Littleport Co-located Schools

Littleport Co-located Schools February 2015 Morgan Sindall

Littleport Co-located Schools 330763 BNI BSE 003 C P:\Cambridge\Murdoch\EST\PROJECTS\330763 Littleport Co-located Schools\12.0 Documents\12.2 Outgoing\ February 2015 Littleport Co-located Schools February 2015 Morgan Sindall Ashwell Point Babraham Road Sawston Cambridge CB22 3LJ Mott MacDonald, Demeter House, Station Road, Cambridge CB1 2RS, United Kingdom T +44 (0)1223 463500 F +44 (0)1223 461007 W www.mottmac.com

Contents Chapter Title Page 1 Introduction 1 1.1 Introduction and Methodology 1 1.2 Site Setting and Topography 1 1.3 Local Geology 2 1.4 Hydrological and Hydrogeological Setting 3 1.5 Existing Surface Water Drainage 4 1.6 Proposed Development 5 2 Flood Risk 6 2.1 Flood History and Existing Flood Defences 6 2.2 Flood Zone Designation 6 2.3 Assessment of Sources of Flooding 6 2.3.1 Fluvial Flooding 6 2.3.2 Groundwater Flooding 7 2.3.3 Pluvial Ponding and Surface Water Overland Flow 7 2.3.4 Existing adjacent Field Ditch Flooding 8 2.3.5 Sewer Capacity 8 2.3.6 Reservoir Infrastructure Failure 8 2.3.7 Tidal and Estuary Flooding 8 3 Post Development Flood Risk 9 3.1 Vulnerability and Flood Zone Compatibility 9 3.2 Surface Water Management and Drainage Strategy 10 3.2.1 Impermeable Areas and Permeable Surfacing 12 3.2.2 Environment Agency Modelling 12 3.2.3 Surface Water Drainage System Maintenance 13 3.3 Proposed Flood Risk Mitigation Measures 13 3.3.1 Site Access and Egress 13 3.3.2 Residual Risk and Effect of the Development on Flood Risk 14 4 Conclusions 15 Appendices 16 Appendix A. Drawings 17 Appendix B. Correspondence and Meeting Minutes 18 Appendix C. Micro Drainage Calculations 19 Appendix D. Anglian Water Pre Development Enquiry Report 20

1 Introduction 1.1 Introduction and Methodology This (FRA) has been prepared by Mott MacDonald Ltd on behalf of Morgan Sindall to support a planning application for co-located schools, access, sports hall, associated car parking, sports pitches, and external works located in the north of Littleport, Cambridgeshire. This FRA has been prepared in accordance with guidance in: National Planning Practice Guidance (2014); National Planning Policy Framework (2012); National Planning Policy Technical Guidance (2012); Department for Environment, Food and Rural Affairs: Draft National Standards and Specified Criteria for Sustainable Drainage (June 2014); East Cambridgeshire District Council Strategic (February 2011); Environment Agency Managing Flood Risk: Great Ouse Catchment Flood Management Plan (Consultation Draft Plan (January 2007); and Construction Industry Research and Information Association (CIRIA) Sustainable Drainage Systems Manual C697 (2007). As part of this assessment Mott MacDonald has consulted with Anglian Water (AW), the Environment Agency (EA) and Littleport and Downham Internal Drainage Board (LDIDB). 1.2 Site Setting and Topography The site is located in the north of Littleport, north of Wisbech Road and west of Camel Road. The existing site comprises agricultural land and the Littleport Leisure Centre and Scout Hut. The nearest postcode is CB6 1EW and the Ordnance Survey coordinates are E 556222 N 287477. The total site (including sports pitches) covers an area of approximately 12.5 hectares. Figure 1.1 overleaf shows the site location. The site is bounded by Blackbank Drain to the south and predominantly agricultural land to the north, west and east. There is an existing access to the Littleport Leisure Centre from Camel Road. The majority of the existing site comprises permeable agricultural land. The topographic survey by MK Surveys (included in Appendix A) shows that the site is relatively flat with a gentle grade from east to west to existing watercourses adjacent to the site boundary. The ground levels on the existing leisure centre portion of the site range from approximately +1.54 metres Above Ordnance Datum (maod) adjacent to Camel Road to -0.63mAOD (below Ordnance Datum) in the west. The ground levels on the proposed school portion of the site range from +0.27mAOD in the south east to -1.31mAOD (below Ordnance Datum) in the north west. 1

Figure 1.1: Site Location and Indicative Site Red Line Boundary Site Source: Ordnance Survey Open Data (2011) contains Ordnance Survey Data Crown Copyright and Database Right 2011 1.3 Local Geology The Mott MacDonald Ground Investigation Report (February 2015) states that the anticipated site geology has been determined through the review of the 1:50,000 scale British Geological Survey (BGS) map (Ely Sheet 173, 1980). The report states that the mapping shows that the southern third of the site is underlain by superficial Tidal Flat Deposits comprising clays and silt, with the remainder of the site underlain by 2

superficial peat. The report notes that the superficial deposits are anticipated to be underlain by solid geology comprising the Kimmeridge Clay Formation. The report notes that made ground is only anticipated in areas currently occupied by the existing Sport Centre, Scout Hut and car parking. 1.4 Hydrological and Hydrogeological Setting There are a number of ditches adjacent to the site. These watercourses fall under the responsibility of a number of different stakeholders. Figure 1.2 shows the stakeholders responsible for the adjacent watercourses. Blackbank Drove (highlighted in green) is the primarily responsibility of the Environment Agency. However, the Littleport and Downham IDB do need to be consulted if works affect this watercourse as the watercourse is in the IDB district. The Sports Centre Drain (highlighted in purple) is the responsibility of Littleport and Downham IDB. The watercourses (highlighted in orange) primarily fall under the responsibility of the respective land owners under riparian law. However, they are located within the Littleport and Downham IDB district. Therefore, Littleport and Downham IDB requirements have to be met and sustained. On the basis of the topographic survey it is understood that the surface water drained by these watercourses flows from Camel Road in the east towards the A10 in the west and north. The River Great Ouse is located approximately 1.4km east of the site. The Environment Agency website (accessed 19.02.15) shows that the site is not located in a groundwater Source Protection Zone. The EA website (accessed 19.02.15) shows that both the superficial deposits and the underlying solid geology are designated as Unproductive Strata. Unproductive strata are defined as rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow. 3

Figure 1.2: Watercourse Responsibility Environment Agency Blackbank Drove Drain in IDB District IDB Drain Landowner Drains in IDB District Source: Environment Agency and Littleport and Downham IDB 1.5 Existing Surface Water Drainage The existing site comprises the Littleport Leisure Sports Centre, Scout Hut, associated parking and agricultural land use. Drawing MMD-330763-C-DR-00-XX-0528 shows the utilities survey carried out by 4

MK Surveys in March 2014. The survey shows that the existing Sports Centre, Scout Hut and associated parking are drained by rainwater pipes and gullies respectively and that these systems discharge to an existing ditch to the north east of the buildings. The Littleport and Downham Internal Drainage Board note that there is the potential that land drains may have been installed in the agricultural portion of the site, see meeting minutes in Appendix B. It is recommended that intrusive ground investigation is carried out to ascertain if there are land drains on site. On the basis of the existing drainage regime and underlying geology it is anticipated that infiltration drainage to the ground is unlikely to be feasible. It is noted that the East Cambridgeshire District Council (ECDC) Strategic (SFRA) mapping shows that the site is located in an area estimated to have low infiltration potential (Figure 11). 1.6 Proposed Development The proposed co-located schools once fully constructed and occupied are proposed to comprise the following: Pre-School: replacement of the existing Stepping Stones Pre-School; Special Education Needs (SEN) School: 110 pupils aged 2 to 19 with complex special educational needs; Primary School: 1 Form Entry, 210 pupil Primary School; Secondary School: 4 Form Entry, 600 pupil Secondary School with expansion capacity to 5 Form Entry (750 pupils) when required; and Leisure Centre: Replacement of the existing Littleport Leisure Centre with a new Sports Centre on-site. Proposed site plans are included in Appendix A. 5

2 Flood Risk 2.1 Flood History and Existing Flood Defences The East Cambridgeshire District Council SFRA mapping shows no records of historic flooding on the site (Figure 8). The Littleport and Downham IDB have confirmed that they are not aware of any historic flooding incidents affecting the proposed development site. The by Michael Thomas Consultancy LLP (MTC) in 2012 for a proposed school development on the site includes data from the Environment Agency. At the time of writing this report the EA have confirmed that the information provided to MTC is the most up to date information available. It is noted that the EA are currently carrying out flood modelling in this area and that the modelling is due to be released in June 2015. The EA data in the MTC report states that the Agency does not hold any records of historic flooding events for this area. There are existing flood defences on the River Ouse located approximately 1.4m to the east of the site. The flood defences are maintained by the EA. The EA website designates the site as land benefitting from flood defences. The East Cambridgeshire District Council SFRA mapping (Figure 7) shows that the flood defences that provide protection to the site have a design storm event standard of 1 in 100 years. 2.2 Flood Zone Designation The site is located in Flood Zone 3 land that benefits from flood defences. Flood Zone 3 is defined by the National Planning Policy Guidance as land assessed as having a 1 in 100 or greater annual probability of river flooding; or land assessed as having a 1 in 200 or greater annual probability of sea flooding. 2.3 Assessment of Sources of Flooding 2.3.1 Fluvial Flooding The site is located in Flood Zone 3 defended, benefitting from the existing flood defences. The flood defences are maintained by the EA and the East Cambridgeshire District Council SFRA mapping (Figure 7) shows that the flood defences that provide protection to the site have a design storm event standard of 1 in 100 years. The Environment Agency have noted the distance of the site from the Ely Ouse, and stated that the flood plain in the area has a compartmentalised nature. In the event of a storm occurring with a return period of greater than 1 in 100 years it is considered that there may be the potential for the existing River Ouse flood defences to be overtopped by fluvial water. The site is located approximately 1.4km from the River Ouse and the EA have noted the compartmentalised nature of the parcels of land located in the local area. The MTC report notes that the Littleport railway line and the land at approximately 1.64mAOD to 2.0mAOD on which Camel Road is constructed would impede flows of flood water, and divert it to lower lying land prior to crossing these obstructions. It is noted that the land in the local area between the site and the River Ouse is drained via a 6

network of field ditches which would drain flood water to low lying areas of land prior to potentially affecting the site. On the basis of the distance of the River Ouse from the site, the provision of field ditches, compartmentalised nature of the land, in the event that should the River Ouse flood defences be overtopped by fluvial water during an extreme storm event with a greater return period than 1 in 100 years, it is considered that the site is unlikely to be affected by the resulting flood water. The EA have stated that there is a very low risk of a breach occurring in the defences and that they anticipate that there will be a sufficient lead time prior to flood water affecting the site to safely evacuate. Therefore, the EA have stated that they do not object to the principle of constructing a school in this location. The EA have recommended a Finished Floor Level (FFL) of 0.4mAOD and to incorporate flood resistance and resilience measures up to 1.40mAOD to minimise the impact of a flood. More detail regarding the FFL and flood resistant and resilient measures outlined in Section 3.3 below. Therefore, on the basis of advice received from the Environment Agency it is considered that the site is at low risk of flooding from fluvial sources. 2.3.2 Groundwater Flooding The Mott MacDonald Ground Investigation Report (February 2015) states that groundwater was found at 3.40 metres Below Ground Level (mbgl) during summer investigations and between 0.70 and 1.20mBGL during winter investigations. The report notes that groundwater flow is considered to be in a north-northwest direction. The report notes that peat was encountered in the majority of the boreholes and window samples to depths of between 0.75mBGL and 1.2mBGL. On the basis of the site groundwater levels recorded and the anticipated extents of peat on site it is considered that the existing risk of flooding from groundwater is moderate. However, it is noted that the proposals comprise the raising the ground levels on site to facilitate achieving a minimum FFL for the school building of 0.4mAOD. The existing ground levels in the centre of the proposed school portion of the site are approximately -0.6m below Ordnance Datum. This results in raising the ground levels up to 1.1m. Therefore, by raising ground levels this significantly reduces the risk of groundwater flooding affecting the proposed school building. More detail regarding the FFL and flood resistant and resilient measures outlined in Section 3.3 below. Drawing MMD- 330763-C-DR-00-XX-5601 (in Appendix A) shows the preliminary proposed construction build up to raise the site ground levels. 2.3.3 Pluvial Ponding and Surface Water Overland Flow The topographic survey shows a gentle gradient across the site from east to west. It is noted that the majority of the existing site comprises green field with anticipated low permeability and drainage provided by a number of adjacent ditches. It is noted that the existing developed part of the site is conventionally drained. The Environment Agency mapping (website accessed 20.02.15) shows that approximately 25% of the site is at a low or moderate risk of surface water flooding. Moderate risk is defined by the EA that an area of land that has a chance of surface water flooding of between 1 in 100 and 1 in 30 year events. Low risk is defined as an area of land that has a chance of surface water flooding between 1 in 100 and 1 in 1,000 year events. 7

Overall it is considered that the existing site is at moderate risk of flooding from surface water overland flow. However, the proposed site will comprise a number of SUDS features, land drainage, landscaping and ground level raising. Therefore, it is considered that the proposals shall significantly mitigate the risks of pluvial ponding and surface water overland affecting the proposed development buildings. More detail regarding the SUDS features, land drainage and landscaping is described in Section 3.2 below. 2.3.4 Existing adjacent Field Ditch Flooding The site has existing drains in the form of field ditches located adjacent to the north, south and to the east of the proposed school land area boundaries. The Littleport and Downham Internal Drainage Board are responsible for maintaining their assets in this area and they have stated that they have no records of flooding in this area. The proposals comprise raising the existing ground level by up to 1.1m. Overall, it is considered that by raising the ground levels on the proposed site by up to approximately 1.1m the risk of flooding to the proposed development buildings from the adjacent drains is low. 2.3.5 Sewer Capacity The majority of the site comprises green field. The East Cambridge District Council SFRA mapping (Figure 10) shows that the site has no recorded sewer flooding incidents. Therefore, overall it is considered that flooding due to sewer incapacity is low. 2.3.6 Reservoir Infrastructure Failure The Environment Agency mapping (accessed 20.02.15) shows that the site is at risk of flooding from the Ouse Washes. The EA reservoir mapping shows that if the reservoir did flood, the site could potentially be affected by the reservoir water flowing at a rate of up to 0.5 metres per second to a depth of approximately 2 metres. This reservoir falls under the responsibility of the Environment Agency. Therefore, the EA are tasked with its inspection and maintenance in accordance with the Reservoirs Act (1975). The EA state that reservoir flooding is extremely unlikely to happen. Therefore, overall, it is considered that the risk of flooding from this source is low. 2.3.7 Tidal and Estuary Flooding The site is located approximately 38.7km south of the mouth of the River Great Ouse at the estuary discharging into the North Sea. It is noted that the River Great Ouse is affected by the tide. However, Denver Sluice, located approximately 14km to the north of the site on the River Great Ouse, controls tidal influence. The Great Ouse Catchment Flood Management Plan (January 2007) notes that The River Great Ouse is tidal in nature downstream of Denver Sluice and that the purpose of the sluice is to provide protection from tidal flooding upstream. Therefore, it is considered that the site is at low risk of flooding from tidal and estuary sources. 8

3 Post Development Flood Risk 3.1 Vulnerability and Flood Zone Compatibility Figure 3.1 below shows the National Planning Policy Guidance (NPPG) (2014) Flood Risk Vulnerability Classification Table. The NPPG details the Sequential Test, Exception Test, Flood Risk Vulnerability and Flood Zone Compatibility. The proposed development comprises education land use and therefore falls under the category of more vulnerable. Figure 3.1: Flood Risk Vulnerability Classification Table Source: NPPG 2014 From the above it is noted that the site requires an Exception Test. The Environment Agency confirmed that the proposals to construct a school and sports centre and associated car parking on the site are acceptable in principle, and confirmed that this acceptance still stands (see correspondence in Appendix B). Paragraph 102 of the National Planning Policy Framework (2012) states following with regard to passing the Exception Test: 1. It must be demonstrated that the development provides wider sustainability benefits to the community that outweigh flood risk; and 9

2. A site specific flood risk assessment must demonstrate that the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall. In order to fulfil the requirements of a the points considered below outline how the conditions of the Exception Test may be met by the development proposals: 1. The proposed development comprises the construction of special education needs, primary and secondary schools and a sports centre. The construction of these schools in Littleport will provide wider benefits for the community as the proposed schools will have a catchment area covering Littleport and relatively small, dispersed communities in the Littleport area. The construction of the sports centre, to replace the existing sports centre building which has reached the end of its design life, will provide wider sustainable benefits to the Littleport community. 2. Section 3.3 below outlines the flood resilient and resistant measures that are proposed to be incorporated into the construction of the proposed development. These measures will mitigate the potential impacts in the very unlikely event of a flood occurring due to a breach in the EA maintained flood defences and facilitate the return of normal operating procedures as expediently as possible after the flood water has receded. Section 3.3.2 outlines how the development will not increase flood risk on or off-site. On the basis of the information above and further details in Section 3.3 and 3.3.2, it is considered that this provides the necessary information to fulfil the Exception Test criteria. 3.2 Surface Water Management and Drainage Strategy The Draft National Standards (DNS) and Specified Criteria for Sustainable Drainage sets out requirements for the design, construction, maintenance and operation of Sustainable Drainage Systems (SUDS). The DNS states the following hierarchy for surface water discharge: 1. Discharge into the ground (infiltration); or where not reasonably practicable, 2. Discharge to a surface water body; or where not reasonably practicable, 3. Discharge to a surface water sewer, highway drain, or another drainage system; or where not reasonably practicable, 4. Discharge to a combined sewer. On the basis of the above hierarchy, existing site drainage, adjacent ditches and site geology it is considered that infiltration drainage to the ground is unlikely to be feasible. Therefore, it is proposed to drain surface water from the site to the existing ditches adjacent to the site. As shown in Figure 1.2 the existing drainage ditches to the north and east of the site fall under the responsibility of the Littleport and Downham IDB. We have consulted with the Littleport and Downham IDB (see attached meeting minutes in Appendix B) and the IDB have confirmed that discharge of surface water to their existing assets is acceptable in principle. A discharge consent form has to be completed and approved by the IDB prior to discharge surface of water to their assets. The Littleport and Downham IDB 10

have the following requirements that need to be fulfilled as part of the surface water drainage strategy for the site to gain approval to discharge surface water: Discharge of surface water from the site should be limited to 1.1 litres per second per hectare; A Discharge Consent Form needs to be completed and approved prior to any discharge into the existing watercourses. The proposed surface water drainage strategy comprises the collection of surface water from the rainwater down pipes of the proposed building and discharge to a proposed surface water attenuation feature located adjacent to the proposed development western boundary. Discharge from the attenuation feature will be controlled to 1.1 litres per second per hectare. The proposed development surfacing will comprise permeable paving, permeable asphalt, permeable green landscaped areas and permeable multi-use games pitches. The surface water drainage strategy proposes to drain the majority of these areas using permeable paving to mitigate the impacts of the development on the proposed surface water drainage system and flood risk on and off-site. Due to the finished floor level requirements the site ground level will need to be built up above the existing ground level. This build up will provide the opportunity to incorporate a granular, permeable sub-base beneath the permeable surface areas providing control at source and thus reducing the peak runoff rate and potential runoff volume, as well as providing effective water quality treatment. The incorporation of conventional (impermeable) asphalt will be limited to the frequently trafficked main accesses. These impermeable surfaced access areas will be drained to filter drains or permeable paved areas. The proposed development permeable sub-base will be drained via a network of land filter drains. The land drain discharge will be limited to 1.1 litres per second per hectare. The proposed development surface water drainage strategy is shown on drawings MMD-330763-C-DR-00-XX-5111 to 5116 attached in Appendix A. The drainage details that accompany the strategy are shown on drawings MMD-330763- C-DR-00-XX5131, 5132 and 5133 attached in Appendix A. Preliminary calculations included in Appendix C demonstrate that surface water from the proposed development buildings can be discharged off site at a controlled rate of 1.1 litres per second hectare utilising the proposed attenuation feature along the western boundary of the site. In accordance with the DNS the preliminary calculations demonstrate that the proposed development building runoff does not cause flooding on site in the critical 1 in 30 year rainfall event. During the detailed design stage the proposed development external levels will be designed to ensure that subsequent to the extreme 1 in 100 year, plus an allowance for climate change, rainfall event, if the surface water drainage system capacity is exceeded, any resulting surface water flooding is contained within the site boundary in shallow depressions and does not adversely affect the buildings or adjacent developments. 11

In summary the proposed development surface water strategy is proposed to comprise the following SUDS features: 1. Surface water attenuation feature located on the surface of the ground; 2. Permeable paving; 3. Permeable asphalt 4. Permeable landscaped green areas with careful level design during the detailed design stage to provide retention of surface water in shallow depressions in localised soft landscaped areas in the extreme 1 in 100, plus an allowance for climate change, storm event; 5. Permeable multi-use games pitches; and 6. Filter drains. The DNS states that the drainage system must be designed and constructed so surface water discharged does not adversely impact the water quality of receiving water bodies; during construction and when operational. It is considered that the clean rainwater falling on the proposed development building roof would be appropriate to discharge directly to the existing IDB assets at 1.1 litres per second per hectare. The proposed development trafficked areas and parking will comprise a combination of filter drains, permeable paving and permeable asphalt which provide a good peak flow reduction and volume reduction of surface water, and good water quality treatment. 3.2.1 Impermeable Areas and Permeable Surfacing The extents of the proposed development permeable and impermeable surface areas are shown on drawings MMD-330763-C-DR-00-XX-5401 and 5402. The drawings show the total areas of each surface in square metres. The surface water drainage strategy proposes to drain the majority of these areas using permeable paving to mitigate the impacts of the development on the proposed surface water drainage system and flood risk on and off-site. 3.2.2 Environment Agency Modelling In correspondence with the Environment Agency, it is noted that the EA are currently progressing with updating flood models that could affect advice given in the Littleport area, in particular, the following two models: The Fenland Project (the Fluvial Ouse downstream of Earith); and The Eastern River Project (the Eastern Tributaries of the Fluvial Ouse). The EA have stated that they anticipate the results of the modelling should be available in June 2015. 12

3.2.3 Surface Water Drainage System Maintenance Maintenance of the proposed surface water drainage system will be undertaken by the owner of the site, or a nominated company. Maintenance of the all the surface water drainage features will be carried out on a regular and scheduled basis and after significant rainfall events and any flood events. Records will be kept of maintenance checks and any remedial actions carried out. Maintenance of surface water drainage features will include regular inspection of all inlets and outlets of all structures, telescopic joints/sleeves, headwalls, litter and silt removal and rodding as required as well as periodic cleaning of permeable surfacing using a suction sweeper. It is recommended that permeable paving is cleaned at least every 5 years. The surface water filtering through the sub-base and into the land drains provides mitigation to peak flows and provides a significant degree of pollution control and treatment, providing the surface us properly maintained. The Littleport and Downham IDB have stated that they require a 9 metre maintenance strip either side of the centreline of the existing IDB ditches to remain free of development to facilitate maintenance of the assets. Maintenance of the assets includes annual grass/vegetation cutting and dredging every 5 years. 3.3 Proposed Flood Risk Mitigation Measures The Environment Agency has stated that the minimum Finished Floor Level of the proposed building must be 0.4mAOD (see attached correspondence in Appendix B). On the basis of the above, the proposed FFL of the building will be 0.5mAOD. The site ground levels will be built up to achieve a FFL level of 0.5mAOD, but will grade away from the buildings to the site boundaries. The Environment Agency has stated that flood resistant and flood resilient measures must be incorporated as part of the development proposals up to a level of 1.4mAOD. On the basis of the above the proposed development will comprise modular fabric construction, incorporating flood resilient measures to facilitate the return to operation of the school as expediently as possible. The proposed development critical infrastructure, for example the electrical substation, will be constructed with a Finished Floor Level of 1.4mAOD or above to provide protection to the infrastructure in the event of a flood event affecting the site. 3.3.1 Site Access and Egress The Environment Agency has stated that: 13

The distance of the site from the Ely Ouse, the compartmentalised nature of the flood plain and the low risk of a breach occurring in the defences means that there will be sufficient lead in time before the site floods to safely evacuate the site. By placing the resistance and resilient measures up to 1.40mAOD will minimise the impact of a flood. On the basis of the advice given by the Environment Agency it is noted that the proposed development will be evacuated prior to the onset of flood water on site and that there will be sufficient time for evacuation to take place. It is noted that the village of Littleport is located in Flood Zone 1, approximately 220 metres from the centre of the proposed school buildings. Therefore, it is considered that egress from the site should be via the proposed south access of the school into Littleport in the event of a flood occurring. The Environment Agency operates a flood forecasting and warning services in areas at risk of flooding from rivers and the sea. The site location is in an area served by the Flood Warnings Direct service. The service is free and provides warnings directly to subscribers by telephone, mobile, email, SMS text message and fax. It is recommended that the proposed development is subscribed to Flood Warnings Direct. In addition, updates on all current warnings in force in England and Wales can be found on the Environment Agency website or by calling the Flood Line Service on 0845 988 1188. 3.3.2 Residual Risk and Effect of the Development on Flood Risk The Technical Guidance to the NPPF (2012) states that it is the responsibility of those planning development to full assess flood risk, proposed measures to mitigate it and demonstrate that any residual risks can be safely managed. The following measures are proposed to manage the residual risks and mitigate the effect of the development on flood risk: Raising the ground levels on the proposed school portion of the site by up to 1.1 metres; Constructing the Finished Floor Level of the proposed school at 0.5mAOD; Incorporating flood resistant and flood resilient measures with the structural fabric of the school building up to 1.4mAOD; Incorporation modular fabric construction to facilitate the return to operation of the school as expediently as possible following a flood event; Construction of critical infrastructure with a Finished Floor Level of 1.4mAOD; Incorporation of SUDS features to reduce the peak flow and volume and provide effective water treatment including: permeable surfacing, attenuation storage, landscaped green areas and filter drains; Controlled discharge of surface water from site to the adjacent IDB drain at a rate of 1.1 litres per second per hectare; and External level design to ensure that subsequent to the extreme 1 in 100 year, plus an allowance for climate change, rainfall event, if the surface water drainage system capacity is exceeded, any resulting surface water flooding is contained within the site boundary and does not affect buildings either on or off-site. 14

4 Conclusions This has been carried out for the proposed Littleport co-located schools development, Littleport, Cambridgeshire. The site has been considered for fluvial, groundwater, pluvial ponding and surface water overland flow, existing adjacent ditch capacity, sewer capacity, infrastructure failure, tidal and estuary flooding. The site does benefit from formal flood defences. The site is located in Flood Zone 3 defended. The existing site is at low risk of fluvial flooding, the River Ouse Environment Agency maintained flood defences provide a level of protection up to the 1 in 100 year storm event. It is considered that raising the ground levels on the site shall significantly reduce the risk of flooding from groundwater. The proposed site will comprise a number of SUDS features, land drainage, landscaping and ground level raising. Therefore, it is considered that the proposals shall significantly mitigate the risks of pluvial ponding and surface water overland affecting the proposed development buildings. It is considered that by raising the ground levels on the proposed site by approximately 1.1m the risk of flooding to the proposed development buildings from the adjacent drains is low. It is considered that flooding due to sewer incapacity is low. The Environment Agency are tasked with the inspection and maintenance of reservoirs in accordance with the Reservoirs Act (1975) and state that reservoir flooding is extremely unlikely to happen. It is considered that the risk of flooding from reservoir infrastructure failure is low. Denver Sluice, located approximately 14km to the north of the site on the River Great Ouse, controls tidal influence, providing protection from tidal flooding. Therefore, it is considered that the risk of flooding from tidal or estuary flooding is low. It is proposed to drain surface water from the proposed development to the existing IDB drainage ditches adjacent to the site. It is proposed to control the flow of surface water from the site to the existing IDB ditches at a rate of 1.1 litres per second per hectare. The Littleport and Downham IDB have confirmed that the proposed surface water drainage strategy is acceptable in principle. It is proposed to incorporate surface water attenuation features within the landscaping areas, permeable paving, permeable asphalt, permeable multi-use games pitches and filter drains as part of the proposed surface water drainage strategy. The proposed SUDS shall reduce the peak flow and volume of surface water drained from the site. The SUDS should provide effective treatment of surface water prior to controlled discharge from site. It is recommended that the proposed development is subscribed to the Environment Agency Flood Warnings Direct Service. This service is provided by the Environment Agency at no cost to subscribers. The Environment Agency has confirmed that the proposals to construct a school on site are acceptable in principle. 15

Appendices Appendix A. Drawings 17 Appendix B. Correspondence and Meeting Minutes 18 Appendix C. Micro Drainage Calculations 19 Appendix D. Anglian Water Pre Development Enquiry Report 20 16

Appendix A. Drawings MK Surveys Topographic Survey Wynne Williams Associates Proposed Development Landscape Plan Mott MacDonald Proposed Development Surface Water Drainage Strategy Drawings: MMD-330763-C-DR-00-XX-5111; MMD-330763-C-DR-00-XX-5112; MMD-330763-C-DR-00-XX-5113; MMD-330763-C-DR-00-XX-5114; MMD-330763-C-DR-00-XX-5115; and MMD-330763-C-DR-00-XX-5116. Mott MacDonald Proposed Development Drainage Details Drawings: MMD-330763-C-DR-00-XX5131; and MMD-330763-C-DR-00-XX5132. Mott MacDonald Proposed Development Surfacing Drawings: MMD-330763-C-DR-00-XX-5401; and MMD-330763-C-DR-00-XX-5402. Mott MacDonald Proposed Development Construction Details Drawing: MMD-330763-C-DR-00-XX-5601. 17