www.metengineers.com
Trustee’s of
Mrs E Guthrie’s 1991
settlement
Development at Racecourse Road East Ayton Scarborough
Flood Risk Assessment
And Drainage Strategy
Ref-13686-5000
Revision No 00
November 2015
Professional, Innovative,
Practical Solutions
Land at Racecourse Road, East Ayton, Scarborough.
Revision Record
Report Ref: 13686-5000-00 FRA
Rev Description Date Originator Checked Approved
00 Initial Report Nov 2015 AK
This report is to be regarded as confidential The Trustee’s of Mrs E Guthrie’s 1991 Settlement. It is intended for your use only and may not be assigned. Consequently and in accordance with current practice, any liability to any third party in respect of the whole or any part of its contents is hereby expressly excluded. Before the report or any part of it is reproduced or referred to in any document, circular or statement and before its contents or the contents of any part of it are disclosed orally to any third party, our written approval as to the form and context of such a publication or disclosure must be obtained.
Prepared For: Prepared By:
Trustee’s of Mrs E Guthrie’s 1991 Met Engineers Limited Settlement Southgate House C/O Mathie Jamie Chartered Surveyors Pontefract Road
Leeds
West Yorkshire
LS10 1SW
Land at Racecourse Road, East Ayton, Scarborough.
Contents Page
1.0 Introduction 1
1.1 Background 1
1.2 Regulatory Guidance 2
1.3 Information Sources 4
1.4 Geology 5
1.5 Hydrogeology & Hydrology 6
1.6 Groundwater Protection 6
1.7 Current Environment 9
1.8 Historical Notes 9
2.0 Flood Risks and Mitigation 10
2.1 Main River Flooding 11
2.2 Non Main River Flooding 13
2.3 Groundwater and Surface Water Flooding 14
2.4 Tidal Flooding 15
3.0 Run-off Assessment 16
3.1 Existing Site 16
3.2 Development Proposal 16
Land at Racecourse Road, East Ayton, Scarborough.
3.2.1 General Drainage Considerations 16
3.2.2 Proposed Foul Drainage 18
3.23 Proposed Surface Water Drainage 18
3.2.2 Sustainable Urban Drainage 18
3.3 Proposed Measures 20
3.4 Sequential Test 21
4.0 Conclusions & Recommendations 22
Land at Racecourse Road, East Ayton, Scarborough.
Appendices
Appendix 1 Site Location
Appendix 2 Site Photographs
Appendix 3 Indicative Flood Plain Map
Appendix 4 Strategic Flood Risk Assessment Plans
Land at Racecourse Road, East Ayton, Scarborough.
1.0 INTRODUCTION
1.1 Background
i. We have been requested by The Trus M E G to undertake a Drainage Strategy and Flood Risk Run Off Assessment, for a parcel of land to the South of Racecourse Road on the Eastern limits of the Village of East Ayton near Scarborough.
ii. The site is predominantly open agricultural land, and at the time of our site visit had recently been ploughed.
iii. The site is roughly rectangular in shape, measuring around 2.18 Hectares, approximately 5.7 Kilometres South West of Scarborough City Centre at map reference 499439 484908.
iv. The site has frontage access onto the public highway of Racecourse Road (A170)and Seamer Road (B1261)and is outlined on the enclosed location plan (Appendix 1)
v. The nearest main watercourse to the site is the River Derwent, flowing in a southerly direction approximately 600m west of the site.
vi. The site falls generally from the North East to the South West by approximately 8m. Highway boundary hedges to Racecourse Road and timber post and rail fence to Seamer Road form the North and south boundary respectively, the western boundary is again defined by Hedgerow to existing residential property with a BT Telephone Exchange in the south west corner to Seamer Road. There is no obvious boundary to the East. vii. The Northern part of the site is allocated within Scarborough Borough Councils (Draft) Local plan designated as residential allocation under policy HA29. viii. The objective of a Flood Risk Assessment is to demonstrate that a proposed development is sustainable in flood risk terms. This means that the development should not itself be at a significant risk of flooding or result in an increased flood risk elsewhere. The guidance given in The National Planning Policy Framework (NPPF) states that Local Authorities should adopt Proactive strategies at a local level through Strategic Flood Risk Assessments.
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ix. As a consequence of NPPF, issued in March 2012, which refers to Flooding and Flood Risk, it is necessary to provide an assessment of the potential problems which are associated with:
a. Permitting the Development.
b. Potential risk of flooding from the watercourse and sewer network.
c. Safety of occupants of the dwellings.
d. Impact upon the local hydrological network.
x. In the absence of a report, the Planning Authority are required to use the P P should refuse the application, unless there are grounds for not doing so.
xi. In order to provide a Flood Risk Assessment, use has been made of the information contained at the offices of the Environment Agency, Yorkshire Water and Scarborough Borough Council.
xii. The Environment Agency and Yorkshire Water have been consulted and their information and comments have been used in this report.
1.2. Regulatory Guidance
i. National Planning Policy Framework (NPPF) along with the Technical Guidance replaces PPS25 and provides the regulatory framework and guidance for Planning Authorities in relation to Flood Risk issues for new developments. Any applications lodged with a Planning Authority will be considered in conjunction with this guidance and dependant on the nature and location of the application, the Planning Authority may request a Flood Risk Assessment as part of the Planning Application documents.
ii. The Environment Agency (EA) are a Statutory Consultee to the Planning Authority in relation to Flood Risk issues. In addition, many Local Authorities have their own Internal Land Drainage Department which advice on Drainage Issues and work with the EA on Strategic issues. The Land Drainage Act 1991 provides a regulatory framework for this arrangement.
iii. The Agency has provided a matrix for Local Planning Authorities, which provides F ‘ A T E Agency Standing advise Development and Flood Ri F tabulates the requirements relative to the scale of development and the predicted
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Flood Zone. The assessment is required for all sites greater than 1Ha in Flood Zone 1, and all sites regardless of size in Flood Zones 2 & 3a.
iv. The Environment Agency have undertaken a national study of flood risk across the whole of England and published flood maps covering the country. The maps can be viewed on the agencies website at www.environment- agency.gov.uk/whatsinmybackyard. Specific locations can be studied by searching either using a postcode or general location. A copy of the Flood Zone Map covering this location is attached in Appendix 5.
v. The EA Flood maps identify 3 zones.
vi. Flood Zone 1. This zone comprises of land with less than 1 in 1000 annual probability of river or sea flooding in any one year (<0.1%) vii. Flood Zone 2. This zone comprises of land assessed as having between a 1 in 100 and 1 in 1000 annual probability of river flooding (1%-0.1%) or between 1in 200 and 1in 1000 annual probability of sea flooding (0.5%-0.1%) in any one year. viii. Flood Zone 3. This zone comprises of land assessed as having a 1 in 100 year or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year.
ix. Flood risks should consider the risk of flooding from all sources ie, tidal and river, surface water and flooding from land, groundwater, sewers and artificial sources, eg canals and reservoirs.
x. The level of detail and complexity of a Flood Risk Assessment can vary considerably, dependant on the scale, nature and location of the planned development. EA guidance sets out the criteria for the level of information which should be included within the FRA.
xi. According to the Environment Agencies Indicative Flood maps, the Application site falls within Flood Zone 1 and is greater than 1Hectare, therefore a site specific Flood Risk Assessment is required. xii. NPPF sets out criteria for vulnerability classifications which are based on the sensitivity of different forms of development. In accordance with NPPF, the intended M V xiii. The Sequential Test: In accordance NPPF LPA should apply the sequential test, to demonstrate that there are no available sites in the area with a lower risk of flooding.
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xiv. The Exception Test: The Exception test is relevant if, following the application of the sequential test, it is not possible for the development to be located in zones of lower probability of flooding. The exception test criteria are detailed in NPPF. The test provides a method of managing flood risk while still allowing necessary development to occur.
xv. Y W S A the standards for adoptable surface water and foul sewers. They also apply development control standards locally which are consistent with current best practice and Building Regulations.
xvi. D - Y W to ensure that there is sufficient time for the company to fully assess the impact of development on their network and Treatment Facilities. This process also ensures that drainage strategies are acceptable in principle, prior to Planning Permission and helps avoid any objections from Yorkshire Water during the Planning Process. xvii. T F W M A change the way developers and Local Authorities approach the design and adoption of SuDS N S DS A B SAB S DS SAB SuDS designs and adopt the constructed drainage. xviii. A new set of SuDS standards is currently out to consultation amongst stakeholders T E S A come into force following adoption of the SuDS Standards and will complement the new standards.
xix. The principals identified in the consultation SuDS standards have been considered in developing the strategy outlined in this report.
1.3 Information Sources:
i. The principal information sources which have been used for this Flood Risk Assessment are:
a. Geological Maps
b. Yorkshire Water Main Drainage
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c. Environment Agency Flood Defence.
d. Scarborough Borough Councils Strategic Flood Risk Assessment.
ii. These have been reviewed in conjunction with an inspection of the current:
a. Geological Maps,
b. Drainage records,
c. Flood maps,
d. Visual inspection of the site and the surrounding area.
1.4 Geology:
i. The BGS 1:50 000 scale bedrock geology description: Malton Oolite Member And Coral Rag Member (undifferentiated) - Limestone, Ooidal. Sedimentary Bedrock formed approximately 156 to 161 million years ago in the Jurassic Period. Local environment previously dominated by shallow carbonate seas
ii. 1:50 000 scale superficial deposits description: Sand and gravel of uncertain age and origin - Sand and gravel. Superficial Deposits formed up to 3 million years ago in the Quaternary Period. Local environment previously dominated by uncertain.
Setting: uncertain. The origin of these deposits is uncertain; they could be river gravels, shallow marine sediments or fluvioglacial outwash spreads; or some combination of these with elements of reworking including solifluction in some instances.
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Land at Racecourse Road, East Ayton, Scarborough. 1.5 Hydrogeology & Hydrology
i. The published Groundwater Vulnerability Map for the area indicates the site to be situated over a Principal Aquifer High. Predominantly lower Permeability layers which may store and yield limited amounts of groundwater due to limited local features such as fissures, thin permeable horizons and weathering.
ii. The site is over an Inner Zone 1 Source Protection Zone. This is defined as the 50 day travel time from any point below the water table to the source. This Zone has a minimum radius of 50m.
1.6 Groundwater Protection
i. It is acknowledged that the site falls over the Zone 1 Groundwater Source Protection Zone (SPZ1) beneath the site for various water supply boreholes.
ii. No Intrusive Investigations have been undertaken at this stage, but record borehole information in the vicinity of the site indicate the site to be underlain with broken yellow sandstone, and blue / yellow sandstone with occasional clay bands to 60m below the site.
iii. Recent discussions with Yorkshire Water and the Environment Agency, have revealed that both Authorities have a common approach to sewers constructed within SPZ1. The Environment Agency refer to Groundwater protection: principals and practice GP3 on the Gov.UK website, but this is not specific in terms of what is a satisfactory in terms of sewer construction. Yorkshire Water have a draft guidance document that is a little more specific, but is not yet released to the public , but they are using it for guidance. The principals to be adopted are roughly outlined in the paragraphs below:
iv. Within SPZ 1 areas there is unlikely to be sufficient time for any contamination entering the ground to be broken down by natural processes in the ground before it reaches the aquifer level.
v. It is imperative that sewers within these environmentally sensitive areas remain water tight to ensure there is no potential for microbiological contamination of the groundwater source, particularly with SPZ 1 boundaries.
vi. Groundwater protection measures are required by the Water Framework Directive and Groundwater protection: Policy and practice (GP3) published by the Environment Agency.
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vii. YWS require that additional protection measures are installed on new foul sewers, including pumping stations and manholes, within SPZ 1 boundaries due to the high concentrations of contaminants present in foul sewage and the risk of contamination of the groundwater source. viii. YWS have identified three preferred options for the construction of foul sewers within SPZ 1 boundaries. These options are listed in order of preference in table 2 below.
Table 2
Preference Protection measure
1 Standard sewer with internal liner
2 Cement lined ductile iron pipes with anchored joints
3 Lining with close fit pipes and the annulus grouted
ix. The disposal of surface water through the use of soakaways/infiltration systems within any SPZ will only be acceptable for uncontaminated surface water arising from building roofs with continuous down pipes without any other inlets (such as gullies).
x. Surface water arising from areas of hardstanding other than building roofs must be disposed of to surface water sewer within SPZ 1 boundaries.
xi. Where potentially contaminated surface water, e.g. arising from trafficked areas, could enter the surface water sewer then the sewer outfall point into a receiving watercourse shall be outside and downstream of the SPZ 1 boundary. xii. Surface water arising from car parks with more than 50 car parking spaces must pass through a fuel interceptor and be attenuated before discharging into a foul water sewer within an SPZ 1 boundary. xiii. YWS have identified three preferred options for surface water storage within SPZ 1 boundaries. These options are listed in order of preference in table 3 below.
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Table 3
Preference Surface water storage system
1 Above ground storage – lined dry basin
2 Plastic pipe with integral electrofusion welded joints
3 Plastic pipe with manually welded joints
Groundwater source protection zone
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Land at Racecourse Road, East Ayton, Scarborough. 1.7 Current Environment
i. The site is currently open agricultural land, and at the time of our site visit, had recently been ploughed and probably seeded with a crop.
ii. Yorkshire Water record plans show public sewers in both Racecourse Road and Seamer Road. A 225mm diameter combined sewer is shown in the far side of Racecourse Road running the full length of the site boundary. A 225mm diameter combined sewer is shown to run in Seamer Road terminating at a point 100m away from the South west corner of the site.
iii. From visually reviewing the topography of the site it is clear that the site is wholly permeable and will shed surface water in a south/ south easterly direction collecting in a low area beyond the site boundary adjacent to the field boundary to the Seamer Road. This is confirmed by the Environment Agencies Surface Water Flood risk plan attached in Appendix 3. Redevelopment of the site for residential purposes will reduce this risk as surface water is collected through the drainage network and attenuated, reducing the risk of flooding on the sites surroundings.
iv. The River Derwent is the nearest watercourse to the site, flowing from the North to the South approximately 600m west of the site. The Derwent rises in the North Yorkshire Moors above Fylingdale travelling southwards to its confluence with the River Herlford North of Ganton then westwards through the Vale of Pickering, and the Vale of York before joining the Ouse at Barmby on the Marsh.
1.8 Historical Notes
i. The Environment Agencies Surface Water Flood Map for this area (Appendix 3) shows the site to be at low risk of flooding from surface water.
ii. The Environment Agencies indicative flood plain map for this area (Appendix. 3) shows the site to be wholly within Flood Zone 1, i.e. having a less than 1 in 1000 annual probability of River or Sea Flooding (<0.1% ) in any year. This is confirmed within the Local Government Strategic Plan.
iii. Yorkshire Waters records database (DG5 Register) shows no attendances in the immediate vicinity of the site, historically there are reports of sewer flooding occurring further south of West Ayton.
iv. There are no reports of historical flooding on this site
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2.0 FLOOD RISKS AND MITIGATION
i. This section describes the potential sources of flooding and their impact on the proposed development and where required, the proposed mitigation measures.
ii. An established framework for environmental risk assessment that can be effectively applied to Flood Risk Assessment is the Source Pathway Receptor Model
a. Sources: The weather and other elements that can trigger flooding
b. P T becomes flooding.
c. Receptors: The people, properties and natural environment that are affected by flooding.
iii. The North East Yorkshire Strategic Flood Risk assessment identifies two principal of flooding within the East and West Ayton catchment :
a. Surface Run-off/ Groundwater Flow flooding
b. Sensitive to changes in Surface Water run- off.
iv. The Pathways are in general the Rivers, drains, sewers and aquifers. High flows in the rivers, drains and sewers can exceed drainage networks and high subterranean ground water levels can cause flooding from artesian pressure.
v. The receptors to flooding in the East Ayton catchment are people, the built environment, agricultural land, infrastructure and environmental assets. Major floods can have significant impact on these receptors.
vi. All these flood risks are described in the sections following.
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2.1 Main River Flooding
i. Flooding from rivers and other natural water courses is usually caused by prolonged and intense rainfall generating high rates of run-off in connection with High Tides which overwhelm the capacity of the river to convey the water downstream.
ii. The River Derwent flows from Fylingdales Moor in the North York Moors National Park, then southwards as far as its confluence with the River Hertford then westwards through the Vale of Pickering, south through Kirkham Gorge and the Vale of York, joining the River Ouse at Barmby on the Marsh. The confluence is unusual in that the Derwent converges on the Ouse at a shallow angle in an upstream direction.
iii. The River Derwent catchment area includes the Upper Derwent, River Rye, River Hertford, Bielby Beck and Pocklington canal and their tributaries. It covers an area of 2,057 square kilometres and includes the towns of Stamford Bridge, Malton, Pickering, Helmsley, Filey and Scarborough. The area is bounded by the Cleveland Hills, North York Moors and Hambleton Hills to the north, the Yorkshire Wolds and the coast to the east, the Vale of York to the west and the River Ouse and Humber Estuary to the south. The area around the river is primarily rural in nature with grazing moorland in the upland areas and a variety of agricultural uses at lower levels.
The Derwent starts its course at Lilla Rig on the North York Moors a few miles from the east coast of Yorkshire. After collecting the waters of the Jugger Howe Beck, Black Beck and Troutdale Beck it flows south through the Forge Valley to West Ayton. From there it continues across lower ground to where it is joined by the River Hertford. The Sea Cut, a man made channel, connects the Derwent to the North Sea near Scarborough to alleviate flooding in the lower reaches of the Derwent, downstream of the Cut. This management area is about 127 km² and largely rural with no major settlements. The landscape is upland moors in the upper reaches with lower lying flatter land near Hackness. The river flows through the narrow Forge Valley and several designated natural conservation sites. Water is retained behind a weir at West Ayton and there are sink holes in the river bed where river water is lost to underlying aquifers, so that in drought years the river below the weir may run dry.
iv. Since the last major flood event of 2000, the Environment Agency, Internal Drainage Board and Lead Flood Authority undertake regular inspection of Critical Ordinary Watercourses and their assets throughout the District. Through data gathering they
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are able to carry out routine and proactive channel maintenance and are committed to regular maintenance and defence improvement activities.
v. Flood flows from the headwaters of the River Derwent are controlled by a major flood diversion channel , the Sea Cut, which diverts flood flows from just upstream of Forge Valley (North of West Ayton) to the sea at Scalby. This channel has been artificially created to provide flood relief to properties at East and West Ayton. This watercourse has been accorded Main River Status. Despite this, the Strategic Flood Risk Assessment indicates that 9 properties in West Ayton are still at risk of flooding from the 1.33% annual exceedance event due to overtopping of the defences to Sea Cut.
vi. The Environment Agencies Indicative Flood Plain maps shows the site to be in Flood Zone 1. This zone comprises of land assessed as having a less than 1 in 1000 annual probability of river or sea flooding. (<0.1%)
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Land at Racecourse Road, East Ayton, Scarborough. vii. The SFRA Level 1 study shows the site to be in Flood Zone 1. This zone comprises of land assessed as having a less than 1 in 1000 annual probability of river or sea flooding (<0.1%). A copy of the Strategic Flood Map is attached in Appendix 4.
viii. The site is at Low risk of flooding from River and Sea.
2.2 Non Main River Flooding
i. Ordinary Watercourses are those Rivers and Streams that are not designated Main River and are therefore the responsibility for maintenance and mitigation falls with the Local Authority. A number of the ordinary watercourses within the North East Yorkshire Catchment are designated Critical Ordinary Watercourses. This designation reflects a known issue with respect to flooding, and is generally associated with limited channel capacity, channel constrictions and a poor maintenance regime.
ii. Many constructed drainage systems such as pipes, sewers, land drainages and drainage channels exist to manage run off from developments. During prolonged periods of heavy rainfall, flooding may occur if the rainfall event exceeds the capacity of the drainage system or the system becomes blocked or inefficient through lack of maintenance. Flooding will also occur if the system surcharges due to a high water level within the receiving watercourse.
iii. There are no Critical Ordinary Watercourses in the vicinity of the site
iv. The drainage system will be designed to a recognised industry standard in a manner that will not increase contributing flows into the adjacent network. NPPS requires that surface water from a development site should as far as practicable be managed in a sustainable manner to mimic surface water flows arising from the site prior to the proposed development, whilst reducing the flood risk to the site itself and elsewhere taking climate change into account.
v. Current guidance indicates that in order to take full account of the climate change event, a 30% increase in rainfall should be accommodated.
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2.3 Ground water and Surface Water Flood Risk
i. High ground water levels can cause flooding if the water table level exceeds the natural ground level. Any significant rainfall particularly where this occurs for a sustained period can increase ground water levels and may result in flooding. The risk of ground water flooding is considered to be greatest where areas are underlain by permeable rocks that form major aquifers.
ii. The nature of the catchment geology means that ground water could be a significant issue in this catchment. Figure 5.1 within the Strategic Flood Risk Assessment shows incidences of River flooding and sewer flooding within the Southern limits of West Ayton but there are no recorded instances of Ground water flooding in the immediate vicinity of the site.
iii. There are several BGS boreholes to the west of the site, focused in a corridor along the River Derwent, but none within the site itself. These show drift deposits comprising of Yellow sands becoming more gravelly with depth but extending 10m below the surface. Bedrock is described as broken and fissured grey Limestone. Water was struck at 16m and 17.5m in the fissured Limestone, below this level there was too much water to identify individual water strikes. A visual inspection of the site did not reveal any sources of ground water from the site.
iv. Flooding from overland flows is caused when the intensity of rainfall exceeds the infiltration capacity of the surface onto which it falls, or when, during prolonged periods of wet weather, the soil becomes so saturated that it cannot accept any more water. Developments that include significant impermeable surfaces, such as roads, car parks and roofs, may increase the occurrence of overland flow.
v. Overland flow will tend to occur for a similar period of time as the rainfall event that causes it, however, the flood water may remain for some time after accumulating at the surface in low areas with no significant outlet.
vi. The Environment Agencies Surface Water flood maps attached in Appendix 3 shows the site to be at low risk, but does indicate a track of water roughly following the Eastern boundary of the site, focusing in a collection of water beyond the boundary, adjacent the field boundary to the Seamer Road. vii. Developments can enhance the risk of flooding from overland flows due to the increased volume of surface water run- off. In the case of the Racecourse Road Site impermeable areas are significantly increased over that of the existing. However,
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surface water attenuation and improved drainage and maintenance of the drainage network will ensure better control of surface water.
2.4 Tidal Flooding
i. The site is shown to be within Zone 1 of the Environment Agencies indicative Flood map for Rivers and sea. Therefore the site is at Low Risk of flooding from Tidal surge.
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3.0 RUN-OFF AND DRAINAGE ASSESSMENT
3.1 Existing Site
i. The site is predominantly open agricultural land, located on the Eastern fringe of the village of East Ayton.
ii. Building Regulations stipulates a hierarchical approach to the disposal of Surface Water by recharging ground water through the use of soak- watercourse, and only if these are not a viable option, draining to the public sewer network.
iii. Soak away tests have not been undertaken on the site at this stage but BGS record boreholes around the site show that the underlying soils and rock may sustain soak away s.
iv. The site is over an Inner Zone 1 Source Protection Zone. This is defined as the 50 day travel time from any point below the water table to the source.
v. The redevelopment of this site will need to fully comply with the requirements of NPPF, Yorkshire Water, Environment Agency and the Planning Authority.
3.2 Development Proposal
3.2.1 General Drainage Considerations
i. There is no current proposal for the site. This application seeks to establish a residential use for the land outlined on the Location Plan attached in appendix 1
ii. The overall site area under consideration amounts to around 2.18Ha and will likely comprise of dwellings with associated gardens, drives, estate roads and Public Open Space areas.
iii. Foul drainage for the site will have to be designed in accordance with Sewers for Adoption 6th Edition and procured through the Section 104 Agreement process with Yorkshire Water. The Surface Water drainage system should be designed not to
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flood in the 1 in 30 year storm event, and any flood waters arising from the 100year Climate Change event are contained within the site so as not to increase the risk of flooding elsewhere.
iv. No Intrusive ground investigation information is available at this time. From reviewing BGS record borehole logs in the locality there are several BGS boreholes to the west of the site, focused in a corridor along the River Derwent, but none within the site itself. These show drift deposits comprising of Yellow sands becoming more gravelly with depth but extending 10m below the surface. Bedrock is described as broken and fissured grey Limestone. Water was struck at 16m and 17.5m in the fissured Limestone.
v. Any subsequent Ground Investigation should undertake soak-away testing within the near surface soils, boreholes should also be undertaken to determine the depth of cover to the Aquifer below the site.
vi. The site is situated within Ground Water Source Protection Zone 1 (SPZ1) Within SPZ 1 areas there is unlikely to be sufficient time for any contamination entering the ground to be broken down by natural processes in the ground before it reaches the aquifer level. vii. It is imperative that sewers within these environmentally sensitive areas remain water tight to ensure there is no potential for microbiological contamination of the groundwater source, particularly with SPZ 1 boundaries. viii. Groundwater protection measures are required by the Water Framework Directive and Groundwater protection: Policy and practice (GP3) published by the Environment Agency.
ix. The Environment Agency and Yorkshire Water have three preferred options for the construction of Foul sewers within SPZ1 boundaries, in order of preference these are 1. Standard sewer with cured in line Internal Liner. 2. Cement Lined ductile iron pipes with anchored joints. 3. Lining with close fit pipes and the annulus grouted.
x. There are also three preferred options for surface water storage within SPZ1 boundaries, in order of preference these are 1. Above ground storage- Lined dry basin. 2. Plastic Pipes with Electrofusion welded joints . 3. Plastic pipes with manually welded joints.
xi. Any surface water outfall from the site must be restricted to the Existing Greenfield run-off rate for the site. Based on a site area of 2.18 Ha, this equates to 3.2litres per second from all sources.
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3.2.2 Proposed Foul Drainage
i. The natural topography of the site dictates that Foul sewers should drain through the South West corner of the site to the head of the 225mm diameter Combined sewer in Seamer Road.
ii. Further investigation is recommended to establish the relative depths of the Combined sewer network downstream in Seamer Road to enable the Drainage designer to determine the best point of connection to the system and whether the requisition procedure is required.
iii. The proposed Foul sewer network for the site should be offered for Adoption by Yorkshire Water under Section 104 of the Water Industries Act 1991 to safeguard the future maintenance of the drainage infrastructure.
iv. In preparing more detailed layouts, designers should consider that Yorkshire Water will require a 6m Sewer Easement around any sewer not located within public highway. They will also require a 5m stand-off distance to any tree planting.
3.2.3 Proposed Surface Water Drainage
i. Piped discharge of Surface Water drainage from this site should only be made into the adopted sewer network if there is no other sustainable drainage outfall available. There are a couple of SUDS options available for the site, but these are heavily limited with the site located within SPZ1.
ii. Any surface water outfall from the site must be restricted to the Existing Greenfield run-off rate for the site. Based on a site area of 2.18 Ha, this equates to 3.2litres per second from all sources.
iii. Any proposed surface water drainage for the site should be offered for adoption either, through a Section 104 agreement with Yorkshire Water, or a section 38 agreement with the Highway Authority to safeguard the future maintenance of the drainage network.
3.2.4 Sustainable Urban Drainage Systems
iv. In determining the arrangements for surface water disposal, the use of SUDS has been considered.
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o Green Roofs Green roofs are more viable on flat roofs and these are not a heavily featured character of this rural area. Such provision of Green roofs would more than likely put restrictive additional construction costs and maintenance implications for the developer and ultimately, the householder, and are considered to outweigh the benefits of the green roof system.
o Basins and ponds Surface Water attenuation ponds could be utilised within any open space features, but these would need to be located adjacent to the southern boundary to be effective. Whether these are fully lined ponds, or allowed to infiltrate into the sub soils depends on the depth of cover above the aquifer. Yorkshire Water will adopt open balancing ponds if their design criteria is fulfilled and the land dedicated as part of the Section 104 agreement. Vehicular access to any control structures is essential. Early consultation with Yorkshire Water and the Environment Agency is essential, once Ground Investigation reports are available.
o Filter strips and Swales Representations have been made to Yorkshire Water to obtain their stance on swales as they have not historically been receptive to them. The response was a little more positive than expected, but still raised many issues of management and function. Due to the heavy limitations placed on drainage within SPZ1 boundaries, it is not an option to incorporate swales, reliant on filtration, within the development proposal due to the risk of contamination of the aquifer. Yorkshire Water historically have issues with land drainage systems draining into their network, and as the sewer network generally in the area is a combined system with some downstream historic flooding issues they need to be sure that such systems are appropriately maintained and function in a manner that does not burden them with a liability. Much work has to be done in establishing a framework for the future in SUD schemes within developments, however the timeframe for agreeing acceptable design principals, maintenance agreements and commuted sum payments are not compatible with the timeframe required to deliver this scheme. Due to these constraints, we do not feel it is likely that this could be adequately resolved in the time frame required, but we are encouraged by Yorkshire Waters consideration of this issue.
o Infiltration devices Full Intrusive Ground Investigations will need to be undertaken to determine the suitability of the sub surface soils for soakaways. If this proves viable, then soakaways could be used in a limited manner that also protected the aquifer within SPZ1. Soakaways could be used to drain roof water from dwellings if sealed rainwater down pipes are used to prevent pollution. Soak away s used for the disposal of highway water are unlikely to be supported by the
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Environment Agency due to the risk of contamination of the aquifer below the site. The site is located over a Major Aquifer of High vulnerability. Predominantly lower Permeable layers which may store and yield large amounts of groundwater due to local features such as fissures, thin permeable horizons and weathering. The site is over an Inner Zone 1 Source Protection Zone. This is defined as the 50 day travel time from any point below the water table to the source. This Zone has a minimum radius of 50m. Early consultation with Yorkshire Water and the Environment Agency is essential, once Ground Investigation reports are available.
o Permeable surface and filter drains Porous paving could possibly be used for private drives and paths if it can be demonstrated that pollutants would be filtered out prior to discharge of surface water to the aquifer. Any Ground Investigation on the site will need to determine the Hydraulic profile of the aquifer across the site to ensure an adequate carry distance is achieved to filter pollutants. Early consultation with Yorkshire Water and the Environment Agency is essential, once Ground Investigation reports are available.
o Tanked systems There is likely to be some form of Surface Water attenuation system provided on the site, the extent of this will be determined by percolation tests and the Hydraulic profile of the aquifer across the site. Yorkshire Water and the Environment Agency require any underground Surface Water attenuation to take the form of Plastic pipes with electrofusion/ manually welded joints. The system will need to be designed to cater for the 100 year rainfall event with a 30% climate Change allowance to mitigate the impact from the development on its surroundings. Outlet control will need to be provided in the form of a Vortex Control device with a maximum output of 3.2 Litres per second.
o Recycling - Consideration should also be given to provide properties with a rainwater collection butt to the rear of properties for use on garden areas.
v. The use of any of these systems will be determined initially by percolation tests, and secondly, by its risk to the aquifer. Early consultation with Yorkshire Water and the Environment Agency is essential, once Ground Investigation reports are available.
3.3 Proposed Measures
i. Ideally the use of soakaways to dispose of all surface water from the development would be the preferred option. If the risk to the aquifer was considered too great, then a combination of soakaways from roof water, and attenuation of Highway run-
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off into any adjacent Highway drainage system at the stipulated outlet rate of 3Litres per second would be one option.
ii. If percolation tests proved to be inadequate, or disposal of surface water from any source was felt to be an unacceptable risk to the aquifer, then attenuation would need to be provided for all impermeable areas of the site within an open attenuation pond, underground storage pipes, or a combination of both.
iii. The system will need to be designed to cater for the 100 year rainfall event with a 30% climate Change allowance to mitigate the impact from the development on its surroundings. Outlet control will need to be provided in the form of a Vortex Control device with a maximum output of 3.2 Litres per second.
iv. The final Foul and Surface Water design will likely be subject to a subsequent reserved matters application, when the design team will be more fully informed of the most viable options.
v. The proposed Surface Water sewer network for the site should be offered for Adoption by Yorkshire Water under Section 104 of the Water Industries Act 1991, or Section 38 of the Highways Act, depending on which option is used, to safeguard the future maintenance of the drainage infrastructure.
vi. In preparing more detailed layouts, designers should consider that Yorkshire Water will require a 6m Sewer Easement around any sewer not located within public highway. They will also require a 5m stand-off distance to any tree planting.
3.4 Sequential Test
i. The aim of the sequential Test, as outlined within National Planning Policy Framework Technical Guidance, is to encourage development to be located in areas at the lowest probability of flooding. The Proposed development site is situated within Flood Zone 1 and therefore satisfies the requirements of the Sequential Test.
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4.0 CONCLUSIONS & RECOMMENDATIONS
i. The current proposals to be submitted for Planning are to develop the site as a residential development.
ii. The site lies within Zone 1 of the Environment Agencies Indicative flood plain. The site is also shown to be within Zone 1 of the North East Yorkshire SFRA Level 1 study
iii. In accordance with NPPF Technical Guidance, Table 2: Flood risk vulnerability Classification the site is classed More vulnerable. Table 3 shows that more vulnerable development within Zone 1 is considered appropriate.
iv. The natural topography of the site dictates that Foul sewers should drain through the South West corner of the site to the head of the 225mm diameter Combined sewer in Seamer Road.
v. Ideally the use of soakaways to dispose of all surface water from the development would be the preferred option. If the risk to the aquifer was considered too great, then a combination of soakaways from roof water, and attenuation of Highway run- off into any adjacent Highway drainage system at the stipulated outlet rate of 3Litres per second would be one option.
vi. If percolation tests proved to be inadequate, or disposal of surface water from any source was felt to be an unacceptable risk to the aquifer, then attenuation would
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need to be provided for all impermeable areas of the site within an open attenuation pond, underground storage pipes, or a combination of both.
vii. Assessment should take account of the 100 year event and Climate Change for the lifetime of the development and this currently indicates an approximate 30% increase in rainfall intensity for the lifetime of the development.
viii. Consideration should also be given to providing rainwater collection butts for use on garden areas.
ix. Development of the site in the manner outlined in this report will reduce the risk of flooding to the site and the surrounding catchment upstream and downstream.
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Land at Racecourse Road, East Ayton, Scarborough. Appendix 1
Site Location Plan
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Land at Racecourse Road, East Ayton, Scarborough. Appendix 2 Photographs
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Racecourse Road Frontage
Racecourse Road- South-To Seamer Road.
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Land at Racecourse Road, East Ayton, Scarborough.
Seamer Road Boundary Looking East
Seamer Road Boundary viewed across the site
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Appendix 3 Indicative Flood Plain Map
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Flooding from Rivers and Sea
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Risk of Flooding from Surface Water
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Flood Map for Planning (Rivers and Seas)
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Risk of Flooding from Reservoirs
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Appendix 4 Strategic Flood Risk Assessment Plans
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Existing Flood Risk Zones in East Ayton
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Revision Number 00 A1 °! Legend ^_ Reported Main River Flooding .! 13/01/2010 15:41:23 ^_ ^_ Reported Ordinary Watercourse Flooding XW )" Reported Coastal Flooding XW .! # ^_ * Reported Groundwater Flooding %, Reported Groundwater and kj Surface Runoff Flooding XW Reported Surface Runoff Flooding .! XW .! XW kj Reported Sewer Flooding XW ^_^_)" XW .! .! Reported Drainage Issues )" kj kj XW )" Whitby kj!( (! Large settlements .!kj ^_ Main River
^_ XW Flood Zone 1 ^_ .!XW^_ .! ^_ ^_ Flood Zone 3 .! ^_ ^_.! XW .! XW XW Flood Zone 2
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XW ^_ XW .! XW XW .! ^_ ^_ XW ^_.! ^_^_^_^_ XW ^_^_ ^_^_ XW .! .! .! XW ^_XW ^_ XW .! XW XW .!^_ XW^_XW ^_ ^_XW kj ^_ ^_ kj ^_ kj Scarboroughkjkj)" XW XW kj (! )" ^_ kj kj)" kjkj XW Kirkbymoorside !(XW ^_ XW kj ^_ ^_ ^_^_.! XW .! ^_ ^_ XW ^_XW ^_ ^_.! kj .!XW Pickering ^_kjkj kj ^_ Helmsley ^_ .! XW ^_ .!XW!( ^_ ^_ .! kj .! XW (! XW ^_ kj XW^_ .! kj kjkjkj.! ^_ ^_ ^_ .! XW XW XW.! XW .! ^_ ^_ .! .! .! XW XW ^_ ^_ XW.!.! kj .! XW ^_ ^_ ^_ .! kjXW .! .! XW XW kj kj !(kj ^_ FileyXWkjkj ^_ ^_ .!XW ^_^_ %, %, %,.!XW XW ^_ ^_ ^_ ^_ !( ^_ Hunmanby kj ^_ %, ^_ kj ^_ ^_ ^_ kj .!XW.! NOTES: 1) For indication only
XW 2) The locations of reported flooding incidents are based on information from a variety of sources, and the accuracy of reported locations is variable. ^_ ^_ This figure should not be relied upon to identify Malton and Norton the precise location where a reported event has *#.!.! occurred. (!^_*# This map is reproduced from Ordnance Survey material with the ^_ permission of Ordnance Sruvey on behalf of the controller of Her Majesty's Stationary Office. Crown Copyright. Licence No's .! ^_ 10002193, DSCA100. ^_ F1 2010-01-13 FH AM GF ^_ ^_ Issue Date By Chkd Appd XW Metres XW ^_ %, 01,750 3,500 7,000
.!
Admiral House Rose Wharf 78 East Street Leeds ^_ LS9 8EE Client ^_ XW Ryedale District Council, Scarborough Council and North York Moors National Park Authority Job Title kj ^_ Northeast Yorkshire Strategic Flood Risk Assessment Update
^_ Drawing Title Existing Flood Risk in Northeast 2 Water\0-12-20 GIS\Workspaces\NEYorkshire_LargeMaps.mxd Yorkshire
^_ Scale at A1 .! 1:125,000 Drawing Status For Issue
Job No Drawing No Issue 209466-00 5.1 F1 \\global\europe\Leeds\Jobs\200000\209466-00\0Arup\0-1 Template A1: Version 2 © Arup A3 ! Legend ° More Vulnerable Intermediate Vulnerability 13/01/2010 13:58:17 Less Vulnerable
This map is reproduced using Ordnance Survey material with the permission of Ordnance Survey on behalf of the controller of Her Majesty's Stationary Office, Crown Copyright. Licence numbers 100021930, DSCA100.
F1 2010-01-13 HB AM GF
Issue Date By Chkd Appd
Metres
0 750 1,500 3,000 xd
Rose Wharf 78 East Street Leeds LS9 8EE Tel +44 (0)113 242 8498 Fax +44 (0)113 242 8573 www.arup.com Client Ryedale District Council, Scarborough Borough Council and North York Moors
Job Title Northeast Yorkshire Strategic Flood Risk Assessment Update Water\0-12-20 GIS\Workspaces\NEYorkshire_SurfaceWaterMaps.m Drawing Title Areas Susceptible to Surface Water Flooding: Sherburn, Staxton & Willerby, Snainton, East & West Ayton, Seamer, Flixton, Brompton and Irton
Scale at A3 1:50,000
Drawing Status For Issue
Job No Drawing No Issue 209466-00 6.3.6 F1 \\global\europe\Leeds\Jobs\200000\209466-00\0Arup\0-12 Template A3: Version 2 © Arup
Land at Racecourse Road, East Ayton, Scarborough.
Appendix 5 Yorkshire Water Records
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499439 : 484908 Map Name : SE9984NW Title
Yorkshire Water, Notes PO Box 500, Halifax Road, Partial Key This plan is furnished as a general guide only and no warranty as to Bradford BD6 2LZ its correctness is given or implied. This plan must not be relied Foul Sewer = F upon in the event of excavations or other works made in the vicinity Contact Name : of public sewers. No house or property connections are shown. Combined Sewer = C Adam GIRDLESTONE Surface Water Sewer = SW Contact Tel : Trade Sewer = TD
Partially Separate = PS
Date Req : 07/10/2015, 11:34:16 Date Gen : 07/10/2015, 11:34:19
Source : Sewer Network Enquiry
UPN: Undefined Originator: Adam GIRDLESTONE, Safemove,