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Whitby Harbour Impoundment Study

Scarborough Borough Council

June 2011

Final Report

9W6668

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Document title Whitby Harbour Impoundment Study

Document short title Whitby Harbour Impoundment Study

Status Final Report

Date June 2011

Project name Whitby Harbour Impoundment Study

Project number 9W6668

Client Scarborough Borough Council

Reference 9W6668/R/303820/Newc

Marlborough House Marlborough Crescent Newcastle upon Tyne NE1 4EE United Kingdom

+44 (0)191 211 1300 Telephone Fax [email protected] E-mail www.royalhaskoning.com Internet

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Drafted by Paul Herickx

Checked by Paul Knight, Steve Cross

Date/initials check PK 22/07/2011

Approved by Nick Cooper

Date/initials approval NC 22/07/2011

Whitby Harbour Impoundment Study 9W6668/R/303820/Newc Final Report June 2011

SUMMARY Scarborough Borough Council has commissioned Royal Haskoning to investigate the potential of constructing an impoundment structure in the inner harbour at Whitby. The harbour has an existing low height rubble weir and the council wishes to construct a larger weir at an increased elevation to permanently impound water in the area upstream. The purpose for the impoundment is to provide additional berthings for small vessels, as a means of creating additional revenue for the local community through mooring charges and increased tourism related revenue. SBC estimate that revenue of £1,000 per annum per berth is typically generated for pontoon moorings. A fixed weir at +3.0mCD elevation, a half-tidal flap-gated weir at +3.5mCD elevation and a mitre gated weir with lock at +4.0mCD were investigated to ascertain the suitability of each weir type for vessel accessibility. It was calculated that the mitre gated weir with lock would allow access at all times between the upstream and downstream areas, the gated weir would provide access for over 10 hours per day on springs and neaps tides, but the fixed weir would provide access for less than 2 hours per day on springs tides and no access on neaps tides. As vessel accessibility is essential for the feasibility of the project, the mitre and flap gated weirs were the most suitable, with there being very little difference economically and environmentally between the two options. With the weir crest height established at +3.5/4.0mCD, the expected upstream impoundment area and number of berthings were calculated. It was found that up to 500 new berthings could be created in the impounded area using a similar pontoon layout to what is currently in use in the upper harbour, but the amount of new berthings would be significantly affected by ownership of and access to land. This figure could therefore be limited to 200 berthings if SBC are unable to obtain access to land beyond their current ownership. If chain moorings were to be used in the impounded area instead of pontoons, a single line of chains with boats moored either side tied fore and aft could create up to 250 new berths in the impounded area. Due to the nature of the proposed project, there are potential environmental considerations that will have a major impact on any/all necessary consents, licences and approvals. The River Esk has important species and habitats that are protected by legislation and it is possible that they may prohibit the construction of a new impoundment structure across the river. It is advised therefore that a consultation meeting with Natural England and the Environment Agency is conducted as the next stage of the project, to determine their position regarding the proposed options for the impoundment weir. This study indicates that it is feasible to construct an impoundment structure in the inner harbour of Whitby, which allows a significant number of new berthings to be created. To develop the feasibility of the scheme further there is a requirement for more detailed information to be obtained, such as producing a business case, establishing berthing demand and further investigation of hydro power generation potential. Pontoon moorings have the potential to generate more income, but also present additional difficulties in terms of land ownership for access and egress and installation. Whereas chain moorings will cause no such issues.


CONTENTS Page

1 BACKGROUND................................................................................................................ 1

2 DESCRIPTION ................................................................................................................. 1

3 KEY POINTS FROM THE SITE VISIT ............................................................................. 3

4 ENVIRONMENTAL ISSUES & FLOOD RISK ISSUES.................................................... 4 4.2.1 Siltation ................................................................................................................. 5 4.2.2 Water Quality ........................................................................................................ 5 4.2.3 Loss of BAP priority habitats................................................................................. 6 4.2.4 Fish Migration........................................................................................................ 6 4.2.5 Water Framework Directive .................................................................................. 6 4.2.6 Flood Risk Considerations .................................................................................... 7

5 OPTIONS FOR IMPOUNDING STRUCTURE................................................................. 8 5.1.1 Fixed Level Weir ................................................................................................... 8 5.1.2 Half-tidal Flap-gated Weir ..................................................................................... 9 5.1.3 Mitre Gated Weir with Lock................................................................................. 10

6 MOORING ANALYSIS ................................................................................................... 14

7 OTHER OPPORTUNITIES & ISSUES........................................................................... 19

8 RECOMMENDATIONS FOR FURTHER STUDIES ...................................................... 20

9 CONCLUSIONS ............................................................................................................. 22

APPENDICES ............................................................................................................................

APPENDIX A..............................................................................................................................

APPENDIX B..............................................................................................................................

APPENDIX C .............................................................................................................................

APPENDIX D .............................................................................................................................

Whitby Harbour Impoundment Study 9W6668/R/303820/Newc Final Report - 1 - June 2011

1 BACKGROUND

Scarborough Borough Council (SBC) is investigating the feasibility of impounding the River Esk in Whitby harbour. The council wishes to increase the number of moorings for boats on the River Esk, as a means of increasing revenue and generally benefiting the town. There is an established harbour on the River Esk at Whitby, but the tidal cycles prevent navigation further up the watercourse than approximately 1.5km from the piers. The impoundment of the river will allow navigation further upstream at times of low tide and provide moorings for more boats and, therefore, increase revenue for the council from additional annual mooring fees and increased visitor numbers.

2 DESCRIPTION

The proposed scheme involves the construction of a weir across the estuary, in the harbour, to impound water upstream of the weir to a level that is suitable to provide new moorings for small boats. As the harbour estuary has a springs tidal range of more than 5 metres, the weir is to be accessible for long enough periods during each day for boats to be able to cross the weir into the impounded area for mooring. The proposed location of the weir is at the site of an existing structure in the River Esk that has previously been a small weir which carried services across the river (most notably an electrical supply from the substation located at the top of the slipway). Services now cross the river via the high level road bridge (Whitby Bridge) and therefore this existing gabion/rubble weir is now redundant. It is understood that the dead service cables are still located within the weir and that rubble has been tipped on top of the cables when they became exposed. It should also be noted that this existing structure is located partially on the line of an ancient ford. It is believed that the ford ran from the slipway on the east bank, towards what is now Coates Marine boat yard on the west bank. Downstream of the proposed location lie boat slipways on both banks and large vessels that would be unable to cross the proposed new weir, therefore, this location for the weir has been chosen to prevent access problems occurring downstream. As the purpose of the proposed scheme is to provide additional mooring opportunities, this study also investigates the potential number of additional berths that may be created through the construction of the weir and introduces the constraints and risks that may be encountered with the scheme overall.

Proposed weir location

Expected extent of

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Potential new berthings

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Whitby Harbour ImpoundmentStudy


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3 KEY POINTS FROM THE SITE VISIT

A site visit was undertaken on the 29th March 2011 to ascertain the main focus of the scheme and to investigate any potential issues at the location. A memo is attached as Appendix A which includes all of the aspects of the site visit, but the key points for this pre-feasibility study are introduced here.

• The proposed weir is at the location of a smaller existing weir upstream of the existing slipways. There is also an old Roman ford that runs diagonally from Coates Marine Boat Yard on the left bank to the opposite bank, which would be partly in the location of the proposed weir, that may require some archaeological analysis before any project could commence.

• The draft of the small yachts with a keel is normally around 2m and the harbours dredger and split hopper draw 2.1m, therefore, a minimum draft of 2.5m is necessary to cross the weir.

• The dredger and hopper have a beam of 8m, as well as fenders, so any weir gate would need to be 10m wide. This would also suit small catamarans which are in the region of 6 - 8m wide normally.

• The bed level at the weir both upstream and downstream is about +1.0m CD • Land access is presently only available from just upstream of the weir, by Coates

Marine Service Yard, and access to any additional moorings will need to be further investigated. A fixed walkway possibly 2m wide at +6.0mCD would be required with access bridges down to the pontoons if the only access is from near Coates Marine.

• There may be environmental considerations with permanent impoundment of the watercourse.

• The study will need to investigate the potential of installing a weir with a fixed sill level, as well as a weir with a gated system, for access to the impounded water.

• Originally electricity cables from a sub-station on the right bank ran through the weir but these are now disused and have been covered by large rocks rather than excavated and removed. The rocks and existing weir can be seen in Photo 1 below.

Photo 1: Left Bank of Proposed Weir Site When Looking Downstream


4 ENVIRONMENTAL ISSUES & FLOOD RISK ISSUES

There are often many environmental issues that require consideration when a watercourse is to be modified. The following information provides an overview of the baseline conditions and environmental constraints that are present at the River Esk from Whitby to the upper tidal limit at Ruswarp Weir. Appendix B of this report contains the full details of the environmental issues that have been highlighted at this stage of the study process.

4.1 Baseline Environment

The River Esk is tidal within the site of the proposed impoundment, with a large weir (Ruswarp Weir) 3.8km from the estuary mouth forming the upper tidal limit. The marine biology of the estuary includes numerous worms including ragworm and species of polychaetes, oligochaetes and enchytraeid oligochaetes, as well as the amphipod Corophium volutator. Whitby is part of the Scarborough Biodiversity Action Plan (BAP), which was adopted in 2005 and covers the same area as the Borough Local Plan, and includes the priority habitats of mudflats and saltmarsh. Mudflats are present between the disused Larpool viaduct and Whitby Bridge, within the mouth of the estuary and throughout the harbour, and have a high biological productivity which, together with other intertidal habitats, supports large numbers of predatory birds and fish. Saltmarsh is present as a tiny fragment near California Beck and will be in the proposed impounded area. The River Esk is principally a salmonid river, supporting healthy stocks of resident brown trout (Salmo trutta), as well as migratory populations of salmon (Salmo salar) and sea trout (Salmo trutta). The upstream migration of salmon (spring fish and grilse) is reported to occur twice, during spring and summer/autumn respectively, with sea trout migration upstream during the summer months. In addition, smolt trapping and electro-fishing undertaken by the Environment Agency has identified low numbers of European eel (Anguilla anguilla), river lamprey (Lampetra fluvialis), tench (Tinca tinca), gudgeon (Gobio gobio) and grayling (Thymallus thymallus). The upper reaches of the River Esk contain a small proportion of Freshwater Pearl Mussel, designated as a nationally important species, and there is an aim to improve the habitat and restore pearl mussel populations whilst also increasing the population of salmon and trout in the River Esk catchment. The Environment Agency monitors water quality within the River Esk at Ruswarp, upstream of the proposed impoundment structure. The water quality results show very low levels of nitrates and phosphates, with biological and chemical parameters being very good and good respectively. The Water Framework Directive (WFD) establishes a legal framework to protect and restore clean water across Europe and ensure its long-term, sustainable use. Permission must be sought from the Environment Agency to ensure that any proposed development is in compliance with the WFD, with no deterioration to the existing status of the water body. The proposed site for the impoundment structure falls within the ESK (E) water body (GB510402703400). The environmental objectives of the WFD applicable to the proposals fall under Article 4 (1) of the Directive, which states:


“Member States shall protect, enhance and restore all bodies of surface water, subject to the application of subparagraph (iii) for artificial and heavily modified bodies of water, with the aim of achieving good surface water status at the latest 15 years after the date of entry into the force of this Directive. Information on the ESK (E) water body is provided below:

Water body ID GB510402703400

Water body name ESK (E)

Current Overall Status Moderate

Status Objective

(Overall)

Good by 2027

Status Objective(s) Good Ecological Potential by 2027

Hydro morphological

Designation

Heavily Modified

Ecological Potential Moderate

Biological elements Invertebrates: Moderate (Uncertain); Predicted Status by 2015 Moderate

Fish: Moderate (Uncertain); Predicted Status by 2015 Moderate

Hydro morphological

supporting conditions

Tidal regime – Freshwater flow: Currently Supports Good, Predicted Status by 2015

Supports Good

Element Current status Predicted status

by 2015

Justification for not

achieving good status

by 2015

Dissolved

inorganic Nitrogen

Moderate

(Uncertain)

Moderate

Supporting elements

Dissolved oxygen High High

Disproportionately

expensive (N1a)

The information above displays that the water body is not currently at Good Ecological Potential due to factors which affect the biological quality elements. The hydro morphology is currently classified as Good and any scheme within this water body should try to avoid deterioration in the status of this element. No specific mitigation measures are provided for this water body within Appendix B of the Humber River Basin Management Plan.

4.2 Environmental Constraints

4.2.1 Siltation

The impoundment structure is likely to result in significant sediment deposition upstream of the structure, which is likely to reduce channel capacity without regular maintenance dredging. Maintenance dredging has the potential to increase the total suspended solid concentrations in the water column, which is likely to impact upon the fish populations within the river. There are also likely to be further implications with regard to water quality due to loss of tidal flushing of the impounded ‘basin’, and potential for smothering of gravel substrate on the river bed during sediment deposition resulting from the impoundment.

4.2.2 Water Quality

Impoundment of the watercourse has the potential to cause stratification between fresh water and denser saline waters. This may lead to isolation of a lower layer of saline water from sources of re-oxygenation, and extend contact with sediments of high oxygen demand, creating an anoxic layer at depth. As freshwater is prevented from reaching the underlying


sediments, nitrates in the water are not removed, and the potential for eutrophication (nutriment enrichment) is increased. This in turn may encourage the growth of green algae, such as Enteromorpha spp., which in some cases can lead to a reduced amenity value in such impounded areas. The proposed impoundment is also likely to lead to an indirect impact upon the water quality through the construction of moorings upstream. Storage of boats within moorings has the potential to result in decreased water quality as a result of leakages and spills from the vessels, which could adversely impact upon the aquatic ecology.

4.2.3 Loss of BAP priority habitats

One of the UK BAP objectives is that there should be no further net loss of intertidal habitats such as coastal saltmarsh or mudflat. The construction of the impoundment structure would result in the loss of both of these priority habitats along the River Esk due to the artificial increase in the water level during low tide and reduction in tidal fluctuation (and hence saline influence). Mudflats upstream of the proposed impoundment structure currently represent a feeding resource for birds and estuarine fish species, which will be lost through permanent inundation. In addition, the loss of regular tidal inundation and associated saline influence is likely to result in the loss of existing saltmarsh vegetation, leading to the out-competing of salt tolerant species (such as sea lavender) by more vigorous terrestrial species. It is considered that the loss of priority habitat which is of high nature conservation value would be a relatively major constraint to this development.

4.2.4 Fish Migration

The installation of an impoundment structure has the potential to impact upon the success of fish migration during low tide. The literature review undertaken for this assessment has identified the importance of the River Esk as a salmonid fisheries resource. The construction of the proposed impoundment structure is likely to act as a barrier to upstream fish migration during low tide; therefore this structure is likely to cause a delay in the upstream migration of fish. It is considered that a suitable fish pass would be required to allow the free passage of salmonids and other species within the river during all water level conditions. The upstream migration of salmonids during spring, summer and autumn also represents a constraint on any construction works within the channel due to potential disturbance to their migration. The Environment Agency may apply restrictions to works during certain tidal states between the months of March to November. It could be expected that such restrictions may apply to the proposed works (especially if piling works are proposed), though the actual limitations applied would be likely to depend upon those construction methodologies proposed.

4.2.5 Water Framework Directive

It is considered that the proposed impoundment works have the potential to prevent Good Ecological Potential being reached by the target date of 2027, even if they do not cause deterioration in status. The proposed works are unlikely to qualify for an exemption under Article 4.7, because the construction of an impoundment structure within the River Esk is not of overriding public interest. In addition, the construction of the impoundment structure has


the potential to cause deterioration in the current status of the ‘Tidal regime – Freshwater flow’ supporting condition, which could prevent the water body reaching its target of Good ecological potential by 2027. There is a need for further investigations and input into the detailed design process to ensure that:

• Any potential impacts are fully assessed; • The structure is designed to minimise any impacts: • Any mitigation measures that are necessary are included in the scheme design.

It is considered that the requirements of the WFD are not ‘show-stoppers’ at this stage, as long as suitable mitigation measures can be incorporated into the design to prevent the deterioration in the status of the hydro morphological quality elements and prevention of the water body reaching Good Ecological Potential.

4.2.6 Flood Risk Considerations

The construction of a weir some 3.5m above the existing upstream bed level, will increase the fluvial flood risk for the Esk Valley. The impoundment effect of the weir is estimated to be as far reaching as Ruswarp, beyond this there is likely to be a limited impact on fluvial flood risk as it is beyond the tail-water impact area of the weir and therefore the level of risk is not increased. The extent and impact of this increased flood risk is not known at this stage and further investigations would be required to determine the change in the floodable area, the onset of changes in the flood regime and the affected areas. The impact of these changes to the local infrastructure assets, residential and commercial properties and potential environmental risk need to be evaluated and the outputs used to influence the design of a potential weir. The weir design could include an integrated flood gate which could be operated automatically, triggered by changes in upstream water levels, to maximise flows passing the structure and reduce the upstream flood risk. Such a structure has not been allowed for in the cost estimate. Alternatively, the weir shape can be amended to maximise the length of the weir and therefore optimise the discharge capacity, for example constructing a horseshoe shaped weir. Maximising the weir crest length will reduce the upstream flood risk. Consideration of the plan shape of the weir and the weir cross sectional profile would be developed during the outline design phase should the project progress.


5 OPTIONS FOR IMPOUNDING STRUCTURE

There are a variety of impounding structures that could be used for the weir, including a fixed weir, half tide gate, flap gate, mitre gates and sector gates amongst others. Each type of structure has advantages and disadvantages and, from the site visit, it was understood that Scarborough Borough Council would particularly like investigation into the construction of a fixed weir. There are many factors for consideration regarding the weir and gate types, with their main advantages and disadvantages outlined here.

5.1 Options:

5.1.1 Fixed Level Weir

This is the simplest option and impounds the water at least construction cost, however, the draft available to boats upstream of the weir would be severely restricted. The impounded level and weir crest would need to be at a maximum level of +3.0mCD to allow passage across the weir at high tides, causing the depth of water upstream of the weir to be less than 2m. At MHWN tides the depth across the weir would only be 1.3m, preventing access and exit to boats of more than 1m draft. If the crest is lower than +3.0mCD the impounded water depth becomes minimal and the number of possible berths is significantly restricted. To construct the fixed level weir, sheet piles are required to form a cut off to resist the differential head across the structure. A single row of piles would achieve this but two rows of piles would have the advantage of containing the fill and providing a cofferdam to construct the concrete slab unaffected by tides. The piles would also support the concrete slab, avoiding settlement in the soft clay layer present at the proposed site. Furthermore, a crane would also be able to travel on steel platforms on top of the piles, avoiding the use of floating plant, if this was preferred by the Contractor. The existing weir at the proposed site is formed from gabion baskets containing locally sourced stone and it would need to be excavated on the line of the sheet piles. The excavated material could be processed and then reused as fill between the piles for the new weir. The construction method for the fixed weir and the weir without lock are the same, with the exception of the installation of the particular gate type for each option which would need further investigation dependent on the type of gate chosen. Due to the environmental considerations outlined previously, a fish pass and a sediment control system would need to be incorporated into the design of the weir. To mitigate against these potential issues, low level pipes with penstocks could be provided through the weir, similarly to an ‘Irish Ford’. The pipes will help to flush the silt past the weir, can be designed to assist fish migration and may also provide a possible footpath across the weir as the crest would be dry for up to 5 hours either side of low water. A footpath at the crest level would be potentially dangerous however because of mud and marine growth. Therefore, if a footpath is desired at the site as an additional means of access between the two parts of the town, a high level footpath and cycle way could be incorporated. This would be undertaken using spans of 10 -12m supported by tubular piles set in the weir, with the wide spans minimising the possibility of floating debris blocking the weir. The potential corrosion of the sheet piles would either be combated by paint and a sacrificial anode cathodic protection system, or by using precast facing units to the pier and filling between the piles and facing unit with concrete.


The order of magnitude construction cost for Option 1 is £1,689,700 (Excl. VAT) with a further £99,994 (Excl. VAT) if the footbridge was to be constructed. The full breakdown of the costs can be found in Appendix D.

5.1.2 Half-tidal Flap-gated Weir

A half-tidal flap-gated weir increases the permissible draft of the boats able to use the facility and impounds the water upstream of the weir from approximately mid tide and below. The gate prevents the berths drying out and significantly increases the time available for access to the inner harbour over the upper part of the tidal cycle. The half-tidal flap gate can be controlled automatically and is the most simple and cost effective type of gate. The access times will depend on the impounded level chosen and on the tidal regime (i.e. neaps or springs) but, if the impounded level and weir crest were set at +3.5mCD, the depth of water upstream of the weir would be up to 2.5m. This would mean that at MHWN tides the depth through the structure would be 3.3m, assuming bed level is 1.0m, so access for a 2m draft boat requiring 2.5m water depth would be possible for 3hrs before MHWN and 2.5hrs before MHWS. These values have been calculated with the sill level for the open gate at +0.5mCD. The timing of closing the gate would require further study but it might be possible to leave this until the water level had dropped to near weir crest level of +3.5mCD giving a total open time of 5-6 hours per high water cycle. A flap gate actuated by hydraulic cylinder(s) would normally be provided for this type of installation as a flap gate is economic and works well in this situation. It can be operated automatically by providing stilling wells which will constantly monitor the water levels upstream and downstream of the gate. The flap gate will be housed in a recess in the sill when in the open position. Silt is likely to collect in the recess and a jetting system and/or maintenance regime may be required with the hydraulic power pack and water pumps potentially located on the river bank in a small building. The construction methods and environmental considerations are the same as for Option 1, with the exception that the crest of the weir would be dry for up to 6 hours either side of low water and that a method of crossing the flap gate recess would also be required if the crest was used as a footpath. The order of magnitude construction cost for this option is £ 2, 754,075 (Excl. VAT) with a further £99,994 (Excl. VAT) if the footbridge is to be constructed and £62,500 (Excl. VAT) for the lifting section of the flap gate. The full breakdown of the costs can be found in Appendix D. Mitre gates or Sector gates could be used instead of a flap gate but they would be installed at the same crest heights as the flap gate, i.e. +3.5mCD and, therefore, only the variation between the gate types is described here. Mitre gates could be considered, but the meeting faces have to be constructed with considerable precision to maintain their structural integrity and produce good seals. Mitre gates are also more difficult to control in the tidal flows when opening and closing, and will be susceptible to the accumulation of silt and debris on the sill. The operating rams for the gates would need to be positioned above water level, therefore, mitre gates would be less


suitable for use in an overtopping mode and they are a more expensive option than the flap gates. The construction methods and environmental considerations are the same as for Option 1, with the exception that the crest of the weir would be dry for up to 6 hours either side of low water and that a method of crossing the mitre gate recess would also be required if the weir was used as a footpath. Due to the increased costs normally associated with installing mitre gates over flap gates a detailed breakdown of the construction costs for their installation has not been undertaken, however, the cost would be more than for installing the flap gates. Vertically hinged sector gates will be less economic than flap or mitre gates and will require extensive civil works to house the gates in the open position. Neither sector gates nor mitre gates are generally used in an overtopping mode. The construction methods and environmental considerations are the same as for Option 1, with the exception that the crest of the weir would be dry for up to 6 hours either side of low water and that a method of crossing the sector gate would also be required if the weir was used as a footpath. Due to the increased costs normally associated with installing sector gates over flap gates a detailed breakdown of the construction costs for their installation has not been undertaken, however, the cost would be more than for installing the flap gates.

5.1.3 Mitre Gated Weir with Lock

A third option for the impounding structure is to construct a mitre-gated weir with lock. The base of the lock would be excavated to -2.0mCD to allow access, both upstream and downstream, across the weir at anytime. With the lowest Mean High Water Neaps (MHWN) tide occurring at +4.3mCD, a crest height of +4.0mCD would be used as it allows partial water passage across the face of the weir for a proportion of each day. To reduce construction costs the main length of the weir would be a single line of steel sheet piles, a concrete cap and facing to bed level would be incorporated to reduce corrosion rates. The piles would be driven downstream of the existing rubble weir. The most significant difference between this option and the previous 2 options is the construction of the lock with mitre gates at either end. The lock will need to be large enough to allow larger boats to be able to use it for passage and, therefore, an internal ‘clear’ space of 20m length by 10m width is required. Similarly, to reduce construction costs on the length of the lock, the passage of the dredger upstream of the weir could only be achieved at times of high tide as the current dredger is longer than 20m. Also, floating plant would be necessary for the construction of this option as it would not be possible to use a crane across the rows of piles as proposed in the previous options. The environmental considerations are as for Option 1, with the possibility of incorporating a notch in the crest of the weir at +3.7mCD to improve fish passage, in addition to the requirement for an integrated fish-pass. The order of magnitude construction cost for this option is £ 2,950,313 (Excl. VAT) with a further £99,994 (Excl. VAT) if the footbridge is to be constructed. The full breakdown of the costs can be found in Appendix D.


5.2 Impoundment Options Conclusion:

Options 2 and 3, the half-tidal flap-gated weir and the mitre gates with lock, are the most suitable options for the impoundment structure based on the current information available. The fixed weir has the lowest construction costs but, as shown by Graphs 1 and 2 below, the accessibility of the vessels over the fixed crest is minimal in comparison to the half-tidal flap gate (Option 3 has not been included as access is available for 24 hours per day through the lock) and it is likely to create significant issues with accessing the berths upstream of the weir. Concept designs are included below for the proposed impoundment structures to illustrate the key features of Options 1, 2 and 3. Outline sketches for Option 3 are also included as Appendix C..

Total Hours Access at Maximum/Minimum Tides

0123456789

101112

Spring Tides With FlapGate

Neap Tides With FlapGate

Spring Tides With FixedWeir

Weir and Tide Type

Num

ber

of H

ours

Total Hours Access Per Day

Graph 1: Total hours of vessel accessibility across weir during one standardised tidal cycle

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les


6 MOORING ANALYSIS

With the types of impoundment structure established in accordance with the financial and environmental considerations of the scheme, it is then possible to quantify the number of additional berths that may be created. As stated earlier, SBC presently only have access to any additional berths from the corner of Coates Marine Yard within Whitby harbour. Although it is feasible to use this location for access to a number of the pontoons that could be constructed in the impounded area, it is deemed to be unfeasible to use this location for access to all of the berths. In light of this, Figures 2, 3 and 4 below have been produced to show the potential impoundment extent, access points and number of additional berths that could be created if the half-tidal flap-gated weir at +3.5mCD or mitre-gated lock at +4.0mCD crest height were to be constructed. If the study were to progress to the next stage a bathymetric survey of the River Esk would be required, from the existing weir at Whitby harbour to Ruswarp Weir, to better understand the bed levels. Therefore, in the absence of this study, existing LiDAR data has been used to calculate the expected extent of the new berthing capability of the impounded river. Further investigation is required to establish the feasibility of all of the access points as they may require permissions to be gained from the relevant landowners, such as the rail company, boat shed owners and the housing complex owner(s). It has also been assumed that SBC would have the land permits to the footpath on the east bank for access purposes. A preliminary construction design has been developed for accessing the pontoons from the corner of Coates Marine Service Yard. The design involves the construction of a fixed walkway adjacent to the existing stone walled bank possibly 2m wide and at +6.0mCD, with access bridges down to the pontoons. It is estimated that up to 200 berths could be accessed from this location using this method, assuming that boats will moor up to four deep (as per current downstream usage). It is possible that private landowners may be interested in creating or purchasing pontoons if the impounded water level was to extend to the point that has been estimated. This includes the boat sheds on the west bank and the housing estate on the east bank. This is therefore a potential source of funding contributions. As a means to reducing the overall scheme costs and to mitigate against potential access issues, it is also possible to incorporate a chain mooring system within the upstream impounded area. Steel tubular piles are driven into the bed at regular points along the entire length of the impounded area that is suitable for moorings, i.e. as far as the draft depth will allow boats to be moored, and a chain is fed between each of the piles. Boats then moor themselves fore and aft to the chains (to prevent movement into the main channel with the changing tides) and use tenders to access mooring points adjacent to the slipways or other access points. It is to be noted that, whilst chain moorings will cost less to establish than the construction of pontoons, it is likely that the mooring fees that can be charged will be less and therefore the potential income will be reduced. It is estimated that, with a 10m length allowed per boat per berth, up to 250 boats could be moored using the chain mooring system. As stated in the environmental issues section, siltation of the impounded river is a factor for consideration in the feasibility of the scheme. The flap gate has been designed to allow the passage of Whitby harbour’s split hopper and dredger, which has a draft of 2.1m and a width of 8m, and regular maintenance dredging of the impounded area will be required to maintain the required draft levels for vessel access. The mitre gate and lock would require the split hopper and dredger to access the impounded area only at times of high tide, when both lock gates can be opened at the same time, and it has been calculated that they would have approximately 2 hours for disposal under these conditions.


As shown by Figure 4, it has been estimated that the total number of additional mooring points that could be created by impounding the River Esk at +3.5mCD could be as high as 500. However, the number of mooring points is significantly affected by the availability of access to the pontoons from the banks and, therefore, the ability to obtain the permissions or interest of the relevant landowners. If the maximum number of pontoons were to be constructed in the impounded area and an annual fee of £1,000 were to be charged per berth, then an annual income of £500k would be brought into the local community via Scarborough Borough Council and the local landowners. However, due to access issues, it may be likely that berthings are limited to the area immediately adjacent to Coates Marine, which would allow up to 200 new moorings to be achieved and a revenue of approximately £200k per annum generated. Given that the estimated construction cost for both weir and gate options is approximately £3M and further appraisal, investigation, consultation, funding applications, licensing consents and planning applications are likely to have an upper range cost of £400k, a total project cost estimate of £3.4M can be used to assess the payback period. If access is only available from the corner of Coates Marine Boat Yard, as stated on the site visit by SBC, then it has been estimated that an additional 200 pontoon berths could be created from this access point. If 200 berths were constructed then a payback period of approximately 17 years is calculated. It is important to note that these calculated payback periods do not account for the construction, operation and maintenance of the new pontoons or chain moorings, as well as any additional dredging of the impounded area. Further studies will need to be conducted to establish the extent that these would extend the payback period of the proposed project but, as Whitby already owns a dredger and hopper, it is envisaged that the extension would be relatively small, potentially limited to staff costs only.

Figure:

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Whitby Harbour Impoundment Study


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7 OTHER OPPORTUNITIES & ISSUES

7.1 Hydro Power Facilities

Archimedes screws and low head turbines have been installed at numerous weirs across the UK and also within tidal areas. Further investigation would be required to establish the feasibility of installing a hydro power scheme at the location, but a turbine(s) installed at bed level that would be able to generate power as the tide enters the estuary and as it retreats is likely to be financially viable. Without accurately establishing the volumes of water that would be passing through the turbine(s) it is not possible to calculate the amount of power and, consequently, revenue that could be generated. However, river-based hydro power schemes with a similar head of ~3m can generate up to £25,000 pa in revenue per turbine.

7.2 Fish-pass

Due to the environmental issues associated with the proposed scheme, as stated previously, a fish-pass would need to be incorporated into the design of any structure that is used to impound the River Esk in Whitby. The ‘Irish Ford’ design, with low pipes in the structure could potentially be designed to allow fish to pass through when tide levels are below the weir crest, but it is likely that an additional fish pass design will need to be included.

7.3 Other Leisure/Recreation Amenity

After careful consideration it has been concluded that the creation of other leisure/recreation amenities is minimal if the water is to be impounded at the designed height of +3.5mCD. Whilst the impounded area would be navigable, the area is intended for the mooring of additional vessels and, consequently, the additional area created would be largely restricted by the new pontoons. Similarly, the pontoons would create additional areas for fishing (and there may be an increase in fish in the impounded area during low tides) but the presence of the pontoons would again limit the area in which new fishing locations would be possible.

7.4 Other Revenue Creation Opportunities

The creation of a navigable watercourse length from Ruswarp to Whitby may provide the opportunity for a River Taxi service, or commercial boat trips that could be operated on a concession basis from SBC.

7.5 New River Crossings

The proposed weir could incorporate a high level pedestrian and cycle crossing that would create a new safe and interesting access route that would allow the creation of new published footpaths and cycle-routes and generate new pedestrian areas for the town. This also creates the potential for alternative funding contributions. The weir location could be used to accommodate a highway crossing which would provide an alternative route to the historic swing-bridge. This would allow traffic to be diverted away from the swing-bridge should repairs be required, or allow traffic to directly access this area of the town and reduce congestion at the swing bridge. This potentially creates alternative funding opportunities.


8 RECOMMENDATIONS FOR FURTHER STUDIES

8.1 Environmental Consultation Meeting

The assessment has shown that it is technically feasible to create a significant number of new moorings as a result of the impoundment weir. Further technical and environmental investigations would need to be carried out to allow progression of the scheme from its initial feasibility study. Regardless of the economic and technical feasibility of this proposal, Royal Haskoning considers that the key issue that will determine the progression of the scheme is its environmental impact. The impoundment of the watercourse will result in the loss of tidal mud flats/banks and could potential limit the migration/passage of fish. These issues could prevent the project progressing. Royal Haskoning therefore recommends that a consultation meeting is held with Natural England and the Environment Agency to discuss the proposed options, the mitigation works that could be carried out and to ascertain their opinion as to whether the environmental issues are such that they would not grant permissions/consents to allow its construction. Royal Haskoning recommend that simple sketches and plans are developed for this meeting and possibly a 3D graphic visualisation. The total costs for this meeting should not exceed £1,000. Royal Haskoning do not recommend any further studies be carried out prior to this consultation meeting.

8.2 Environmental Reporting

Initial Environmental Screening and Scoping Surveys (and Reports) would need to be carried out with statutory consultees and local interest groups (stakeholders). This is likely to cost £10k (dependent upon extent of Scoping work required). Dependent upon the findings of the above, the Environmental Statement and Environmental Impact Assessment are likely to cost in the region of £45k to £60k.

8.3 Outline & Detailed Design Development

Numerous activities will be required to progress the project to the Construction stage. These include;

• Site Investigation (including Ground Investigation) • Topographic Survey • Bathymetric Survey • Utilities Searches • Analysis of Berth Demand • Further development of Business Case • Investigation of Alternative Funding Opportunities • Further assessment of Hydro Power scheme potential • Appointment of Construction Design & Management Controller (CDMC) and services to

advise the Client • Further Option Development leading to selection of Preferred Option • Consultation (statutory and others) • Environmental Impact Assessment and Environmental Statement • Flood Risk Assessment (to assess the consequences of the weir in terms of increased

fluvial flood risk)


• Assessment of impact on River Regime (Hydro-Geomorphology) as a result of impounding watercourse

• Detailed Design of Weir and Berthings • Production of Works Information and Contract Documents for Tendering purposes • Applications for Funding • Applications for Consents and Licences • Planning Application

The likely costs for these activities is estimated to be between £250k to £400k, dependent upon the type of structure required and the extent of services required from the consultant/contractor. Should the project proceed beyond the Feasibility stage SBC will need to assess the required scope of services before progressing to either an Open Tender or Framework Tender procurement route for appointment of a Consultant/Contractor to carry out these roles.


9 CONCLUSIONS

The Feasibility Study has indicated that it is technically feasibly to construct a weir which impounds the River sufficiently to create a number of new berthings and generate additional income and tourism interest for the town. The report has shown that a fixed weir structure would be the most cost effective, but it would be least effective in terms of accessibility for boats and is not therefore recommended. A weir which incorporates a gate mechanism or lock provides a more flexible solution that maximises the accessibility for boats and has therefore been recommended. Access to and from any proposed moorings will be an issue as the council do not own any land upstream of Coates Marine boat yard and therefore legal and financial agreements would need to be made with landowners to allow other berthings to be created. The impact of any proposed weir and structure in terms of fluvial flood risk to the upstream Esk Valley will need to be carefully considered as part of any option development studies. The flood risk impact can be reduced by maximising the weir crest length (for example as a horseshoe shape) or through integration of a flood gate, which can be lowered to maximise flows passing the structure. The proposed access gate could be designed to provide a dual function role and act as a flood gate. Impoundment of the watercourse will result in sediment deposition on the upstream face of the weir. This would result in the need to periodically remove the silt to ensure navigational access is maintained and possibly for flood risk purposes. The report proposes that the weir structure incorporates low level pipes which would reduce the rate of siltation upstream by encouraging natural scouring to continue at bed level. In addition to the physical issues of siltation in the upstream channel, there may also be environmental issues associated with the water quality changes that may occur and the potential obstruction of fish passage, which may result in the project not receiving the necessary licences, consents and permissions. This would therefore prevent the project progressing. A consultation meeting with Natural England (NE) and the Environment Agency (EA) is therefore recommended to assess whether the environmental issues will prevent the project from being realised. Further studies are not recommended until an initial consultation meeting with the EA and NE has been undertaken and their position regarding potential consenting and licensing agreements is understood.


APPENDICES


APPENDIX A

SITE VISIT AND PHOTOGRAPHS

30 March 2011 1 9W6668/M001/303820/Newc

HASKONING UK LTD.

COASTAL & RIVERS

A COMPANY OF

Memo To : Steve Cross, Paul Knight, Gregor McNiven From : Paul Herickx Date : 30 March 2011 Copy : Nick Cooper, Paul Hart Our reference : 9W6668/M001/303820/Newc Subject : Whitby Impoundment Site Visit The information contained in this document is to verify and clarify the main points discussed during the site visit to Whitby Harbour on the 29th March 2011. Attendees of the site visit were Alex Richards (AR) of Scarborough Borough Council (SBC) and Paul Knight (PK), Steve Cross (SC) and Paul Herickx (PH) of Royal Haskoning. The purpose of the site visit was to meet the client (SBC) and to visually assess the feasibility of constructing a weir type structure within the harbour limits of the River Esk, predominantly for the purpose of providing additional pontoons for berthing boats upstream towards the village of Ruswarp. The location under investigation for the weir is the site of an existing low weir that, according to a local fisherman, comprises of medium-large locally sourced stones and wire (gabion) baskets. It was not possible to verify the composition and exact location of the current weir as it was inundated, but the site has traditionally been used for structures, including a ford and another higher weir, and there are slipways immediately downstream on both banks that would indicate the potential presence of a structure beneath the tidal waters. Through discussion of the client’s requirements, AR has indicated that they want options to be developed for a fixed weir with or without a gate. SC developed the idea of incorporating a hinged flap gate using hydraulic rams that would provide access across the weir at high tide and for up to 1.5 hours either side, which AR was interested by. AR also wishes an option to be developed for a weir with no gate, which would only allow access upstream of the weir at high tide and which would also restrict the draft of the boats. It was confirmed with AR that draft for the small yachts currently in the harbour is 2m. Discussions with Deputy Harbour Master Ian Vasey (IV) established that the loaded drafts of the harbour’s dredger and split hopper barge are 2.1m and, therefore, a 2.5m draft over the cill of the weir would be required. In addition, the width of the hopper and dredger are 8m which indicates that the gate or cill would need to be 10m wide to allow their passage. The harbour is regularly dredged and indicates that, if a higher weir structure to present was constructed, regular dredging would be required upstream of the weir to maintain flows. Ian Vasey also indicated that the bed level upstream and downstream of the weir is approximately +1.0m CD. The Harbourmaster is Capt Martin Willis. Scarborough Borough Council retains access rights from the proposed weir site to the corner of Coates Marine (approximately 50m) but access further upstream is owned by Network Rail and local landowners, including a small number (4-5) of small private boatyards. It was confirmed that SBC are not intending to purchase the access rights further upstream from Coates Marine and, therefore, access to any additional pontoons that are constructed due to the implementation of the weir would need to be accessed from their currently owned areas. There is the presence of a stationary caravan park off Airy Hill further upstream that may be interested in accessing the river

30 March 2011 2 9W6668/M001/303820/Newc

for any additional pontoons but the North Yorkshire Moors Railway line currently intersects the caravan park from the river and, therefore, it is unlikely that it would be possible to facilitate access without incurring considerable costs. SRC has noted that a fixed walkway of approximately 2m width and at +6.0m CD with brows down to the pontoons would be required for facilitating access to the berths. Establishment of an efficient access route to the pontoons is an important factor for consideration due to the limited access currently available. Through further discussion with AR it was established that the pontoons to be added, if scheme was to be developed, would be similar to the existing system of 2 boats on each side of the pontoon and, therefore, 4 boats in total. The pontoons would also be to one side of the river to maintain river access. The client also commented about the effects that the impounded river may have on the existing structures including the concrete and masonry reinforcement on both banks. It was confirmed that the main problem that may arise would be maintenance of the banks at low water but, if a water control feature such as a gate was used, there would be more control over the impoundment water levels to facilitate maintenance. Establishment of the upstream limit of the impounded water needs to be made as the condition of the banks on the right hand side, when looking downstream, is potentially an issue through increased erosion rates as small sections of the bank are currently missing masonry block reinforcement. However, it was established that the high water level in the river will not be increased, as it will remain tidal and, therefore, it will only retain water at a higher level during times of lower tides. With the increased water retention level, it was discussed that there are potential flood risk issues associated to the small boatyards on the left bank and the railway line. Options were discussed between all present and included the possibility of creating a dry access route between the two sides of the town by creating a weir crest that, during times of low tide, was possible to cycle or walk across. Currently the only pedestrian route in the town across the river is via a swing-bridge near the harbour entrance and it was felt that by providing an additional access route the scheme may be more appealing to local stakeholders, with AR stating that there have been schemes in the past that have not been initiated due to local pressure. Whilst the proposal indicates that a fish pass is an ‘added value’ aspect of the project, it was established that any structure would require a fish pass to be incorporated into it. PK suggested an innovative idea that is based on an ‘Irish Ford’ whereby low level pipes are added to the weir, possibly with penstocks, which allow fish passage through them and the ability to flush sediments when required. AR confirmed that the River Esk has sea trout and also stated that salmonid species are present and worms, all of which will need to be accounted for in any design and potential mitigation measures. The other ‘added value’ aspect of potential hydropower incorporation was briefly mentioned with AR stating that the Ruswarp weir upstream has an Archimedes Screw turbine. The method of construction for the weir was outlined by SC with parallel sheet piles either side of the cill required and a diaphragm type system at either end to tie into the existing structures. Without being able to visually inspect the existing weir it was not possible to establish the exact method of construction but it was established that it would be likely to require the excavation of the current rubble weir, most notably to install the sheet piles. It was felt that the material from the existing weir could then be used on site as fill for the cofferdams during construction. With the presence of concrete slipways in very close proximity to the proposed location of the weir it was established that there would be no access constraints for construction plant on either bank of the river.

Whitby Harbour Impoundment Study 9W6668/M001/303820/Newc Appendix A 3 April 2011

Photo 1: Potential access point from new housing complex

Photo 2: Service pipes in impounded area at new housing complex


Photo 3: Potential access point from new housing complex

Photo 4: Existing boat sheds


Photo 5: Right bank of proposed impounded area when looking downstream

Photo 6: Intertidal mudflats


Photo 7: Location of existing weir and proposed new impoundment structure


APPENDIX B

ENVIRONMENTAL CONDITIONS

Whitby Harbour Impoundment 9W6668/R/303820/Newc Appendix B - 1 - April 2011

Introduction The following information summarises the baseline conditions for the environmental receptors in terms of features, characteristics and key issues relevant to the proposed impoundment structure at Whitby Harbour on the River Esk. This assessment has been undertaken to determine the feasibility of the works with regard to environmental receptors. Professional judgement has been used to target the environmental baseline information to the receptors which have the potential to be affected by the proposed works. Baseline Environment The Watercourse The River Esk rises on the Westerdale Moor in North Yorkshire and merges with a number of becks prior to flowing through Ruswarp and Whitby before flowing into the North Sea. The River Esk is tidal within the site of the proposed impoundment, with a large weir 3.8km from the estuary mouth forming the upper tidal limit. Marine Biology Sand flats within the estuary mouth behind the East Pier show a gradation from stable, clean, well sorted sand at their seaward end (characterised by the polychaetes Nephtys hombergii, Scoloplos armiger and Lanice conchilega), to more species rich, muddy sand further upstream. Soft anoxic mud adjacent to the existing weir (and the probable site of the proposed new impoundment structure) are characterised by low species rich community dominated by the ragworm Hediste diversicolor and the amphipod Corophium volutator (JNCC, 1998). The upper reaches of the estuary are predominantly muddy sand characterised by a number of polychaetes, oligochaetes and enchytraeid oligochaetes. Towards the upper limit of tidal influence, cobbles and pebbles form a coarse matrix in sand with sparse wrack (F. ceranoides) and green algae Enteromorpha spp. attached to larger cobbles. Habitats immediately downstream of the weir at Ruswarp are freshwater in character, with no marine or estuarine species present. Biodiversity Action Plan (BAP) Habitats There are national UK targets for ‘priority habitats and species’ which are translated at the local level by Biodiversity partnerships. Scarborough Biodiversity Action Plan (BAP) was adopted in 2005 and covers the same area as the Borough Local Plan, which includes Whitby. The main priority habitats which have the potential to be affected by the proposals are listed below. Mudflats Mudflats are present within the proposed impoundment area of the River Esk, between the disused Larpool viaduct and Whitby Bridge. Additional areas of mudflat are present downstream of the proposed impoundment structure within the mouth of the estuary and throughout the harbour. Mudflats consist mostly of silts and clays with a high organic content (Natural England, 2011), and have a high biological productivity which, together with other intertidal habitats, support large numbers of predatory birds and fish.


Saltmarsh The following information is taken from the Scarborough Biodiversity Action Plan (Scarborough Biodiversity Steering Group, 2005): “Within the Borough there is only a tiny fragment of Coastal Saltmarsh occurring at Whitby, on the California Beck, a small inlet on the River Esk. Despite being less that 0.1ha in size, it exhibits some of the typical suite of saltmarsh plants, including Sea Lavender Limonium vulgare. A localised area of Coastal Grazing Marsh occurs on the banks of the River Esk inland from Whitby at Ruswarp. The resource has not yet been fully examined and there may be more grazing marsh as yet unidentified, although all in the same general locality.” Fish The River Esk is principally a salmonid river, supporting healthy stocks of resident brown trout (Salmo trutta), as well as migratory populations of salmon (Salmo salar) and sea trout (Salmo trutta) which are nationally important species (Fishtek Consulting, 2009). Smolt trapping and electro-fishing undertaken by the Environment Agency has identified low numbers of European eel (Anguilla anguilla), river lamprey (Lampetra fluvialis), tench (Tinca tinca), gudgeon (Gobio gobio) and grayling (Thymallus thymallus). The River Esk is known to be an excellent sea trout fishery (JNCC, 1998), with catch numbers increasing in recent years. The number of salmon within the river has also recovered dramatically in recent years from very low numbers during the 1980s (Fishtek, 2009). The upstream migration of salmon (spring fish and grilse) is reported to occur twice, during spring and summer/autumn respectively, with sea trout migration upstream during the summer months (Fishtek, 2009). The upper reaches of the River Esk contain a small proportion of Freshwater Pearl Mussel, designated as a nationally important species. The Esk Pearl Mussel and Salmon Recovery Project (a partnership of the Environment Agency, Natural England, Durham University and the North York Moors National Park Authority) aims to improve the habitat and restore pearl mussel populations whilst also increasing the population of salmon and trout in the River Esk catchment. Water Quality The Environment Agency monitors water quality within the River Esk at Ruswarp, upstream of the proposed impoundment structure. The water quality results show very low levels of nitrates and phosphates, with biological and chemical parameters being very good and good respectively. Water Framework Directive (WFD) The Water Framework Directive (WFD) establishes a legal framework to protect and restore clean water across Europe and ensure its long-term, sustainable use. Permission must be sought from the Environment Agency to ensure that any proposed development is in compliance with the WFD, with no deterioration to the existing status of the water body. The proposed site for the impoundment structure falls within the ESK (E) waterbody (GB510402703400). The environmental objectives of the WFD applicable to the proposals fall under Article 4 (1) of the Directive, which states:


“Member States shall protect, enhance and restore all bodies of surface water, subject to the application of subparagraph (iii) for artificial and heavily modified bodies of water, with the aim of achieving good surface water status at the latest 15 years after the date of entry into the force of this Directive. Information on the ESK (E) waterbody is provided below:

Waterbody ID GB510402703400 Waterbody name ESK (E) Current Overall Status

Moderate

Status Objective (Overall)

Good by 2027

Status Objective(s) Good Ecological Potential by 2027 Hydromorphological Designation

Heavily Modified

Ecological Potential Moderate Biological elements Invertebrates: Moderate (Uncertain); Predicted Status by 2015 Moderate

Fish: Moderate (Uncertain); Predicted Status by 2015 Moderate Hydromorphological supporting conditions

Tidal regime – Freshwater flow: Currently Supports Good, Predicted Status by 2015 Supports Good Element Current status Predicted

status by 2015 Justification for not achieving good status by 2015

Dissolved inorganic Nitrogen

Moderate (Uncertain)

Moderate

Supporting elements

Dissolved oxygen

High High

Disproportionately expensive (N1a)

The information above displays that the waterbody is not currently at Good Ecological Potential due to factors which affect the biological quality elements. The hydromorphology is currently classified as Good and any scheme within this waterbody should try to avoid deterioration in the status of this element. No specific mitigation measures are provided for this waterbody within Appendix B of the Humber River Basin Management Plan. Environmental Constraints Siltation The impoundment structure is likely to result in significant sediment deposition upstream of the structure, which is likely to reduce channel capacity without regular maintenance dredging. Maintenance dredging has the potential to increase the total suspended solid concentrations in the water column, which is likely to impact upon the fish populations within the river. There are also likely to be further implications with regard to water quality due to loss of tidal flushing of the impounded ‘basin’, and potential for smothering of gravel substrate on the river bed during sediment deposition resulting from the impoundment.


Water Quality Impoundment of the watercourse has the potential to cause stratification between fresh water and denser saline waters. This may lead to isolation of a lower layer of saline water from sources of re-oxygenation, and extend contact with sediments of high oxygen demand, creating an anoxic layer at depth. As freshwater is prevented from reaching the underlying sediments, nitrates in the water are not removed, and the potential for eutrophication (nutriment enrichment) is increased. This in turn may encourage the growth of green algae, such as Enteromorpha spp., which in some cases can lead to a reduced amenity value in such impounded areas. The proposed impoundment is also likely to lead to an indirect impact upon the water quality through the construction of moorings upstream. Storage of boats within moorings has the potential to result in decreased water quality as a result of leakages and spills from the vessels, which could adversely impact upon the aquatic ecology. Loss of BAP priority habitats One of the UK BAP objectives is that there should be no further net loss of intertidal habitats such as coastal saltmarsh or mudlfat. The construction of the impoundment structure would result in the loss of both of these priority habitats along the River Esk due to the artificial increase in the water level during low tide and reduction in tidal fluctuation (and hence saline influence). Mudflats upstream of the proposed impoundment structure currently represent a feeding resource for birds and estuarine fish species, which will be lost through permanent inundation. In addition, the loss of regular tidal inundation and associated saline influence is likely to result in the loss of existing saltmarsh vegetation, leading to the out-competing of salt tolerant species (such as sea lavender) by more vigorous terrestrial species. It is considered that the loss of priority habitat which is of high nature conservation value would be a relatively major constraint to this development. Fish Migration The installation of an impoundment structure has the potential to impact upon the success of fish migration during low tide. The literature review undertaken for this assessment has identified the importance of the River Esk as a salmonid fisheries resource. The construction of the proposed impoundment structure is likely to act as a barrier to upstream fish migration during low tide; therefore this structure is likely to cause a delay in the upstream migration of fish. It is considered that a suitable fish pass would be required to allow the free passage of salmonids and other species within the river during all water level conditions. The upstream migration of salmonids during spring, summer and autumn also represents a constraint on any construction works within the channel due to potential disturbance to their migration. The Environment Agency may apply restrictions to works during certain tidal states between the months of March to November. It could be expected that such restrictions may apply to the proposed works (especially if piling works are proposed), though the actual limitations applied would be likely to depend upon those construction methodologies proposed.


Water Framework Directive It is considered that the proposed impoundment works have the potential to prevent Good Ecological Potential being reached by the target date of 2027, even if they do not cause deterioration in status. The proposed works are unlikely to qualify for an exemption under Article 4.7, because the construction of an impoundment structure within the River Esk is not of overriding public interest. In addition, the construction of the impoundment structure has the potential to cause deterioration in the current status of the ‘Tidal regime – Freshwater flow’ supporting condition, which could prevent the waterbody reaching its target of Good ecological potential by 2027. There is a need for further investigations and input into the detailed design process to ensure that:

• Any potential impacts are fully assessed; • The structure is designed to minimise any impacts: • Any mitigation measures that are necessary are included in the scheme design.

It is considered that the requirements of the WFD are not ‘show-stoppers’ at this stage, as long as suitable mitigation measures can be incorporated into the design to prevent the deterioration in the status of the hydromorphological quality elements and prevention of the water body reaching Good Ecological Potential. References Fishtek Consulting, 2009. River Esk Hydro Power Proposal Fisheries Assessment JNCC, 1998. Marine Nature Conservation Review, Sector 5. South-east Scotland and north-east England area summaries. Natural England, 2011. Nature of the map website. Scarborough Biodiversity Steering Group, 2005. Scarborough Biodiversity Action Plan.


APPENDIX C

OPTION 3 – MITRE GATE AND LOCK SKETCHES


APPENDIX D

COST BREAKDOWN

Royal Haskoning

Royal Haskoning Whitby Impounding Weir

SRC Quantity Unit Material P/L Sub & Rate Total MC OH Gross Total P/L Mat SubOption Costs at March 2011 Temp £ £ Max 30% incl OH Option 1 Fixed Level Weir Mobilisation / Demobilisation / Costs 1 sum 40,000 40,000.00 40,000 1.25 50,000 0 0 40,000Temporary works 1 sum 0 25,000 25,000.00 25,000 1.25 31,250 0 0 25,000Excavate existing rubble and store on site for piling 1,650 m3 20 0 20.00 33,000 1.25 41,250 33,000 0 0AZ18 sheet piles supply incl cross walls 298 t 800 800.00 238,400 1.25 298,000 0 238,400 0AZ18 sheet piles drive 2,520 m2 50 0 50.00 126,000 1.25 157,500 126,000 0 0Walings 10 t 1,100 0 1,100.00 11,000 1.25 13,750 0 11,000 0Tie rods 20 nr 250 250.00 5,000 1.25 6,250 0 5,000 0Fill with rubble from excavation 500 m3 7 0 7.00 3,500 1.25 4,375 3,500 0 0Tangs welded to piles 120 nr 5 15 20.00 2,400 1.25 3,000 1,800 600 0Concrete slab 315 m3 100 100.00 31,500 1.25 39,375 0 31,500 0Reinforcement to slab 39 t 800 800.00 31,500 1.25 39,375 0 0 31,500Cut off piles tidally 180 m 25 25.00 4,500 1.25 5,625 0 0 4,500Pipes with penstocks 4 nr 7,500 2,000 9,500.00 38,000 1.25 47,500 8,000 30,000 0Plant & labour general 12 wks 40,000 40,000.00 480,000 1.25 600,000 480,000 0 0

Summary Total 1,337,250 0 652,300 316,500 101,000 Contingency 20.0% 267,450 Prog wks 12

Design 50,000 £/wk 54,358 1,069,800Supervision 25,000 25.00% 267,450Permissions 10,000 1,337,250Grand Total excl VAT 1,689,700

Option 2 Weir with Flap Gate

Mobilisation / Demobilisation / Costs 1 sum 60,000 60,000.00 60,000 1.25 75,000 0 0 60,000Temporary works 1 sum 0 40,000 40,000.00 40,000 1.25 50,000 0 0 40,000Excavate existing rubble and store on site for piling 1,650 m3 20 0 20.00 33,000 1.25 41,250 33,000 0 0AZ18 sheet piles supply incl cross walls 298 t 800 800.00 238,400 1.25 298,000 0 238,400 0AZ18 sheet piles drive 2,520 m2 50 0 50.00 126,000 1.25 157,500 126,000 0 0Walings 10 t 1,100 0 1,100.00 11,000 1.25 13,750 0 11,000 0Tie rods 20 nr 250 250.00 5,000 1.25 6,250 0 5,000 0Fill with rubble from excavation 450 m3 7 0 7.00 3,150 1.25 3,938 3,150 0 0Tangs welded to piles 120 nr 5 15 20.00 2,400 1.25 3,000 1,800 600 0Concrete slab 273 m3 100 100.00 27,300 1.25 34,125 0 27,300 0Reinforcement to slab 34 t 800 800.00 27,300 1.25 34,125 0 0 27,300Cut off piles tidally 180 m 25 25.00 4,500 1.25 5,625 0 0 4,500Pipes with penstocks 4 nr 7,500 2,000 9,500.00 38,000 1.25 47,500 8,000 30,000 0Plant & labour general 18 wks 40,000 40,000.00 720,000 1.25 900,000 720,000 0 0Gate incl M&E & water jetting 1 sum 375,000 375,000.00 375,000 1.25 468,750 0 0 375,000Gate chamber 110 m3 100 100.00 11,000 1.25 13,750 0 11,000 0Reinforcement 28 t 800 800.00 22,000 1.25 27,500 0 0 22,000Cut off gate chamber piles under water 20 m 100 100.00 2,000 1.25 2,500 0 0 2,000

Summary Total 2,182,563 891,950 323,300 530,800 Contingency 20.0% 436,513 Prog wks 18


Option 3 Lock with Mitre Gates

Mobilisation / Demobilisation / Costs 1 sum 60,000 60,000.00 60,000 1.25 75,000 0 0 60,000Temporary works 1 sum 0 40,000 40,000.00 40,000 1.25 50,000 0 0 40,000Excavate existing rubble and store on site for piling 100 m3 20 0 20.00 2,000 1.25 2,500 2,000 0 0AZ18 sheet piles supply 341 t 800 800.00 272,800 1.25 341,000 0 272,800 0AZ18 sheet piles drive 2,892 m2 50 0 50.00 144,600 1.25 180,750 144,600 0 0Walings 2 t 1,100 0 1,100.00 2,200 1.25 2,750 0 2,200 0Tie rods 5 nr 250 250.00 1,250 1.25 1,563 0 1,250 0Tangs welded to piles 120 nr 5 15 20.00 2,400 1.25 3,000 1,800 600 0Concrete to walls and floor of lock 1,334 m3 100 100.00 133,400 1.25 166,750 0 133,400 0Walkway on one side of lock 1 sum 15,000 15,000.00 15,000 1.25 18,750 0 0 15,000Reinforcement to slab 83 t 800 800.00 66,700 1.25 83,375 0 0 66,700Cut off piles tidally 61 m 25 25.00 1,525 1.25 1,906 0 0 1,525Pipes with penstocks 4 nr 7,500 2,000 9,500.00 38,000 1.25 47,500 8,000 30,000 0Plant & labour general 18 wks 40,000 40,000.00 720,000 1.25 900,000 720,000 0 0Mitre gates incl M&E & water jetting 1 sum 375,000 375,000.00 375,000 1.25 468,750 0 0 375,000Cut off gate chamber piles under water 20 m 100 100.00 2,000 1.25 2,500 0 0 2,000

Summary Total 2,346,094 876,400 440,250 560,225 Contingency 20.0% 469,219 Prog wks 18


Additional Items

Footbridge 96m long at +7m / +8m CD 15 t 4,000 1,333 5,333.00 79,995 1.25 99,994 0 60,000 19,995E.O. for lifting section at flap gate Option 2 only 1 sum 50,000 50,000.00 50,000 1.25 62,500 0 0 50,000

07/07/2011 1 Whitby Impounding Weir Costs (3).xls