Flood Control at Rivers and StreamsWegleitungen des BWG – Directives de l‘OFEG – Direttive dell‘UFAEG – Guidelines of the FOWGBerne, 2001

1

In cooperation with:Federal Office for Spatial DevelopmentSwiss Agency for the Environment, Forests and LandscapeFederal Office of Agriculture

Flood Control at Rivers and Streams

Obtainable from: SFBOL, Distribution of Publications, CH-3003 Berne, www.bundespublikationen.chOrder number: 804.801.eng

Wegleitungen des BWG – Directives de l‘OFEG – Direttive dell‘UFAEG – Guidelines of the FOWGBerne, 2001

Eidgenössisches Departement für Umwelt, Verkehr,Energie und KommunikationDépartement fédéral de l‘environnement, des transports,de l‘énergie et de la communicationDipartimento federale dell‘ambiente, dei trasporti,dell‘energia e delle comunicazioniFederal Department of Environment, Transport, Energyand Communication

2

RDB;

Key

ston

e

EditorFederal Office for Water and Geology FOWGLändtestrasse 20PostfachCH-2501 Biel

Editing CommitteeHans Peter Willi (FOWG)Jean-Pierre Jordan (FOWG)Ulrich Roth (Sigmaplan AG; Berne)Bernhard Frei (Advokaturbüro Keller, Mesmer,Frei, Degiorgi; Berne)

TranslationLyn Shepard, FilisurMartin Jaeggi, Ebmatingen

Conception and RealizationFelix Frank, Berne

QuotationFederal Office for Water and Geology:Flood Control at Rivers and Streams.Guidelines of the FOWG, 2001 (72p.)

© FOWG, Biel 2002

12.02 1000 84293

3

Contents

Strategy• Where Do We Stand? 7• What Do We Want? 8• Principles for Flood Protection 9• How Can These Demands Be Fulfilled? 10

Action• Recognizing the Need for Action 13• Ascertaining the Hazard Situation and Damage Potential 14• Assessing the State of a River or Stream 15• Setting Protection Objectives 16• Determining the Necessary River Space 18• Defining the Need for Action 20

Procedure• Responsibilities 23• Legal Standards 24• Framework Conditions 26• Federal Subsidies 27• Regular Procedure 28• Accelerated Procedure 30• Participation 32• Overcoming Conflict 33

Project Design• The Sequence of Project Design Work 35• Conditions in the Catchment 36• Uncertainties of Basic Data 38• Hydraulic-Engineering Conditions 40• Types of Hazard and Influencing Factors 42• Assessing Hazards 44• Graphical Presentation of Hazards 46

Measures• Order of Priorities 49• Appropriate Maintenance 50• Forestry Aspects 52• Alluvial Zones 53• Land-Use Planning Measures 54• Off-Limits Zones 56• Object Protection 57• Protective Structures 58• Construction Methods 60• Emergency Planning 62• Emergency Organization 63

Appendix• Glossary 65• Checklists 68• Contact 72

Com

et (

3); K

eyst

one

(1)

4

The first edition of the guidelines“Flood Control at Rivers and Streams”was edited in 1982. Since then the le-gal and professional framework haschanged considerably. However, al-ready then the federal counsellor LeonSchlumpf wrote in the preface, that”for interventions made for flood con-trol reasons more attention has to begiven the other functions of a river orstream. With their varied riparianvegetation they subdivide landscapeand enhance its value. They offer habi-tats for animals and plants and theirnatural value makes them an idealplace for relaxation.”

5

Editorial

The disastrous floods of the year 1987 remain not only in the memoryof those immediately hit by the events. For a new way of flood riskassessment as well, the year 1987 has become a milestone: the analysisof the causes of those events led to considerable new knowledge whichin the meantime had a strong influence on the related legal bases.

The strategy of the Federal Department ofEnvironment, Transport, Energy and Com-munication is governed by the principle ofsustainability. This results in the follow-ing objectives:• to protect and maintain the naturalconditions and natural resourcebases for social well-being (ecologicalsustainability);• to provide up-to-date services in trans-port, energy, water resources, postalservice, telecommunications, and elec-tronic media that benefit the populationand the economy in such a way that thefinancial burden on the state and theeconomy is acceptable (economic sus-tainability);• to ensure access to the natural resourcebase and to public services for the entirepopulation and all parts of the country un-der equitable conditions and to protectpeople from hazards and health risks(social sustainability).

BasicsFlood protection plays a major role in sus-tainable development. Appropriate floodprotection has been and continues to be abasic condition for a prosperous society. Intheir efforts to fulfil the common task offlood protection, the cantons and munici-palities receive financial support from thefederal government through the federallaw on flood protection policy, datingfrom 1877.The recent Federal Law on Flood Con-trol (Wasserbaugesetz, WBG, 1991) pro-vides a new basis for hazard assessment,differentiation of protection objectives, ad-equate planning of measures, and limita-tion of remaining risks (emergency plan-

ning). The respective Ordinance onFlood Control (Wasserbauverordnung,WBV), revised in 1999, regulates thesegeneral considerations.

Increased demandsIn recent decades, stream and river train-ing have contributed much to the generaleconomic development of many areas inSwitzerland. Only in recent years has floodprotection policy been updated. The 1987flood disasters in particular proved thatthere is no absolute safety from floods.These disasters triggered a complete re-view of flood protection policy, whichconcluded that a sustainable policy re-quires land-use practices that take accountof existing natural hazards and minimizedirect impacts on rivers and streams.This is possible only when sufficient con-sideration is given to the multitude offunctions fulfilled by rivers and streams.Reduction of damage following extremeevents presupposes that these events betackled in detail. The results have to beconsidered in emergency planning proce-dures as well as in structural and land-useplanning.Therefore, a modern flood protectionpolicy will not only take account of safetyaspects but consider other aspects of sus-tainable development as well. Environ-mental concerns and economic factorsmust be included in the planning processas early as possible.The present manual is designed to con-tribute to the solution of complex tasks inthis context. It was developed in a waythat should allow the principles involvedto remain valid for a long period of time.We hope that it will meet the expectations

of all present and future readers. No stan-dard solutions are presented, however. Onthe contrary, this manual is intended tohelp the authorities, associations and hy-draulic experts concerned with flood pro-tection schemes to ask the right ques-tions.Landowners and insurance companies areaddressed as well; they can also contrib-ute much to reducing damage potential.This should make it possible to approachflood protection in a way that satisfies allthe parties concerned.

Christian FurrerDirector of the Federal Officefor Water and Geology FOWG*

*Former Federal Office for Water Management

Strategy

7

UFA

EG–F

OW

G

Where Do We Stand?

➜ Legal standards

hazard assessment, differentiation of pro-tection objectives, adequate planning ofmeasures, and limitation of remaining risk(emergency planning).The Ordinance on Flood Control(Wasserbauverordnung, WBV) representsan additional cornerstone. It came into ef-fect in 1994 and was revised in 1999. Inaccordance with these laws, the cantonsdelineate hazard zones and the necessaryspace to be allocated to rivers and streamsfor flood control reasons, but also in orderthat they can fulfil their ecological func-tions. This means that the areas in ques-tion must be included in structural andland-use planning and be considered in allland-use activities.

Loss of diversityThere are other deficiencies besides thesesafety aspects. In the past, the space allo-cated to rivers was limited to a narrowchannel. From an ecological point of view,such rivers are deficient and can no longerfulfil various functions for the followingreasons:• Geometrically lined channels are mo-notonous landscape elements.• Intense land use up to the border of ariver or stream does not leave enoughspace for natural dynamic changes tohappen.

A new orientationThese problems have been recognized andhave led to a conceptual reorientation offlood protection. The 1987 flood eventsand subsequent analysis of theircauses provided a decisive impulse for abasic reconsideration of flood protectionand development of new strategies.Safety for everyone and everything is notpossible. This is not only a question of lim-ited financial resources owing to budgetconstraints in the public sector. The valueof the goods at risk has also increasedenormously. Therefore, defence againsthazards is no longer the only issue. Whatparticular risks are accepted or may be ex-pected to be accepted also needs to be dis-cussed: What might happen, and wheremight it happen?

The legal frameworkAll of the above findings have had legalconsequences. The new Federal Law onFlood Control (Wasserbaugesetz, WBG)came into effect on January 1, 1993. It pro-vides a strategic basis for comprehensive

Numerous river training projects in Swit-zerland, including additional construc-tions, have considerably improved floodsafety and contributed extensively to theeconomic development of large areas infloodplains.Despite the efforts of many decades andlarge investments, there is no absolutelyfull protection against floods. This wasdefinitely proven by the major flood disas-ters of 1987, 1993, 1999 and 2000. In ad-dition, all the minor floods of recent yearshave indicated again and again that struc-tural measures have a limited effect onexceptional natural events.

The need for concrete actionReducing the impacts of floods on socio-economic life will require major efforts infuture if the amount of economic damageis to be held in check. In particular,damage potential should be reduced.There are numerous reasons for rapid ac-tion:• Economic development frequently takesplace in hazardous areas, particularly infloodplains. Flood damage is steadily in-creasing in these areas.• Flow is accelerated in canalized riversand streams. The peak discharge increasesin the downstream reaches.• In general, there are not enough deten-tion areas available for incoming waterduring extreme events.• The maintenance of river channels is of-ten neglected. Thus, hazardous conditionsmay suddenly change and new areasmight be threatened.• The risk of hazards could generally in-tensify in coming decades due to externalinfluences (e.g. global climate change).

Hazard: Condition or process from which danger canarise for human beings, the environment, and/or property.

Risk: Size and probability of potential damage.

Residual or remaining risk: Risks that remain aftercompleting all foreseen protective steps.

Streams and rivers not only cause floods.During an average 340 flood-free daysper year they fulfil other functions that shouldalso be considered in flood protection.

8

Fran

k

• Strategy

Action

Procedure

Project Design

Measures

Appendix

What Do We Want?

Recommended reading

FOWG (flyer, 1995): Demands on FloodProtection

BWG (flyer, 2000): Raum den Fliessgewäs-sern! [Space for Rivers!]

Up-to-date flood protection is not limitedto complete and maintain existing rivertraining works. On the contrary, major ef-forts have to be made to include flood pro-tection aspects in the planning and co-ordination of all land-use activities.This includes the legitimate demands of allconcerned partners and of activities suchas water quality control, fishery, forestry,agriculture, protection of landscapes, wa-ter supply, and hydropower generation.Flood protection today is facing numerousdemands that reflect conflicts of interest.In order to devise good solutions, floodprotection must fulfil a number of require-ments:• Living space and the economic en-vironment must be adequately pro-tected.• Further economic damage must be lim-ited by means of a comprehensive pre-vention strategy.• Handling of uncertainties needs to beimproved and included in flood protectionconcepts.• Rivers and streams have to be regardedand respected as an essential link elementin nature and the landscape.

Continuous processThe federal law and the federal ordinanceon flood control clearly emphasize theserequirements. Only a minimum of floodprotection activities is allowed along riv-ers and streams. Flood prevention hasa high priority. Despite preventive meas-ures, functional emergency planningand emergency organization are indis-pensable.On this basis a number of flood protectionprinciples can be formulated (see p. 9).Sustainable flood protection can only beachieved if these principles are put intopractice. Consequently, the will to col-laborate and achieve consensus among allparticipants in this process is indispens-able.In addition, federal policies pertaining toflood protection, water quality control,conservation of nature and landscape,fishery, forestry, hydropower generation,etc., are in a process aimed at better co-ordination.Step-by-step revision of the respectivelaws has a common aim that can besummarized under the heading ofsustainability: Impacts on nature andlandscape must not endanger living con-ditions for future generations.

Requirements

• Residential and commercial spaceshould be protected properly.

• Comprehensive preventionshould allow costs of damagenot to continue to increase.

• Handling natural dangers shouldbe improved and consideredin flood protection concepts.

• Rivers and streams should berespected as vital and integratedparts of nature and the landscape.

9

Principles for Flood Protection

Flood

Crisismanagement

State of ariver channel

Catchment

Damagepotential

Meteorology

DamageVulnerability

Danger

✓

✓

✓

✓

✓

✓

✓✓

✓

Event

Two main strategies must be pursued to prevent an exponential increaseof flood damage in the near future: (i) priority should be given to land-useplanning in order to reduce vulnerability and damage potential, and (ii)emergency planning to reduce flood damages should also be undertaken.

Analyse the hazards. Comprehensive knowledge of hydrological and hydraulic conditions and prevailing hazards withinrivers is necessary if protection requirements are to be properly evaluated. Existing hazards and conflicts can be understood bydocumenting flood events, by making complete event inventories, and by establishing hazard-index maps. The hazard situationshould be updated regularly. The existing hazards are to be considered in structural and land-use planning.

Assess and eliminate ecological deficiencies. Sustainable flood protection supports abundant riparian vegetation andprovides ample space for the development of natural diversity in the aquatic, amphibian, and terrestrial ecosystems. It pro-vides links between habitats.

Differentiate the protection objectives. Flood protection concepts are based on a clear differentiation amongobjectives. Areas and objects of high value require a greater degree of protection than those of lower value. According to thissimple rule, agricultural land and individual buildings require less protection than towns, industrial plants, or infrastructure.Furthermore, no specific protection may be necessary for low-intensity agricultural areas. However, assessment of possibledamage may result in different weightings. Thus, the measures taken have to be evaluated and judged according to theirappropriateness.

Retain where possible, let pass where necessary. In order to dampen flood peaks, flood discharge should be retardedwithin detention areas wherever possible. Therefore, natural detention areas should not only be maintained but also re-estab-lished wherever appropriate. Flood waves should only be allowed to be passed downstream without dampening where thelocal situation requires it, e.g. in narrow settlements. Flood corridors should be established there or kept free in order to pro-vide enough space for extreme events.

Minimize impact. Cross sections with sufficient flow capacity are a basic condition for securing flood protection, to keep thesediment regime in equilibrium, and to guarantee drainage of an area. Nevertheless, flood safety should be provided withminimum impact on natural habitats.

Check possible failure points. Natural uncertainties have to be considered carefully. In consequence, the safety of protec-tion structures needs to be adapted and optimized. Moreover, their functioning and structural safety need to be checked foroverstress during extreme events. Possible failure points might be recognized and eliminated in time through periodic checksof the fitness and usefulness of existing structures.

Guarantee maintenance. Appropriate maintenance of river and stream channels is a permanent task. It ensures mainte-nance of the substance of existing protection structures and of corresponding discharge capacity.

Secure the necessary space of a river. A stream must be more than a simple gutter and a river more than a canal. Landuse in their vicinity requires respect of sufficient distance. The cantons are obliged to determine the necessary space for rivers,to establish it within the structural or land-use plan, and to consider it for all activities affecting land use.

Respect needs. For many people streams and rivers serve as recreational areas for leisure or relaxation. These demands haveto be considered along with demand for sustainable use of water resources, particularly for hydropower generation.

10

➜ http://www.bwg.admin.ch

Isel

i

How Can These Demands Be Fulfilled?

Area of sustainability

Environmental aspects:protecting nature and the environment

Social aspects:protecting the public

Economic aspects:ecological and economic proportionality

* This procedure corresponds to the VSEGuideline (2000): Der regionale Entwässerungs-plan REP [The Regional Drainage Plan REP].

Every flood protection project is biased ac-cording to conditions determined by (i)the prevailing natural hazards, (ii) existingor projected land use, and (iii) the hydrau-lic and ecological conditions of the river inquestion. On the other hand, the federallaw on flood protection determines prior-ity among respective measures. Sustain-able measures have a clear priority:• Flood protection is to be guaranteedthrough proper maintenance of theriver or stream channel. This also includesthe maintenance of forests with a protec-tive function throughout the entire catch-ment.• Land-use planning measures topreserve open space along rivers and pre-vent uncontrollable increase of damagepotential on floodplains have the same pri-ority as maintenance of river channels. Ur-ban development that considers existingnatural hazards is a better form of preven-tion than expensive protection works toprotect thoughtlessly delineated buildingzones.• Structural measures are only to beconsidered when maintenance work andplanning measures cannot provide thenecessary safety.• Determination of priorities requires con-sideration of other measures such asflood-proofing of buildings and otherexisting structures.

Guiding principlesfor flood protectionThe particular need for concrete actionmust be determined with the cooperationof all parties concerned, based on a pre-determined framework. This is only possi-ble when (i) knowledge of the prevailinghazards is available, (ii) the hazards areproperly assessed, (iii) the various interestsare coordinated, (iv) the relevant laws arefollowed, and (v) the priorities are set:• Holistic planning is necessary for ten-able solutions. The result is a package ofmeasures that considers all types of natu-ral hazards and incorporates all land-useactivities. These measures have to beadapted to existing development plans.*• The current state of the river or streammust be preserved through maintenanceworks and land-use planning, providedthat the degree of safety is sufficientfrom the point of view of flood protectionand ecological conditions are acceptable.• A plan for measures to be undertakenhas to be established if deficiencies arerevealed by a safety assessment. Measureshave to be adapted to local conditions. Inthe process, flood safety as well as ecologi-cal deficiencies must be taken into ac-count. These are of equal importance inguaranteeing appropriate flood safety andmaintaining the ecological functions of theriver or stream.• Flood protection is no longer just limitedto the prevention of overbank flooding andinundation by any means. Streams and riv-ers are ecosystems that host a variety ofanimals and plants, as well as excellentrecreational sites. Therefore, up-to-dateflood protection needs to show considera-tion for the numerous functions of the

river or stream and must try to preserveand strengthen them wherever possible.• Every flood prevention concept has to beassessed in terms of technical, economicand ecological balance. If a particularproject is disproportionate in this respect,then land-use or protection objectiveshave to be reconsidered.• A detailed project must be estab-lished if the measures are deemed propor-tionate.• Residual risks always remain. These re-sidual risks must therefore be assessedand the planned measures supplementedby emergency planning and relatedemergency organization (includingwarning concepts and evacuation plans).The efficacy of the measures in place needsto be examined in case of overstress dur-ing extreme events. This integral examina-tion leads to living being conscious of pos-sible hazards in the sense of a global riskculture.

• Strategy

Action

Procedure

Project Design

Measures

Appendix

11

Hazardoussituation

Use(existing

or planned)

Rivercondition

Emergency planning and emergency organization

Measures implemented

Measures are proportionatePreserving

actual status

Propermaintenance

Land-use planning steps

Preservingactual status

Cultivation

Land-use planning steps

Setecological

goals

Determineprotection goal

Deg

ree

of

pro

tect

ion

su

ffic

ien

t

Go

als

ach

ieve

d

Goals unfulfilled

Planning of measures

Cultivation steps

Land-use planning steps

Restoring nature

Planning of measures

Proper maintenance

Protective forestcultivation

Land-use planning steps

Protective structures

Protection deficit present

Residual risk

Measures aredisproportionate

Assessmentof steps taken

Determineusage goal

Action

13

Fran

k (2

)

Recognizing the Need for ActionWeighing interests

Many risks are obvious, but others can hardlybe recognized without precise examination.Flood risk particularly falls into oblivion afterlong periods without threatening events.

Determining the need for action depends on the following points:

• Ascertaining the risk situation and damage potential.

• Assessing the state of a river.

• Setting protection objectives.

• Determining the necessary space for rivers and streams.

• Setting ecological development goals.

• Confirming existing or planned land use.

Flood control and ecological concerns arenot in conflict, but are equal priorities inany flood control plan.

The need for action from a floodcontrol standpointFrom a flood control standpoint, a hazardassessment must be made before as-sessing the need for action. One may rec-ognize possible protection deficits byweighing the risk situation against the ex-isting or planned land use.If a deficit exists, the next step is to ascer-tain the degree of potential damage. If theexisting risk is great, the protection deficitmust be offset by plans of measures.If no deficit exists, maintenance workshave to be ensured. Suitable areas shouldbe examined if they can be safeguarded aspotential flood detention areas orfloodways.

The need for action from an en-vironmental standpointFrom an environmental standpoint, thestream or river reach in question must bechecked for ecological viability, andthe ecological development goals must beset in order to assess the need for action.Rivers and streams have multiple func-tions. They are not only habitats for localfauna and flora but also network corri-dors. Therefore, the situation at the upperand lower reaches must also be consid-ered.Monotonous, heavily trained river chan-nels do not fulfill these functions (or onlyin a limited sense). Hence, maintenance orrestoration of conditions close tonatural also belongs to the flood controltasks: rivers should become evident as

landscape-forming elements, and a watercycle close to natural should be main-tained as much as possible. Moreover,greater attention should be given to thepopulation’s recreation needs.

The key role of farmingWhen weighing the interests of land-usedemands and environmental concerns,farming plays a key role. This is becauseecological compensation measures de-manded for infrastructure projects oftenuse up agricultural areas. Yet solutions canstill be found that serve both farming and

flood protection. Thus, farmers affectedmust be involved in planning from the out-set. They may take over maintenanceworks on the river in question, getting ap-propriate remuneration.In addition, financial incentives rewardnearly natural use of areas adjoining wa-terways. Ecological compensation areasare taken into account for a performanceassessment, and areas of low intensityfarming adjoining rivers are priority areasfor which bonus payments may be re-ceived in keeping with the Eco-Quality De-cree (EQD).

14

9000

8000

7000

6000

5000

4000

3000

2000

1000

0

72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00

1800

1600

1400

1200

1000

800

600

400

200

0

Fran

k ; K

e yst

one

Ascertaining the Hazard Situationand Damage Potential

Dam

ages

per

yea

r

Tota

l d

amag

es

Values in millions of Swiss francs (adjusted to include inflation)Strategy

• Action

Procedure

Project Design

Measures

Appendix

Flood and sediment disasterdamage in Switzerland since 1972.

The major events of 1978, 1987,1993, 1999, and 2000 are crucial.

The effects of a flood in a specific area arebasically determined by three factors:• by the processes occurring,• by their intensity,• and by their duration.Therefore, the degree of potential damagein a defined area is not a fixed amount butdepends on a series of assumptions whichoften cannot easily be verified.Wrong hypotheses obviously lead to mis-judgments. Hence, a variety of sce-narios have to be elaborated that are jus-tified by the broad spectrum of potentialflood processes. Only in this way is it pos-sible to obtain usable results that allowobjective and comprehensive cost/ben-efit ratio comparisons. All those involved– technical experts, design engineers, andrepresentatives of municipalities, the can-tons and the federal government – shoulddebate those scenarios and agree on them.The hazard situation ascertained in thismanner enables assessment of a flood’spotential consequences – i.e., the numberof people at risk, the amount of mate-rial damage, the degree of collateraldamage (interrupted production, productsubstitutions), and the degree of environ-mental damage.

VulnerabilityWater penetrates into buildings mainlythrough entrances, cellar openings, or ga-rage doors. Therefore, building vulnerabil-ity to damage depends largely on the el-evation of these potential weak pointscompared to the level of the surroundingterrain. The sealing of the external surfacesof a building, the supply equipment andelevator facilities are also potential weakpoints.

Ascertaining damageA rough assessment of potential damagesuffices generally. Basic data are particu-larly available in the case of material dam-age. It is often very difficult to assignmoney values for other categories. Usuallydamages for specific land-use categoriesare ascertained in costs per area unit.However, sensitive individual objects mustbe given special attention.

Special risksSpecial risks include chemical and biologi-cal production plants, storage sites, rub-bish incineration plants, dumps, switchingcenters, and production plants housingmachinery of above-average cost. Specialprecautions are also necessary in case ofdisaster for important infrastructure sitessuch as command centers, hospitals, andemergency shelters.Usually investigations of special risks havealready been undertaken in connectionwith the ordinance on major accidents andmay be used. Otherwise they must be or-dered. Detailed studies are justified only ifthe economic viability of a flood con-trol project becomes the focus of discus-sion.

15

Assessing the State of a River or Stream

Rivers or streams imbedded in culverts present a special problem.Whenever possible, they should be opened and their channeltransformed back into a state close to natural. New culvertsshould only be permitted in compelling cases, and their numberought to be restricted to an absolute minimum.

Recommended reading

BUWAL (Mitteilungen zum GewässerschutzNr. 27): Methoden zur Untersuchung undBeurteilung der Fliessgewässer – Ökomor-phologie Stufe F [Methods for Examiningand Assessing Rivers and Streams – Ecomor-phology Grade F]

A natural stream and river landscape con-sists of a mosaic of different habitats.Flowing and still water, deep and shallowreaches, as well as periodically and epi-sodically flooded bank areas are foundclose to each other on a narrow space inrivers or streams that have remained natu-ral or have been laid out close to a naturalstate. Hence they provide a large habitatdiversity for plants and animals.Yet these transitional areas betweenwater and land – areas that perform mul-tiple functions – have disappeared in manyregions due to the pressure of heavy landuse. Therefore, all flood-control projectsmust take seasonal flow variation and va-riety of currents into greater account. Inorder to ascertain the need for action fromthe standpoint of both the ecology andflood control, three factors stand in theforefront:• Does the river or stream have a varietyof structures? Have existing migrationobstacles or training works diminished thisstructure’s variety?• How much room does the stream orriver need to fulfill its ecological func-tions?• What cross section does the river needto evacuate flood flow?

Ecomorphological assessmentThe need for action concerning a river’snatural functions can be derived froman ecomorphological assessment. Whenplanning flood control measures, this needfor action should be considered in pre-cisely the same way as protection objec-tives for land use.The term ”ecomorphology” covers the en-tirety of structural conditions in and at

the river channel, i.e., both training works(e.g., bank protection, weirs, or bedstabilization structures) as well as the con-dition of nearby surroundings (cultures,land use, vegetation, and river or streamspace).The related assessment can be carried outwith varying degrees of detail. In case of aregional assessment of rivers or streams(the so-called grade F), five main char-acteristics are sampled:• average bed width;• variation of the free surface width;• bed stabilization structures

(and stream migration barriers);• bank toe protection works;• bank width and bank characteristics.

16

Setting Protection Objectives

Hold it back when you can, let it pass when necessary. The general use of onespecific design flood no longer has any general validity. Instead, the protection objectivesshould focus on specific objects and the damage potential at hand. Yet the 100-yearflood (Q100 ) in settlement areas is now, as in the past, an important reference value.Higher protection should be the aim in case of very high damage values and special risks.

Strategy

• Action

Procedure

Project Design

Measures

Appendix

Protection objectives are set differently,depending on the type of hazard thatcould endanger a specific location andwhat form of protection is needed: wherehuman lives or high material damage val-ues may be at stake, the protection ratingis set higher than it may be in areas usedfor farming or forestry. Thus, a few objectsmay be flooded often, others seldom, stillothers as far as possible never.This is a crucial innovation in comparisonto past planning. In the past, flood controlmeasures were often designed for a spe-cific event. Hence, a 100-year event(Q 100) was usually selected. Almost fullprotection was guaranteed for this event.Yet this procedure led to disproportion-ately expensive solutions in many areas.And the effects of an event exceeding thisdesign flood were usually not ascertained.

New planningIn the meantime the following procedurehas proven its value: Defining protectionobjectives should occur in relation to landuse and objects to be protected.This has resulted in a so-called protec-tion objective matrix that forms thebasis of methodology and differentiationin setting protection objectives. Such aprotection objective matrix was firstgraduated by object categories after theflood event in Uri canton of 1987. This ex-ample has also proved itself in other loca-tions.

Differentiation of protectionobjectivesFlood control efforts concentrate on re-ducing and preventing damage. Incase of high material values, the degree of

Main parametersThe protection objective is basically linkedto probability of occurrence, and this ischaracterized by specific parameters. Thequantity parameter used most often is thepeak discharge Q expected for a certainreturn period.• The damage limit Qa refers to a dis-charge that should run off without caus-ing damage to objects requiring protec-tion.• The hazard limit Qb refers to a dis-charge that, when exceeded, can lead toan uncontrolled flow situation. The secu-rity of objects to be protected is no longerguaranteed.• Flood processes for flood dischargeamounting between the damage limit Qa

and the hazard limit Qb may cause limiteddamage, but neither objects to be pro-tected nor flood control structures shouldnormally be destroyed.• For certain object categories, the designdischarge must be raised from the damagelimit Qa to the hazard limit Qb, if the pro-cess involved induces high danger.• In case of differing object categories, thedefinitive protection objective should beascertained by assessing the residual risks.If a project leads to disproportionate costsor impacts, the protection objectives or theland-use practice must normally beadapted.• The concerns of other domains af-fected (e.g., farming, protection of natureand the landscape, settlement develop-ment, and energy production) must beconsidered when weighing interests.

protection is set higher than for low val-ues. According to this principle, the protec-tion objective is graduated by the value toprotect, whereby the processes involvedshould be considered. The most importantobject categories are:• Closed settlements. They shouldusually be protected against rare events.• Industry and trade. The same princi-ples apply for these facilities and installa-tions as for closed settlements. Theyshould usually be protected against rareevents.• Infrastructure facilities. Differentia-tion occurs here between installations ofnational, regional, or local importance.The protection objective will be higher orlower, depending on its value, as well asits vulnerability.• Cultivated areas. It is better to pro-tect intensively cultivated areas than lowintensity cultivation areas. There is also agreat difference to be made between theprocesses that reduce land fertility andthose that lead to a one-time crop loss inthe worst scenario.• Special objects. These must be as-sessed individually, but again, the prin-ciple has to be used that the higher thepotential for damage, the higher the pro-tection goal.

Qa

Qa

Qa

Qb

Qb

Qb

Qb

Qb

Qa

Qa

Fran

kA proposal for a protection objective matrix

Qa Damage limit

Qb Hazard limit

FQ1 Annual flood

FQ100 Flooding occurring only onceevery 100 years (100-year flood)

EFQ Flooding occurring for extremein hydrological and meteorological situations

PMF Probable maximum flood

Nature landscapes

Low-intensityfarming areas

High-intensityfarming areas

Single buildings; localinfrastructure facilities

Infrastructure facilitiesof national importance

Closed settlements;industrial facilities

Special objects;special risks

No design discharge

To be determined case by case

Full protection

Limited protection

No protection

Object categories Q1 Q10 Q20 Q50 Q100 EFQ PMF

Differentiating protection objectivespermits suitable reaction to the flood

hazard based on local danger factors. Thiscuts costs while enabling even extreme

events to be handled. Such a protectionobjective matrix was used for the

first time in Uri canton (after a devastatingflood of the Reuss river in 1987).

Dependence on the processesinvolvedThe protection objective not only dependson how a specific area is used (object cat-egories) but also on the frequency andcharacteristics of floods occurring there.Therefore, important parameters besidepeak flow must always be considered. Incase of bank erosion or debris flow,the protection objectives must be in-creased according to the hazards of thesedangers. Definitive parameters linked tothe various processes can set for the re-lated scenarios:• In case of inundation, the main pa-rameter is the volume of water flowing outof the channel and the duration of flood-ing.• In case of erosion and deposition,the decisive quantity is not so much thepeak discharge, more the duration of theflood.• In case of debris flow, the volume isoften more crucial than the peak dis-charge.

18

Determining the Necessary River Space

Minimum space needed from an ecological standpoint.Minimum space needed from flood protection standpoint.

Bank area Bank areaNaturalchannel bed

Slope1:2

Slope1:2

Maintenancestrip (3m)

Legallypre-

scribeddistance

frombuildings Bank area Bank area

Legallypre-

scribeddistance

frombuildings

Requiredchannel

bed width(hydraulic)

Maintenancestrip (3m)

Qd

Strategy

• Action

Procedure

Project Design

Measures

Appendix

Recommended reading

BWG (flyer, 2000): Raum den Fliessgewäs-sern! [Space for Rivers!]

Any project presents a crucial question:How much space does the stream or riverneed? Basically the minimum necessaryriver space includes the channel’s bed andthe bank area. The stream or river can re-work this space. It makes itself availablefor flood flow, and it usually remains freeof any kind of use (buildings and facilitiesmay only restrict the minimum river spacein well-justified exceptions). Moreover, theanswer to the question about the neces-sary space can be derived from the follow-ing needs:• The flood control standpoint.Given the hydrologic basics and the pro-tection objectives set, a river space tobe secured in the long-term must be de-fined. The corresponding design flood per-mits determining hydraulically the re-quired theoretical bed width whenconsidering local framework conditions.When considering a 1:2 bank slope and amaintenance strip of 3m that ensures ac-cess, the minimum space required can beestimated from the flood control stand-point.• The ecological standpoint. Streamsand rivers are not only habitats of a variedflora and fauna native to the location. Theyare also a link in networking the habitats.They form the landscape, they contributeto self-purification of the water, and theyprovide a crucial contribution to regener-ating groundwater. From the ecologicalstandpoint, a simple method of calculation– a key curve – is available to set theminimal necessary space. It ascertains thewidth of the bank area. This working aid isapplicable for small and medium-sizedstreams that comprise a major part of thewater network.

Minimum necessary spaceThe larger of the two river spaces deter-mined this way is finally definitive. Build-ings and facilities should basically main-tain the legally prescribed distance to theriver space ascertained in this manner.

Other space requirementsWhere leisure activities are expected, rec-reational space complements the spacerequirement of rivers and streams. In rarelyused areas, necessary space can be ex-panded by the meander width of a natu-ral channel. Setting up a buffer zone cor-responding to the meander width makesspace available for dynamic developmentof rivers that are close to nature.

Approach to secure spaceA wide range of planning measures canassure the necessary space for rivers andstreams to secure flood control and eco-logical functions:• Acceptance in cantonal guidelinesor action plan (imperative): it maintainsthe primary hydraulic engineering funda-mentals valid in the long run and providesguidelines binding on the authorities.• Consider in cantonal or municipalityland-use plans (imperative): defineflowing waterways space by clearly identi-fied parcels and property lines (e.g., by re-lated frontage lines).• Consider in a municipality structuresordinance (optional): also define riverspace by clearly identified parcels andproperty lines.• Define a municipality planning zone(optional): rapid temporary assurance ofthe required river space to prevent furtherrestrictions.

• Acquire land through the publicsector (optional): assures space perma-nently for rivers and streams.• Transfer land (optional): relievesproperty owners of disproportionate re-strictions.• Resolve through contracts (op-tional): governs management and care ofbank areas as well as compensation forthese ecological services.• Legally prescribe distance tobuildings in urban areas (recom-mended): In order to maintain leisurespace in river areas, we recommend thatthe defined river space benefits from theusual legally prescribed distance to build-ings (i.e., from the bank area onwards).

15

10

5

0

0 2 4 6 8 10 12 14 16 18

19

Fran

k (2

); Sc

häub

lin (

1)

Natural channel bed. Corresponds at meanflow to the water level width and serves as thedecisive parameter for calculating the bank areaand meander width.

A natural channel bed indicates a marked varietyin width. If natural comparative stretches aremissing, the following multipliers apply:• With limited variety in width

Factor 1,5• With lack of variety in width

Factor 2,0

Natural bed width in meters

Ban

k w

idth

in m

eter

s

Bank width to secureflood protection

and ecological functions

Bank width for ensuring biodiversity

Bank area. The bank area required for river orstream functionality is determined by the keycurve. Depending on the width of the channel bedon both sides of the river, it amounts to a mini-mum of 5 m. This consists of the minimum nu-trient buffer zone that is set at 3m accordingto the material decree. In areas with excessivenutrients input from neighboring farming regions,this buffer zone should be extended.

Leisure space. An additional space of 3m isrecommended globally (e.g., for paths) near set-tlements and on traditional hiking and bikingroutes. Furthermore, enough room must be fore-seen for rest areas and camp grounds.

Meander. In little used areas, a stripe corre-sponding to the meander width of a natural chan-nel can be superimposed on the bank area, and itcan be widened accordingly. Its width amounts tofive or six times the width of the channel bed .

Settlement areas. Even under limited-spaceconditions, flood control and ecological net-working should also be secured to the maximum.

Key curve. The decisive parameter in ascertain-ing the necessary space of a river is the naturalbed width. The bank area’s recommended mini-mal width can be derived from this: Even in caseof brooks, it amounts to at least 5m. At a width of15m, a bank strip can function as an independ-ent biotope. In case of smaller streams in parti-cular it makes sense to determine a wider bankarea (hatched green line). This will promote bio-diversity – the natural variety of plants and an-imals – along the stream.

20

Des

air;

Doc

umen

ta N

atur

a

Defining the Need for Action

Expansion of river space has a positiveimpact in a great variety of areas: It

reduces risks of flood damage. It enablesmore cost-effective solutions for flood

control structures. It protects rivers andstreams from input of undesirable

ingredients and improves water quality. Itcontributes to maintenance of natural

habitats. And it upgrades recreation space.

Strategy

• Action

Procedure

Project Design

Measures

Appendix

After a hazard situation has been identi-fied, the damage potential ascertained, thestate of the river assessed, the protectionobjectives set, and the necessary spacedetermined, the decision must be taken onthe degree of planning measures neces-sary. Four individual cases or combinationsof these individual cases can be distin-guished.

Case A:No flood control deficitCurrent use is in harmony with the hazardsituation posed by nature. This fortunatesituation should be secured over the longterm. Therefore, it is necessary to imple-ment it in structure and land-useplanning. The maintenance already guar-anteed should be continued, and the func-tionality of protective structures on hand(and their susceptibility to hazards) shouldbe checked periodically.

Case B:Flood control deficitIf a flood-control deficit is identified,studies within planning corrective mea-sures must determine how to eliminate orreduce it. Possible ecological deficitsshould be considered at the same time.After the measures have been realized, re-maining hazards must be identified. Ahazard map should be compiled for thispurpose to be implemented in structureand land-use planning. Residual risksshould be clarified and should be consid-ered in emergency planning and organiza-tion. Maintenance of protective structuresand of river channels must be secured overthe long term.

Case C:No ecological deficitThere are no land-use conflicts, and theriver is in a condition close to natural. Thisshould be assured in the long term throughstructure and land-use planning. Themaintenance and care already carried outare to be guaranteed and continued.

Case D:Ecological deficitIf ecological deficits are identified, withinplanning of corrective measures must alsobe determined how the situation can beimproved. Flood control concerns mustalso be taken into account. After improve-ment of the situation has occurred, it mustbe secured for the long term. If deficits re-main that cannot be eliminated immedi-ately, the necessary land for it must at leastbe secured in a land-use planningsense.

21

AB

C DNo flooding deficit

recognizable

Flooding deficitpresent

Long-term guarantee

No ecological deficitrecognizable

Ecological deficitpresent

Planning measuresin the environmental sector

Planning measuresin the flood control sector

Planning measuresin the flood control

as well asenvironmental sectors

Need for action

Need for action Need for action

Procedure for planning corrective measures andintegrating ecological demands. A sustainableflood control project basically treats both aspects.

Procedure

23

Keys

tone

The Federal Law on Flood Control (Wasserbaugesetz, WBG)sets the following framework conditions:

• the goals of flood control;

• the order of priorities in planning and when carrying outflood control measures;

• qualitative requirements in case of unavoidable interven-tions in the river space and maintenance.

Responsibilities

All flood control measures – but especiallyplanning and construction measures – lead tocomplex decision-making processes in whicha number of standards should be noted.

The federal government has broadsweeping legislative authority in the floodcontrol sector. Yet each canton is respon-sible for related projects. This task isbroad-ranging and includes both riverchannel maintenance and land-useplanning as well as structural measures.The cantons are also responsible foremergency planning and emergency or-ganization.Accordingly, the cantons carry out federalflood control laws and enact regulationsnecessary to implement them. In particu-lar, they regulate inner-cantonal responsi-bilities (task distribution between the can-ton, the districts, and the municipalities)and the applicable procedures for planningand realizing the measures needed.*

Distribution of tasksThe cornerstones of federal law mark outthe material framework that the can-tons fulfill on their own. For its part, thefederal government must provide compen-sation regarding certain flood controlmeasures and may give financial aid forriver restoration (no legal claim). The fed-eral government also promotes training

and continuing education for peopleentrusted with flood control. And it carriesout surveys of interest to all Switzerlandon flood control matters and hydrologicconditions.Furthermore, the responsible Federal Of-fice for Water and Geology (FOWG) pro-vides the basic data and manuals requiredfor suitable and sustainable flood control.It also advises the cantons as well as otherinstitutions. The FOWG’s opinion is neces-sary (see below) for certain projects. In allother cases the cantons may opt to seekthe FOWG’s opinion.But in case subsidies are sought, earlycontact with the FOWG is recommended.

Federal supervisionA central federal task is to supervise can-tonal enforcement of federal law. TheFOWG is also responsible in this area. Itchecks conformity of flood control projectswith federal legislation – particularly envi-ronmental law – and looks after appropri-ate use of federal resources.Before they make a decision, the cantonspropose their flood control projects to theFOWG for federal comment. This appliesespecially in case of projects that:• affect a river forming a national border,• affect flood control measures of othercantons,• require an environmental impact study,• affect a protected area or an object onthe national inventory.

Procedural coordinationAll decisive cantonal and federal law pro-cedures used in individual cases must becoordinated in a material and formal senseand then be brought into harmony witheach other in terms of content. The mate-rial agreement and balancing of inter-ests related to it permit integral treatmentand assessment, even in complex projects.Two different approaches are possible inthe formal respect:• Coordination model. Several au-thorities remain responsible in various pro-cedures and harmonize decisions in termsof content.• Concentration model. A single au-thority carries out the various procedures.The FOWG coordinates the relevant proce-dures at the federal level.

*Due to the variety of federalist structures,these 2001 guidelines must be restricted tothe collaboration between the federal govern-ment and the cantons.

24

UFA

EG–F

OW

G

Legal Standards

Strategy

Action

• Procedure

Project Design

Measures

Appendix

*Other interfaces. Flood control measurescan also affect national treaties and other inter-national agreements. There are also interfaceswith other concerns of federal law. Those espe-cially worth mentioning are:

• the decree on security precautions forpipeline facilities (in connection with safedistances);

• the decree on security of dam facilities (StaV,in connection with risks for riparians).

Other federal standardsBeside the WBG and the ordinance relatedto it (WBV), there is a series of other fed-eral legal standards* that can relate toflood control. They often require specialdecisions or procedures:• Federal Law on Land-Use Planning(RPG). Planning of flood control is a stepin establishing a cantonal structure andland-use plan. It has to be coordinatedwith space requirements of other sectorsby weighing interests. In particular, plan-ners must consider the river’s or stream’sspace requirements needed for flood con-trol and to guarantee ecological function-ing. Structural measures for flood controlrequire a construction permit. A waiverpermit must be obtained outside construc-tion zones. Engineers must prove that themeasure is bound to the location, and apreponderance of interests must not op-pose it.• Federal Law on Water Quality(GSchG). Hydraulic engineering projectsmust not cause water pollution. The imple-mentation of such projects is only condi-tionally possible in water protection areasand groundwater protection zones. Hy-draulic flood control measures need a le-gal permit for water quality control pro-tection, in particular endangered waterprotection areas. The law basically forbidsto cover rivers or streams by structures orto lay them into culverts. Extraction ofsand, gravel and other material requires afederal law permit (it cannot be granted ifthe sediment regime in rivers or streams isadversely affected). The water quality law(like the hydraulic engineering law) re-quires maintenance or restoration of natu-ral rivers.

• Federal Law on Fisheries (BGF).Interventions in rivers, their discharge re-gime, or their course as well as in bank andbed areas assume a legal fishery permit (tothe extent that no permit is required inconnection with the water quality law).• Federal Law on Protection of Na-ture and Landscape (NHG). Objectslisted as of national importance in the fed-eral inventory of alluvial zones are of spe-cial importance. They are to be maintainedundiminished (thus flood-control mea-sures are only permitted in a restrictedmanner). In all other protection areas, ac-cording to the NHG, unavoidable interven-tions require compensation or restorationmeasures. Ecological compensation is alsoforeseen in intensively used areas (e.g., byrestoring riparian vegetation) and by iden-tifying ecological buffer zones to protectbiotopes.• Federal Law on the Forests (WaG).The law enacted a ban on clearing in prin-ciple. Waivers are only granted under strictconditions, especially if the envisionedstructure or facility is confined to the loca-

The Federal Law on Flood Control(Wasserbaugesetz, WBG; SR 721.100) andsupplemental Ordinance on FloodControl (Wasserbauverordnung, WBV; SR721.100.1) occupy center stage amongfederal legal tasks concerning flood con-trol.The federal legal outlook can be summa-rized as follows: Legislative attention fo-cuses primarily on land use which recog-nizes existing natural hazards andmaintains (or creates) the necessary bufferareas. Thus recognized hazards should notbe punctually removed but imbedded in aglobal concept for the entire area.As soon as structural protective measuresbecome necessary, federal law makesqualitative demands that lie in the interestof a varied animal and plant world as wellas river ecology. In each case a minimumspace must be reserved for rivers andstreams. Therefore, maintaining or creatingfloodplains while establishing and ensur-ing floodways also belongs to expedientplanning of measures.

25

➜ http://www.admin.ch/

Already in 1874 the Swiss people through Article 24 of that era’s federalconstitution has given the federal government competence for hydraulicengineering and forest police. The related hydraulic police law was approvedon 22 June 1877. At first it applied only to high mountain areas, but from1897 on it affected other areas as well. This law was replaced in anupdated constitutional version by a water resources managementarticle in 1975 (in the revised federal constitution’s Article 76 ”Water”).However, the hydraulic police law was only replaced during the 1990s by theFederal Law on Flood Control (Wasserbaugesetz, WBG) and its relatedOrdinance on Flood Control (Wasserbauverordnung, WBV).

tion. Basically, property compensation isto be provided. But this can be waived incase of flood control measures. Nature andlandscape protection measures can also beused for compensation instead of property.The clearing permit does not obviate theneed for a construction permit waiver inregard to land-use planning. Training ofstreams by forestry engineering methodsthat serves to maintain forests is alsoruled by the forest law. Details are derivedfrom the hydraulic engineering law (if thesituation arises, responsibility is to be co-ordinated between forestry managementand hydraulic-engineering). Based on theWaG, the federal government grants sub-sidies in case of any other protective mea-sures that supplement hydraulic engineer-ing (avalanches, rockfalls, erosion zones,landslides not related to river activity).• Federal Law on EnvironmentalProtection (USG). The legally regulatedprecaution principle manifests itself in theenvironmental impact study that is to becarried out in case of important hydraulicengineering measures. USG regulationsare also to be observed for noise control,soil pollution, and waste planning.• Federal Law on Hunting and Pro-tection of Mammals and Fowl Livingin the Wild (JSG). The federal govern-ment declares reservations for water andmigratory birds of national and interna-tional importance. The opinion of the re-sponsible Federal Office for Environment,Forestry, and Landscape must be obtainedin case of hydraulic engineering plans thatimpact protection areas.• Federal Law on Footpaths and Hik-ing Paths (FWG). The cantons are con-cerned with planning footpaths and hiking

networks. They coordinate them with theirother space impact activities including thehydraulic engineering sector.• Federal Law on Hydropower Use(WRG). Requires coordination of hydrau-lic engineering measures with concessionrights (and vice versa). In particular, it con-cedes a right to compensation to thehydropower concessionaire if interven-tions in the river’s course affect his previ-ous use of it permanently (presuming ad-aptation of the plant is unreasonable). Onthe other hand, the concession can alsoenvision the concessionaire’s financialparticipation in maintenance costs andpossible structural protection measures.• Federal Law on Agriculture (LwG).The federal government can support sub-sidies for low intensity use of farmland.Moreover, cantons, communities, and hy-draulic engineering associations can com-pensate for measures that serve floodcontrol goals (e.g., inundation zones).Stream restoration (including land acqui-sition) can also be supported in connectionwith rural engineering. Basically, hydraulicand rural engineering projects should becoordinated.• Federal Law on Dispossession(EntG). In implementing the law on hy-draulic engineering law, the cantons candispossess the rights in question or trans-fer the right to dispossess to third parties.• Federal Law on Financial Aid andCompensation (SuG). This governs thefederal government’s guarantee of com-pensation and financial aid. In accord withit, among other features, possible partici-pation of beneficiaries and those liableshould be considered. Before receivingthe contribution guarantee, those granted

subsidies may only begin construction ormake major acquisitions if the subsidizingauthority gives its approval.• Federal Law on Use of a Special-Purpose Mineral Oil Tax (MinVG). Thefederal government uses a portion of themineral oil tax revenue earmarked forhighway traffic for structures protectingagainst natural hazards along highwaysand particularly flood control measures.• Minimum requirements for linking eco-logical compensation zones are set out inthe Ordinance on Ecological Quality(ÖQV).

26

Fran

k; K

eyst

one

Framework Conditions

Protection objectives are to be examined (and adapted,if necessary) within a interest-weighing procedure

concerning their economic and ecological proportionality.

Strategy

Action

• Procedure

Project Design

Measures

Appendix

Flood control cannot be planned or real-ized in a manner detached from other de-mands for space. Coordination and agree-ment with other space-impact plans (e.g.,from the sectors of highway design, for-estry management, farming, water qualitycontrol, water use, and river restoration)and other intentions for land use (e.g.,development of building sites) are cogentin any case, and the related fundamentalsshould be considered.Therefore, any flood control project shoulddetermine right from the start if other dis-ciplines are affected. Only in this way willpotential conflicts be recognized on timeand considered properly in planning.

ProportionalityBasically every measure has to fulfill thefollowing conditions in connection withflood-control: On one hand, the measuresenvisioned must achieve the goal desired.On the other, they should be as unobtru-sive and cost as little as possible. More-over, a reasonable ratio should exist be-tween the desired goal and the intrusioninto protected legal goods (e.g., pri-vate property). Therefore, any flood controlmeasure should be examined from theviewpoint of its proportionality:• Costs. Flood control projects must beeconomical and expedient. Thus, a balanceis necessary between the cost of theprotective measures and the potentialdamage expected. No claims for compen-sation or financial aid can be justified foruneconomical or inexpedient flood-controlprojects. If such a project involves not onlythe public interest but especially that ofprivileged third parties, the costs are to beapportioned among the participants.

• Ecological claims. Proportionality hasalso to be respected in case of claimslodged on behalf of nature and the land-scape. Basically the existing conditionsshould not be worsened but improved asmuch as possible. In case of supplementalclaims, the costs related to the ”ecologicalbenefit” (even if they cannot be deter-mined monetarily) should be factored intothe comparison.• Private interests. Often hydraulic en-gineering needs and private interests failto harmonize. Owner positions must bowwhenever a sufficient public interest exists.Therefore, the cantons have the right todispossess property in the interest of floodcontrol. On the other hand, private partiesaffected may present their concernsthrough the procedures envisioned forthem by the cantons and the federal gov-ernment.

27

Federal Subsidies

The crucial assumption for a subsidy issuedby the federal government is expedientplanning of the related flood-controlproject:• Agreement and coordination with otherinterests and partners is secured.• There is no dual subsidy (e.g., from hy-draulic engineering and forestry manage-ment).• The work is in the public interest.• Cost participation corresponds to the in-terest situation ascertained.• In case of conflicting goals, the verdictsare justified.• The project fulfills the requirements ofall federal laws (i.e., regulations on water-way protection, land-use planning, natureand landscape protection, environmentalprotection, etc.)

DocumentationIn case of subsidy applications for struc-tural measures, the natural hazards, possi-ble damage, selected protection objec-tives, and impacts of measures envisionedshould be identified, clarified, and under-standable.Another assumption for a federal subsidyapplication is that the responsible can-tonal authorities have already made a le-gally binding decision on the relatedproject.Federal authorities also require projectdocumentation in order to carry out athorough examination of the project. Thisincludes documentation on technical andcost factors as well as opinions andascertainments of cantonal authorities.

LegitimizationWithin approved loans, the federal govern-ment carries out settlements for:• Preparation of basic data for assessinghazards (including concepts, hazard andevent register, or hazard maps).• Planning and building flood-controlstructures and flood control facilities (aswell as restoring or replacing them).• Clearing channel beds and restoring asufficient flow section after the occurrenceof extreme events.• Setting up and operating gauging sta-tions in the interest of flood control.• Building up early-warning services.• Acquiring land for protective structures.• Restoring rivers when stressed by hy-draulic engineering measures. There is nobasis for legal claims. Priority is given toprojects that enhance natural river dynam-ics and serve to network habitats (e.g.,through culvert removal and by creatingenough buffer zones and transition areasbetween land and water).

28

Luft

bild

Sch

wei

z

Regular Procedure

The step-by-step approach within proceduralplanning can identify an optimum solution

for flood control balancing technology,ecology, and economics: maintenance as

well as planning and structural measures of-ten stand in close correlation, since they

exercise a mutual influence on each other.

➜ Appendix: Checklists

Strategy

Action

• Procedure

Project Design

Measures

Appendix

The first planning level is the preliminarystudy (in flood control also frequently re-ferred to as the concept). All possibleoptions (i.e., the ”do nothing” approach,too) should be discussed, and the optionworth pursuing should be defined. Impor-tant framework conditions should be con-sidered here, and potential conflict pointsshould be listed.

At the preliminary project planninglevel (often called the general projectin flood control), planning measures forthe elected options are detailed to the ex-tent that (1) a rough cost estimateemerges, (2) major dimensions of poten-tial structural measures are known, and (3)an overview of the hydraulic, economic,and ecological impacts of the related ap-proaches can be provided.

The construction project includes thetechnical report, the project plans, and thecost estimate. It becomes the basis for thebuilding permit procedure, the decision onsubsidies, and the call for tenders. Thosedirectly affected must be able to recognizethe related impacts on each parcel pre-cisely (except for urgent measures afterfloods and sediment disasters).

The implementation project (oftenalso called the detailed project in floodcontrol terminology) presents all calcula-tions, dimensions, construction details,and instructions needed to realize themeasures selected.

The regular procedure for flood-controlmeasures can be divided into foursubsteps.

Step 1: Laying out the projectEach canton usually has a specializedoffice responsible for flood control. Thisoffice has multiple tasks:• It is responsible for handling and coor-dinating project applications.• It advises local responsible persons oragencies, farming cooperatives, privatelandowners, and third parties on floodcontrol issues and in connection with riverrestoration.• It is the direct contact in the flood con-trol sector for the Federal Office for Waterand Geology (FOWG). The procedure canbe simplified considerably if an early in-formation exchange on the flood con-trol project takes place between the can-tonal office and the FOWG. This appliesespecially if important fundamentals (e.g.,design parameters) are to be determined.Yet early agreement by all involved is alsoof great usefulness if other federal inter-ests are involved (e.g., projects in areaswith a claim for protection due to federalinventories).

Step 2: FOWG opinionIn case of important projects and in spe-cial cases (see also page 23), the respon-sible cantonal field office consults with theFOWG which issues a binding opinion. The

FOWG can also express itself here on theamount of a possible federal contribution.

Step 3: Cantonal decisionThe next step is the canton’s legally bind-ing decision on the hydraulic engineeringplan and its financing. In case of plans re-quiring an environmental impact study(UVP), cantonal law determines the proce-dure definitively.

Step 4: Subsidy procedureBased on the legally binding decision ofthe cantonal authorities, the cantonaloffice can submit applications for subsi-dies to the FOWG. The FOWG checks theproject documentation and determines theamount of the federal contribution as wellas related conditions. The project’s harmo-nization with other federal laws is alsochecked in this connection.

29

Monitoring and maintenance

Plan implementation

Implementation project(detailed project)

Cantonal authorities’ decision

Preliminary study(concept)

Preliminary project(general project)

Construction projectRelated cantonalopinion reports

Possible environmentalimpact study

Important projector special case?

no

yes

Services of theFederal Office

for Water and Geology(FOWG)

Advising

Harmonizingbasic requirements

Ascertainingkey parameters

Coordinating

Cooperationand information

FOWG opinionInternal opinion:

BUWAL – ARE – BLWASTRA – EFV – BAK – ENHK

Subsidy decision by FOWG(coordinated with EFV,

possibly linked to conditions)

Subsidy application to FOWG

Procedural flow at the cantonal level Procedural flow at the federal level

30

UFA

EG-F

OW

G; F

rank

; Ke y

ston

e

Accelerated Procedure

After a disastrous event, acanton can request support from

the federal government, e.g., inpreparing event documentation.

Strategy

Action

• Procedure

Project Design

Measures

Appendix

If obvious security deficits appear afterfloods and sediment disasters and imme-diate measures have to be taken, an accel-erated procedure can be used to approvesubsidies. To justify such an approach, im-mediate measures are defined as:• work immediately after an event, i.e.,clearing channels or restoration of ruinedprotective structures;• anticipated measures that reduce exist-ing security deficits as soon as possible.

Checkpoints to be notedThe following should be considered inplanning and implementing immediatemeasures:• Priority should be given to measuresthat reduce an existing risk or damage po-tential as quickly and effectively as possi-ble. On the other hand, measures that af-fect security only marginally should behandled in connection with regular pro-cedure (see page 28).• Before starting any work, the canton’sspecialized offices should be consulted(and also third parties, if necessary).• Coordination with other projects inthe area affected should also be assured.• If projects are important, coordinationwith the Federal Office of Water and Geol-ogy (FOWG) is also necessary. This espe-cially applies for plans with important costconsequences or for work in an area thatis protected by federal inventory.• If necessary for security reasons, theFOWG can grant a temporary buildingpermit based on subsidy law for urgentwork before definitive funding approval.This allows work to be undertaken imme-diately without having to wait for comple-tion of the subsidy procedure.

• Before restoring destroyed protectivestructures, investigation should confirmwhether simple restoration of these struc-tures makes sense. The cause of failureshould be determined as far as possible,and structure security should be enhanced.• Basically, space which the river hastaken during the event should be securedas river space. New space restrictionsshould be avoided. Greater flexibility canbe achieved for definitive measures in thismanner.• Definitive solutions should be real-ized in case of local problems and clearframework conditions.• On the other hand, in case of majorplanning that has to balance the variousinterests, low-cost temporary struc-tures should be built. Hence, time can besaved for expedient project management.• Immediate measures and restorationsteps should create no prejudgmentsabout definitive solutions.• Special fundamentals apply to alluvialzones (see page 53).

31

Services of theFederal Office

for Water and Geology(FOWG)

Advising

Supportingevent documentation

Engage experts

Organizingaerial photography

Securing financing

Coordinating(with other federal offices

and other cantons)

Information,coordination, and

supportAssessing hazardafter storms

No, notnecessary

Harmonizing at federal level(temporary building permit from

FOWG based on subsidy law)

Subsidy application to FOWG

Implementing emergency measures

Are immediatemeasures

necessary or not?

Decision of cantonal authorities

Harmonizing with thoseaffected and interested

Yes, necessary

Proper procedurefor planning measures

Procedural flow at cantonal level Procedural flow at federal level

Subsidy decision by FOWG(possible conditions)

32

Fran

k (3

); Sc

häub

lin (

1)

Participation

Conflicts in flood control plans areusually the result from differing interests

concerning use in the planning area.

Strategy

Action

• Procedure

Project Design

Measures

Appendix

All flood control measures should bebased on an understandable, transparent,and comprehensive weighing of interests.This means that a compromise satisfac-tory for all involved must be found throughcommunication and discussion. It shouldbe noted here that differing concernsshould be rated in terms of the goals for-mulated and considered according to theirimportance.

InformationLandowners and farmers directly affectedby the plan should be informed of theplanning approach in a timely, understand-able, and schedule-related manner.Informing those affected should not occuronly once but in an expedient ongoingmanner at the right moments during theentire planning process.

Forms of participationIf concerns are raised from the public, aspirit of give-and-take should be promoted(to the extent that individual interests arecompatible with the general welfare). Co-ordination of hydraulic engineering plansis also important for both downstreamriparians along rivers and streams (sincethey are directly affected by the project’simpact) and those upstream (e.g.,hydropower plant operators).The level at which participation begins de-pends on the project in question. Variousforms of involvement are possible. Thegoal of this approach is to realize soundprojects and thus improve acceptance ofmeasures related to them. Public involve-ment also offers the opportunity to useknow-how of local residents and to drawthem into planning at an early date. Possi-

ble forms of involving the public and thoseaffected are varied:• Presentations by experts, public gather-ings, or discussion evenings.• Local visits or excursions to areas withsimilar situations.• Exhibitions and public-informationpostings.• Study groups or expert panels in whichvarious interest groups discuss goals andoptional solutions with a moderator.• Interdisciplinary monitoring committees,e.g., one established with success alongthe River Thur.• Information in local and regional newsmedia.

33

Goal: Involving those affected.

Overcoming Conflict

Planning’s goal is to work out a projectthat wins consensus and can be realizedwithin a reasonable period. Nonetheless:rivers and streams and their related floodproblems are so closely bound to totallydiffering demands for use that planningflood control measures often leads to con-flict. The reasons are varied. They may liein divergent claims for use. Yet it is alsoconceivable that conflicts arise throughshortcomings of the planning pro-cess. This applies, for example, if doubts,desires, or demands of collaborators andthose affected are not assessed on time ortaken seriously. Differences could thusarise that end up in objections (and thuspostponements).

RecommendationsThere are various recommendations onhow conflicts can be recognized, avoided,and resolved. The most important arenoted here: Before working out a project,involve all affected early and within theframework of an open and comprehensiveinformation policy. Identification with thecorresponding plans and understandingfor the measures needed can be promotedin this way. The following points should beobserved in addition:• The legal framework and space re-quirements for natural habitats as wellas procedural flow are expressed clearly atthe beginning of planning.• In case this framework cannot be con-sidered, the reasons for it should be pre-sented openly.• Broad-based discussion of the draftproject including local visits contributes tomutual understanding and early clarifica-tion of potential points of conflict.

• Conflict points that cannot be resolvedimmediately may be neutralized at times,if improved decision-making basesare made available through more detailedexamination.• If, despite all efforts, further conflictscannot be overcome, responsible authori-ties at the cantonal level must weigh theinterests involved.• A decision by the responsible author-ity follows. It may be appealed, dependingof the law involved.• Finally, it is important that decisionsmade are explained and made known toall involved.

Project Design

35

The Sequence of Project Design Work

Depth of study dependson project step

Project design work,an iterative ormultistep process:

In order that gaps never completely bridgedbetween the natural framework and society’sclaims are not excessive, a change incourse regarding flood control proceduresmay also be necessary: ”Back away frompure flood control defense; advance to aculture aware of risks” is the thrust of thenew motto that should be experienced atall levels – i.e., the federal government, thecantons, and municipalities – in the future.

Recommended reading

FEDRO/FOT/FOWG/SBB (1998/2002): Safetyof Structures in Water. Recommendation forthe Surveillance and Indications for the Con-struction of New Structures ➜ Order of priorities

Problem formulation

Goals

Fundamentals

Study of options

Third-party participation

Weighing interests

Cost effectiveness

Assessing remaining risks

There are no standard recipes for solvingflood-control problems. Yet recommenda-tions can be made based on experiencesfrom the recent past on how flood-controlgoals can be achieved in a timely and cost-effective manner:• In any project the necessary should beseparated from the desirable in order tokeep costs within reason.• The depth of study should be adaptedto project requirements.• The necessary basis for decision-mak-ing must be prepared early.• Basic data needed for the project mustbe complete. There are enough examplesto show that a single unclarified issue candelay a project for years (or even cause afailure).• Expertise from various disciplines is usu-ally required during a project’s stages. It istherefore important that partners as-signed special tasks be selected carefully.Those bidding for project tasks must beable to demonstrate their specialized tech-nical skill, qualitative record, and businessperformance in managing the work envi-sioned. Furthermore, they must be able towork in a team.• If the interest-weighing process es-tablished that economic, ecological, oreven technical measures lack proportion-ality, adaptations must occur in the uses

foreseen – and also the protection objec-tives selected (see also guiding principles,page 10).

Optimizationby multistep approachOnce the need for action, the problem for-mulation and the necessary fundamentalsare established, the goals to achieve withplanning measures need to be defined. Fortheir part, these goals influence the natureand quality of the basic data required, andthe measures again lead to adaptationsand supplemental steps. Project optimiza-tion through such a multistep approach istherefore an iterative procedure. At-tention should be paid to:• Documentation of the originalsituation. This includes documentationon the hazard situation and the state ofthe river or stream, as well as the questionof an extreme flood’s impact.• Estimate of possible damages. Thisstudy provides information on the finan-cial consequences of a certain event.• Planning measures. A rule of thumbstates that impact on rivers should be assmall as possible. Another principle callsfor upholding the priorities set by federalLaw (maintenance and land-use planningmeasures have priority over structural pro-tection measures). Important improve-ments for flood control may often beachieved at little cost, and finally compre-hensive weighing of interests leads to bet-ter options.• Assessing the residual risks. Clari-fying residual risks belongs to a completeplanning of corrective measures. This canbe done only being aware of uncertaintieslinked to natural events.

• Emergency planning and emer-gency organization. Each flood controlproject also includes a catastrophe mana-gement plan oriented towards the currenthazard situation.• Maintenance and monitoring. Anessential component of a flood controlproject is also to set up a maintenanceconcept (total security and use plan).

Implementinginto land-use planningThe remaining danger situation after real-izing protective measures should be pre-sented in the form of a hazard map andconsidered in establishing the structureand land-use planning.If the project is rejected, the responsibleflood control authorities must work outthe hazard map corresponding to the origi-nal situation and make sure that it is im-plemented into structure and land-useplanning.

36

Conditions in the Catchment

A phenomena map produced by field survey is ameaningful supplement to event documentation. It records

characteristics and indicators observed in the field inmap and text form. It also refers to the status, triggering

mechanics, and impact of potential types of hazards.

Recommended reading

BWW/BUWAL (1995 recommendations):Naturgefahren. Symbolbaukasten zurKartierung der Phänomene [Natural Hazards.Symbol Toolbox for Mapping Phenomena]

PLANAT/BWG/BUWAL (2000 compendium):Vom Gelände zur Karte der Phänomene[From the Field to the Map of Phenomena]

Strategy

Action

Procedure

• Project Design

Measures

Appendix

Processes occurring in rivers or streamswill be determined largely by conditions inthe corresponding catchment. Importantparameters are:• topography (surface, form, gradients,readiness of a zone in relation to a certainprocess);• structure and distribution of varioustypes of soil;• geology;• geomorphology (processes that haveshaped the catchments);• precipitation conditions;• degree of glaciation;• forested area (and its condition);• discharge regime;• channel geometry (longitude profileand cross sections) and channel mor-phology (grain size diameter of bed sub-strata).

Available basic dataAny flood-control project is based on nu-merous pieces of basic information on theriver and its catchment. Part of these datais also available in digital form (e.g.,topographic and topical maps as well asaerial photographs) or is integrated intogeographic information systems (GIS).Various cantons as well as the federal gov-ernment also operate coordinating offices.The following working and planning toolsare of particular importance:• Precipitation data. Governmentaland private institutions collect this data.Evaluations of weather radar data are of-ten valuable in assessing and classifyingmajor precipitation events.• Discharge data. Governmental andprivate institutions also collect this data;rated and made accessible to the public

(e.g., in the form of the FOWG’s ”Hydro-logisches Jahrbuch der Schweiz” [Hydro-logic Yearbook of Switzerland] also on theInternet).• Registered events. Those who wantto foresee the future need to look backinto the past. Therefore, experiencesgained from earlier events are of great usein assessing and estimating future events.This assumes a comprehensive and accu-rate documentation of individual events.Besides noting the crucial processes anddegree of damage, event documentationprovides information on areas affected bythe natural hazard involved as well as themeteorological, geological, geomorpho-logic, and hydrological conditions.• Basic data concerning geology.Geological conditions influence runoff, thenature of sediment and its yield, as well asthe sediment’s physical characteristics.Stability calculations related to massmovement cannot be carried out withoutknowing the geological conditions. More-over, when intervening in groundwater,drainage as well as measures near sourcesrequires investigations of the hydrogeo-logical situation.• Inventory. The so-called federal inven-tory represents important tools for protect-ing nature and the landscape. It distin-guishes between landscape and biotopeinventories, because they differ in legalimportance. Accepting an object of na-tional importance in a landscape inven-tory in accord with Article 5 NHG mainlycommits federal agencies themselves (aswell as those that fulfil federal tasks orclaim federal funds for their plans). Ex-cepted is the inventory of moor land-scapes, which is based on Article 23b NHG

and is applied directly to property owners.Substantially more authority has beengranted to the federal government since1987 in the sector of biotope protection.The legal basis of the biotope inventory(including a federal inventory of nationallyimportant alluvial zones) is Article 18aNHG. After hearing testimony from thecantons, the Federal Council identifies thebiotope of national importance, deter-mines its status, and sets protection goals.• Damage potential. Based on theirdocuments, cantonal building insurancecan provide data on potential damage andobject protection measures.

37

Basic data Contact/Sources

• Heavy precipitation: Federal Research Institute for Water, Snow, and Landscape (WSL), Birmensdorf• Entire Switzerland surveys: SMA MeteoSwiss, Zurich• Radar weather assessments: SMA MeteoSwiss, Zurich• Local surveys: hydropower plants; private meteo offices

• Entire Switzerland surveys: FOWG-LHG, Biel and Berne• Local surveys: waterpower plants; cantonal flood control offices; cantonal water management offices

• Cantonal land-use planning offices

• Cantonal land-use planning offices• Municipality administrations

• Federal Office for the Environment, Forestry, and the Landscape (BUWAL), Berne• Cantonal land-use planning offices

• BUWAL, Berne (Forestry Directorate)• Cantonal flood control offices

• Entire Switzerland documentation: FOWG, Biel; BUWAL, Berne• Regional and local surveys: cantonal flood control offices

• Cantonal flood control offices• Cantonal land-use planning offices• Municipality administrations

• Cantonal flood control offices• Cantonal space planning offices• Municipality administrations

• Cantonal flood control offices• FOWG, Biel

• Cantonal structure insurance

• Federal inventory (landscape and biotope inventories): BUWAL, Berne• Regional and local inventories: cantonal nature protection offices• Red lists: BUWAL, Berne; cantonal nature protection offices; environmental associations

• Geological maps (however, the National Geology Atlas at a 1:25000 scale is incomplete).

• Geological studies that were carried out for other projects. The National Geology Division (FOWG)operates the Swiss Geology Documentation Center (SGD), which also collects unpublished documents.

• Additional geological, geotechnical, or hydrogeological studies on reservoirs, check-dams, dams,and interventions into water regime (e.g., lowering groundwater).

Precipitation data

Discharge data

Structure plans

Land-use plans (local)

Landscape developmentconcepts (LEK)

Events register

Protection structuresregister

Hazard index maps

Hazard maps

Project files (old)

Damage potential

Inventory

Basic dataconcerning geology

38

Keys

tone

Uncertainties of Basic Data

Calculating return periods is quite tricky, as the example of the Reussin Uri cantone shows. During the mid-1980s this river was designed for

a flood discharge of 600m3/s, and that value was considered as a100-year event (Q 100). Yet a detailed hydrologic study after the 1987flood showed that this design value only corresponded to a 30- to 40-

year flood. Thus the probability that a discharge of 600m3/soccurred during a 100-year period rose from about 64% to 90%.

Recommended reading

LHG (1998): Ausgewählte Tätigkeiten undLeistungen [Selected Activities and Perfor-mances]

Strategy

Action

Procedure

• Project Design

Measures

Appendix

Discharge is an important parameter inany flood control project. It has a crucialinfluence on the design of corrective mea-sures.Discharge refers to the amount of volumethat flows through a river cross section persecond. Usually it cannot be measured di-rectly and continuously but determinedonly sporadically (normally by measuringvelocity distribution over the entire flowsection, but in some cases by using tracersor by laboratory tests).

Fundamental relationA correlation curve for stage/discharge(the so-called H/Q curve) can be deter-mined discharges measured (Q) at differ-ing water levels (H). It forms the basisfor converting water levels into discharges.This correlation curve can change withtime (especially through river channeldeformation during floods). Hence, themeasurement of discharge must be re-peated periodically to test the curve andupdate it.The H/Q curve must often be extrapolatedmathematically for extreme values (thisapplies to both floods and draughts), sincemeasurements are often lacking for theseexceptional situations.

Return periodsThe term ”return period” refers to thelong-term average interval or number ofyears within which an event will beequaled (or exceeded). The term ”recur-rence interval” is also used frequently forthis value:• Q1 is in the average expected once ayear (the so-called annual event).• Q100 is in the average expected every100 years (the so-called hundred yearevent).• Q300 is in the average expected every300 years (the so-called 300-year event).

Conservative estimatesAs for all natural processes, uncertaintiesare also great in determining probability.Viewed statistically, even very long recordsshow great scatter. This condition must betaken into account when estimating de-sign values. This usually leads to conserva-tive estimates. Therefore, hydrological dataused for flood control planning must indi-cate the prevailing uncertainties.The design discharge Qd corresponds tothe discharge that can be evacuated with-out damage owing to the measures pro-jected. In parallel to the determination ofthe design discharge, within the planningof protective measures the consequencesof a flood exceeding this value must al-ways be ascertained.

Event sediment yieldUncertainties are already great when de-termining peak discharge values. They areeven greater when determining sedimentyields. This applies for bed load trans-port as well as assessing potential de-bris flow. A reason for these uncertain-

ties is the lack of basic data. Yet the mainreason is procedural complexity (and thegreat variability related to it). It is impossi-ble to find a simple correlation between acharacteristic parameter of observeddebris flow and the easier-to-measure pre-cipitation.It is still more difficult to classify prob-ability of occurrence (i.e., the possibil-ity that such an event can occur during acertain observation period with a definedrecurrence interval). Therefore, one mustsettle for a definition of plausible sce-narios that can be classified qualitativelyas a probability of occurrence: frequent,seldom, very seldom.Moreover, it is practically impossible toproduce a correlation between peak dis-charge of debris flow and its volume.Debris flow often occurs in surges. Modeltests have also shown that addition ofsediment at given velocities and channelslopes does not lead to an increase in theflow depth. It is rather the volume of de-bris flow that increases.

39

1800

1600

1400

1200

1000

800

600

400

200

0

2.33 5 10 20 50 100 200 500 800

2.5

2.0

1.5

1.0

0.5

0

0 100 200 300 400 500 600

Return period (by years)

Dis

char

ge

in m

3 /s

Confidence interval 80%

Discharge Q in m3/s

Stag

e H

(in

m)

Discharge (Q) measured at varying water lev-els (H) can be plotted on the so-called H/Qstage-discharge correlation. The curve’s im-precision rises with increasing discharge, asshown by this example of the Emme river atBurgdorf: This flood was ascertained at350m3/s with a confidence interval between280m3/s and 420m3/s. Therefore, when de-termining the discharge, the margin of errorfor the respective water levels must be in-cluded in the indications for precision.

The example of the Rhone river at Sionshows how great the uncertainty in deter-mining probability can be. A return periodof 100 years can be attributed to the dis-charge of 1050m3/s (without considering thehydropower storage impact).

Yet a confidence interval of 80% also meansthat the corresponding recurrence intervalcan be classified as a 40-year event as wellas an 800-year event. If these confidencelimits are applied to discharge, the corre-sponding value varies between 900 m3/s and1200m3/s.

40

Q

Q347100 200 365

Q

Vol.t t

Hydraulic-Engi-neering Conditions Hydrology Hydraulics

Effectiveflow section

The mean roughnesscoefficient km in case ofthe simplified determina-tion of flow capacity:km = 20–25m1/3/s

Flow duration curve

Hydrogramme

Qd

Qd

Strategy

Action

Procedure

• Project Design

Measures

Appendix

Every natural river or stream finds itself ina constant state of change. Normally, ero-sion occurs in the upper course, while de-position takes place in the lower course.Thus, special attention should be given tothe following four points in hydraulic-en-gineering assessment:• hydrology (discharge regime, type offlood);• hydraulics (flow capacity):• sediment regime (debris flow hazard,sediment yields; braiding; meander for-mation);• weak points along the river course.

Regular checksHydraulic-engineering assessment allowsto draw conclusions on both short-termprocesses during an event causing damageand long-term developments. The hazardsituation can change over the course oftime. This requires regular checks of thehydraulic-engineering situation.

Hydrology records the occurrence and cir-culation of water resources and the watercycle at, above, and below the earth’s sur-face (and is also concerned with waterquality and material transported in thewater).

In connection with flood control, the mostinteresting factors are potential peak dis-charge and flow volumes. They form abasis for assessing the degree of the ex-isting flood protection (hydraulic basicdata), evaluation of existing protectivestructures and the design of new struc-tures, identifying inundation areas, inves-tigating detention capacity, as well as as-sessing system behavior in case ofoverload (EFQ).

In recent years the methods to estimateflood discharge have been developedgreatly, and old measurement recordswere checked for errors. Numericalmethods (mathematical models and si-mulations) have provided a crucial contri-bution to this. Yet even these methods areaffected with uncertainties. Therefore,flood estimates should be conducted withvarious methods: sensitivity analysesare useful, and plausibility checks arenecessary.

Additional data are required to assessthe ecological condition of a river orstream: flow duration curves, mean flowrates, low flow rates.

EFQ

Hydraulics is concerned with the water’sflow conditions and determines a channel’sflow capacity.

The geometry of the river or stream channel(cross sections and longitudinal profile) andthe dimensions of protective structures canbe derived from the design discharge Qd.Yet it should always be noted that rivers aredynamic systems that change their geom-etry over the course of time. The causes arevaried and extend from the influence of ripar-ian vegetation to bank and bed erosion andon to channel fills.

In case of variation of the cross section ge-ometry or of the longitudinal profile, simpleuniform flow calculations will not suffice.Backwater curve calculations must bemade instead. The water level and energylines are calculated systematically. In caseof local problems, detailed calculations arenecessary (e.g., at structures with a hydrau-lic effect as submersible dikes, culverts, orbridge piles).

Space-related flood danger is usually as-sessed by determining inundation zones.Various methods are available to determinethis. Detailed mathematical model calcula-tions to identify inundated surfaces requireprecise altitude in critical sections of be-tween 10 and 20 cm.

Flow depths and velocity are the two deter-mining factors for hazard assessment at aspecific point. In case of complex issue for-mulations (e.g., for special structures), itis proper to check the hydraulics more pre-cisely with the help of physical scale models.

41

Fran

k; R

DB

Weak pointsSediment regime

Dynamic equilibrium in case of a series of check dams

Disturbanceby flood

Relaxation phaseConditionat outset

Mo

rph

olo

gy

(wid

th, b

ed)

The destructive and at the same time forma-tive power of water shapes a river or streamchannel. On one hand, water is an effectivesolvent. On the other, it manages to trans-port weathered material and to deposit it atother points. Therefore, erosion and accumu-lation of bed load and other sediments areintegrally bound to each other at any riveror stream.

Flood events with a return period of two toten years are particularly crucial for thesebed-forming processes, which are alsoreferred to as morphology. A dynamicequilibrium prevails over a longer period oftime, and changes are small.

This dynamic equilibrium is disturbed assoon as extreme flood events induce wide-spread erosion and accumulation. Therefore,such processes must be taken into considera-tion in planning corrective measures. Themost important thing to determine iswhether a new equilibrium can be achieved,or if even a system collapse has occurred (orcould occur).

The great significance of sediment regimewas often neglected in hydraulic projects.Channel fill can lead to major problems –especially in case of knick points. This hasproved to be case several times in recentyears (e.g., at the Saltina river in Brig during1993).

Mountain torrents (>15% slopes) are espe-cially dangerous. Critical here is the size ofthe sediment potential available for debrisflow formation.

Weak points are locations or stretches of ariver course where a hazard can emerge.Classical weak points are too narrow cul-verts, bottlenecks, sharp curves, obstructions,or knick points in the longitudinal profile.Such weak points can be recorded andmapped in the field survey.

Scenarios are necessary to enable assess-ment of weak points. There are variousmeans of recognizing them: observations(flood marks; remaining freeboard during aspecific flood), comparisons (smaller cul-verts than upstream or downstream, simpleestimates, and finally numerical calcu-lations (e.g., for determination of flow ca-pacity). Hence, indications on the precisionof related assessments must always be madein the documentation.

In order to permit statements on the need foraction, a periodic assessment of the protec-tive structure’s functionality is needed, in-cluding checking the hazard situation whichhas eventually changed, and also the over-load case (EFQ).

A databank on protective structures – a so-called registry of protective works – istherefore a useful aid in monitoring floodsecurity. Good documentation also permitscomparisons with earlier assessments.

Numerical simulation models are alsoavailable today that allow analysis of sedi-ment transport and estimation of erosionand channel fill. These methods are usuallybased on data concerning bed material sizedistribution, channel geometry (cross sectionand longitudinal slope) as well as dischargehydrographs.

Scour processes in a river channel areclosely linked to channel bed forms. Scoursappear in river bends and confluences, at achange of bed roughness, and near specialconstructions such as drop structures, piles,and groynes. Quite important scour may de-velop in a channel with three-dimensionalflow patterns and bed forms, compared tochannels with nearly plane bed and one-di-mensional flow conditions. New approachesallow to assess these scour depths and thusto design the foundations of bank protectionworks, for which this process has to be con-sidered. Thus, morphological effects of inter-ventions should be checked carefully at eachflood-control project.

42

Types of Hazard and Influencing Factors

Channel migration

Channel blockage

Bank failure

Bank erosion

Scour

Inundation

Undercutting

Our highly networked industry,services, and leisure society is very

vulnerable to disturbances that stemfrom uncontrolled water forces.

Dogging

Debris flow

Strategy

Action

Procedure

• Project Design

Measures

Appendix

Floods repeatedly prove to be a serioushazard that cannot be averted by protec-tive structures alone. Efforts are also nec-essary to prevent a continued rise in thesum of damages and to reduce the dam-age potential. Thus precise knowledge andcorrect estimates of possible processestake on major importance.Floods are dangerous in several regards:They can overflow and damage cultivatedland and structures through the sedimentthey transport. They can erode and thusundercut the foundations of existing struc-tures. They can mobilize bed load andother sediment and destabilize protectivestructures through their dynamic impact,sweep away people and motor vehicles,and destroy buildings.Depending on the prevailing impact of aflood, we distinguish between inunda-tion, bank erosion, and debris flowdeposition. Most events result in a com-bination of these three types of hazard.In addition, overbank sedimentation– i.e., a widespread sediment depositionoutside the channel – often occurs. Butthis process is usually not entered as ahazard type in its own right, since it is al-ways linked to a dynamic flooding.Besides these basic types of hazard, thereare other important influencing fac-tors:• Clogging. After avalanches, during vio-lent winds, and in heavy storms, felled tim-ber, driftwood, and other debris clog theflow section, especially at bottlenecks suchas weirs, bridges, or ravine stretches. Be-hind such blockages the water level israised. Resulting consequence: the waterleaves the channel and searches for newflow outlets. If it suddenly breaks through,

it may surge downstream in a dangerousgush of water (or in steep reaches, form-ing a debris flow containing wood andsediment).• Channel blockage. Rock falls, land-slides, avalanches, or debris flow can raisethe bed level of a channel (or block it to-tally). Such blockages induce upstreamflooding. For the downstream area, thereis also a risk of breaking through (and aflood wave resulting with all its possibleeffects).• Dike failure by inner erosion. Ifflood levels remain high for a long time,inside the dikes, seepage flow appears. De-pending on permeability and homogeneityas well as on tunnels produced by rootsand animals, fine-grained material alongthese pipes will be washed away (piping).This process can destroy older dikes, in par-ticular, from inside (without them beingovertopped).• Dike failure by overtopping. Dikescan be overtopped because of a too highdischarge, bed level raising, log jams, orblockages. A dike not specially protectedagainst erosion usually does not resist fora long time against the overtopping water,what increases in a short time the dangerof flooding a large surface.

43

BWG

-OFE

G (

1); F

r ank

(2)

; Key

ston

e ( 1

)

Inundation Bank erosion Debris flow deposit

Inundation (or flooding) describes when aland surface is temporarily covered withwater outside the channel. Inundation is of-ten related to other types of hazard – for in-stance, to bank erosion or of sediment depo-sition. We distinguish between two forms ofinundation, which can arise in alternatingform within a close distance during the sameevent:

• Static inundation. The water flows veryslowly if at all in this case. The water depthincrease outside the channel occurs gradu-ally (except in field troughs). Static floodingoccurs in flat fields and along lakes.

• Dynamic inundation. This is character-ized by high flow velocity and occurs onsloped ground along mountain torrents andrivers. High dynamic stress can be expectedin flat areas near bottlenecks and dikebreaches.

There are many terms for this type of hazard,but their meaning always suggests extensiveamounts of debris shifted by great volumesof water in pulses. The sediment concen-tration amounts to between 30 and 70 %.

Debris flows are not triggered by accident. Ifthe related topographic, geomorphologic,and geologic conditions are fulfilled, unsta-ble material can liquefy in storms, duringstrong rain, or in case of snow melt. Thissurges into the valley as a mixture of water,silt, sand, and stones interspersed with boul-ders weighing tons and uprooted trees. And,depending on its composition, this occurs ata velocity of up to 60km/h.

Part of the material relocated is often depos-ited at the side as levees. Yet damage oc-curs mainly because of the dynamic impactof the debris flow front, which may con-tain large boulders.

Erosion processes are the most damagingtype of hazard in many cases, because theyhappen accidentally and uncontrollably.

Flowing water can erode laterally as well asvertically. Subsequently, when banks collapseor fail (bank failure), even buildings and in-frastructure facilities are endangered abovethe flood level.

During extreme floods channel migrationoccurs, the eroded material is deposited inthe immediately adjoining reach down-stream.

Bed erosion, related to bank erosion, in-duces additional sediment input. Loweringof the bed can endanger building founda-tions. The determining shear stress forstreambed erosion is mainly dependent onwater depth and flow velocity. Local condi-tions – e.g., channel morphology or obsta-cles – can heavily influence bed shear stress.Resistance against erosion depends on bedand bank material grain size, bank vegeta-tion as well as the types of protective struc-tures.

Assessment criteria

For flooding flow velocity and inunda-tion depth are the decisive parameters.Flow velocity normally depends directly onthe slope. In case of great velocity, coarse-grained deposits are to be expected, and lo-cal erosion may occur.

Assessment criteria

The decisive assessment criteria are bankstability or stability of bank protections aswell as depth of erosion.

Assessment criteria

The dynamic impact of debris flows is usu-ally estimated by observing the height ofdeposits and the superelevation incurves (as an index of flow velocity).

44

Assessing Hazards

Recommended reading

PLANAT (2000): Empfehlungen zur Qualitäts-sicherung bei der Beurteilung von Natur-gefahren im Sinne der Wald- und Wasserbau-gesetzgebung [Recommendations on QualityAssurance in Assessing Natural Hazards asEnvisioned in Forestry and Hydraulic Engi-neering Legislation]

The actual degree of flood hazard can be derived fromworking and planning tools that are by now used routinely.Hazard index maps provide a first rough estimate on the

hazardous situation; intensity maps show overflowdepths and flow velocities; hazard maps form the techni-cal basis for drafting community use plans (local planning).

Strategy

Action

Procedure

• Project Design

Measures

Appendix

Overall observationWithout assessing the entire river system(i.e., the interactions between the upper,middle, and lower reach of a streamor river) these questions cannot be an-swered. Therefore, it is vital that all poten-tial processes that define a potential haz-ard area be elucidated.Proven experts carry out hazard assess-ments, and cantonal natural-hazard ser-vices are responsible for a correct techni-cal execution.Many basic data must be gathered and as-sessed, because preparing hazard indexmaps and hazard maps requires the in-volvement of all available references andinformation on the proven, assumed, andpotential processes in a certain area:• Proven process. An event that isdocumented.• Assumed process. An event that can-not be verified at the considered locationbut has occurred in comparable hazard ar-eas.• Potential process. An event that over-all assessment shows could occur in a veryspecific catchment area.

ScenariosThe chronological course of an event maybe of decisive importance. Finally, the as-sessment of potential weak points in thesystem is particularly significant. They canlead to a collapse and hence to completelydifferent behavior.The potential processes are often interde-pendent and occur in combination. There-fore, in assessing them, it is recommendedthat specific hazard situations – so-calledscenarios – be developed. Such scenarioscan be compared with load assumptions in

structural engineering. Yet it is relativelysimple there to determine uniformly de-fined standard load cases. In case of natu-ral hazards the starting point is more com-plex.Given the diversity of conditions in nature(among them the topographic and geo-logical conditions) and potential changesduring a process under way, reactions al-ways occur in the river system in question.At a minimum the assessment of potentialhazards should be developed through twomain scenarios with different recurrenceintervals:• For settlement areas, a flood eventwith a recurrence interval of Q 100 to Q 300

should be used (conservatively selectedQ 100).• Another scenario should consider anextreme flood event (EFQ). This is asignificantly greater event than used fordesign. Yet no unrealistic scenario shouldbe developed (i.e., in general there shouldnot be cumulative consideration andsuperposition of independent events).

Ability for dialogThe scenarios chosen must also be ex-plained to the public affected by the haz-ard assessment and the protective mea-sures related to it. Therefore, the scenariosmust be transparent and understandable.Coordinating and exchanging informationmust also be ensured among specialistsand the authorities.

Correctly recognizing and estimating thetypes of hazard existing and their influenc-ing factors is of central importance. In or-der to make statements about them, thefollowing questions in particular must beanswered in connection with flood haz-ards:• How large is the channel’s flow capacity(with and without sediment)?• Where can water and sediment escapeout of the stream or river channel – andhow much?• Where and to what degree are erosionand deposition possible?• Where will material be eroded or depos-ited from debris flow and how much?• Are there bottlenecks and obstacles inthe channel?• Do existing protective measures influ-ence the course of potential processes?• Where can potential weak points beidentified at protective structures?• Is it conceivable that a global climatechange affects events and must be consid-ered?

45

Hazard index map Intensity map Hazard map

Important for:

Application Project author Officials Population

Hazard index maps Perimeter ❑ ■ ■

Sensitizing ❑ ■ ■

Points of conflict ❑ ■ ❑

Structure planning ■ ■ ❑

Intensity maps Design of protective structures ■ ❑ ❑

Conditions for building permit ■ ■ ■

Hazard maps Structure planning ■ ■ ❑

Land-use planning ■ ■ ■

Conditions for building permit ❑ ■ ■

■ important ❑ less important

Hazard index maps provide an overview ofthe hazard situation. They provide a compre-hensive record of where natural hazardsmust be taken into account and which ones.Potential points of conflict can easily bederived from this. In case of flood hazards theextension of the inundated area is presentedfor the EFQ. Related priorities can be set, andareas free of conflict can be defined at thesame time.

Purpose: Basic document for a structureplan.

Content: Rough overview of the hazardoussituation; data on types of hazards (usuallywithout indicating degrees of danger); gen-eral definition of the areas concerned.

Depth of detail: Little.

Scale: 1:10000 to 1:50000

Checking: Periodically within the structureplan framework.

The intensity map provides the extension ofthe overflow area, the overflow depth, theflow velocity, as well as the direction of flowin a specific scenario. This information canbe used in many ways. Security measuresfor buildings and facilities (conditions forbuilding permits, measures for object protec-tion) can be derived from flow depths andflow velocities.

Purpose: Basic document for emergencyplanning, for planning measures, and for de-veloping a hazard map.

Depth of detail: Requires hydraulic calcu-lations and detailed topography.

Scale: Analogous to hazard maps.

Hazard maps form the technical basis forconsidering the natural hazards when devel-oping municipality land-use plans (localplanning). They are also of importance foruse in planning and ordering of object pro-tection measures (and other measures toreduce damage). Hazard maps contain dataon causes, course, intensity, impact areas,and probability of natural hazards occurringin a precisely defined area. The depth of de-tail is correspondingly high.

Purpose: Serves as synthesis map of allnatural hazards, providing basics for ad-justed land-use planning (local planning)with a precision corresponding to a plotsize.

Content: Precise data on types of hazards,spatial range, and degree of danger; detaileddocumentation.

Scale: 1:2000 to 1:10000

Checking: Periodically in connection withland-use planning.

123123123123

46

Graphical Presentation of Hazards

Recommended reading

BWW/BRP/BUWAL (1997 recommendations):Berücksichtigung der Hochwassergefahrenbei raumwirksamen Tätigkeiten[Considering Flood Hazards in Regard toActivities with an Impact on Land Use]

BRP/BWW/BUWAL (1997 recommendations):Berücksichtigung der Massenbewegungs-gefahren bei raumwirksamen Tätigkeiten[Considering Mass-Movement Hazardsin Regard to Activities with an Impact onLand Use]

Hazard level Material importance Importance for land-use planning

Red Substantial danger Prohibition area

Blue Medium danger Conditional-use area

Yellow Low danger Index zone

Yellow-white Remaining danger Index zone

White No danger* No restrictions*

*According to current knowledge

Strategy

Action

Procedure

• Project Design

Measures

Appendix

Based on the ”Guidelines for consideringavalanche hazards in land-use activities”available since 1984, standardized dia-grams showing hazard levels werealso developed for floods and land-massmovements. They were made public withrelated recommendations.

Standardized classificationDangers posed by all natural hazards arepresented in terms of the intensity andprobability (frequency or return period).These parameters are compiled by gradu-ated levels of danger in a so-called inten-sity/probability diagram color-coded withred, blue, and yellow:• Red = substantial danger. Basically,no structures or facilities may be built orexpanded that serve for shelter of humanbeings or animals. In case of existingbuildings, risks should be minimized andsecurity measures should be improved byrenovations or when a change in use oc-curs.• Blue = medium danger. Structuresare permitted under certain conditions.

These should be indicated in the buildingand zoning regulations according to thetype of hazard.• Yellow = low danger. Landownersare made aware of the existing danger andmeasures to prevent damage. Planning onspecial measures is required for sensitiveobjects.• In case of flood control, the hazardsituation is also investigated for very rareevents (to clarify remaining dangers orrisks). The surfaces affected are repre-sented in cross-hatched yellow-white.• White = no danger according to cur-rent knowledge.

Levels of dangerThe levels of danger are chosen so thatthey can be linked to a special type ofbehavior or use regulation. They show thedegree by which people, animals, andthings of considerable material value areendangered. It is taken into account herethat safety of human lives is usuallymuch higher inside buildings than in openfields.The damage impact of the hazard is de-scribed for every type of hazard and levelof danger. The levels of danger are basi-cally determined separately for each typeof hazard. In case several types of haz-ard threatened a surface – e.g., floodingand debris flow – this condition is shownin suitable form on the hazard map. Thehighest level of danger is decisive ineach case.In general, no upgrading to a higher leveloccurs in case of an overlap by severaltypes of danger, since measures can betaken against each individual danger toavoid damage.

ProcedurePractical implementation of the corre-sponding assessment diagram in connec-tion with planning corrective measuresalso shows a few special situations in theflood control sector. Thus, major uncertain-ties exist in assessing the probabilityof occurrence. Therefore, historic (ob-served) events and the quality of basicdata must also be considered. If a planningof measures is introduced, a need for ac-tion has normally been demonstrated (orhas been recognized, at minimum).If the current hazard situation has notbeen assessed and presented, this must bedone promptly (assessing outset and ex-treme situations according to illustra-tions on facing page). In this phase alreadyone must also consider the possible limitsof flood protection (choice of design pa-rameters).Knowledge of remaining risks for anextreme event is indispensable, whetherduring planning of measures to minimizeremaining risks (optimizing project effec-tiveness), preparing a hazard map, oranalyzing weak points (collapse of build-ing structures), protection concepts, andemergency planning.

47

1234512345123451234512345123451234512345123451234512345123451234512345

1234512345123451234512345123451234512345123451234512345123451234512345

1234512345123451234512345123451234512345123451234512345123451234512345

EHQ

1212121212121212121212121212

high medium low very low high medium low very low high medium low very low

Outset situation Extreme situation Hazard map

Probability Probability Probability

Inte

nsi

ty

Inte

nsi

ty

Inte

ns i

ty

strong

medium

weak

strong

medium

weak

strong

medium

weak

Intensity h < 0.5m

Intensity 0.5m < h < 2m

Intensity h > 2m

Qd

Analysis of hazard situation for a rareevent. Floods between Q 100 and Q 300 quali-fy as rare events. This corresponds to thefrequently used protection objective for en-closed settlements. In many cases one can-not avoid considering important historicevents also, when setting design values (Qd),and thus taking into account the natural un-certainties.

The river’s flow capacity should already beknown when setting this scenario. More-over, besides the flood peaks, it is also im-portant to know water outflow volumes andthe total volume of debris flow.

The result of this check, based on the cor-responding scenarios, provides the exten-sion of endangered surfaces. In addition, ineach case we recommend determining thesurfaces threatened by high intensity. Otherareas affected are represented by one- ortwo-color gradations.

Determining the remaining risks in anextreme event. To analyze EFQ, eventsshould be used that represent an importantadditional stress for the system studied. Ingeneral, values derived from the 100-yearevent can be used for these studies.

Multiplication factors of 1.3 to 1.5 timesthe Q 100 are used for flood peaks. For exam-ple, in the case of the Reuss in Uri canton, avalue of 1.5 was derived from plausibilityconsideration of possible events. Compara-ble factors were also considered expedientand suitable for the system in the Rhone’scase.

In keeping with the uncertainties, higher se-curity factors up to about 2 are appropriatefor smaller catchments (for comparison:a security factor of 2.25 is required for reser-voir dam security). Added surfaces affectedby an extreme event are represented bycross-hatching.

Preparing a complete hazard map. Ifthe problems can be solved with land-useplanning measures alone, or if structuralmeasures cannot be realized in the shortterm, a complete hazard map must be pre-pared for the current danger situation. Thismeans that the affected surfaces must bestudied to find if, in case of more frequentevents (e.g., Q 30), added red (prohibited)and blue (conditional use) as well as yel-low (index) areas should be defined.

In each case a complete hazard mapshould be prepared and implemented forland-use planning covering the conditionsafter realizing the related structural mea-sures.

EFQ

Measures

49

Des

air

Order of Priorities

Recommended reading

PLANAT (1998): Von der Gefahrenabwehrzur Risikokultur [From Defending againstDanger to the Risk Culture]

Drainageplan

Flood controlconcept

Water supplyplan

Restorationconcept

Agricultureplan

Integrated planning for protective measures

Structure/land-use plan

There are two basically different routes foraction in planning flood control measures:• Passive measures in endangered ar-eas that adapt present or planned land useto the danger (and thus to reduce the dam-age potential).• Active measures at the hazard’ssource and/or in endangered areas thatreduce the existing danger in accord withpresent or planned use (and thus decreasethe hazard potential).

Prevention has priorityThe issue of what measures to take in spe-cific cases is often controversial. The re-lated fundamentals are actually set unmis-takably, and this applies not only to theflood control law (WBG) but to laws onland-use planning (RPG) and forestry(WaG) as well. They unanimously demandthat protection against natural hazardsoccurs mainly through preventivemeasures:• Appropriate maintenance of riverand streams. Maintain flow capacity andthe efficiency of existing structural protec-tive measures.• Protective forest cultivation. Now,as before, one of the most reasonablypriced measures to defend against naturalhazards (above all in cases of avalanchesand rockslides).• Land-use planning measures.Avoidance of hazardous areas, object pro-tection, and establishment of no-buildzones and inundation surfaces can limit oreven prevent an increase in damage po-tential. Local land-use and landscape plan-ning that takes natural hazards seriouslyand designates space for extraordinaryevents is preferred as a precautionary step

to building and maintaining costly protec-tive structures to secure settlements or in-frastructure facilities.

Material constraintsHowever, intensive building developmentduring recent decades and related land-use pressure have created protection defi-cits in many areas that can no longer becorrected by maintenance and planningmeasures alone. Therefore, protectivestructures and object protections (per-manent or temporary) and other technicalmeasures at rivers and streams will also benecessary in the future.However, planning such measures pre-sumes thorough and demonstratedknowledge of the existing types of hazardsand the measures’ ability to influencethem as well as the buildings’ susceptibil-ity to damage. The measures carried outshould respect as far as possible the natu-ral character of the river and landscapeprotection goals. Even emergency inter-ventions following sustained damage maynot disregard this principle, at least overthe long term.

Residual risksEach and every item cannot be protected.On the other hand, cantonal and localauthorities must do their best to makethe population secure. There will only be aviable way out of this obvious dilemma iffuture actions not only defend againstnatural hazards but also accept certainrisks and factor them into the equation.This pushes two questions into the fore-front: What protection may be offered (andat what price)? And how great can the re-maining risk be that it may be acceptable?

Security can be guaranteed most eco-nomically if natural hazards are avoidedand risks are not taken at all. This principleis anything else than new. Our forefathersobeyed it, even if possibly out of fatalism.Generally they had no other option thanto bow to the dictates of natural hazards.Now, at the beginning of a new millen-nium, this familiar adaptation strategy hasregained its meaning, since the risingdemands for protection can no longer becomplied with through technical measuresalone. Usage must again adapt moreclosely to the natural situation (and notthe reverse).

A flood control concept should involve an integratedplan for protective measures. It usually includesa package of measures that cover proper maintenance,cultivation of protective forests, land-use planningmeasures, object protection, construction measures,emergency planning, and emergency organization.

50

Fran

k; Is

enri

ng

Appropriate Maintenance

Strategy

Action

Procedure

Project Design

• Measures

Appendix

Recommended reading

BWW (1993): Ingenieurbiologische Bauwei-sen [Soil Bioengineering Techniques]

Various cantonal offices (e.g., those ofAargau, Berne, and Zurich cantons) havepublished guidelines on appropriate mainte-nance of rivers and streams.

Appropriate maintenance covers all periodic worksrequired to assure a minimum flow profile for a

flood. Maintenance also prevents occurrence ofdamage to the stream channel protection structures

and obviates the need for major renovation work.

Standards of how stream and river chan-nels should be maintained can differ quitestrikingly. The challenge within this area ofconflict between wishes and real possibili-ties is to find a workable solution. For thedays are long past when flood control con-sisted in preventing overflow out of a riverchannel at any price. Instead, protection oflocal sites and landscapes as well as pre-serving or restoring habitats for animalsand plants must also be taken into ac-count. Therefore, appropriate maintenanceof rivers and streams places priority onother measures, above all:• First, it guarantees the long-term func-tioning of existing protective structures.• Second, it assures the needed flow sec-tion for a flood.• Third, it contributes to maintaining andimproving habitats in and along rivers.

Permanent taskAppropriate maintenance of a river orstream is a permanent task that the can-tons regulate, finance, and monitor as re-quired by their laws.The type, scope, and frequency of mainte-nance depend on the type of river andlocal conditions. The spectrum of possiblemeasures is correspondingly broad. It cov-ers clearing of bushes and trees that re-

duce the flow section and endanger exist-ing protection structures. It also includesremoval of driftwood and dangerouschannel fill, repairing minor damage at thechannel, regular emptying of sedimentdetention basins, as well as restoringriparian vegetation. The following pointsshould be given special attention whencarrying out these measures:• All maintenance work should be per-formed in agreement with propertyowners, specialized cantonal offices, andservices for nature protection andfisheries.• During clearing for soil bioengineeringmeasures and new plantings, cooperationwith the forestry services and technicaloffices are necessary and useful.• Maintenance and restoration of struc-tural variety are important goals of ap-propriate maintenance. This includes chan-nel diversity with varying flow conditions,variable bank slopes, and a rich variety ofbank vegetation which, however, must cor-respond to the specific location. Yet natu-ral development of different plant andanimal communities – the so-called suc-cession – should also definitely be con-sidered.• Soil bioengineering techniques that useliving plants as construction materialsshould be preferred. If ”hard” measuresremain necessary, natural stones should beused so that at least small animals andplants can settle in the gaps.• But even the best intentions are worth-less if they are not implemented. Thisonly succeeds if all involved are convincedof the plan. It should also be noted herethat water pollution and water turbidityshould be avoided.

Maintenance conceptPlanning appropriate maintenance mustbe integrated in the flood control concept,because it can immediately influence thechoice of corrective measures (e.g., build-ing a sediment detention basin). Yet thisplanning also allows making a distinctionbetween building and maintenance mea-sures and assures that future maintenancemeasures be carried out expediently.Therefore, it is wise to develop a mainte-nance concept for the river or stream. Itlays down general goals and provides in-formation on the following issues:• Who monitors the river and checks re-lated bank protection works and protec-tive structures?• At what time interval do these check-ups and investigations occur?• Who assumes the maintenance duties?• When should the related maintenancetasks be conducted?• When are further structural or technicalmeasures necessary?

Maintainbank slopes

Managesediment

Weed outchannel bed

Repairminor damage

Empty sedimentdetention basins

Plant riparianvegetation

Cultivatebank vegetation

52

➜ http://www.wsl.ch/hazards

Forestry Aspects

Strategy

Action

Procedure

Project Design

• Measures

Appendix

Root stumps, wooden debris resulting from avalanches,timber, bushes, shrubs, and trees swept away by floods oftenlead to blockages with severe consequences at bottlenecks.

The subsequent backwater effect leads to uncontrollableoverflows. The potential input of wooden debris is difficultto quantify and depends on the condition of the forest, on

input by affluents, and on debris already lying in the channel.

When snow melts or after heavy rainfall,mountain torrents swell up rapidly. Theyundercut banks, entrain earth, sand andstones, leave the streambed, and relocatetransported bed load to other points. Es-pecially dangerous debris flow can also betriggered in sediment-loaden torrents.

Maintenance of protective forestsStable forest stock – structured like a mo-saic by age, height of trees, and species –offers good and cost-effective protectionagainst the power of natural processes.But these forests must be cared for con-stantly, so that they can fulfil their protec-tive function in a sustained manner.Depending on the natural hazards threat-ening at a given location, an ideal protec-tive forest has to fulfil very specific re-quirements. Closed forests with deeplyrooted trees in the catchment of the tor-rent in question protect against the haz-ards of torrents and formation of debrisflow:• Treetops hold back precipitation andevaporate part of it in the atmosphere (in-terception).• Soil enmeshed with roots soaks up pre-cipitation like a sponge and gives it backonly very gradually.• Tree roots reinforce the earth, stabilizestream banks, and retain potential bedload and other sediment.• Trees and tree trunks in deceleration anddeposition zones of debris flow act asnatural brakes.

Clearing in caseof restoration projectsCultivation of forest areas located close tostreams and rivers is also a constant task,as for those near torrents. But if these riv-ers or streams are granted more freedomof motion in connection with restorationprojects, it can lead to erosion of theneighboring forested areas.This raises the issue of diverting forest landfrom its proper use (clearing permit con-sistent with forest law). Plans that restorethe natural dynamics of a river are notdiversions from proper use. Therefore, theyrequire no clearing permit – always assum-ing that the following conditions are ful-filled:• Interventions are limited to the naturalriver zone.• No other uses are allowed within theriver zone defined (e.g., camping grounds,motocross tracks, parking lots).• Within the defined river zone, develop-ing potential forest locations are left tonatural succession (in agreement with pos-sibly existing forest development plans).

53

Fran

k; W

eiss

man

n-Ze

h

Alluvial Zones

Recommended reading

BUWAL (1995): Vollzugshilfe zur Auenver-ordnung [Implementation Regarding theOrdinance on Alluvial Zones]

Alluvial zones are dynamic habitats thatare periodically or episodically flooded bywater (and in which the groundwater levelperiodically is at the elevation of as far asthe roots of plant life). Moreover, erosionand deposition play a major role in thesehabitats. Vegetation is influenced by theresettlement, aging, and coexistence ofvarious development stages. Floods are noproblem for alluvial zones. On the contrary,floods help their regeneration:• The dynamics of water and the sedimenttransport invigorates the alluvial forest.• Floods increase the biodiversity, sincenewly created gravel bars and depositsbecome the habitats of pioneer vegeta-tion.• Floods change the relief and create newflow routes that contribute to the survivalof these valuable ecosystems.

Points to notein case of interventionAfter an extraordinary flood event, it maynevertheless be necessary to take immedi-ate structural action to protect the sur-rounding area. In such a case, the follow-ing principles should be observed:• Before carrying out emergency mea-sures, an agreement with the responsiblecantonal authorities or the federal alluvialzones advice center is absolutely neces-sary.• Dikes, groynes, embankment backfill, orcanalization, by which the alluvial zonecould be separated from the main channel,are not permitted. They influence alluvialdynamics and water regime in the alluvialzone.• Lowering the groundwater level and thedrying related to it must be avoided.

• When removing material and installinginitializing channels (pilot canals), takecare that it does not lead to lowering thechannel bed and thus to drying of the allu-vial zone.• Excess material should be depositedoutside the alluvial zone.• After an extraordinary event, special at-tention has to be given to flora and faunastill present.

Exploit opportunitiesOpportunities that arise with floods shouldbe exploited in alluvial zones. If possible,the new channel conditions should remain,because improving the alluvial dynamics isusually desirable.Therefore, after extraordinary events, thereis also a possibility of setting up protectivestructures outside the alluvial area (to al-low the waterway greater freedom).If existing structures or infrastructures arethreatened, their removal from the hazardzone should be examined.

54

RDB

Land-Use Planning Measures

Strategy

Action

Procedure

Project Design

• Measures

Appendix

Hazard index maps or hazard maps only reveal their full impact ifthey are also implemented in the related cantonal and local planningtools. There are two relevant levels for action: structural planning

at the cantonal level and land-use planning at the municipalitylevel. Specific details and legally binding phrasing are set at these

levels to guarantee proper consideration of natural hazards ingeneral and flood hazards specifically. The goal is to identify legally

binding hazard zones (or equivalent legal implementation).

Despite all difficulties that a densely set-tled and intensively used living area likeSwitzerland presents in this regard, thedamage potential should usually be re-duced by land-use planning measures.Only when a land use worth preservingexists or when, after weighing all inter-ests, a land-use change is absolutely nec-essary, should structural and technicalmeasures reduce the hazard potential.The following land-use planning measurescontribute to flood prevention:• Considering endangered areas in thecantonal structure plan and in municipal-ity land-use plans (local planning).• Identifying river space in the cantonalstructure plan and in the community land-use plans (local planning).• Defining off-limits zones (floodways)or inundation zones in the cantonalstructure plan and in the community land-use plan (local planning).• Excluding or rezoning endangeredland use from recognized hazard areas.• Introducing restrictions for construc-tion permits and demanding object protec-tion for existing and planned objects inendangered areas.

Land-use planThe land-use plan lays down permissibleland use regarding purpose, location, andamount, is detailed down to the plot sizeand is thus binding on property own-ers.According to Article 18 of the Federal Lawon Land-Use Planning (RPG), cantonalplanning law can envision other land-usezones beside construction, farming, andprotection zones. Based on this legal foun-dation, for example, hazard zones can bedefined that overlap the other uses.Yet it is also possible that the various usesrelate to the hazardous situation definedor are restricted in the definition (positiveor negative planning).The corresponding levels of danger wereagreed to primarily after regarding theconsequences of structural use. Hazardsto people and animals should be avoided,and material damage ought to be kept aslow as possible. The same requirementsconcerning levels of danger for structuresapply in farming zones as in construc-tion zones. Alarm and evacuationzones (emergency planning) should bedefined for all hazardous areas.

Structure planThe structure plan paraphrases the activi-ties required to realize the spatial devel-opment sought, and it sets the frameworkfor mutual agreement binding on theauthorities.Formally, the structure plan consists ofmap and text. One has to be restrictedin the map to a rough summary of the haz-ardous areas at the outset situation. Themajor weight for natural hazards in thestructure plan lies in the text. This textshould give an overview of basic studiesalready available and those being carriedout (concept of hazard maps). It shouldalso expound principles to protect againstnatural hazards and list measuresneeded, including the affected specializedoffices. Hence the structure plan assumesthe following tasks in the natural hazardsarea:• Early recognition of potential con-flicts between land uses and natural haz-ards as well as identifying the specializedoffices to call in.• Giving an overview of basic studies al-ready available and those still to be formu-lated regarding natural hazards (e.g., pre-paring hazard maps, coordinated plans forvarious sorts of hazards).• Formulating cantonal principles toprotect against natural hazards.• Setting guidelines and tasks for thenext planning stage, especially for munici-pality land-use planning (defining hazardzones).

55

Emergency planningand emergency organization

Structure plan level Land-use plan level

Overviewof hazards

Generaldanger assessment

Buildingregulations

Conflict areas

Hazardous areas

General spatial needsof rivers and streams

Hazard index map

Co

mm

un

ity

par

tici

pat

ion

Part

icip

atio

n o

f ca

nto

nal

of f

ices

and

insu

ran

ce c

om

pan

ies

Hazard map

Hazard zonesRiver space

Currentevent

Provenprotection

deficit

Local planrevision

Municipalityland-use planning

Zoning plan

Cantonalstructure planning

Action ordersbinding

on authorities

Conflict-free areas

Detailed assessmentof hazards

56

Off-Limits Zones

Flood controlat the Reuss riverInundation zoneat a 50-year event.

Overflow area ata 100-year event:Motorwayas flood spillway.

Overflow areaat an extreme event(greater than 1987).

Flood control wall

Spillway

Reuss delta spillway/Reuss delta secondary dam

Secondary measures (Giessen, Altdorf)

Channelimprovement

Culvert

Strategy

Action

Procedure

Project Design

• Measures

Appendix

Experiences from the 1987 flood of the Reuss in Uri cantonled to a protection concept defining off-limits space

(see illustrations below): From a Q50 level a flood canovertop the dike at the right bank and flow on the A2 motor-

way. But another protective dike along the motorwayconfines the overflow area, and a new culvert inserted in a

transverse embankment prevents a backwater effect towardsthe plain area. Yet during an extreme event even the motor-way does not suffice as a spillway channel. Then secondary

dikes prevent overflow into the nearby settlement areas.

If inundation zones were not developed orused intensively, floods could overflow thebanks freely without causing damage. Yetsuch off-limits zones have become ex-tremely rare in Switzerland. But there arestill areas where no great damage poten-tial exists – and where no costly structuralflood control steps are necessary.Land-use planning measures should helpcontinue to make such space available toovercome major floods.

Limited spaceIf a floodplain is to be kept off limits, itmust be spatially defined in advance. Out-lining this area’s dimensions occursthrough hydraulic calculations and assess-ment of past events. However, due to in-tensive use of practically all river valleys,the areas still remaining free are not un-limited considering extreme events.If the remaining risks are to be masteredas well as possible, we recommend that ar-eas left open to uncontrolled flooding beintentionally limited by secondary dams,topographical adjustments along roadsand railway lines, or by local terrainremodeling to create floodways:• First, steps must be taken to prevent un-controlled dike breaks for canalized rivers.Special spillway structures should be fore-seen for this. Submersible dikes and fuseplugs are also conceivable.• When designing the channel the possi-bility exists to raise one dike to a higherlevel than the other and thus preventovertopping there.• The intensively used area of the valley’splain is protected by secondary dikes alongthe main river and related adjustments ofthe road level in case of underpasses.

57

Luft

bild

Sch

wei

zObject Protection

*Building insurance companies also give infor-mation concerning object protection measures.

All potentially endangered areas in whicha new or changed structure use is envi-sioned, after weighing all interests, mustconsider existing hazards by concrete con-struction permit restriction.This object protection* can be guaranteedby permanent or temporary arrangements– or a combination of these measures(whereby warning times and availability ofthose responsible must also be consid-ered):• Design for foundations and other ex-posed parts of buildings in accordancewith potential load (e.g., by scour protec-tion at the foundations).• Build structures on supports, walls, em-bankments, or provide dikes or protectionwalls.• Seal structural casing and select water-repellent materials to build floors, walls,and roofs.• Elevate ground floors, entryways (eventhose in shelters), or garage entrances.• Secure drinking water and electricalsupply against flood influences by well-chosen routing of line wiring and piping.• Anchor oil tanks and protect sewersagainst backwater effects by automaticgates or manual valves.• Bolt openings such as light wells, doors,or windows with protective shields.• Include emergency escapes in plans andguarantee their permanent access.

Debris flowParticularly dangerous processes includedebris flow as well as spitting mudflowsand superficial landslides often occurringduring storms. In cases of major Alpine de-bris flow, fairly often sediment volumesattaining several hundred thousand cubic

meters are transported to the valleys, andthe debris flow can attain a velocity of60km/h or more.Even these natural hazards can be reactedto – at least to a certain degree – throughrelated construction permit restric-tions:• Adapt structures to the terrain andadapt building shape to possible pres-sures.• Lay down use of interior space in keep-ing with the danger of debris flow at hand.• Give special attention to the locationand elevation of doors, windows, or ga-rage entrances.• Reinforce outer walls, and protect open-ings.• Place structures on embankment terrain(above all in case of new buildings, assuch structures are among the most rea-sonably priced and most effective correc-tive measures).• Embank detention dams to protectagainst minor debris.• Build diversion walls or diversion dikes.• Set up split structures upstream of build-ings and pylons.

58

➜ http://www.bwg.admin.ch/

Protective Structures

Dam

age

po

ten

tial

(res

idu

al r

isk)

Time axis Later intervention(e.g., object protection)

Added land-useplanning measures

No land-useplanning measures

Structuralmeasures

Limits of Efficiency. Structural and technicalprotective measures reduce the original risk

to a certain residual risk. But if the settlementarea is expanded, streets or other infrastruc-

tures are built within the area secured by pro-tective structural measures, the residual risk

can soon be higher than the original risk. Land-use planning measures (and targeted interven-

tion as with object protection) can stabilizethe damage potential over the long term.

Strategy

Action

Procedure

Project Design

• Measures

Appendix

Note on limitationsStructural protection measures have stoodin the foreground for a long time in plan-ning corrective measures. Meanwhilethings have changed, because this ap-proach in defending against hazards mustcope with several limitations at the sametime:• Technical limitations. Even costlyprotective structures will never be able toachieve absolute protection from the natu-ral hazards.• Ecological limitations. Structural in-tervention often contradicts efforts to im-pact the least in natural and nearly natu-ral landscapes.• Economic limitations. In view of thefrequently overextended financial situa-tion in the public sector, planning, imple-mentation, and even maintenance ofcostly protective structures can no longerbe taken for granted.• Efficiency limitations. The expecta-tion of being armed by protective struc-tures against the power of nature leads inmany areas to a disastrous concentrationof values. This in turn increases demandsfor protection.

water regime, neighboring land use, andcharacter of the surrounding landscape,different design options also open up indefining structural measures.• Protective structures must always beconsidered in terms of how they combinewith the river and its catchment – andthus the possible types of hazard and in-fluence factors.• The impact of structural measures onthe lower course must also be clarifiedvery precisely.• Protective measures may not lead to anincrease in potential damage in case de-sign values are exceeded. Thus, the impactof an overload should be clarified withinproject design (and the proper measurespossible to limit damage should also beindicated).• Impact factors must be studied incase of protective structure overload(EFQ). Indication should also be givenwhich suitable measures (on constructionor object protection) are possible to limitdamage and increase system security.• If protective structures are destroyed,the reason for failure should always beanalyzed. It should also be determined if itmakes sense to rebuild them at all.• Besides improving flood control, envi-ronmental aspects must also be consid-ered: The natural dynamics should befavored, the landscape be revalued, andnetworking of the habitats be promoted.• Wherever natural dynamics must be re-stricted, ongoing study should occur onhow sufficient flood control can beachieved with soil bioengineeringmeasures.• Special attention should be given to themeasures’ long-term effect.

The spectrum of proven structural protec-tive measures is great, and a combina-tion of corrective measures is usually re-quired. The table on the facing page showsa compilation of conceivable correctivemeasures.A few of these protective structures – onesthat correspond especially well to the prin-ciples set forth in these guidelines – areexplained in greater detail on the follow-ing pages. Further details can be retrievedon the FOWG website.

Demands on protective structuresStructural measures are only justifiedwhere proper maintenance of existing pro-tective structures, land-use planning ef-forts, object protection, as well as protec-tive forest cultivation do not lead to thegoal. If structural measures are stillneeded, they must fulfill the following ba-sic requirements:• There is no such thing as a standardstream or standard river. Depending on thecatchment, geological conditions, local

59Measures at upper course

Detention measures

Inundation zones; off-limits areas

Flood detention basins

Stabilization measures

Anchoring

Drainage

Structural measures at river channel

Increasing flow capacity

Clearing

Flood protection dike; submersible dike

Channel improvement

Bridge sheeting; vertical-lift bridge

Stabilizing

Block ramp (ground sill)

Placing of blocks

Channel widening

Sill

Check dam; torrent check dam

Stabilizing cross section

Groyne

Sidewall; riprap

Soil bioengineering protection

Sediment management

Grid

Debris flow breaker

Sediment detention basin

Sediment management

Object protection

Object protection against floods

Object protection against debris flow

Proc

esse

s

Floo

ding

Bed

eros

ion

Bank

ero

sion

Und

erc u

ttin

g

Chan

nel m

igra

tion

Bed

load

tra

nspo

rt

Chan

nel f

ill

Clog

ging

Deb

ris

flow

Land

slid

e

Important connection (influence)

Protective measures

60

ConstructionMethods Submersible dikesBlock ramps

The spectrum of proved structural protec-tive measures is great. Five examples areexplained in closer detail here. It is an in-tentional selection of sustainable pro-tective structures. Their purpose andfunction is introduced and their advan-tages and disadvantages are shown(based on experience in recent years).Groynes are an example of this. They are awell-known structural measure in protec-tive hydraulic engineering. Yet new meth-ods caused them to fall into oblivion. Inthe meantime, however, they have experi-enced a renaissance, since they have someadvantages over linear bank protectionworks.

Purpose. Block ramps, also referred to asground sills, permit the channel bed to bestabilized artificially along the longitudi-nal profile (checkpoint).

Function. One can overcome a majorhead by placing coarse blocks (densepacking block by block or by leavinggaps). Various flow conditions develop,depending on the head difference thatmust be overcome. Uniform flow (an equi-librium situation) will occur if the ramp islong enough.

Advantages /disadvantages. Blockramps allow designing a checkpoint in amore natural way. The longitudinal waternetwork can be assured. Ramps can adaptto practically all channel sizes (step-poolsystems). Ramps also improve free migra-tion of aquatic animals (fish, macroinver-tebrates).

Purpose. Dikes purposely designed to per-mit overflow or lateral weirs evacuate floodpeaks that exceed the flow capacity of thecanalized channel. These relief measuresserve as ”security vents” to protect dikestretches which are not designed for over-flow.

Function. A lowered local dike crest – andin this case one protected against erosion –is the main element of these structural mea-sures. Another option is to set up a local fuseplug with an erodable dike part (the dikeremains stable up to a certain discharge,overtopping then results in erosion down toa predetermined elevation). Submersibledikes can be fairly long, because the specificdischarge spilled amounts to a maximum of1m3/s per meter. However, the overflowlength can be reduced by local narrowing ofthe river’s cross section. This can also im-prove flow conditions and assure smoothfunctioning. In any case, the performance ofsubmersible dams must be examined for anextreme flood (EFQ).

Advantages /disadvantages. Submers-ible dikes do not reduce security in flow cor-ridors. Normally the discharge spill is re-duced, because the entire dike cannot bedestroyed. Yet the lateral overflow functionis complex and sometimes quite difficult tomaster. Long structures are needed for largeroverflow discharges. Under certain condi-tions even several overflow sections shouldbe provided for stability reasons. Lateralspill influences bed load transport. This caninduce bed level changes and lead to alteredoverflow conditions.

Strategy

Action

Procedure

Project Design

• Measures

Appendix

61

AG

W (

1), D

ocum

ent a

Nat

ura

( 1) ,

Elbe

r ( 1

) , Fr

ank

( 2)

Channel widening Debris flow breakersGroynes

Purpose. Channel widening stabilizesthebed level and improves its structural di-versity as well as that of the transition zonebetween river and land. This is because chan-nel widening is a measure favoring naturalconditions in the river and particularly onchannel morphology. Application range forchannel widening are midland rivers with asufficiently large bed load transport rate.

Function. The transport capacity of the wa-terway is reduced by widening, which leadsto local deposits. By a slope increase inthe widened reach, the original transport ca-pacity will be reestablished in a natural way.Yet a rising of the upstream channel bed levelis the consequence.

Advantages/disadvantages. Widening achannel induces bed structures close to na-ture. Changed flow conditions alter the flowstress on the banks. Widening leads to locallyincreased energy slopes and thus to higherflow velocities. This must be considered indesigning bank protection measures.

Purpose. Groynes are structures that areplaced more or less at right angles to themain-flow direction and protect the banks ofa stream or river against erosion. They canbe used to influence flow and to improvestructural diversity.

Function. On the one hand, they serve toprotect the bank from erosion (spur dikeskeep the main flow of a river from the bank).On the other hand, they improve the struc-ture and increase flow diversity. The depth ofdischarge in the middle area between thespur dikes is elevated by the narrowed crosssection, and this strengthens its ability totransport). In general, discharge depth in-creases in comparison to a cross sectionwithout spur dikes.

Advantages /disadvantages. Groynesare very adaptable if built in a flexible style.Supplements and reinforcements are possi-ble at any time. Besides functioning as bankprotection, the groyne offers habitats foraquatic fauna and increases biodiversitysignificantly. In dynamic rivers with rapidlychanging channel morphology, groynesmust cope with all possible flow conditions.Therefore, in case meanders shift, groynesmust be arranged at shorter distances thanat morphologically stable sections of a river.Protective concepts with groynes requiremore space but favor more diverse bankareas. They have several advantages overlinear bank security:• the impact is locally limited;• they integrate themselves into the

landscape;• their flexibility is greater in case

of overload;• they can adapt easier to changed

conditions;• they improve structural diversity.

Purpose. These protective structures canforce debris flow to be diverted into suitableareas with little damage potential. Hence,settlement areas often lying on the alluvialfan can be protected.

Function. The debris flow is drained by per-meable elements of a debris flow breaker. Asa result, the debris flow loses an essentialdriving element and deposits its load. A de-bris flow breaker allows to stop the first de-bris flow surge. Depending on the structure’sarrangement, the following surges are di-verted to lateral deposition areas. A massivediverting structure can intentionally divertdebris flow to a preferred deposit area. Inthis regard, the high dynamics of a debrissurge must be considered. A diversion struc-ture should allow minor floods carrying bedload to pass, and diversion should only beactivated in case of debris flow. A diversionstructure consists of a lateral overflow weirand a diversion facility. The structures are laidout for rare events.

Advantages /disadvantages. Channelimprovement designed for debris flow on analluvial fan can lead to disproportionatestructures and impacts. This can be avoidedwith punctual measures in the headwaters.Impact on landscape is local for debris flowbreakers or diversion structures.. There arestill few design rules for structures that caninfluence debris flow behavior. They areoften based values gained by experience(from Japanese grids or debris flow breakersin Austria) but also on model testing.

62

Fran

k

Emergency Planning

There is no absolute protection againstfloods and the hazards related to them.Violent waters hold a hazardous poten-tial that is neither totally comprehensiblenor fully controllable. Extreme or long-last-ing precipitation can turn streams and riv-ers in any part of the country into ragingfloodwaters, trigger debris flow, or activatelandslides.Thus, flood waters rising to extraordinarilyhigh levels repeatedly prove themselves tobe serious threats that can indeed be re-duced and limited by proper maintenance,planning measures, and protective struc-tures. Yet they can never be turned awayentirely. Moreover, it cannot be forgottenthat any hydrologic calculation is afflictedwith certain uncertainties. Even properlydefined design values accepted by all canbe exceeded in the extreme case.Hence, emergency planning is necessary inany case that can reduce the risk thatalways remains to an acceptable level.The highest priority is given saving peopleand livestock as well as limiting collateraldamage (e.g., from hazardous goods orchemical plants).

Manage preventionIt is crucial that the responsible local orregional authorities are aware of the floodhazards looming. Given the preparednesscalled for, the effects of flood events canat least be reduced. In connection withplanning measures, these principles onconditions in the respective catchment aresurveyed and assessed. In a second step,the results will be integrated into a com-prehensive prevention plan.The municipalities will be supported in thisimportant work by the cantonal specialist

offices and – in case of major plans – alsoby the federal government’s specialist of-fices. It is useful to create potentialsynergies with existing organizations andfacilities (e.g., in connection with earlyalarms). There is no standard solution forassessing the remaining risks. Any floodcatchment has its own characteristicsthat are determined by local topography,geology, hydrology, topsoil, and land use.

There is always a remaining risk

Collect basic data

Assess basic data

Formulate a prevention plan

Monitoring and warningEvacuation and rescue

SupplyCoping with damage

Strategy

Action

Procedure

Project Design

• Measures

Appendix

63

Emergency Organization

➜ Appendix: Checklists

An emergency organization’s task areas

Municipalityor cantonalauthority

Localor cantonal

leadership body

Support

Logisticalcoordination

Administration

Securityand

order

Rescueoperations

Infra-structure

Protectionandcare

Healthand

sanitation

Immediate action

The major responsibility for emergency planningand organization lies within the municipalities. Thereare no standard solutions. A flood is only one of a seriesof possible emergencies caused by natural hazards.

A clearly structured emergency organiza-tion with assigned task areas and re-lated action plans is a central assump-tion in coping with an emergency causedby flooding or other natural or man-madehazards. But this organization is only use-ful if it can assume its tasks without delay.The following areas must be covered inthis regard:• Warning. Hazardous developmentsmust be recognized promptly in order toorient the local people, to alarm the emer-gency services, and to take immediate ac-tion.• Countermeasures. In certain cases,action can be taken to prevent flooding ifpotential events are recognized early (e.g.,by clearing the river channel of woodendebris transported by avalanches or float-ing debris in general, by reinforcing dikes,or building mobile dikes).• Special risks. Objects with major dam-age potential (e.g., hospitals, homes, cul-tural objects, petrol stations, chemical stor-age sites, supply facilities, switchboards orcommunications centers) require a special”flood action plan” so that damage can beprevented effectively.• Salvage operations. Eventual victimsshould be salvaged, transported to secureareas, and treated medically.• Evacuation. If a flood cannot be pre-vented or is a serious threat, people mustbe brought to secure areas and treated.Under certain conditions valuable itemsshould also be removed from the hazard-ous area. However, it is not easy to deter-mine the right moment for such measures.In principle, one strives for an early mo-ment, but the problem of possible falsealarms also arises.

• Infrastructure. Machines and materi-als for immediate emergency action mustremain prepared to keep transport routesopen and to ensure access to the area af-fected.• Monitoring. Weather and events in thecatchment should be monitored constantlyto support salvage and clearing work.• Communication. Related devicesmust not only function in an emergencybut be available at the right locations.• Object protection. Individual housesand limited areas can be protected from

floods by temporary measures (e.g., sand-bag barriers, mobile walls, or – if time per-mits – even walls).• Partners. Cooperation with the emer-gency organizations of neighboring com-munities should be part of the preparationand training plans.

Appendix

65

INTERNET

INTRANET

➜ http://termdat.bk.admin.ch

➜ http://europa.eu.int/eurodicautom

Fran

k

Glossary

TERMDAT definition Legal reference Source

Dictionaryon flood control terminology

These guidelines contain an abun-dance of specialized expressionsfrom various sectors of flood con-trol. In order to simplify under-standing and prevent possible mis-understanding, the FOWG hascooperated with the federal chan-cellery’s terminology section forseveral years to compile a four-lan-guage dictionary with emphasis onthe flood control, hydraulics, hy-drology, geomorphology, and natu-ral-hazards sectors. This workcovers more than 800 entries withabout 1500 definitions in English,German, French, and Italian.

The dictionary is on TERMDAT, thecentral terminology databankof the federal administration,and is already accessible to all pub-lic services in Switzerland via In-tranet or Internet (KOMB/KTV). Theterminology section of the FederalChancellery will answer furtherquestions on access to TERMDAT.

Interested parties with no access tothe federal administration’s Intra-net can use the European Union’sterminology databank dictionaryvia EURODICAUTOM.

Alarm. Warning the public ofdanger or a threat by a signal(usually a siren).

Bank. Side part of the channel.

Bank vegetation. All plant lifeat the bank of a river.

Biotope

Discharge. Water volume thatflows through a specific channelcross section per unit of time.

Dispossession

Downstream riparians. Peopleor objects found downstream froma certain point of a river or stream.

Environmental impact study

Financial aid

Flood control. All measures toprotect people and things of highvalue from damage by water,especially from floods, erosion,and sediment deposition.

Gravel mining

Groundwater. Undergroundwater network that fills out hollowspaces of the earth’s crust.

Hazard index map. Overviewmap that is compiled by scientificcriteria and identifies hazardsthat are recognized and localizedbut not analyzed and assessed indetail.

Hazard map. Map at scale of1:2000 to 1:10 000 compiledaccording to scientific criteria andwithin detailed forecasts of a studyperimeter made on types ofhazards, degrees of hazards, andspatial extent of hazard processes.

Creation and operation of early-warning services

Protection of habitats for fishFishery permit for intrusions (esp. bank clearing)Bank design

General protection; active promotionSpecial permit restricted to facilities for local useaccording to WBG and GSchG

Protection of indigenous animaland plant typesDiffering degrees of protectionSubstitution in case of unavoidable intrusionBiotope of national, regional, or local importance;ecological balanceFederal subsidies

Discharge capacity by maintaining rivers orstreams, banks, and flood control structures; alsoin forestry stream trainingResponsibility: cantons

Dispossession of rights necessary for WBG/WBVimplementation; cantonal authority or that it con-fers on third parties; applicable law

Coordination in case of intercantonal riversor streams

Before planning, construction, change of facilitiesdesignated by the Federal CouncilEnvironmental compatibility report

Federal subsidies for restoring strained rivers,without legal claim

Protection of people and things of high value fromdamage by water; defining protection goals andprotective measures in isolated cases

Permit according to water quality control lawand fishery lawGroundwater protection zones

Groundwater protection zones; groundwater area

Basis for structure plan giving rough recognitionof conflicting interest area in case no hazard mapis available.

Basis for structure and land-use planning as wellas for projecting protective measures

WBV 24, 27 I f.

BGF 7BGF 8 I, IIIcWBG 4

NHG 21NHG 22 II

NHG 18 ff.NHV 14 ff.NHG 18 Ibis

NHG 18 IIter

NHG 18a, b

NHG 18c

WBG 4 IWaG 19

WBV 23

WBG 17

WBG 5

USG 9 I, IIUVPVAppendix 30.2

WBG 7, 9 f.WBV 5 ff.

WBG 1 I

GSchG 44 IBGF 8 III gGSchG 44 II

GSchG 20 f.

WBV 21

WBV 21WBV 27 l c

66

TERMDAT definition Legal reference Source

Glossary

Strategy

Action

Procedure

Project Design

Measures

• Appendix RPG 18WBV 1II

NHG 5 ff.NHG 18aNHG 23a ff.

RPG 14 ff.

RPG 22RPG 24RPG 21

WBG 3 IWBG 4 IWBV 23

NHG 23a ff.NHV 21a ff.

WBG 6, 8 ff.WBV 1–4, 8 ff.SuG

RPG 22RPG 24GSchG 19 II

GSchG 29WBG 4 IIIGSchG 28 IIIGSchG 38GSchG 44BGF 8NHG 22 IIWaG 5GSchG 37

WBV 3–15WBV 16 f.

WBV 18

WBG 3

WBG 4WBG 5

Area with land-use restrictionsLand-use prohibitions

Area of nature and homeland protection/federalinventory with objects of national significance:seek (mandatory) expert opinions by Swiss Feder-al Commission on Protection of Nature and Home-land (ENHK) in case of possible damage

Organizes permitted use of land (e.g., building,agriculture, protected zones)Building permit within construction zoneSpecial permit outside it; only if restricted to loca-tion and no overriding public interest opposes it;binding on property owners

Priority flood control measureSecuring existing flood protectionConsideration of ecological requirements

General protection, restricted landscape designand land use, protection goals according to feder-al law, protection and maintenance measures ofthe cantons; federal subsidies

Legal claim to federal subsidies for structuralmeasures, restoration of structures and facilities,hazard registers and hazard maps, gauging sta-tions, early-warning services

Building permit within building zoneSpecial permit outside building zoneConstruction of / changes in structures andfacilities in especially endangered waterprotection zonesWater diversion from rivers and streamsSpecial permit for ecological design of hydraulicmeasuresSpecial permit for laying streams into culvertsMining sand, gravel, or other materialFishery permit for technical impacts on riversSpecial permit to remove bank vegetationSpecial permit for forest clearingTraining of rivers and streams

Subsidy procedureFederal opinion on cantonal flood controlmeasuresFOWG opinion on measures by other federaloffices with impact on flood control

Priorities: maintenance and spatial planningmeasures (passive measures)RequirementsIntercantonal rivers; coordination

Hazard zone. An area underthreats by natural hazards, whereland-use restrictions apply bindingon property owners according toa hazards analysis.

Inventory

Land-use plan. Plan that definespermitted use of land regardingpurpose, location, and dimensionsdetailed to the plot size andbinding on property owners.

Maintenance. All measures tomaintain discharge capacity and ef-fectiveness of protective structures.

Moor and moor landscapes

Payment

Permit

Procedure

Protective measures. Measuresto reduce or remove a risk, distin-guished by active and passiveprotective measures: active pro-tective measures counteractthe natural event to reduce thedanger or to have an essential in-fluence on the course of an eventor its probability of occurring; pas-sive protective measures re-duce damage without influencingthe course of the event.

67

➜ http://www.admin.ch/

Glossary

TERMDAT definition Legal reference Source

Legal Basis

Federal Law on Public Procurement

Intercantonal Agreement on PublicProcurement

BGBM Federal Law on the Domes-tic Market

BGF Federal Law on Fisheries

GSchG Federal Law on WaterQuality Control

NHG Federal Law on Protection ofNature and Landscape

NHV Ordinance on Protection ofNature and Landscape

RPG Federal Law on Land-usePlanning

RPV Ordinance on Land-usePlanning

LwG Federal Law on Agriculture

ÖQV Ordinance on EcologicalQuality

SuG Federal Law on Financial Aidand Payments

USG Federal Law on EnvironmentalProtection

UVPV Ordinance on EnvironmentalImpact Testing

WaG Federal Law on the Forests

WBG Federal Law on Flood Control

WBV Ordinance on Flood Control

Federal laws on the Internet

BGBM 1 ff., 6

BGBM 5 II

BGBM 11

RPG 25a II b

NHV 3

WBG 5 II

WBG 4 IIWBG 7, 9 f.

USG 55 ff.NHG 12–12b

NHG 12a I

RPG 5

RPG 6 ff.RPG 14 ff.

RPG 3WBG 3

RPG 8, RPV 5RPG 9

SuG 10 II aWBV 8c

Federal government: federal law on public pro-curement, free access to the market in keepingwith domestic lawCantons: official publication of plans and criteria,financial participation and added chargesAdjustment of cantonal regulations to domesticmarket lawIntercantonal agreement on procurement proce-dures

According to cantonal procedural lawWhen building/changing a structure/facility withcoordination needsWhen fulfilling federal task in area of nature orhomeland protection

Cantons or, according to cantonal law, coopera-tives or the private sector; the Federal Council’sdecision-making authority in case of inter-cantonal waterways if no agreement can bereached between the cantons affected

In case of hydraulic-engineering impacts on riversFederal subsidies

Responsible in sectors of nature and landscapeprotection: federal offices, cantons, municipalities,all-Switzerland environmental organizations (des-ignated by the Federal Council)Opening of availability in written announcement,in federal register, or in bulletins published bycantons

Advantages/disadvantages of property restrictionsdue to planning as per RPG

Structure plan (binding on authorities to coordi-nate space-impact activities) and land-use plan(property owners bound to provide specifics ofstructure plan)Planning principlesSpatial planning measures: in hydraulic-engineering, they take priority over structuralmeasures

Harmonizes space-impact activities; shows the de-velopment to strive for, the time sequence, andthe resources to be usedBinding on authorities

Cost-sharing in case of federal subsidies

Public procurement

Public planning restrictions

Responsibility for riversor streams

Restoration to nature. Allmeasures with which landscapesor landscape elements changedby human influence (e.g., riversor streams) are restored to a con-dition close to nature.

Right of appeal

Settlement/Compensation

Spatial planning. Anticipatedcoordination of space-impactactivities and their steerage overa longer period.

Structure plan. Plan that para-phrases activities required torealize the spatial order soughtafter and defines the frameworkfor mutual agreement which isbinding on authorities.

Third parties (special advan-tages)

68

Contents Available: yes no

Summary ❑ ❑

1 Occasion and task ❑ ❑

2 Situation at outsetHistoric events (chronicles; event documentation) ❑ ❑

Existing or planned land use ❑ ❑

Characteristics in catchment area ❑ ❑

Hydrologic conditions ❑ ❑

Current channel flow capacity ❑ ❑

Geologic conditions ❑ ❑

Potential types of hazards (processes):• Floods ❑ ❑

• Bank erosion ❑ ❑

• Debris flow deposit ❑ ❑

Scenarios ❑ ❑

Assessment of existing protective structures ❑ ❑

Analysis of weak points along rivers ❑ ❑

Existing hazards situation ❑ ❑

River condition ❑ ❑

3 Project assumptionsSelected protection goals ❑ ❑

Ecological development goals ❑ ❑

Defined design values ❑ ❑

4 Potential damageAssessment of potential damage ❑ ❑

5 Planning corrective measuresOption studies and decisions ❑ ❑

Maintenance measures ❑ ❑

Spatial planning measures ❑ ❑

Structural measure:• Description of measures including technical ❑ ❑

justification and evidence (especially hydraulicassumptions and evidence)

• Weighing of interests ❑ ❑

6 Impact of corrective measuresImpact on settlements and land-use surfaces ❑ ❑

Impact on nature and the landscape ❑ ❑

Impact on river ecology and fisheries ❑ ❑

Impact on groundwater ❑ ❑

Impact on agriculture ❑ ❑

7 Remaining hazards and risks ❑ ❑

8 Implementing action on remaining hazards ❑ ❑

into structure and land-use plans

9 Emergency planning ❑ ❑

Checklists

Technical report

Strategy

Action

Procedure

Project Design

Measures

• Appendix

69

Content Available: yes no

1 Technical report (see opposite page) ❑ ❑

2 Cost estimateConstruction costs (based on budgetary estimate ❑ ❑

and unit prices for construction work; main items)Project and building management costs ❑ ❑

Costs of land procurement ❑ ❑

Contingency costs (list separately) ❑ ❑

3 Plans3.1 Oversight plans 1:10 000 to 1:50 000

Construction plan ❑ ❑

Subcatchment areas ❑ ❑

Possible precipitation measuring stations ❑ ❑

Possible discharge measuring stations ❑ ❑

Waterway names ❑ ❑

Realized protective structures and secured stretches ❑ ❑

Presentation of existing hazards ❑ ❑

3.2 Situation plan 1:1000 to 1:2000Measures envisioned ❑ ❑

Top priority points (bridges, buildings) ❑ ❑

Existing and planned vegetation ❑ ❑

3.3 Longitudinal profileFlood level / energy line for Qd and EFQ ❑ ❑

Low water level ❑ ❑

Bed level at outset ❑ ❑

Mean project bed level ❑ ❑

Slope ❑ ❑

Possible exploration ❑ ❑

Possible sediment removal points ❑ ❑

Bridges, sills, ramps ❑ ❑

Weirs, rock outcrops ❑ ❑

3.4 Technical cross section (pre- and post-renovation)Water levels Qd and EFQ ❑ ❑

Low water level ❑ ❑

Property borders ❑ ❑

3.5 Normal profiles and design profilesWater levels ❑ ❑

Low water level ❑ ❑

Bank protection ❑ ❑

Streambed protection ❑ ❑

Design and planting ❑ ❑

3.6 Photo documentation ❑ ❑

4 Accompanying cantonal reportsWater protection and groundwater conditions ❑ ❑

Nature and landscape protection ❑ ❑

River ecology and fisheries ❑ ❑

Forest (in case of clearing) ❑ ❑

Agriculture ❑ ❑

Spatial planning ❑ ❑

5 Environmental impact reportPlans requiring environmental impact studies mustinclude a separate report on environmental effects andbe opened to a public hearing. ❑ ❑

6 Cantonal decisionsLegally binding decision (for all permits granted) ❑ ❑

Funding key and cost participation ❑ ❑

Perimeter duties of federal government and its agencies ❑ ❑

In case of applications for sub-sidies, the basic data must becompiled in a project file toenable comprehensive assessmentof the plan with all its decisiveimpact factors. This project fileusually corresponds to the publiclyadvertised building project.

In connection with floodcontrol measures and plans,environmental impact studiesare compulsory for:

• Structures to regulate waterlevel or discharge from naturallakes exceeding 0,5km2 of averagelake surface.

• Hydraulic-engineering measuressuch as river training, canalization,diking, corrections, or sedimentand flood detention facilities at abudgetary estimate of more thanCHF 15 million.

• Debris dump in lakes coveringareas of more than 10 000 m3.

• Mining more than 50000m3

of gravel, sand, and other materialsfrom rivers per year (excludingone-time removal for flood securityreasons).

Procedure: All four cases todecide by the cantonal right .

Project file on applications for federal (FOWG) subsidies

Checklists

70

Each catchment indicates specificcharacteristics for flood formation.Depending on these specifics, arange of hazard criteria results:

• Winter floods. Indicated(usually) by slowly flowing floodwaves and relatively long-lastingflood situations. Bed load trans-port problems seldom reach majorproportions.

• Summer floods. They resultfrom intensive rains or hailstormsand are characterized by brief buthigh-peak discharges. In smallcatchments one must reckon withinundation or even destruction ofstream channels as well as floodedlandscapes, not to mention struc-tures and infrastructure facilities.Great volumes of sedimentscan accumulate as a resultof hill slope and riverbed erosion.

The hazardous potential in aflood situation is especially high atthe following points:• in river channels with insuffi-

cient capacity;• in damaged channels;• at channel bottlenecks;• along possible channel alterna-

tive routes such as roadwaysor railway tracks;

• in terrain depressions;• at artificial barriers formed by

houses or embankments;• at knick points in longitudinal

profile.

Emergency planning: Gathering and assessing basic data

Checklists

Hazardous situationsAnalyze historic sourcesAssess event registerAssess hazard maps if availableNote technical studies with local referenceAssess current observations

Meteorological constellationsSnow situationsThunderstorm situationsSoil saturation by precipitation

Topography and ground coverSteepness and form of catchmentProportions of meadows, forest, developed areas, cliffs,glaciers, lakesPossibilities of infiltrating precipitationNatural and artificial barriers

Conditions in catchment areaSediment potential available in catchment (danger of debris flow)Sediment potential available along river channels (danger ofchannel debris flows and intensive bed load transport)Condition of vegetation (ground cover influences runoffof rainwater)Soil condition (has a significant impact on extent of surfacerunoffs)

Condition of the river channelDegree of river trainingFlow capacity of the trained riverStability of training worksDamage to channel bank and bedReduction of flow sections because of growing vegetationor sediment depositsBottlenecks (bridges, culverts, covered sections such as timberdepots)Mass accumulation in sediment detention basinsLoose wood in streambed area (danger of clogging or damages)

Endangered buildingsSensitivity to structural damage (openings, materials, supplyfacilities, institutions)Earlier cases of damage

Endangered human beingsJobs in potential flood areasJobs in potential landslide areasResidential population in potential flood areasResidential population in potential landslide areas

Endangered infrastructures in the catchment areaRoad connectionsRailway linesElectricity power plantsGas and water supply facilitiesTelephone exchangesTransmitting facilities

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

❑

Strategy

Action

Procedure

Project Design

Measures

• Appendix

71

Early-warning systems. Set up permanent or situation-relatedearly-warning systems. This permits timely and targeted use ofprecautionary measures.

Machines and material. Dredgers, transport vehicles, compres-sors, pumps, emergency power-generating sets, and tools mustbe available in case of catastrophes. Under certain conditions, re-serve equipment from other communities or regions are alsoused.

Communication. Local and regional communication systemsare conceived so that they cannot be put out of service by floodsor related events. If the facilities on hand do not suffice, prepara-tions should be made for radios, megaphones, mobile transmit-ters, and communication equipment outside the hazard zone.

Road and railway connections. Check in advance if settledareas can be cut off from the outside world by floods or relatedevents. If so, reserve equipment should be prepared forthe first-aid teams, military service, and civil defense as well asbuilding materials (e.g., wood for emergency bridges) and, if nec-essary, machines and tools as well.

Medical care. Rescue, transport, and care of casualties mustbe assured. A related concept must be prepared with appropriatespecialists and institutions, to the extent that cantonal or localorganizations and institutions cannot provide the necessary infra-structure.

Evacuation. Prepare emergency housing and care options.

Aid. Various offices at the federal, cantonal, and also local levelare in a position to perform direct or indirect aid in emergencies.Therefore, offices responsible for overcoming an extraordinarysituation should inform themselves and study documents in ad-vance on the following questions:❑ What institutions or organizations can provide any form of

aid and to what extent?❑ Who are the responsible contact people, and what are their

current telephone numbers?❑ What costs would arise, and how are the procedures?❑ Who is responsible for distributing donations?

Weather conditions. Organize weather observation and set upthe related alarm concept, because weather changes endanger allpeople who are engaged in post-event clearing and security work.

Work on the crisis team. The following strategy has proveditself in crisis situations:❑ Settle issues with authorities in advance regarding

monitoring, alarms, as well as organizational and structuralarrangements.

❑ Assure smooth information flow.❑ Submit reports briefly and to the point.❑ Inform the public promptly, fully, and regularly on the course

and consequences of damage events.❑ Summon the courage to make decisions (and also to imple-

ment them in a timely manner).

Outside assistance

Personal helpUse of outside assistance (e.g.,members of the military, of civildefense, of volunteers) can hardlybe defined in advance. Each dam-age event has its own individualdemands to cope with.

Financial aidIn case of a flood, the federal,cantonal, and – in case relatedcontacts have been finalized – in-surance companies provide contri-butions to cover damages. Wherecantonal insurance on houseproperty exists, comprehensive andunlimited insurance automaticallycovers elementary damage ofbuildings. Advance research shoulddetermine items left uncovered insuch an event. Alternative financialoptions to cover these remainingcosts should be sought in the pre-vention phase.

Cooperationof the authoritiesThe federal and cantonal govern-ments are in the position to sup-port communities with appropriatecontributions – and in catastrophiccases usually with extraordinarycontributions as well. So that thesefunds can also flow, regulationscall for responsible offices beingcontacted even in the first phase ofcoping with the catastrophe (andthat work be arranged with thecantonal and/or federal offices).

Each damage event has a specialcharacter and must therefore becoped with individually. A precau-tionary plan serves in this caseas a basis and guiding principle.

Checklists

Emergency planning: Pecautionary plan elements

❑

❑

❑

❑

❑

❑

❑

❑

❑

72

➜ http://www.raumentwicklung.admin.ch

➜ http://www.bwg.admin.ch

➜ http://www.planat.ch

➜ http://www.umwelt-schweiz.ch

➜ http://www.blw.admin.ch

➜ http://www.astra.admin.ch

➜ http://www.kultur-schweiz.admin.ch

Contact

Specialized officesof the Federal Administration

Swiss Agency for the Environment, Forestsand LandscapePapiermühlestrasse 172CH-3003 Berne

Federal Office for Spatial DevelopmentEinsteinstrasse 2CH-3003 Berne

Federal Office of AgricultureMattenhofstrasse 5CH-3003 Berne

Swiss Federal Roads AuthorityWorblentalstrasse 68CH-3003 Berne

Federal Office of CultureSection for Preservation of CultureHallwylstrasse 15CH-3003 Berne

Strategy

Action

Procedure

Project Design

Measures

• Appendix

PLANAT SecretariatLändtestrasse 20CH-2501 Biel

Federal Office for Water and Geology (FOWG)Division of Natural Hazards MitigationLändtestrasse 20CH-2501 Biel

National Hydrological SurveyPapiermühlestrasse 172CH-3003 Berne