Report to the:- Wards All Cabinet – July 2011 Planning Committee – 21 June

Hull City Council Aqua Greens Progress Report

Report Number: CDR/2011/034

Report of the City Planning Manager on behalf of the Corporate Director for Regeneration

1. Purpose of the Report and Summary

1.1 The purpose of this report is to brief members on the Aqua Greens project progress. The project has reached the end of the feasibility stage and a review of the document prepared by the Councils Flood Risk Planning Manager is presented below, it can be used alone or as a guide when viewing the document. Future funding options have been explored and recommended next steps are given in the options section.

1.2 The council developed a Surface Water Management Plan which was completed in December 2009, the plan recommended surface water storage options as Aqua Greens – dual purpose flood storage and amenity green spaces – at Orchard Park and Derringham. The council retained Halcrow Group Limited to deliver the feasibility study for these two locations. Funding is via DEFRA surface water management grant and Flood Defence Committee Local Levy.

1.3 The study has investigated the options to develop a business case to fund technically, environmentally and financially beneficial schemes at both sites through hydraulic modelling, survey and investigations.

1.4 Aqua Greens have been shown as feasible at both sites with flood storage options at Springhead Park Golf Course in Derringham and diversions of Creyke and Wanlass Beck north of Cottingham and an Aqua Green storage site protecting Orchard Park. Both schemes present wider benefits to Willerby and Cottingham respectively.

1.5 Additional schemes are being promoted by Council, these schemes look to address the origins of flood flows nearer their source to the west of the city. Funding organisations recognise that there are benefits to the city in these additional schemes and have recommended that they receive joint bids for funding where ERYC and HCC schemes are hydraulically dependant upon each other.

1.6 All appraisal information is being shared and joint funding bids are currently being prepared for DEFRA grant in aid and European Regional Development Fund financial support, these would be match funders delivering 100% of scheme costs. This will give the maximum benefits to all residents and businesses across the whole catchment and will show close partnership working between two Lead Local Flood Authorities.

2 Recommendations

It is recommended that the Committee:

2.1 Agree to the findings of the Aqua Greens Feasibility document and to agree to the progression of the Aqua Greens options in combination with ERYC schemes – a combined Willerby and Derringham scheme and a combined Cottingham and Orchard Park scheme through partnership working and joint funding submissions.

This is a none key decision.

3. Introduction

3.1 The Hull City Council Surface Water Management Plan (SWMP) identified high risk surface water flooding locations across the city, it recommended development of Aqua Greens, dual purpose surface water flood storage and green space amenity sites, at Derringham and Orchard Park. Halcrow Group Limited were retained to deliver a feasibility study to develop the business case for these options. Funding has been obtained from DEFRA surface water management and Yorkshire Flood Defence Committee Local Levy grants.

3.2 Flood modelling and mapping has been undertaken at both locations to develop the findings of the SWMP, survey and site investigations have been undertaken and discussions have been held with all partners to further understand the issues during flood conditions.

3.3 Preferred options have been developed at both sites which reduce the risk of flooding in the Derringham and Orchard Park areas of the city and provide wider benefits across the administrative border to Willerby and Cottingham respectively. Both solutions are cost beneficial and would allow further funding discussions to be progressed with partners.

3.4 Funding bids have been made to DEFRA Grant in Aid (GiA, via the Environment Agency) and European Regional Development Funding (ERDF). Recommendations have been made that works progressing further to the west of the city by ERYC should be considered with Aqua Greens schemes and joint funding bids would be most likely to receive future funding allocations. This is currently being considered by both authorities.

4. Aqua Greens Feasibility Report

Derringham

4.1 A technical note appended to this paper as Appendix 1 details the approaches taken within this commission, further information on the options considered is given within this note. The full report will be made available to members if required.

4.2 Halcrow Group Limited developed their work on the SWMP through detailed hydraulic modelling of the watercourses and surface water flow routes affecting Derringham and Orchard Park. An assessment of the major sources of flood risk for both sites was made and options were developed to reduce the impacts of future flooding.

4.3 Flood flow routes into the Derringham area were confirmed to be from the higher rural areas to the west, flows pass through Willerby and surrounding urban areas and eventually pond in the lower lying land around Derringham. Flows pass along Willerby Road, Wolfreton Lane and ultimately spread through surrounding streets.

4.4 Options considered looked at attenuating flows at Derringham – an aqua green at Springhead Park Golf Course, attenuating flows north of Derringham (Willerby Carrs) and diverting flows from the north of Derringham. The major flows into the area were found to be from the west and north west and although attenuation or diversion of flows from the Willerby Carrs area would have some benefit this would be minimal in comparison, all flows held or diverted in this area would also ultimately pass into the Setting Dyke system which would put further pressure on the sewerage infrastructure as the Setting Dyke flows directly into the main trunk sewer.

4.5 The proposed option is to store surface water flood flows in a terraced set of lagoons on Springhead Park Golf Course, flows would be diverted in a new dyke constructed from Well Lane at Willerby Carr Lane Primary school. Flood flows would be carried in a new dyke system to the north- west corner of the golf course to utilise the terraced storage system.

4.6 The costs of the scheme would be £2.56M providing benefits of £3.31M for Derringham and Willerby through the reduction of flood damages – a 60% optimism bias is included in the costs according to HM Treasury guidelines, all relevant HM Treasury approaches have been used throughout. The scheme has a benefit cost ratio of 1.3.

Orchard Park

4.7 The hydraulic modelling confirmed that flood flows into Orchard Park were derived from the large rural areas to the north and west draining through Wanlass and Creyke Becks to the north of Cottingham, when flows overtop the left banks of these watercourses surface water flows into the Orchard Park area. Further flood flows are derived from the west of Cottingham, ERYC are currently developing a scheme to attenuate flows from the Raywell Valley. This scheme has received planning permissions and construction is due to start, the flood storage and resultant reduction of flood levels in Orchard Park due to this work have been factored into the base case scenarios for the Orchard Park Aqua Green feasibility works.

4.8 The project team considered options, 20 options were identified, and these are discussed further in the technical note, Appendix 1. Options included the Raywell Valley Scheme and an increased version of this but this still left flood flows from the north and west of Cottingham as an issue. Attenuation further north and west around provides benefits but this is too far up the catchment to have significant effect, a diversion to the would be too costly. Property level protection was considered and a range of diversion and attenuation of Creyke and Wanlass Beck options were investigated.

4.9 The preferred option is the diversion of Creyke and Wanlass Beck into the and Barmston Drain via Counter Dyke, attenuation is required to ensure flood flows do not present an increased flood risk to the drain during storm conditions. Storage would be provided around the edge of the Orchard Park estate as an Aqua Green site, this could be a linear site along the length of Counter Dyke or a separate storage area, amenity values would be considered for both options. The resultant stored flood flows would be slowly released into Beverley and Barmston Drain when levels in the drain recede.

4.10 The costs of the scheme would be £2.92M providing benefits of £22.92M for Orchard Park and Cottingham through the reduction of flood damages – a 60% optimism bias is included in the costs according to HM Treasury guidelines, all relevant HM Treasury approaches have been used throughout. The scheme has a benefit cost ratio of 7.6. 4.11 Both proposed options have significant implications for land purchase or acquisition (although the majority of land lies in Local Authority ownership), cross boundary working, land management and options working alongside existing land usages – i.e. the operations of the golf course. These issues are raised and discussed to some extent in the feasibility study but considerable work will be required to ensure that all partners understand the issues and risks and these are managed as the projects move forward.

Future Funding Options

4.12 HCC have made funding bids to DEFRA Grant in Aid (GiA, via the Environment Agency) and European Regional Development Funding (ERDF) via the Adaptation to Climate Change operational programme to take the Aqua Green options through their detailed design and construction phases. They would provide 100% costs as match funding organisations. The HCC bid was provisionally successfully for ERDF funding but no allocation of funds was received for 2011/12 from GiA. ERYC are currently working on schemes upstream of both Aqua Greens options: Northmoor Scheme to the North and West of Cottingham and Great Gutter Valley above Willerby, in addition to this the Raywell Valley scheme will be completed in 2011 / 2012, ERYC have received provisional allocations of both ERDF and GiA (for 2011/12).

4.13 All funding authorities have identified that they would want to see joint bids as a catchment wide solution, this would give both authorities the best chances of achieving further funding.

5. Consultation

5.1 The Aqua Greens feasibility document was prepared in consultation with all partners through a project team process. Local Flood Groups have inputted to the options. Full consultation with public and all other interested parties would be made through the detailed design process. 5.2 This report will be taken to the June Planning Committee meeting and July Cabinet.

6. Options

6.1 Joint DEFRA GiA and ERDF bids are being completed by ERYC and HCC to ensure funding deadlines are met. All ongoing modelling and studies are being developed in a manner to allow joint schemes to be progressed.

6.2 The Derringham Aqua Green option could work as an additional storage site to the Great Gutter Valley scheme, the feasibility works for this joint scheme will begin in the 2011 / 2012 financial year, the outputs of the Derringham Aqua Greens feasibility will contribute to this. Both options working together could provide upstream storage above Willerby and storage further down the catchment around Derringham, this would present a catchment wide solution which would reduce flood risks to the maximum amount of people across the two administrative boundaries.

6.3 The Orchard Park Aqua Green proposed option allows both authorities schemes to be combined, the ERYC scheme is considering conveying flows away from the north of Cottingham and the original Aqua Green options at this location looked at storing flows before they reach Orchard Park. This has allowed both schemes to be combined, the Aqua Green feasibility works have considered this and the resultant investigations will feed directly into the Northmoor feasibility works in 2011 / 2012. A conveyance / storage option gives the maximum benefit to Cottingham and Orchard Park and when combined with the Raywell Valley scheme they will vastly reduce the chances of a significant flood event affecting this area.

6.4 The project partners are working to the below timescales, these are still being confirmed at this early stage, the Flood Risk Planning Manager will update committee following the submission to the EA Project Assessment Board (PAB) early in 2012.

ERDF / Yorkshire Forward Outline Business Plan submission – June 2011 EA PAB joint scheme feasibility submission – Dec 2011 EA PAB joint scheme detailed design submission – Dec 2012 ERDF / CLG Full Business Plan submission – Dec 2013 Project Contracting Date (ERDF) – March 2014 Construction begins – April 2014 Construction Ends – October 2014

All dates are provisional at present.

6.5 A different approach would be to continue Aqua Greens scheme delivery in isolation of other schemes, this would not require any partnership working with other authorities and would give full control of any schemes to HCC. Funding would be an issue, both GiA and ERDF want to see joint funding approaches and would not be receptive to a single funding bid, with no allocation in 2011/12 from GiA and ERDF dependant on match funding this approach would require input of funds from HCC to progress.

6.6 The options available to Committee are:

- To agree to the findings of the Aqua Greens Feasibility document and to agree to the progression of the Aqua Greens options in combination with ERYC schemes

- To agree to the findings of the Aqua Greens Feasibility document and to agree to the progression of the Aqua Greens options in isolation without consideration of joint options and joint funding approaches

- To not agree with the findings of the Aqua Greens feasibility document

7. Council Priorities

7.1 Flood Risk Management in Hull is a material planning concern and forms an important part of our SFRA and emerging Core Strategy.

7.2 The legislative changes surrounding the enhanced role of the council as a Lead Local Flood Authority bestow statutory duties and powers on us dictating the work that we need to undertake to manage flood risk in the city and to work in partnership with all Flood Risk Management Authorities.

8. Comments of the Head of Legal and Democratic Services, and Monitoring Officer

8.1

9. Comments of the Interim Section 151 Officer

9.1

10. Comments of Human Resources

10.1

11. Comments of Overview and Scrutiny

11.1

12. Conclusions

12.1 The options are the observations and recommendations of the councils Flood Risk Planning Manager, they are recommended actions and have been informed further by the views and comment of the wider council.

Alex Codd City Planning Manager on behalf of Pauline Davis Corporate Director Regeneration.

Contact Officer : Steve Wragg, Flood Risk Planning Manager Telephone No. : 612129

Officer Interests: None

Background Documents: Hull City Council Aqua Greens Feasibility Study - April 2011 Halcrow Group Limited Appendix 1 Dunedin House Riverside Teesdale Business Park Stockton-on-Tees TS17 6BJ Tel +44 (0)1642 632800 Fax +44 (0)1642 632801 www.halcrow.com

Technical note

Introduction and Background This Business Case provides a brief summary of the preferred options to alleviate surface water flooding in the Derringham and Orchard Park areas of the city and the economic justification for implementing these options. The business case is part of our feasibility studies to investigate the aqua green concepts for the Derringham and Orchard Park areas of the city to establish how they can be successfully realised in practice. This will provide a means by which Hull City Council’s Economic Development and Regeneration Department can gain financial approval to allow the project to proceed to the next stage, which would normally be detailed design and tender document preparation. The aqua green concept involves the creation of specially-designed water storage areas capable of holding back surface water, preventing it from entering the urban areas of the city during extreme weather. Multiple-use objectives are built into scheme design to support flood risk management, recreational and biodiversity / environmental enhancements. Prior to June 2007 the city of Hull had recorded only isolated incidents of local flooding and the city was not considered to be at high risk of surface water flooding. A review of the Yorkshire Water DG5 register made available during the Surface Water Management Plan (SWMP) studies corroborates this assessment. In June 2007 Hull experienced high volumes of rainfall, with the wettest month recorded in Yorkshire since 1882 according to Environment Agency records with over 250mm of rainfall being recorded. Whilst there is still debate into the exact return period it has been estimated that the June 2007 event was a 1 in 150 year magnitude event. This rainfall fell onto ground that was already heavily saturated following the sustained rainfall of previous days. These combined conditions resulted in severe flooding, city wide disruption and damage to over 1300 businesses, over 8600 residential properties and loss of life. Cottingham to the west of Orchard Park also experienced significant flooding in June 2007. The source of flood risk was believed to be from Wanlass and Creyke Becks, which collect rural runoff from the Wolds and conveyed it to Cottingham and then into areas of Hull. The combined conditions explained above meant that the Cottingham Branch Sewer, into which Wanlass and Creyke Becks flow, was at capacity which exacerbated the flooding.

Hydraulic modelling Hydraulic modelling has been undertaken to better understand surface water flood risk at Derringham and Orchard Park and to help assess the effect of alleviation options including Aqua Greens. Outputs from the hydraulic modelling have been

Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

att19678 Halcrow Group Limited Appendix 1 Dunedin House Riverside Teesdale Business Park Stockton-on-Tees TS17 6BJ England Tel +44 (0)1642 632800 Fax +44 (0)1642 632801 www.halcrow.com

Technical note used in the economic appraisal to determine flood damages and economic benefits as well as water levels to inform outline designs and costs. The following data has been collected and used in the hydraulic modelling: • Surface water model developed for the Hull City Council SWMP. • LiDAR ground level data (provided by Environment Agency). • Modelled flow rates at Yorkshire Water pumping stations (provided by MWH). • Design outflow from Raywell Valley scheme (provided by ERYC). • Topographic survey including Wanlass Beck, Creyke Beck, Counter Dike channel and structures (2011). Hydraulic modelling has predominantly been carried out using 2D surface water models developed using TUFLOW modelling software and associated GIS (Geographical Information System) software. This type of model simulates flooding by applying rainfall directly to the topography, which is represented using a regular grid of ground levels derived from LiDAR data. Overland flow routes and ponding are simulated in the model. Some additional elements have been incorporated into the model to better represent flow routes and obstructions. The rainfall data applied in the surface water model comprises rainfall profiles (hyetographs), which have been derived for various return periods and storm durations using Infoworks software. These rainfall profiles are specific to the contributing catchments to Derringham and Orchard Park. As the modelling has been used to inform the design of flood storage areas, flood volumes, as opposed to flood peak flows, are critical. Consequently, flood events with very long storm durations of 72hrs have been simulated as these result in slightly larger flood volumes and correspondingly slightly higher water levels in storage areas than 24 or 48hr duration storms. Losses due to infiltration and the underlying drainage system are included in the surface water models. Infiltration is assumed to vary depending on the degree of urbanisation. The runoff coefficient, i.e. the proportion of rainfall that is not lost due to infiltration, has been derived using hydrology calculations to be 0.26 (26%) for rural areas. Aerial photography has been used to estimate the degree of urbanisation in terms of hard standing area and the runoff coefficient has been set to between 0.6 (60%) and 1.0 (100%). Losses due to the underlying drainage system have been incorporated by removing a portion of the rainfall on the urban area, based on the modelled flow rates of the Yorkshire Water pumping stations. The underlying drainage system is Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

att19678 Halcrow Group Limited Appendix 1 Dunedin House Riverside Teesdale Business Park Stockton-on-Tees TS17 6BJ England Tel +44 (0)1642 632800 Fax +44 (0)1642 632801 www.halcrow.com

Technical note assumed to have the same effect across all of the area served by the pumping station. The Bransholme area is assumed to be served by Bransholme pumping station and the remaining urban areas are assumed to be served by East Hull pumping station and West Hull pumping station. Surface water models covering the entire contributing catchment for Derringham and Orchard Park have been used to ensure all possible runoff into these areas from the Wolds are represented. Surface water model results have been qualitatively validated against Hull City Council records of observed flooding from June 2007 (Map of flooded roads, homes and businesses). The surface water model results for large flood events show very similar areas of flood risk to the areas that were affected in June 2007 for Derringham and Orchard Park. For Orchard Park a 1D ISIS model of Creyke Beck, Wanlass Beck and Counter Dike comprising 2011 survey data has also been developed to represent the hydraulics of these channels more accurately than the 2D surface water model. Rural runoff into Wanlass and Creyke Beck was obtained from a surface water model of the contributing catchment and input into the 1D model. The 1D model was used to assess flooding mechanisms from the becks and to assess the effect of diverting flows into Counter Dike. Calibration of this 1D model has not been carried out due to the lack of flow and level gauge records for these watercourses. Under certain storm conditions the model showed that the banks of the becks are overtopped. Overtopping flows from this 1D model were input into a surface water model of Derringham and the rural area to the north (up to Dunswell Lane) and west (up to Creyke Beck).

Derringham Current flood risk Similar to the findings of the SWMP the updated flood risk models for Derringham and Orchard Park indicates that the majority of flood risk to the urban areas is the result of overland flows from the rural areas of the Wolds to the west.

Surface water model results for Derringham indicate the main source of flooding in Derringham is from run-off from the west through Willerby. The model shows run-off entering Springhead Park Golf Course from Wolfreton Lane, ponding behind Sand Dyke and subsequently flowing along Willerby Road and into Derringham. The general direction of surface water flow through Willerby and into Derringham is validated by anecdotal evidence from the 2007 flood event. Further investigation however undertaken as part of this study indicates that the majority of surface water would likely flow down Wolfreton Lane to the junction

Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

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Technical note of Willerby Road with a smaller portion flowing across Springhead Park Golf Course. Once onto Willerby Road surface water is then found to flow into numerous side streets off Willerby Road.

The Do Nothing flood map below is generated using a 10m model grid. With a grid of this size it is not possible to pick up local variations in level such as the difference in level between the carriageway and back of footpath along Wolfreton Lane. The flooded area on the golf course may therefore be less that indicated with this water flowing into the urban areas. If this is the case, the business case is conservative because the flood damages are based on the modelled flood outlines.

Derringham – Do Nothing Flooding

Alleviation options considered 1) Attenuate lagoon at Derringham (aqua green): The attenuation lagoon will intercept the flow of surface water from the west towards Derringham. A suitable area within Derringham will be identified to be used as an aqua green. This is the option that has been taken forward and is described in more detail later in this note.

2) Attenuate north of Derringham to free up Sand Dyke: This option was ruled out because the drains to the north feed into Setting Dyke, not Sand Dyke. Setting Dyke discharges into a sewer pipe and

Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

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Technical note diverting flood water into the sewer is not a sustainable use of this infrastructure.

3) Divert flow from the north into Setting Dyke: This option was ruled out for the same reasons as the attenuation option 2) above.

Proposed option 1) Attenuation lagoon at Derringham (aqua green): This is the option that is taken forward. It involves the use of the Springhead Park golf course as an aqua green. Flows from the west would be intercepted in Willerby, at Willerby Carr Lane Primary School and Well Lane. A new dyke to the north of Well Lane would divert flows to the north west corner of the golf course joining with Sand Dyke. A series of tiered flood storage areas would be created on the golf course and Sand Dyke diverted through these areas. Sand Dyke will pass through a throttle pipe in each embankment forming the tiers. Everyday flows would pass through the storage areas. Extreme flows would be throttled causing the storage area to fill. The rate at which the water is released will depend on the throttle restriction. Should the storage area become full water would spill over the embankments. Drawdown of the stored flood water will be to Sand Dyke.

Key risks envisaged with this option taken forward are as follows:

§ Stakeholder agreement for using the golf park as an aqua green § Landowner agreement needed for new dyke. § Conflicts with underground services at pipe crossing on Carr Lane § Stakeholder agreement relating to modifications to the school grounds § Suitability of ground conditions for construction elements. § Joint funding arrangements.

Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

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Technical note

Derringham – Aqua Green Option

Derringham - Costs Costs have been estimated for the aqua green option which includes:

• Embankment at Willerby Primary School to intercept the surface water flows • Pipes under Well Lane to divert the flows north to a new open drain • Open drain around north of Well Lane • Pipe crossing under Carr Lane • Diversion of Sand dyke • Embankments forming the tiered storage areas • Headwalls at the inlet and outlet of the tiered bunds and any pipe crossings • 60% optimism bias on the capital costs The estimated capital costs for the aqua green option is £2.38M.

Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

att19678 Halcrow Group Limited Appendix 1 Dunedin House Riverside Teesdale Business Park Stockton-on-Tees TS17 6BJ England Tel +44 (0)1642 632800 Fax +44 (0)1642 632801 www.halcrow.com

Technical note Maintenance costs include grass cutting and clearing the drains. The annual cost of this is estimated to be £6,000. Over a 100 year appraisal period the present value of maintenance is £178,900

The total capital and maintenance present value cost is £2,560,300

Derringham - Damages Direct property damages were calculated using Modelling and Decision Support Framework (MDSF) software. This was developed by the Environment Agency, DEFRA and others for the preparation of Catchment and Shoreline Management Plans. It provides a tool for the assessment of flood depth damages from 2D modelled flood depth grids.

Flood depth damage values for various property types were obtained from the Flood Hazard Research Centre Multicoloured Handbook 2010 (MCH 2010). This has a price base date of January 2010.

Property location and type were obtained from the Environment Agency National Receptor Database (NRD). This does not list property value, which is required to cap the Present Value Damages. Therefore average residential property values were obtained from www.upmystreet.com at July-September averages for postcode HU5 and HU6. For commercial property a rate of £400 per metre square as a mid range price from Davis Langdon’s rebuild cost model data, was applied as a cap.

Property threshold levels are taken as 150mm above ground level. Ground levels are taken from LiDAR (Airflown laser survey).

An addition of 5.6% of damages is made for Emergency Services.

All damage values were factored up using the Consumer Price inflation Index (CPI) to a price base date of January 2011 (an increase of 4.0%).

Derringham (Hull CC area) - Benefits Option Damages (£M) Benefits (£M)

Do Nothing 2.30

Aqua Green 0.07 2.23

Because the surface water stored in the Aqua Green is intercepted at Well Lane and diverted around Willerby, the scheme benefits properties outside the city boundary. These benefits are summarised below.

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Technical note Derringham (Willerby) - Benefits Option Damages (£M) Benefits (£M)

Do Nothing 9.63

Aqua Green 8.55 1.08

Outcome Measure Derringham HullCC Derringham ERoYC

2 304 106

2b 98 51

3 11 0

Derringham - Benefit / Cost ratio The PV benefits are £3,310,000, and the PV costs are £2,560,300, giving a benefit / cost ratio of 1.3.

Orchard Park Current flood risk Surface water model results for Orchard Park indicate that the main source of flooding in Orchard Park is overland flow from the west caused by large volumes of rural runoff entering Wanlass Beck causing Creyke Beck to overtop its left bank just upstream of the rail culvert. The Orchard Park model shows extensive flooding in the north west of the urban area with streets adjacent to Hall Road severely affected. The area around the police training centre also appears to be susceptible to deep flooding due to run-off from surrounding rural areas. Surface water flooding in the Orchard Park area is alleviated to some extent with the proposed Raywell attenuation scheme being developed by East Riding of Yorkshire Council.

Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

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Technical note

Orchard Park – Do Nothing Flooding

Alleviation options considered Alleviation options considered:

1) Do nothing: This option is ruled out because the flood risk would remain and the objectives of the project would not be met.

2) Do minimum: This option assumed that existing assets are maintained and the standard of protection would not increase. This option is ruled out because the existing flooding risk remains.

3) Raywell Valley scheme: The Raywell Valley scheme will attenuate surface water flowing east from at a location west of Cottingham. This option was ruled out because we have identified another surface water flow route to Orchard Park which flows north of Cottingham and near Skidby. The two flow paths are linked by Wanlass Beck. The Raywell Valley Scheme would reduce surface water flooding to Orchard Park, but a significant residual risk remains due to flow from the second catchment. The benefits this

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Technical note option delivers are included in the baseline scenario. It is ruled out however because of the residual risk.

4) Raywell Valley scheme with increased attenuation: Option 3) above mentioned that the Raywell Valley Scheme would reduce flooding to Orchard Park but not prevent it. Increasing the storage will reduce surface flooding further. We have modelled this option by attenuating all flow upstream of the A164. Due to the connectivity of the Eppleworth and Skidby flows through the Wanlass Beck, we have modelled attenuation at Eppleworth and upstream of Skidby together. Results showed a significantly reduction in flooding at Orchard Park. The Raywell Valley Scheme would reduce surface water flooding to Orchard Park, but a significant residual risk remains due to flow from the second catchment. 5) Increase the flow conveyance in the sewerage system: This option involved passing more of the surface water flows through the sewerage system. This option is ruled out because it would be costly to modify the sewer system and the long term treatment of surface water is not sustainable. 6) Attenuation upstream of Skidby: The flow route from Skidby follows a route north of Cottingham Park towards Wanlass Beck and the A1079. With the exception of Skidby, this flow path misses the densely populated areas, but intersects Wanlass Beck, which carries water south. This option is considered in combination with option 4 and modelling results demonstrate a significant reduction in flooding at Orchard Park. This option is however ruled out because surface water downstream of Skidby reaches Cottingham via Wanlass and Creyke Beck to cause flooding. 7) Diversion of Creyke Beck and Wanlass Beck into Skidby Drain: The route of this diversion will need to cross the A1079, minor roads and other drains. Working near overhead power lines, including pylons introduces restrictions. Without developing this option further we can compare it with the alternative diversion option 11. From this comparison we conclude that option 11 would be more cost effective and so this option (Option 7) is ruled out.

8) Diversion of Creyke Beck and Wanlass Beck into Skidby Drain with additional storage: This option has the same issues described in Option 7 and is therefore ruled out for the same reasons. 9) Attenuation lagoon at Orchard Park (aqua green): This option involves the creation of a lagoon at Orchard Park. The lagoon would be formed using earth banks that intersect the flow route. 10) Include storage in the redevelopment of Orchard Park: Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

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Technical note Without firm plans for the redevelopment of Orchard Park there is no opportunity to deliver this option and so it is ruled out. 11) Divert Creyke Beck and Wanlass Beck into Counter Dyke Creyke Beck and Wanlass Beck intersect the surface water flow paths from Eppleworth and Skidby. Diverting surface water from Wanlass Beck to Counter Dyke reduces the amount of water that spills out of Wanlass Beck during extreme events. Ultimately, the diverted surface water reaches Beverley & Barmston Drain. This options is ruled out because at times of flood the Beverley & Barmston Drain is at full capacity and so it is not possible to the divert the flow. 12) Divert Creyke Beck and Wanlass Beck into Counter Dyke via a high level carrier: This option is similar to option 11. A high level carrier would start at a point along Dunswell Road and cross the field to the east. The route passes under power lines and over North Moor lane and this would need further consideration. Compared with option 11 a high level carrier will be more costly and introduce the need for supplementary drainage where the new bank intersects existing drainage paths. A diversion option would work without a high level carrier and therefore this option is ruled out. 13) Divert Creyke Beck and Wanlass Beck into Counter Dyke with additional storage: This option is similar to option 11. It however provides a means of storing the diverted water at times when it cannot be discharged to Beverley & Barmston Drain.

14) Divert Creyke Beck and Wanlass Beck into Counter Dyke via a high level carrier with additional storage: This option is similar to option 12 and is ruled out for the same reasons. 15) Construction of a pumping station to the east of Creyke Beck and a rising main taking water from Creyke Beck and Wanlass Beck straight to the : Construction of a pumping station would be expensive and so this option is ruled out. 16) Construction of a new carrier pipeline from the junction of Creyke Beck and Wanlass Beck straight to the Humber: This option is complex and given the site constraints it is ruled out. 17) Reopen historic watercourses: This option may be suitable for solving local flooding in Hull but is not technically viable to meet the objectives of this study and so is ruled out. 18) Property level flood defences: Given the number of properties in the area this option is ruled out because it would be costly.

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Technical note 19) Offline pumped attenuation: Pump infrastructure is costly to maintain and operate and so this option is ruled out. 20) Construction of storage in the field to the east of Priory Road with a gravity return to the sewer system This option would require a significant amount of new infrastructure to divert flows to the site. Discharging to the sewer is not sustainable and so this option is ruled out. Out of the long list of options two options have been considered in detail for reducing flood risk to Orchard Park, these are:

• 9) Attenuation lagoon at Orchard Park (aqua green) - Build an embankment around the north and west boundaries of Orchard Park and tie into higher land. The location of the proposed embankment is indicated by the green line in the figure below.

Orchard Park - Attenuation lagoon at Orchard Park (aqua green)

• 13) Divert Creyke Beck and Wanlass Beck into Counter Dyke with additional storage - This is the same as Option 9 but also involves connecting Creyke Beck to Counter Dike using the existing drains as a diversion route. The location of the diversion route is shown in the figure below. It would not be possible to discharge any diverted flood flows from Counter Dike into Beverley and Barmston Drain during a flood event. Therefore, for design purposes, it is assumed the outfall at the downstream Registered office: Vineyard House 44 Brook Green London W6 7BY. Registered in England and Wales. Registered number 3415971

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Technical note end of Counter Dike would remain closed for the duration of the flood event.

Orchard Park - Divert Creyke Beck and Wanlass Beck into Counter Dyke with additional storage

The Aqua Green with diversion option will benefit the wider community including Cottingham because flood water is diverted to a storage site rather than flowing overland through Cottingham.

Preferred Option Divert Creyke Beck and Wanlass Beck into Counter Dyke with additional storage: This involves diverting Creyke Beck into Counter Dyke. This involves construction of a culvert under Dunswell Road and North Moor Lane to connect Creyke Beck to the existing drains which flow into Counter Dyke. It is possible to prevent the stored water from passing north of the A1079 with the use of non- return values installed in the drains. The existing dyke from Dunswell Road to North Moor Lane would be widened to carry the flow. A new embankment would be constructed to control the stored water. This embankment would include land drain to allow rainfall/ground water to discharge into counter dyke once the flood level has receded. Key risks that are envisaged with this option taken forward are as follows:

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Technical note § Stakeholder agreement for using the land as an aqua green § Landowner agreement § Conflicts with underground services for pipe crossing § Suitability of ground conditions for creating bunds near Counter Dyke. § Agreement of works in vicinity of ground water source protection zone Orchard Park - Costs Costs have been estimated for the aqua green option which includes:

• Diversion pipes at Dunswell Road and North Moor Lane. • Widening of the existing drain between Dunswell Road and North Moor Lane • Embankment along the south of Counter Dyke • 60% optimism bias on the capital costs The estimated cost for this option is £2.83M.

The estimated capital costs for the aqua green option is £2.38M. Maintenance costs include grass cutting and clearing the drains. The annual cost of this is estimated to be £3,000. Over a 100 year appraisal period the present value of maintenance is £89,500. Orchard Park - Damages Refer to Section 3.5, (Derringham) for an explanation of the damage assessment. Orchard Park (Hull CC area) - Benefits

Option Damages (£M) Benefits (£M)

Do Nothing 23.74

Orchard Park Embankment / 1.50 22.24 Aqua Green

Orchard Park Diversion 1.50 22.24

Orchard Park (Cottingham) - Benefits

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Technical note

Option Damages (£M) Benefits (£M)

Do Nothing 0.29

Orchard Park Embankment / 0.29 0 Aqua Green

Orchard Park Diversion 0.24 0.05

Outcome Measure Orchard Park Cottingham

2 922 4

2b 617 0

3 617 0

The damage and benefit values above assume there is no sewer capacity as outlined in section 1.5. In some circumstances the sewers may be able to accept flow from Wanless and Creyke becks and therefore the damages may be overestimated. However, to demonstrate the robustness of the business case for Orchard Park 'Do Something' option, a sensitivity test has been carried out where the Do Nothing damages for events smaller than the 1 in 10yr (10% annual probability) flood have been omitted. The results show damages for the 'Do Nothing' option would reduce from £23.74M to £15.51M. However, this reduction would still provide a benefit cost ratio of 4.8, which is still high enough to justify this scheme on economic grounds. Orchard Park - Benefit / Cost ratio The PV benefits are £22,290,000, and the PV costs are £2,923,700, giving a benefit / cost ratio of 7.6.

Conclusions Derringham The preferred option with a benefit cost ratio of 1.3 is the aqua green. This option delivers benefits to the wider community of Willerby. Orchard Park

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Technical note The preferred option with a benefit cost ratio of 7.6 is the aqua green with diversion to Counter Dyke. This option delivers benefits to the wider community of Cottingham. This option also prevents flow from entering the sewer system and therefore delivers associated sustainability and economic benefits.

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