river structures health check - foundry weir, milfordindustries which predate strutt’s textile...

2018s0632 - Foundry Weir Assessment (Final) v3.0 i

River Structures Health Check - Foundry Weir, Milford

Final Report

March 2019

www.jbaconsulting.com

http://www.jbaconsulting.com/

2018s0632 - Foundry Weir Assessment (Final) v3.0 i

JBA Project Manager

Jeremy Benn

JBA Consulting

No.1 Broughton Park

Old Lane

Broughton

Skipton

North Yorkshire

BD23 3AQ

Revision History

Revision

Ref/Date

Amendments Issued to

Draft v1.0

November 2018

- Rachel Costigan,

DerwentWISE

Final Draft v2.0

December 2018

Edit to fish pass selection justification;

altered hydrology.

Rachel Costigan,

DerwentWISE

Final v3.0

11 March 2019

Minor re-structuring; increase in

emphasis on importance of cost/benefit

& technical performance. Incorporation

of Historical Assessment

Rachel Costigan,

DerwentWISE

Contract

This report describes work commissioned by Rachel Costigan on behalf of DerwentWISE, by a

letter dated 14th May 2018. Katie Burnham, Jon Whitmore and Jeremy Benn of JBA Consulting

carried out this work.

Prepared by .................................. Katie Burnham MSc BSc

Analyst

.................................................... Jon Whitmore BSC MIFM Prince 2

Technical Director

Reviewed by .................................. Jeremy Benn FREng MA MSc CEng CWEM FICE FCIWEM MASCE MIEI

Executive Chair

Purpose

This document has been prepared for the DerwentWISE Landscape Partnership which is hosted

by the Derbyshire Wildlife Trust. DerwentWISE is funded by the Heritage Fund and the 15

organisations within the Partnership.

Key members of the Partnership supporting this project are the Derbyshire Wildlife Trust, the

Environment Agency, the Derwent Valley Mills World Heritage Site, and Historic England (who

have also provided funding for this project).

Acknowledgements

Tania Pells and Rachel Costigan from the DerwentWISE Landscape Partnership provided

background information and facilitated the site visits with landowners. Ian Jackson and Adrian

Farmer were also an invaluable source of knowledge of the history of the weirs and the

associated mills. Jon Needle of Derwent Hydroelectric Power Limited and Julie Wozniczca of the

Trent Rivers Trust also provided useful background information.

2018s0632 - Foundry Weir Assessment (Final) v3.0 ii

Abutment

Upstreamcut-off

Downstreamcut-off

End sillStillingbasin

h

Apron

GlacisHydraulicjump

Erosionprotection

Weir crest

p

Upstream Water Level

Downstream Water Level

Drop inWaterLevel

Not to Scale

Carbon Footprint

A printed copy of the main text in this document will result in a carbon footprint of 58g

if 100% post-consumer recycled paper is used and 73g if primary-source paper is used.

These figures assume the report is printed in black and white on A4 paper and in duplex.

JBA is aiming to reduce its per capita carbon emissions.

Some Conventions

In river engineering, “left bank” and “right bank” are used to denote the position of a

feature as seen when looking downstream.

Distance across a river or weir is usually taken with the left bank as the reference point.

Where there are multiple components to a structure (such as piers) the convention is

to number these consecutively from the left bank.

“Tailwater” and “Headwater” refer to the downstream and upstream water levels on a

weir respectively.

Common terms used for a weir

2018s0632 - Foundry Weir Assessment (Final) v3.0 iii

Executive summary

JBA Consulting was commissioned to undertake an assessment of condition of Foundry

Weir on the River Derwent in Milford, as well as consider the feasibility of installation of

a fish pass and hydropower scheme at the site.

A condition assessment has previously been undertaken of this weir in 2016.1 It found

that all components of the weir and its adjacent structural elements were in a Fair or

Good condition – except for four sections of the iron weir crest plate/board and the

northern sluice gate (which is leaking and gradually deteriorating). There were mature

trees growing out of the river walls upstream of the northern sluice and also

downstream of the right weir abutment and in Pier No.5 of the former footbridge.

The southern (right bank) sluice gate which controls flow into the mill goyt and the

supply of water to the hydroelectric turbine downstream was refurbished in 2017 with

new timbers being installed and general repainting. As a result the condition grade of

this part of the weir structure has changed from 3 (Fair) to 1 (Very Good).

The condition of the weir has not materially changed since 2016. The mature trees and

saplings should be removed and the roots killed using an approved systemic weed killer.

The presence of an operational hydropower scheme downstream means that

opportunities for installation of a further scheme are likely to be limited (Section 5.4).

Several options for fish passage were considered; a Larinier fish pass with dedicated

eel pass facility within the left bank sluice channel and extending downstream from the

sluice gate (which would be removed) is recommended as the preferred option. A

prioritised series of costed actions are recommended (Section 6.2) to enable

recommendations to be taken forward to next stage design.

————————————————————————————————————————

1 Engineering Assessment of Foundry Weir, Milford. Report by JBA Consulting for DerwentWISE, December 2016.

2018s0632 - Foundry Weir Assessment (Final) v3.0 iv

Contents

1 Background 1 1.1 Introduction 1 1.2 Purpose of report 1

2 Historical Assessment 2 2.1 Derwent Valley Mills World Heritage Site 2 2.2 Heritage Designations 2 2.3 Assessment of Significance 2 2.4 Setting 3 2.5 Opportunities for Change without Damaging Sensitivities 3 2.6 Potential Interventions and Degree at Risk 3 2.7 Conclusions and Recommendations 3

3 Description of the weir 5 3.1 Location 5 3.2 Layout 6 3.3 Purpose of structure 8 3.4 Ownership 8 3.5 Ecology 8 3.6 Rights of way 8 3.7 Existing studies 8

4 Condition Assessment 9 4.1 Basis of assessment 9 4.2 Findings 9

5 Fish passage & hydropower 10 5.1 Approach 10 5.2 Hydrology 10 5.3 Flood risk 11 5.4 Hydropower feasibility 12 5.5 Fish pass feasibility 12 5.6 Design criteria 13

6 Conclusions and recommendations 16 6.1 Conclusions 16 6.2 Recommendations 16

Appendices

A Maps 17

B Options appraisal matrix 17

2018s0632 - Foundry Weir Assessment (Final) v3.0

1

1 Background

1.1 Introduction

Derbyshire Wildlife Trust hosts the DerwentWISE Landscape Partnership Project which

is seeking to safeguard and restore the unique landscape of the Lower Derwent Valley.

A key objective of the project is to understand risk to the Derwent Valley Mills World

Heritage Site associated with deterioration of condition of the historic mill weirs, and

to understand whether improvements to fish passage are feasible, and if so, what are

the preferred measures.

1.2 Purpose of report

The purpose of this report is to present an assessment feasibility of the

implementation of fish passage at Foundry Weir complex on the River Derwent north

of Milford. A condition assessment of Foundry Weir was previously completed by JBA

Consulting in 20162.

————————————————————————————————————————

2 JBA Consulting, 2016. "016s4759 - Foundry Weir Milford - Assessment (Final).docx


2

2 Heritage Assessment

This section is a precis from the Heritage Assessment report prepared by Trent and

Peak Archaeology for the DerwentWISE Partnership in March 2019.

2.1 Derwent Valley Mills World Heritage Site

In 2001 Derwent Valley Mills World Heritage Site was inscribed on the World Heritage

List by the United Nations Educational, Scientific and Cultural Organisation (UNESCO).

Sites included on the World Heritage List are protected under the UNESCO Convention

Concerning the Protection of the World Cultural and Natural Heritage 1972 of which

the UK Government is a signatory.

The statement of Outstanding Universal Value for the Derwent Valley Mills World

Heritage Site emphasises the relationship of the industrial buildings and their

associated settlements to the River Derwent, which provides a constant focal point

through the entirety of the World Heritage Site.

As a key component connecting the industrial buildings to the river, the weirs are at

the core of the Outstanding Universal Value of the World Heritage Site.

The management plan for the World Heritage Site has as its core mission:

To maintain the Outstanding Universal Value of the Derwent Valley Mills World

Heritage Site by protecting, conserving, presenting, enhancing and

transmitting its unique culture, heritage, economy and landscape in a

sustainable manner.

Any proposed works which have the potential to cause harm to the Outstanding

Universal Value of the World Heritage Site are unacceptable.

Any proposed works should utilise opportunities for intervention or change which do

not harm the Outstanding Universal Value of the World Heritage Site.

2.2 Heritage Designations

DERWENT VALLEY MILLS WORLD HERITAGE SITE List Entry No.: 1000100

Foundry Weir, Milford falls within the Derwent Valley Mills World Heritage Site. The

Statement of Outstanding Universal Value specifically highlights the importance of the

relationship of the industrial buildings and settlements to the river and topography. It

should therefore be considered that any scheme of works that impacts upon the weir

has the potential to affect the Outstanding Universal Value of the World Heritage site.

RETAINING WALLS TO WEIR ADJACENT TO GLOW WORM FOUNDRY List Entry No.

1087361

The retaining walls of the weir are Grade II* listed.

BELPER & MILFORD CONSERVATION AREA - Amber Valley Borough Council

The Belper & Milford Conservation Area covers the industrial structures and associated

settlements built to house the Strutt factory communities.

2.3 Assessment of Significance

Evidential Value

The Foundry Weir provides evidence of exploitation of the watercourse for a range of

industries which predate Strutt’s textile mills including corn processing and fulling.

The alteration of the structure to power Strutt’s mills provides evidence for the

evolution and expansion of the industrial settlement of Milford. The current weir was

redeveloped immediately after the construction of Belper Horseshoe weir, and also

included flood gates, showing the ongoing innovation of weir construction through the

Derwent valley.


3

As at other sites there is a high potential for survival of the remains of pre-industrial

structures such as mills, fishing weirs or crossing places.

Historical Value

The weir is associated with the later Strutt foundry and Milford Cotton Mills but

predates Strutt’s association with Milford.

Aesthetic Value

Foundry Weir was constructed to divert water to mills further downriver. However,

there are no substantial industrial buildings in the immediate vicinity and no direct

visual association with the mills further downriver.

More recent development on the left bank of the river, despite containing elements of

industrial reference in the architecture is in general unsympathetic and has had a

negative impact on the aesthetic value of the site.

Recent work has cleared out features such as the sluice gates, making the site more

visibly accessible.

Communal Value

The weir is accessible from a public right of way along the left bank of the river, and

its history and purpose is explained by a nearby information board. The site has

recently been cleared and enhanced by the local community and the site is regularly

visited as part of heritage tours.

2.4 Setting

The river is set within a largely ‘natural’ landscape with wooded slopes to the right

bank of the river, and osier beds on the left bank. The modern development on the

left bank has negatively impacted on the setting of the weir, reducing its contribution

to overall significance.

The setting of the weirs makes a substantial contribution to their aesthetic value and

therefore to their significance. Any alteration to the landscape surrounding the weir

has the potential to impact upon its significance and thereby on the Outstanding

Universal Value of the World Heritage Site.

2.5 Opportunities for Change without Damaging Sensitivities

Fish Passage

From a heritage perspective, existing sluice gates and bypass channels could

potentially be utilised to provide a fish passage without harming the Outstanding

Universal Value of the World Heritage Site. Existing watercourses run from upriver of

the duck-bill weirs to upriver of Foundry weir through the former mill site. These water

courses should be investigated as a potential fish passage.

2.6 Potential Interventions and Degree at Risk

The following potential intervention has been identified in this report:

Fish Passage within the left bank sluice channel and removal of sluice gate

The location of a fish passage within the left bank sluice channel would minimise the

impact on the aesthetic value of the weir. However, the removal of the sluice gate

would negatively impact on the evidential value of the structure. In addition, the sluice

gate has been proposed for repair by Derwent Hydro-electric in order to facilitate

maintenance of the weir. Maintenance and conservation of the sluice gate would add

to the integrity and authenticity of the Outstanding Universal Value of the World

Heritage Site and therefore should take precedence over its removal.

2.7 Conclusions and Recommendations


4

As the site lies both within the World Heritage Site and Belper & Milford Conservation

Area, where possible the preference should be for adaptation of existing water courses

to reduce the overall impact on the setting and aesthetic value of the sites, which will

in turn prevent harm to the Outstanding Universal Value of the World Heritage Site.

In order to reduce the impact on the aesthetic values of the structures the introduction

of new materials should be where possible using traditional techniques, and

complementary and sympathetic materials e.g. masonry rather than concrete. The

visual impact of any work should be minimised as far as possible to maintain the

authenticity of the Outstanding Universal Value.

Any impact on evidential value should be minimised, but where necessary should be

mitigated through a process of archaeological evaluation to gain as much information

on the material lost or altered during the works.

The Derwent Valley Mills World Heritage Site Research Framework provides a list of

key questions relevant to archaeological investigation of these sites:

2C – Investigate riverine locations for archaeological traces of early mills and other

historic water management assets

4C – Investigate the impact of natural resources and geography upon the Derwent

Valley textile industry and evaluate the distinctiveness of the Derwent’s resource

base

8D – Investigate the harnessing of hydropower from rivers in the Derwent

catchment and the reconciliation of competing interests

As specific designs are developed, a detailed Heritage Impact Assessment should take

place for each site. This will involve assessing the existing significance values (as

outlined in the criteria above) against the impact that the works will have on those

values. In each case the negative impact on the values should be minimised.

It is recommended that Heritage Impact Assessment takes place during the

development stage of any proposed works in coordination with the engineering group

or contractor to ensure that proposed designs do not harm the Outstanding Universal

Value of the World Heritage Site, and to minimise impact on the individual sites and

structures.

Larger programmes of maintenance and repair should also be subject to a process of

Heritage Impact Assessment.


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3 Description of the weir

3.1 Location

The foundry weir complex is located at OS NGR: SK 34861 45403 approximately 400m

upstream of Derby road bridge, and 500m upstream of Duckbill Weirs.

Figure 3.1: - Location of Foundry Weir

Contains Ordnance Survey data © Crown copyright and database right 2018.


6

3.2 Layout

The foundry weir has four main components (Figure 3.2), as detailed below.

Figure 3.2: - Components of Foundry Weir structure

1. A concave or ‘horseshoe’ masonry weir crest, with a wide (50m) shallow

sloping weir glacis. The crest extends for approximately 80m across the

channel.

2. Notch in the weir crest, as a result of damage to the weir.

1

2 3

4


7

3. Left bank sluice gate and mechanism, channel downstream of gate joins

back into main channel downstream of the weir apron.

4. Right bank sluice gate, leading into mill run that feds hydropower downstream at Duckbill Weirs.


8

3.3 Purpose of structure

The purpose of the structure historically would have been to maintain upstream water

levels in the mill leat downstream, fed by the right bank sluice gate. The historic water

wheel has since been removed and the leat now feds a new hydroturbine downstream

at Duckbill Weir.

3.4 Ownership

The ownership of the Weirs is unknown to the authors, but it is believed to be in

private ownership.

3.5 Ecology

The following statuary ecological designations are present within a 5 km radius of the

site3:

Allestree Park (LNR) – 4.3km south of the site

Duffield Millennium Meadow (LNR) – 2km south of the site

Belper Parks (LNR) – 1.5km north of the site

Kedleston Park (SSSI) – 4.8km south west of the site

3.6 Rights of way

There are no public rights of way adjacent to the river in the vicinity of the weir

complex4.

3.7 Existing studies

An outline design for a fish pass solution at this structure has already been produced5.

The design consists of a rock ramp extending downstream from the relic sluice on the

left bank.

Harton et al 2012 have undertaken an assessment of hydropower resource in the

Derwent Valley including the Foundry weir complex. The site includes an offtake for

an operational 180kW Francis turbine with a design flow of 6.3m3/s 6.

————————————————————————————————————————

3 Source: Statutory ecological designations from Magic https://magic.defra.gov.uk/MagicMap.aspx. Accessed 20th November 2018.

4 Source: Derbyshire County Council Mapping Portal [Accessed 26th Nov 18]. Available from: https://maps.derbyshire.gov.uk/connect/analyst/mobile/#/main?mapcfg=Ordnance_Survey_Maps

5 Fish passage in the Derwent Valley World Heritage Site. Presentation material authored by Trent Rivers Trust.

6 Harton, S., Chandler, P. & Beardmore, J., 2012. Estimate of Hydro Resource in the Derwent Valley. Report for Transition Belper.

https://magic.defra.gov.uk/MagicMap.aspx


9

4 Condition Assessment

A condition assessment has previously been undertaken of this weir in 2016.7

4.1 Basis of assessment

The condition assessment is based on the 2016 report plus a new visual inspection by

Jeremy Benn of the weir and its surroundings on 14 August 2018 (a day of relatively

low flow). Access to the structure other than by public rights of way wasn’t possible

and observations were limited to using binoculars from a position on the river bank.

The conclusions that are drawn must therefore be read in the context that there could

be damage or other defects to the weir that could not be detected without entering

the river and undertaking a probing survey.

Condition grades have been based on the widely used ‘Condition Assessment Manual’

published by the Environment Agency (March 2012 issue). The grades range from 1

(Very Good) to 5 (Very Poor), as shown below:

4.2 Findings

All components of the weir and its adjacent structural elements were in a Fair or Good

condition as in 2016 – except for four sections of the iron weir crest plate/board and

the northern sluice gate (which is leaking and gradually deteriorating). There were

mature trees growing out of the river walls upstream of the northern sluice and also

downstream of the right weir abutment and in Pier No.5 of the former footbridge.

The southern (right bank) sluice gate which controls flow into the mill goyt and the

supply of water to the hydroelectric turbine downstream was refurbished in 2017 with

new timbers being installed and general repainting. As a result the condition grade of

this part of the weir structure has changed from 3 (Fair) in December 2016 to 1 (Very

Good) today.

The condition of the weir has not materially changed since 2016. The mature trees

and saplings should be removed, and the roots killed using an approved systemic

weed killer.

————————————————————————————————————————

7 Engineering Assessment of Foundry Weir, Milford. Report by JBA Consulting for DerwentWISE, December 2016.

Grade Rating Description

1 Very Good Cosmetic defects that will have no effect on performance

2 Good Minor defects that will not reduce the overall performance of the asset

3 Fair Defects that could reduce performance of the asset

4 Poor Defects that would significantly reduce the performance of the asset. Further investigation needed

5 Very Poor Severe defects resulting in complete performance failure


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5 Fish passage & hydropower

5.1 Approach

Design criteria in the following documents have been used to produce a list of options

for fish passage measures at the site and to consider feasibility of installation of a

hydropower scheme:

Environment Agency Fish Pass Manual8. This reference provides a

framework for decision making on selecting suitable fish passage options;

this piece of work has used a combination of the framework listed in this

reference, as well as expert judgement to propose potential fish passage

solutions.

Environment Agency Guidance for run of river hydropower development9.

Environment Agency Guidance for run of river hydropower development -

Competing hydropower schemes10.

It should be noted at this point that all the fish pass solutions considered in this study

are likely to be expensive to construct (>£0.5M). Whilst the importance of minimising

the risk of any negative environmental impacts associated with the construction and

operation of any fish pass solution cannot be emphasised enough, particularly with

regard to the important heritage receptors in the immediate area of the weir,

construction costs of this magnitude mean that achievement of optimal fish passage

efficiency has to be a core design criteria; compromise to passage efficiency would

quickly render such significant expenditure non-cost beneficial.

5.2 Hydrology

There is an existing Environment Agency gauge located at Horseshoe Weir,

approximately 4.5km upstream of the site, although this is a level gauge only.

The nearest flow gauge downstream is at St Mary's, Derby, approximately 11.5 km

downstream (NGR 435390 336880 Station ID 4085). It is important to note however

that a number of inflows join the Derwent between Foundry weir and the St Mary's

gauging station, these include:

River Ecclesbourne 2.5km downstream

Bottle Brook 5.25km downstream

Boosemoor Brook 6km downstream

Dam Brook 9.3km downstream

The nearest flow gauge upstream is at Whatstandwell, approximately 11.5km

upstream (SK0331405456; ID 28117). It is important to note however that a number

of inflows join the Derwent between Foundry weir and the Whatstandwell gauge

however; these include:

Peatolts Brook, approximately 7km upstream.

Pendleton Brook, approximately 6km upstream.

River Amber, approximately 3.8km upstream. This inflow is substantial and drains a catchment area of approximately 140km2, compared to a

catchment area of the Whatstandwell gauge of approximately 755km2. A

flow gauge exists at Wingfield Park, approximately 5km upstream of the

confluence with the Derwent.

————————————————————————————————————————

8 Environment Agency Fish Pass Manual: Guidance Notes On The Legislation, Selection and Approval Of Fish Passes In England And Wales. 2010. Environment Agency, Bristol.

9 Guidance for run of river hydropower development. LIT 4122. 2017. Environment Agency, Bristol.

10 Guidance for run of river hydropower development - competing hydropower schemes. LIT 7517. 2017. Environment Agency, Bristol.


11

Coppice Brook, approximately 2.7km upstream.

Given the approximate scale of ungauged catchments between Foundry weir and the

Whatstandwell/Wingfield Park and St Marys/Duffield gauge options, it was decided

that the Whatstandwell/Wingfield Park option is most reflective of the situation at

Duckbill. Mean daily flow data for the full record was obtained from the National River

flow Archive (NRFA) for the Whatstandwell gauge (1st January 1997 to 30th

September 2017) and Wingfield Park (1st January 1997 to 30th September 2017) and

a flow duration curve constructed using that data - Figure 5.1.

Key flow statistics based on the Whatstandwell mean daily flow dataset are

summarised below and expressed as the percentage of time that flow is exceeded

at key flows relevant to the designed-for species of interest:

Flow exceeded 95% of the time (Q95) – 0.71m3/s

Average daily flow (Qmean) – 12.07 m3/s

Flow exceeded 10% of the time (Q10) – 26.83m3/s

It was beyond the scope of this study to refine flow data from the nearest gauge.

Figure 5.1 - Flow duration curve – Whatstandwell & Wingfield Park

5.3 Flood risk

A copy of the current flood model for the River Derwent was requested from, and

supplied by, the EA. The supplied model (linked 1D/2D) includes Foundry Weir. The

hydrology within the model has made an allowance of 20% above the 100-year return

period flood flow value to reflect the impacts of climate change.

Current climate change guidance11 specifies differing allowances for increases in flood

flow depending on the type of development; a hydropower scheme is likely to be

classed as Essential Infrastructure whereas a stand-alone fish pass scheme is likely

to be classed as Water-compatible Development. Assuming a design life of 30 years

for both a hydropower scheme and a fish pass scheme, and therefore the need to

consider the impacts of climate change into the 2050s, it is recommended that the

————————————————————————————————————————

11 Guidance - Flood Risk and Coastal Change. Gov.uk. 2014. [viewed 30th October 2018]. Available from

https://www.gov.uk/guidance/flood-risk-and-coastal-change#flood-zone-and-flood-risk-tables

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90 100

Flo

w (m

3/s

)

Percentage of time equalled or exceeded


12

following allowances are made above the 100-year flood flow to predict the flood risk

impacts arising from the scheme when considering the impacts of climate change:

standalone hydropower scheme - 30%

standalone fish pass scheme - 15%

5.4 Hydropower feasibility

Hands off flow

Hands off flow is a condition of any hydropower licence issued by the Environment

Agency (EA) which is the flow at which abstraction must stop, to maintain flow in the

river for the purposes of maintenance of natural ecological processes.

The EA confirms that the site is within Abstraction Sensitivity Band 3 - High Sensitivity

(A Lumsdon, pers comm). When considering the Q95/Qmean value is 0.3 (meaning

the river has a high base flow), Table A of the EA Guidance for run-of-river hydropower

development indicates that the EA would likely apply a Hands off Flow exceedance

value of Q97, limit turbine abstraction to Qmean (4.4m3/s) and the percentage of take

above HoF to 35%. It should be highlighted that the EA may be willing to licence a

variation from these guideline values if various conditions are met; only direct

engagement with the EA would clarify the likelihood of licensing such variation.

Flow split

Considering the above guideline scenario of a peak turbine abstraction of 4.4m3/s, the

minimum acceptable flow to any fish pass installed as part of any hydropower scheme

would likely be 0.4m3/s at Q95.

Other

The presence of an existing hydropower scheme offtake substantially complicates the

feasibility of installation of any subsequent hydropower scheme. It is highly likely that

there is insufficient, un-used water resource at the site to enable the development of

a second hydropower scheme without the need for substantial engagement and

negotiation with the operator of the existing scheme, Derwent Hydro.

In the unlikely event that the existing operator is willing to negotiate a re-

apportionment of the licensable water resource to enable establishment of a second

scheme, it is likely that the following issues will be key to enabling any scheme to

secure appropriate licences:

Co-location of two parallel schemes (which, to all intents and purposes,

would likely mean a single large scheme) will likely be looked on more

favourably than two independent schemes that are remote from each

other, i.e. one on the main river channel, one on the mill leat.

The schemes will need to ensure that any re-apportionment of flow does

not compromise achievement of Water Framework Directive objectives by

resulting in changes to the existing flow split that give rise to any depleted

reach that is more ecologically-constraining than current.

Early engagement with the EA would be essential in ensuring efficient progression and

delivery of any second hydropower scheme.

5.5 Fish pass feasibility

Options

Topographic survey has been supplied for the Foundry weir and associated sluice

structures at the site (Figure ). The glacis of the weir extends for approximately 50m,

and has an estimated overall height of up to 2m. Surveyed water levels provided on

the topographical data indicate a head of at approximately 2m on the day of survey.

The below option was considered but discounted on the grounds specified:


13

Any option associated with the right bank sluice, leading into the mill leat

as a result of both the existing hydropower scheme downstream and the

large culverted section of the leat itself presenting a behavioural barrier

to migration.

Options taken forward and considered in more detail are given below:

1. Larinier fish pass with dedicated eel pass facility within the left bank sluice

channel, and extending downstream from the sluice gate (which would be

removed)

2. Pool and traverse within the left bank sluice channel extending downstream

from the sluice gate (which would be removed)

3. Regularisation of left-hand extent of weir glacis downstream of left bank notch

and installation of low-cost baffle arrangement on resulting slope

4. Partial rock ramp on left side of the weir glacis downstream of left bank notch.

5.6 Design criteria

Impact on the following design criteria have been used in the appraisal of the above

2 options:

Designed-for species: engagement with local staff from the Fisheries

function of the EA (A Lumsdon, pers comm) confirms that the designed-for

species of any proposed fish passage measure are as follows:

o Atlantic Salmon

o Brown Trout and sea trout

o Coarse fish

o European eel

Hydromorphic condition

Engineering feasibility

Heritage features of interest

Landscape and visual impact

Stakeholder opinion

Public health and safety

Operational phase - maintenance

Appendix B presents a rapid assessment of the two options proposed above in the

context of the above design criteria. Each criterion is assigned a score using the

regime given in Error! Reference source not found. below.

Table 5.1 - Scoring of design criteria

Score Achievement of criteria

3 Significant positive impact (compared to existing)

2 Moderate positive impact

1 Minor positive impact

0 Neither positive or negative impact

-1 Minor negative impact

-2 Moderate negative impacts

-3 Significant negative impact


14

Figure 5.2: - Topographic survey at the site

Foundry weir

Left bank sluice – main channel

Right bank sluice – upstream mill leat


15


16

6 Conclusions and recommendations

6.1 Conclusions

Appendix B suggests that Option 1 - Larinier fish pass with dedicated eel pass facility

within the left bank sluice channel and extending downstream from the sluice gate

(which would be removed) is the recommended solution. The Grade II* listed status

of the weir and sluices and the location being within the boundary of the World

Heritage Site means that there is a necessity to consider in detail the compatibility of

the recommended solution and the heritage value of the structure to confirm

feasibility.

Although there are other statutory ecological designations within 5km of the structure

their proximity means they are unlikely to be impacted by implementation of the

recommended solution.

6.2 Recommendations

The promotor of any fish pass scheme is recommended to undertake the following

work, given in priority order, to inform next stage design of any fish passage and

hydropower scheme:

1. Engage with Derwent Hydro to determine feasibility of a renegotiation of their

existing abstraction licence.

2. Undertake a services search of the immediate area around the weir to identify

the presence of any services that may constrain or limit feasibility (approx.

£0.5k).

3. Commission a contractor to provide Early Contractor Involvement to inform

next stage feasibility/design (approx. £1.5k).

4. Produce a concept design of the proposed fish passage solution to determine

outline geometry to further inform feasibility (approx. 1k).

5. Scale the hydrology data from the St Marys gauge to determine a more

precise flow at the Foundry Weir site (approx. £1k)

6. Undertake a desktop geological study, or Phase 1 contaminated land study,

to determine bedrock/superficial geology and risk of accumulated

contaminated sediments upstream of the weir to inform construction

options/feasibility (approx. £1.5k).

7. Consider installing a water level data logger downstream of the weir to

complement the same available upstream, to inform design water levels for

any solution, or use the hydraulic model to determine approximate design

head (approx. £3k - £5k).

8. Undertake a Preliminary Ecological Appraisal to define the ecological baseline

in the area of potential works (approx. £2.5k).

Indicative design costs associated with the recommended option, excluding those

given above, are given below:

Outline design - £10,000

Detailed design - £75,000

Indicative constructed costs for the considered options are given in Appendix B.


17

Appendices

A Maps

B Options appraisal matrix

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