the tailwater. Therelationship between the total number of all fishmarked and the number recaptured must be takeninto account when assessing the results.

6.2.4 Electro-fishing

Electro-fishing is frequently used for qualitative andquantitative investigation of fish stocks. Under theinfluence of an electric field in the water any fishpresent first swim towards the anode (galvanotaxis)and are then anaesthetised for a short period(galvanonarcosis), which allows them to becaptured. The fish can then be investigated as tospecies, size category etc. (Figure 6.3). If theelectro-fishing equipment is used correctly the fishare not injured. Electro-fishing (in Germany##) mustonly be carried out by specially trained persons andrequires the approval of the relevant authority andthe agreement of the holder of the fishing rights.

Electro-fishing gives qualitative and semi-quantitative estimates of the fish stock in theheadwater and tailwater of dams. The determinationof stock size can be used to assess the ascentactivity of the fish fauna at the time of monitoringand also constitutes the basis for estimating thefunctionality of the fish pass (see section 6.3). Incombination with other methods, such as blockingthe water inlet to the fish pass or marking, electro-fishing gives the possibility of proving that fishmanage to negotiate the pass.

6.2.5 Automatic counting equipment

Automatic counting equipment allows theascending fish to be observed without disturbingthem. The various methods are based on differentprinciples, including movement sensors, lightbarriers or video control, and many are still largely

in the exploratory stage. Optical systems can onlybe applied if there is sufficient viewing depth. Lightbarriers and movement sensors only allow the fishto be counted without distinguishing species orsize. A more sophisticated combination of videomonitoring and image processing systems allows adifferential assessment of the functionality of thefish pass (TRAVADE & LARINIER, 1992).

In most cases the application of automatic countingequipment presupposes separate observationchambers, devices or installations mostly at the waterintake (fish exit#) of the pass. If these methods are tobe used, provision must be made at an early stage inplanning, before building the fish pass. Expenditureon regular checks and maintenance of automaticcounting equipment is high.

6.3 Assessment of results

The assessment of the results of controls of thefunctioning of fish passes presupposes detailedrecording of data. In addition to locality-specificdata for the river stretch and other factors that mayinfluence the test results, data on the methodologyused, including the duration of exposure of the fishtraps or the cycle of emptying these traps, arerequired for correct assessment.

Unrestricted functioning and complete failure of afish pass are both easy to demonstrate, but proof ofrestricted or selective functioning for specificspecies or sizes is considerably more difficult.Proof of the full functioning of a pass by theanalysis and assessment of fish ascent figuresshould be carried out using the following criteria:

m Results of monitoring are to be assessed inrelation to the main periods of migration that arespecific to species and waterbody. Here,concomitant factors such as dischargeconditions, temperature, moon phase etc,should be considered.

m Fish migrating through the fish pass are to beassessed in relation to the stock densities in theheadwater and tailwater of the dam. This can bedone by comparing the results of the fish passmonitoring with the natural dominancerelationships (as percentage data) and the sizerange of the species actually present in thewater.

According to the general requirements defined inChapter 3, a fish pass can be recognised asfunctional if all species of the potential natural fish

106

# remark added by the editor## “in Germany” was added by the editor

fauna, in the different stages of development and innumbers that reflect their relative abundance in thewatercourse, can find the fish pass entrance andnegotiate the pass. However, this frequentlypresents methodological problems because:

m Usually not all species of the potential naturalfish fauna are represented in the water,

m In particular the presence of small fish speciesis difficult to prove with traditional methods suchas fish traps,

m Species that are extremely rare in the river maynot be detected during monitoring, althoughthese species may in principle be able tonegotiate the pass.

Therefore, it is now allowed to believe that a fishpass functions well if:

m It can be proved that all fish species actuallypresent in the affected river stretch, in theirdifferent stages and relative abundance, canfind the entrance and negotiate the pass. Thepass can be considered functional even forextremely rare species or species that are notrecorded because of the methodologicaldifficulty to catch them, if other species with thesame ratio of body size to pass dimensions andsimilar swimming performance are able tonegotiate the pass.

m The plausibility that the fish pass entrance canbe detected and the pass be negotiated mustalso be given for species of fish of thepotential natural fish fauna that are currentlynot represented in the population of thewatercourse.

107

Policy Law] require an Environmental ImpactAssessment (UVP).

The Environmental Impact Assessment includesthe determination, description and assessment ofthe impacts of a planned action on people, animalsand plants, soil, water, air, climate and landscape,including their mutual interactions in each case, aswell as their impacts on cultural property and othergoods.

In the context of the Environmental ImpactAssessment, conservation or restoration oflongitudinal connectivity is usually an aim, althoughfishery laws of some Länder provide formalexceptions with regard to building fishways.

The fisheries requirements also have to beconsidered where an approval, licensing oragreement procedure has to be carried out insteadof Planning Permission Hearings. Within theframework of the relevant laws the planningprocedure should balance the interests of fisherieswith the benefits associated with the project that isobject of the application.

7.2 Existing installationsThe legal situation for existing dams and weirs isdifferent if modifications are carried out that do notrequire approval as here, in first instance, the oldlaws, conferred with their ancillary clauses, apply.An amendment of the old laws is usually notpossible without the agreement of the holder of theright, as defined by the guarantee of ownershipunder Article 14 of the Constitutional Law. Theseold rights may, however, be revoked in accordancewith § 15 WHG in return for compensation whereconsiderable disadvantage to the general well-being can be expected from a continued use. MostFishing Acts of the Länder offer the possibility tooblige the owner of a dam to retrofit it with a fishpass if the building costs and any possiblecompensation claims are met by the third partyinsisting on the construction.

In Hesse, North Rhine-Westphalia, Rhineland-Palatinate, Saxony-Anhalt and Thuringia, the Landcan only insist on retrofitting an obstruction with apass if the measure has a reasonable cost/benefitratio and a reasonable ratio of cost-to-production-power of the liable party. If the liable party cannotafford to pay, the Land has to care for the provisionof an appropriate part of the funding of retrofitting.

7 Legal requirements

The relevant laws must be observed whenplanning, building and operating fishways. As setout in Article 70 of the Constitutional Law of theFederal Republic of Germany, inland fisheries aresubject to the jurisdiction of each Land (FederalState). Therefore, each of the Länder (FederalStates) has its own fishery act, which usually differswidely in a number of points from similar acts of theother Länder. All federal fishery acts contain detailson the construction and operation of fishways, thatcan be implemented directly and independently ofother regulations or laws.

On the other hand, as regards the Water Law, thereexists a higher-ranking skeleton law, theWasserhaushaltsgesetz (Water Resources PolicyLaw) (WHG). This contains in § 1a, Subsection 1,the principle that waterbodies should be managedin such a way that they add to the well-being of thegeneral public and also benefit individuals wherethis does not interfere with the public good. Thesubsection also states that all negative influencesmust be avoided. According to §§ 4,8 unfavourableeffects on waters deriving from uses that requirepermission or approval are to be prevented orcompensated for.

This principle is also in accordance with § 8 and§ 20 of the Federal Law on Nature Conservationand the relevant Nature Conservation Acts of theLänder. The proposal of Council’s Guidelines onthe ecological quality of waterbodies, that wassubmitted by the Commission of the EuropeanUnion, includes the provision that migratory fishspecies may not be impeded by human activities.

7.1 New installationsThe Water Law requires that the necessarypermissions or planning procedure approvals besought from the relevant authorities prior to buildingdams or weirs in waterways. Such constructionsusually represent a substantial structural modificationof the waterbody in the sense of § 31 WHG, in thatthey lead to an essential change in habitats, so thatPlanning Permission Hearings in accordance with§ 31, Subsection 1, must be undertaken. In addition,complementary law regulations of the Land have, ofcourse, also to be respected.

According to the annex (here Point 6) of § 3 of theUVP # Law (Environmental Impact AssessmentLaw), planning procedures that are to be carriedout according to § 31 WHG [Water Resources

109

# remark by the editor: UVP = Umweltverträglichkeitsprüfung(Environmental Impact Assessment)

GEBLER, R.-J. (1991): Naturgemäße Bauweisenvon Sohlenbauwerken und Fischaufstiegen zurVernetzung der Fließgewässer. – Diss. Univ.Karlsruhe, Mitteilungen des Institutes für Was-serbau und Kulturtechnik, Nr. 181.

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HENSEN, W. & F. SCHIEMENZ (1960): Eine Fisch-treppe in Stromlinienform. Versuche mit leben-den Fischen und Modellversuche. – Mitteilungendes Franzius-Institutes für Grund- und Wasser-bau der Technischen Hochschule Hannover 18,162-177.

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113

115

Symbol Unit Used for

a m Distance between baffles in Denil passes; stagger distance of the deflecting block relative to the cross-wall in slot passes

A m2 Area, flow sectionAtot, Ages m2 Total flow section

Ao m2 Base area

As m2 Cross-section of submerged orifice in pool passes; wetted area of an immersed object (e.g. a perturbation boulder)

ax, ay m Distance between perturbation boulders, (ax) in longitudinal direction and (ay) in lateral direction

b m Width, channel widthba m Width of baffle section in Denil passes; width of notches in pool passesbm m Mean widthbs m Width of submerged orifice in pool passes; width of gaps (for discharge)

in a boulder sill (cascaded ramp)bSo, bbot m Bottom width bSp m Width of waterbody at its surface c m Length of hook-shaped projection in slot passesc1, c2 m Height of triangular section of baffles in Denil passescw - Form drag coefficientd m Thickness, e.g. of substrate layer; thickness of wall

in pool and slot passesdS m Boulder or stone diameterd90 m Grain diameter for 90% mass sieving

E W/m3 Volumetric power dissipationf m Width of deflecting block in slot passesFr - Froude numberg m/s2 Acceleration due to gravity, g = 9.81 m/s2

h m Height or water depth, generally the minimum water depthh* m In Denil passes: distance from the deepest point of the cutout section

of the baffle to the bottom of the channel, measured perpendicular to the bottom

ha m Height of notches in pool passes; height of baffles in Denil passeshE m Energy levelhE,min m Minimum energy levelhF m Fall headhgr m Limiting depth, water depth for discharges with minimum energy levelhm m Mean water depthho m Water depth above a dam, or above a cross-wall or sill

(be aware of reference level!)hs m Height of submerged orifice in pool passes

(measured from bottom surface or substrate surface)hu m Water depth below a dam, or below a cross-wall or sill

(be aware of reference level!)hü m Weirhead (sometimes as hweirhead)hv m Losses in energy level caused by dischargeshw m Height of cross-walls in pool passes� - Slopek m Absolute roughnessks m Equivalent sand roughness

9 Table of symbols and signs used

116

Symbol Unit Used for

l m Length, distancelb m Pool lengthlu m Actual length of the wetted channel cross-sectionn - Number of poolsQ m3/s Discharge or flow Qa m3/s Discharge through the notches in pool passes

Qs m3/s Discharge through the submerged orifices in pool passes rhy m Hydraulic radius, rhy = A / lus m Slot width in slot passesV m3 Volumev m/s Flow velocityvgr m/s Flow velocity at critical flow depthvm m/s Mean flow velocityvmax m/s Maximum flow velocityvs m/s Maximum flow velocity in the slot or in the submerged orificew m Height of weir, height of sill x,y,z - Axes in Cartesian coordinate system� º Angle�h m Water level difference, e.g. between pools v - Volume ratioo - Area ratio� - Resistance coefficient in Darcy-Weisbach flow law�tot, �ges - Total resistance coefficient�o - Resistance coefficient due to bottom roughness�s - Resistance coefficient due to perturbation boulders or similar objects� - Spillway coefficient for calculating spillover�r - Discharge coefficient in slot passes kg/m3 Density (of water), = 1000 kg/m3

s kg/m3 Density of stone, s � 2700 kg/m3

� - Backwater coefficient, takes account of the influence of the tailwater level� - Outflow coefficient � - Loss coefficient

Abbreviation Meaning

OW Headwater: water level above a damUW Tailwater: water level below a damMNW, MNQ Mean low-water level and mean low-water dischargeMW, MQ Mean water level and mean dischargeMHW, MHQ Mean high-water level and mean high-water dischargeHW, HQ High water level and high water dischargenW, nQ Water level/discharge not reached on n days in the yearn̄W, n̄Q Water level/discharge exceeded on n days in the yearHHW, HHQ Highest known water level, highest known discharge

Hydrological information and abbreviations

117

Critical discharge: Water volume per unit of time,which is decisive for defining the dimensions ofa fish pass. Unit: [m3/s].

Directional current: Current without cross-currents.

Diversional hydropower station: A hydroelectricpower station where the exploitable fall or head,as existing at the dam structure, is increased asa result of the diversion.

Draft tube: Funnel-shaped opening thatconstitutes the connection from the turbine rotorto the tailwater in reaction turbines ofhydropower stations and that delays the watercoming out of the turbine, thus reducing its flowvelocity.

Energy dissipation: The withdrawal of potentialand/or kinetic energy from the water dischargeenergy and its transformation into heat. – See:volumetric power dissipation.

Eurytypic: Organisms that can tolerate verydifferent environmental conditions and thuschanges in their living space (habitat). – See:stenotypic.

Flow transition: Change of water depths fromturbulent to laminar flow or conversely. Thetransition from laminar to turbulent is alwayssteady, while the change from turbulent tolaminar always shows a disturbance in thesurface water level in the form of a hydraulicjump.

Gabions: Cuboid wire baskets filled with stonesthat are mainly used for revetting riverbanksabove and below water.

Habitat: The normal living space occupied by aspecies of plant or animal within an ecosystem.

Ichthyocoenosis: Community of living fish. – See:biocoenosis.

Interstitial: Water-filled spaces within the riversediments forming the river bottom or adjacentto it.

Invertebrates: Collective term for animals withoutbackbones.

Invertivorous fish: Fish species that feed oninvertebrates, whether aquatic, flying orterrestrial. – See: invertebrates.

Kelts: Salmon returning to the sea after spawning.

Olfactory orientation: Orientation of many fishspecies results from a highly developed senseof smell.

Parr: A young salmon living in freshwater.

10 GLOSSARY

Abiotic factors: Non-living chemical and physicalfactors, e.g. geology, temperature, waterbalance, that influence biological systems andbiocoenoses. – See: biotic factors.

Adult: An organism from the time it reached sexualmaturity.

Allochthonous: Living organisms or dead materialthat is exotic to the environment from which itwas sampled. – See: autochthonous.

Autochthonous: Living organisms or deadmaterial that is indigenous to the environmentfrom which it was sampled. – See:allochthonous.

Autotrophic: Characterizing the physiologicalmechanism of green plants and manymicroorganisms, whereby the organism growsusing photosynthesis to convert inorganicmatter (minerals, CO2, NH4) to organic matter.

Benthic zone: Bottom of a body of water. Benthicorganisms live on or in the bottom. Thebiocoenosis of this habitat is termed “benthos”;the biocoenosis of bottom-dwelling invertebratespecies is termed “benthic invertebrate fauna”.

Biocoenosis: Living community of plants andanimals of a specific living space (biotope). –See: ichthyocoenosis.

Biotic factors: Factors pertaining to the livingenvironment, e.g. nutrition, competition,parasites etc., that influence biological systems.See: abiotic factors.

Biotope: Space (habitat) occupied by a livingcommunity (biocoenosis) of plants and animalswith its own specific environmental conditions.

Bypass: A means of conducting water andorganisms around the main channel. In theseGuidelines often used in the sense of a meansto supply additional attraction current.

Bypass power station, synonym with channelpower station: A bypass power station is ahydroelectric power station that lies on a bypasschannel (water is deviated from the mainchannel into an artificial turbine canal. Ingeneral, the river course is artificially shortenedby the bypass in order to achieve a greater fallor head for the generation of electricity. Water isextracted from the main channel by means ofthe bypass and conveyed to the hydroelectricpower station.

118

Photo credit:

Baumann, A.: Figure 4.2BAWAG: Figures 4.21, 4.26, 4.45Gebler, R.-J.: Figures 4.33, 4.37, 5.40Heinrichsmeier, G.: Figures 4.38, 4.39, 4.40, 4.41Krüger, F.: Figures 2.9, 2.11, 3.1, 3.2,

3.14, 4.9, 4.10, 4.11, 4.17,4.24, 4.28, 5.7, 5.15, 5.20,5.25, 5.29, 5.30, 5.36, 5.37,5.38, 5.39, 6.1

Lippeverband: Figures 5.12, 5.13Marmulla, G.: Figures 4.29, 4.34Mathis, R.: Figure 2.15RWE AG: Figures 3.3, 5.11, 5.44Schaa, W.: Figure 4.49Schwevers, U.: Figures 2.6, 2.7, 2.8, 2.12,

2.13, 5.46, 5.47, 6.2, 6.3Städtler, E.: Figure 4.35Steidl, J.: Figure 4.15Stolzenburg, H.: Figure 2.14Surhoff, P.: Figures 4.22, 4.36, 5.3Touschek, A.: Figure 4.13

Graphic design by Krüger, F. and Schaa, W.

Phytoplankton: Small to very small algae that livepassively in fresh or salt water and manufacturetheir own nutrition by photosynthesis (i.e. theyare autotrophic).

Piscivorous fish: Fish species that feed on otherfish.

Planktivorous fish: Fish species that feed onplankton.

Population: The totality of all individuals of onespecies in a specific living area that reproducesexually with one another over manygenerations and are thus genetically linked.

Sluice: Device for relief, flushing or emptying theimpoundment behind a dam.

Sluice gate: Constructional, adjustable elementinstalled at weirs, reservoirs and hydroelectricpower stations to regulate the flow of water.Sluices are generally made of rectangular steelplates sliding or rolling in lateral guide grooves.

Smolts: Young salmon, with typical silvery colour,migrating to the sea.

Spillover jet: A water jet passing over a realspillway, either falling free or flowing along thespillway back as a gushing jet

Stenotypic: Stenotypic species are very sensitiveto changes in their living conditions. – See:eurytypic.

Stock: Genetically distinct community of individualsof one species in a specific living area.

Volumetric power dissipation: Amount of energyper unit of volume that is dissipated in the poolsof a fish pass. The hydraulic energies are nolonger available for further discharge. It is ameasure of the turbulence conditions in a pool.Unit: [W/m3 pool volume]. – See: energydissipation.

Type Sketch Principle Dimensions* and discharge

Range of application Advantages and disadvantages

Effectiveness

Bottomramps andslopes(sect. 4.1)

Ramps and slopes arestructures that have a roughsurface and extend over theentire width of the river.Loose rockfill constructionsand dispersed constructionsare favoured.

The ramps are as wide asthe river (b = width of river),their slope normally < 1:15. Ifthe main body of the ramp issteeper, then at least themarginal areas must be lesssteep. Height h > 0.2 m.Discharge must beq > 100 l/s m. Construction inseveral layers and withsecured downstream bottom.

Recommended where aprevious use has beenabandoned and where theheadwater level needs nolonger be regulated. Usedfor the modification of steepdrops and fixed (very steep)weirs, as a protective sill tohinder erosion.

There is a danger of dryingout at low discharge, sosealing may be necessary.Relatively low costs. Theyblend well into thelandscape, look natural,require little maintenance.No problems with attractioncurrents, so can easily befound by fish.

They are passable in bothdirections by all aquaticfauna. Long term silting ofthe impoundment restoresalso upstream the typicalflow velocities and substrateconditions.

Bypasschannels(sect. 4.2)

Offer an alternative routeround a dam with a natural-looking stream bypassingthe impoundment.

b > 1.2 m;h > 0.20 m;

< 1:20.The bypass should extendup to the upstream limit ofthe backwater. Dischargemust be at least q = 100 l/s m.

Suitable for all barriers andheads if there is sufficientspace, particularly useful forretrofitting existinginstallations. They are notsuitable when impoundingheads vary; in the lattercase, inlet constructions forwater regulation might benecessary.

Their financial cost is low,their demand for spacehigh! Deep cuts into thesurrounding terrain may benecessary or combinationwith other technicalstructures. Bridges orunderpasses are oftenrequired.

They are passable for allaquatic fauna, provide livingspace for rheophilic species,are the only fish pass thatcan bypass the whole areaof the dam and theimpoundment, blend wellinto the landscape.

Fish ramps(sect. 4.3)

Ramps with gentle slopesand a rough surface;integrated into the weirstructure. Their body may beof rockfill, with perturbationboulders or boulder sills toreduce flow velocities.

b > 2 0 m;h > 0.3 to 0.4 m;

= 1:20 or less.Necessary discharge qapproximately 100 l/s m.

They can be used toovercome heights notgreater than about 3 metres.Used at fixed weir sills, andat multi-bay weirs as asubstitute for a weir bay.They are not suitable forvariable impounding heads.

Their construction is oftentechnically demanding, witha need for high structuralstability. There is a dangerof drying out at low water,therefore sealing may benecessary. Require littlemaintenance; good self-cleaning during floods.Good attraction current.

They are passable for allaquatic fauna in bothdirections, i.e. upstream anddownstream.

Close-to-nature types of structures

Appendix: Overview of the most frequently used construction types of fish passesThe various fish passes are classified by functional and ecological aspects, but no account is taken of local geographical factors that may limit the use of some structures.

*Where measurements are given, they are only minimum requirements.

Type Sketch Principle Dimensions* and discharge

Range of application Advantages and disadvantages

Effectiveness

Slot passes(sect. 5.2)

Slot passes are generallyconcrete channels withcross-walls of concrete orwood and with one or twovertical slots that extendover the whole heightbetween the cross-wall andthe lateral bounds.

Pool dimensions:lb > 1.90 m;b > 1.20 m;h > 0.5 m;Slot width: s > 0.17 m.Discharge can be fromQ = 140 l/s up to severalcubic metres per second.

Used for small and mediumheads, suitable for variableimpounding heads. Can beused for small streams andlarge rivers. The minimumtailwater depth must beh > 0.5 m.

Relatively high dischargescan be sent through, thusgood attraction currents canform. More reliable thanconventional pool passesbecause of the lower risk ofclogging of the slots.

They are currently the besttype of technical fish pass,being suitable for all speciesof fish and are passable forinvertebrates if a continuousbottom substrate is built in.

Pool passes(sect. 5.1)

Are generally concretechannels with cross-walls ofwood or concrete which arefitted with submergedorifices and top notches onalternate sides.

Pool dimensions depend onthe river zone;lb > 1.4 m;b > 1.0 m;h > 0.6 m.Submerged orifices:bS/hS > 25 ⋅ 25 cmDischarge Q = 80 to 500 l/s.

Used for small and mediumheads, at melioration damsand at hydroelectric powerstations.

Only relatively lowdischarges allowed; there isgreat risk of clogging withdebris.

Suitable for all species offish if the dimensions of thepools and orifices arechosen as a function of thefish size that can beexpected to occur. Theremight not be sufficientattraction current at lowdischarges.

Denilpasses(sect. 5.3)

Wooden or concretechannel with sectionedbaffles (usually of wood)that are U-shaped, and areset at an angle of 45°against the flow direction.

Channels:b = 0.6 to 0.9 m;h > 0.5 m;

< 1:5;Q > 250 l/s.Channel lengths can be 6 to8 metres; resting pools arerequired for heights> 1.5 to 2 m.

Suitable for small heads,particularly for retrofitting ofold milldams when there isnot much space.

Relatively high discharges;should not be used forvariable headwater levels;not sensitive to varyingtailwater levels; need littlespace; cheap; goodformation of attractioncurrent.

According to presentknowledge, less suitable forweak swimmers or smallfish. Selective. Benthicfauna cannot pass.

Technical structures

Type Sketch Principle Dimensions* and discharge

Range of application Advantages and disadvantages

Effectiveness

Eel ladders(sect. 5.4)

Generally, eel ladders aresmall channels with brush-type fittings, layers ofbrushwood or gravel, withwater just trickling throughthem; also "eel pipes" thatare led through the weirbody and are filled withbrushwood or brush-typematerial.

Channel:b = 30 to 50 cm;h = 15 to 25 cm.Slopes usually 1:5 to 1:10,but can be steeper.

Often used as a bypass inpool passes, but only usefulwhere migration of glasseels and elvers occurs; ingeneral not strictlynecessary if there is anotherfish pass.

Low construction costs, onlylittle space required, onlylow discharges needed.

Only suitable for glass eelsand elvers. Eel pipes are notproven satisfactory becauseof their tendency to becomeclogged and the difficulty inmaintenance. On their own,they are not sufficient toconnect upstream anddownstream habitats andcannot guarantee freepassage for all fish.

Fish locks(sect. 5.5)

A pit-shaped chamber withcontrollable closures atheadwater and tailwateropenings. The attractioncurrent is formed bycontrolling the sluice gateopenings or by sendingwater through a bypass.

Their dimensions can vary,with minimum chamberwidth and water depth beingsimilar to those in a poolpass. Water quantityrequirements depend onchamber size, cycleintervals for lock operationand required intensity ofattraction current.

Used for high heads, andwhere space or availablewater discharge is limited.

Planning and construction isoften technically demanding.Require high efforts inmaintenance and operating,high construction andservice costs, low waterconsumption. Useful wherevery large fish (e.g.sturgeon) are to be takeninto consideration.

According to presentknowledge, suitable forsalmonids and fish withweak swimming capacities.Less suitable for bottom-living and small fish.

Fish lifts(sect. 5.6)

Lifting device with transporttrough and mechanical driveto hoist fish from tailwater toheadwater; connection toheadwater through achannel; water sent througha bypass creates attractioncurrent.

Dimensions variable,volume of transport troughabout 2 to 4 m3. Continuousflow through a bypassneeded to create attractioncurrent.

Used for same situations asfish locks, but often the onlytype of pass that can bebuilt for heights greater than10 metres, e.g. at highdams.

Need little space. Planningand construction is oftentechnically demanding.Require high efforts inmaintenance and operating,high construction andservice costs.

According to presentknowledge, suitable forsalmonids and fish withweak swimming capacities.Less suitable for bottom-living and small fish. Notsuitable for macrozoobenthicfauna or for downstreammigration of fish.

Special constructions

Many fish species undertake more or less extended migrations as part of their basic behaviour. Amongst the best known examples in Europe are

salmon (Salmo salar) and sturgeon (Acipenser sturio), which often swim several thousands of kilometres when returning from the sea to their spawning

grounds in rivers. In addition to these long-distance migratory species other fish and invertebrates undertake more or less short-term or small-scale

migrations from one part of the river to another at certain phases of their life cycles.

Fish passes are of increasing importance for the restoration of free pas-sage for fish and other aquatic species in rivers as such devices are often the only way to make it possible for aquatic fauna to pass obstacles that block their up-river journey. The fish passes thus become key elements

for the ecological improvement of running waters. Their efficient function-ing is a prerequisite for the restoration of free passage in rivers. However,

studies of existing devices have shown that many of them do not func-tion correctly. Therefore, various stakeholders, e.g. engineers, biologists and administrators, have declared great interest in generally valid

design criteria and instructions that correspond to the present state-of-the-art of experience and knowledge.

Fishways can be constructed in a technically utilitarian way or in a man-ner meant to emulate nature. Bypass channels and fish ramps are among

the more natural solutions, while the more technical solutions include conventional pool-type passes, slot passes, fish lifts, hydraulic fish locks

and eel ladders. Comprehensive monitoring is crucial.

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TC/M/Y4454E/1/12.02/2600

ISBN 92-5-104894-0