VILLAGE MASTERPLAN PHASE 2 & EXTRA“...an exemplar CARE for sustainable suburbs”

illustrative plan oth proposed masterplan 10 Berkeley Homes (East Thames) Ltd

0801 - Floodcovering Risk letter Assessment & application form 14th September November 20092008

Phase 2 Kidbrooke Regeneration Project PPS25 Flood Risk Assessm ent Berkeley Homes (East Thames) Limited September 2009

QM

Issue/revision Issue 1 Revision 1 Revision 2 Revision 3

Remarks DRAFT DRAFT 2 FINAL

Date 14/08/2009 07/09/2009 09/09/2009

Prepared by J. Tang J. Tang J.Tang

Signature

Checked by J. Greene J. Greene J.Greene

Signature

Authorised by A. Atkinson A. Atkinson A.Atkinson

Signature

Project number 11012229 11012229 11012229

File reference 2229\PH2 FRA 2229\PH2 FRA 2229\PH2 FRA

WSP Development and Transportation Mountbatten House Basing View Basingstoke Hampshire RG21 4HJ

Tel: +44 (0)1256 318800 Fax: +44 (0)1256 318700 http://www.wspgroup.com

WSP UK Limited | Registered Address Buchanan House, 24-30 Holborn, London, EC1N 2HS, UK | Reg No. 01383511 England | WSP Group plc | Offices worldwide

Contents

1 Introduction 4

2 Existing Site 6

3 Proposed Developm ent 10

4 Assessm ent of Potential Sources of Flooding to the Developm ent Site 12

5 Probability 15

6 Clim ate Change 17

7 Flood Risk M anagem ent M easures 18

8 Residual Risk 20

9 Conclusion and Recom m endations 21

Appendices

APPENDIX A – REFERENCES

APPENDIX B – EXISTING SITE

APPENDIX C – PROPOSED DEVELOPMENT

APPENDIX D – PLANNING POLICY AND CONTEXT

APPENDIX E – DRAINAGE STRATEGY

APPENDIX F – FLOOD RISK MAPPING

1 Introduction

1.1 BACKGROUND 1.1.1 WSP has been commissioned by Berkeley Homes (East Thames) Limited to carry out a Supplementary Flood Risk Assessment and Surface Water Drainage Strategy for the Phase 2 Area of development at the Kidbrooke Regeneration Site, located near to Greenwich in . 1.1.2 The Berkeley Homes (East Thames) Limited Application Site, for which this Flood Risk Assessment has been prepared to support, sits within the wider Kidbrooke Development Area (KDA). Berkeley Homes received Outline Planning Permission for the whole site in March 2009. The Application included a Detail Application for the Phase 1 area. 1.1.3 As part of the original application a Flood Risk Assessment was prepared by WSP in November 2008 to assess the potential flood risk at the site and to define the over-arching drainage strategy. Two Addendums to the Flood Risk Assessment were later issued to the Environment Agency to support the development in Phase 1 and to discharge the Planning Condition relating to the modelling of the Lower Kid Brook. These reports included further 1-D and 2-D modelling of the Lower Kid Brook watercourse. 1.1.4 A further planning condition was placed on development at the site to ensure that later phases were assessed based on the best available data. This Supplementary Flood Risk Assessment has been prepared to support development in the Phase 2 area of the site and to satisfy the Planning Condition. 1.1.5 The Phase 2 area of the Kidbrooke Regeneration Project will provide new residential apartment blocks and properties to the west of Kidbrooke Park Road (A2213), including Extra Care Units and the adjacent section of the Metropolitan Open Land. 1.2 OBJECTIVE OF THE STUDY 1.2.1 The objective of the study was to undertake a supplementary Flood Risk Assessment (FRA) in accordance with Planning Policy Statement 25 – Development and Flood Risk, (PPS25) to support the Environmental Impact Assessment (EIA) and the detailed Reserved Matters Application for the Phase 2 Area. This Flood Risk Assessment assesses any implications to the previously approved principles as a result of modifications to the Masterplan. 1.2.2 The study assesses flood risk to:

¢ The Phase 2 area of the proposed development and,

¢ Any impact on flood risk to other land as a result of the Phase 2 development proposals. 1.2.3 This report also provides an outline drainage strategy for the surface water flows from the proposed development which reconfirms the principles of the strategy previously agreed with the Environment Agency. The strategy demonstrates that the principles of attenuation to Greenfield runoff rates can still be achieved as the Masterplan and site plans have progressed and evolved.

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1.3 STUDY M ETHODOLOGY 1.3.1 The previous appraisal process consisted of a desk study, data research and consultation with regulatory bodies and third parties. 1.3.2 A list of documents used to obtain data in relation to the site and the proposed development is provided in Appendix A. Consultation was sought with the Environment Agency, and copy of their response has been provided. 1.3.3 Preliminary calculations for surface water flows have been undertaken based on the requirements of the London Plan and the adopted Supplementary Planning Documents for Kidbrooke. These calculations take into account the conditions at the site, existing drainage systems and current development proposals. 1.3.4 This is an assessment of potential flooding from all principle sources, including fluvial, tidal, surface run-off, overland flows, groundwater, sewers and man made infrastructure. The assessment also identifies and examines the residual flood risk to the proposed development. 1.3.5 Whilst completing the assessment, consideration has been given to the Practice Guide June 2008. The assessment has been undertaken in accordance with CIRIA C624, ‘Development and Flood Risk - Guidance for the Construction Industry' (2004) and Flood Risk Assessment Guidance for New Development, Phase 2, R & D Technical Report FD2320/TR2 (2005). 1.4 LIM ITATIONS 1.4.1 Whilst furthermore detailed modelling work has been undertaken by WSP to discharge planning conditions at the time of writing this report the results of this modelling are being reviewed by the Environment Agency. For this reason two flood levels are used in the report, and in keeping with the precautionary approach, the highest predicted flood level has been considered in the recommendations. These flood levels are referred to as follows:

¢ EA Detailed Modelling Level (Results of the Ravensbourne Detailed Flood Risk Mapping Study – October 2006)

¢ WSP 2D modelled flood level. The WSP modified Ravensbourne TUFLOW Model of the Quaggy – 2009 draft model). 1.4.2 It should be noted that the flood levels referred to above do not impact on the site; both the Environment Agency’s detailed mapping and WSP’s 2D modelling show that the Phase 2 Area of the Kidbrooke Development Site is situated outside of the 1 in 100 year + climate change allowance event. 1.4.3 This Flood Risk Assessment has been prepared on the best available information at the time of making this application.

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2 Existing Site

2.1 SITE LOCATION 2.1.1 The Kidbrooke Regeneration Site is located in Kidbrooke, Greenwich, Greater London and is situated immediately east of Blackheath Park with Sutcliffe Park forming the western and southern boundaries. 2.1.2 The Phase 2 area is located in the most south western section of the site to the west of Kidbrooke Park Road (A2213) and immediately north of Weigall Road. To the north of the Phase 2 area is the area of the existing Ferrier Estate which is proposed to be developed as Phase 5 (the last phase of development). 2.1.3 The Phase 2 Application area of the Kidbrooke Development will cover approximately 5.57ha. This area is currently occupied by the dilapidated Ferrier Estate, a 1960’s de-graded housing estate which includes mainly high rise apartment blocks. Refer to Figure 1, Site Location Plan in Appendix B. 2.2 SITE DESCRIPTION 2.2.1 Table 2.1 describes the general site characteristics. A key feature plan (WSP Drawing No. 2229/GA/201) is included in Appendix B. Table 2.1 Characteristics of the site Area Phase 2 = 5.57 ha including Extra Care Units General Topography Phase 2 of the Kidbrooke Site generally slopes from north to south. Levels range from 28.00m AOD along the existing Gallas Square, north of Phase 2 area, to 21.50m AOD along Weigall Road, south-west of the Phase 2 area. Areas of artificially raised landscaping present within existing estate. Existing surfacing Approximately 75 % impermeable. Current use Phase 2 – Occupied by dilapidated Ferrier Estate Boundaries North Existing developments fronting Moorhead Way South Weigall Road East Kidbrooke Park Road (A2213) West Moorhead Way Access Vehicular: Weigall Road connecting onto Kidbrooke Park Road (A2213) and surrounding road networks Pedestrian: Permeable street network surrounds site 2.2.2 A Topographical Survey of the Application Site was undertaken by ELS Land Surveys in September 2008. An extract of the survey relating to the Phase 2 area plotted at a scale of 1:1000 is provided in Appendix B. 2.2.3 The survey shows that the Phase 2 site has levels from approximately 21.50m to 28.00m AOD. The average level of the site is approximately 24.44m AOD.

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2.2.4 The Topographical Survey shows that Phase 2 and the area proposed for the Extra Care Units generally slope in a southern direction towards the open channel of the River Quaggy located west of Sutcliffe Park. 2.3 DRAINAGE 2.3.1 Thames Water records, (Appendix B), show that there are a number of public surface water sewers and combined sewers in the area, albeit the large majority of the existing Ferrier Estate is privately drained to one of two culverted watercourses. 2.3.2 A detailed investigation of the onsite drainage was undertaken in August 2008 by ELS Land Surveys Limited, a copy of which is provided in Appendix B. 2.3.3 The existing development to the west of Kidbrooke Park Road is shown to be privately drained. An existing 600mm surface water sewer conveys the majority of the site flows to the south, before discharging into the River Quaggy south of the site. A smaller section is drained by a 225mm diameter sewer to Weigall Road. 2.3.4 Thames Water Utilities Ltd records confirm the existence of a 2438mm diameter combined sewer flowing from south to north along Kidbrooke Park Road. 2.3.5 Thames Water records also indicate a 225mm diameter surface water sewer running from north to south along Kidbrooke Park Road. This sewer starts at the junction between Weigall Road and Kidbrooke Park Road and outfalls into the River Quaggy at the head wall. 2.3.6 The existing catchments are shown on Drawing No. 2229/PH2/D/203 provided in Appendix E. 2.3.7 The Environment Agency has confirmed that the northern part of the overall Kidbrooke site lies on London Clay, which is classed as an unproductive stratum. As the proposed Phase 2 Area and Extra Care Units of the Kidbrooke Development are situated in the northern section of the overall Kidbrooke site, it was assumed to be unlikely that infiltration systems will be adequate, due to the underlying unproductive stratum. Therefore a positive sewer system with attenuation and storage has been proposed to be employed for Phase 2 and the Extra Care Units. 2.4 GEOLOGY AND HYDROGEOLOGY 2.4.1 A review of the geological sequence based on Geological Map Sheet 271 was undertaken as part of the Environmental Statement a summary of the findings together with the aquifer potential is presented in the table below: Table 2.2 Geological Description

Location On Site Geological Unit Aquifer Status West of Kidbrooke Lambeth Group: Woolwich and Reading Beds Minor Park Road – Phase 2 Lambeth Group: Thanet Sand Formation Minor London Clay Non 2.4.2 The geological descriptions of the units are as follows:

¢ Made Ground – mainly landfill, flood defences or road and railway embankments.

¢ London Clay – clay, silty, sandy at top and base (up to 70m thick).

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¢ Harwich Formation – Sand with black flint pebbles, locally shelly (between 0-12m thick).

¢ Lambeth Group: Woolwich and Reading Beds – sand and clay, locally shelly and flint pebble beds (between 5-20m thick).

¢ Lambeth Group: Thanet Sand Formation – sand, fine grained silty green coated nodular flints at base (between 6-30m thick). 2.4.3 The Environment Agency’s website shows that the site does not lie within a currently defined Groundwater Source Protection Zone. There are no active licensed groundwater abstractions within a 1 km radius of the site 2.5 HISTORICAL FLOOD RECORDS 2.5.1 Table 2.2 summarises the historical flood records obtained through consultation and liaison with the various bodies contacted as part of the original study. Copies of the responses were included in the original Flood Risk Assessment. Whilst consultation has been sought with the Environment Agency as part of this supplementary study, given that the original Flood Risk Assessment was submitted less than a year ago the consultations with other parties have not been refreshed. It is the intention that for later phases consultation will be re-done.

Table 2.3 Flood Records Summary

Information Source Flood Records/Details

Environment Agency Provided historical flood map data for the 1968 flood event – this flood event was prior to the implementation of the Flood Alleviation Scheme.

The Environment Agency confirms that they do not have details of groundwater levels for the site.

Greenwich Council Greenwich Council confirmed that they have no historical flood records for flooding in the vicinity of the Kidbrooke Site.

Greenwich Council’s Highway Department has confirmed that they have no recorded knowledge of any public highways flooding in the vicinity of the overall Kidbrooke Site.

Thames Water Thames Water has confirmed that their records show no incidents of any flooding as a result of surcharging sewers in the vicinity of the overall Kidbrooke Development Area.

Refer to the attached Thames Water Correspondence dated 24 January 2008 provided in Appendix B.

Transport for London Transport for London (TfL) has confirmed some records of flooding close to the development site. There is one record of flooding event associated with Road, 2 events for Kidbrooke Park Road, 8 events for Rochester Way Relief Road and 5 events for the Rochester Way Roundabout.

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2.6 FLOOD M APPING 2.6.1 The Environment Agency’s Detailed mapping indicates that the Phase 2 Development Area lies in Flood Zone 1: outside both the 1 in 100 year and the 1 in 1,000 year flood extents associated with the River Quaggy. A copy of the detailed flood map is provided in Appendix B. 2.6.2 The WSP 2D-modelling shows the site to lie outside of the 1 in 100 year + 20% increase in flow flood extent. An extract of the modelling showing the extents together with the predicted flood levels is provided in Appendix F as drawing No. PH2/FIGURE3.

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3 Proposed Development

3.1 PROPOSED DEVELOPM ENT DESCRIPTION 3.1.1 Phase 2 of the Kidbrooke Regeneration Project is for 629 residential units, including 170 Extra Care units, 87.5m2 of community floorspace (Use Class D1), a LEAP, a NEAP, associated car parking, cycle parking and servicing. The proposed Masterplan and cross-sections through the park area are shown on Fabrik Landscape Architecture Planning Drawings No. D1784/600 to 603 in Appendix C. 3.1.2 Proposed external levels generally are to remain as per existing with access being created to Weigall Road and the Blackheath area. Additional pedestrian/cyclist routes to be created ensuring better links between the new development and the surrounding communities and parkland. As part of the overall earthworks strategy for the site, levels will however, be increased within the MOL to prevent material arising from the demolition of the site being disposed of offsite in landfills. 3.1.3 The main Phase 2 development area covers approximately 5.57 hectares. The percentage impermeable for the Phase 2 development area has been estimated as 75%, calculations supporting this are shown on WSP Drawing No. 2229/D/202 provided in Appendix E. 3.2 POLICY BACKGROUND 3.2.1 The re-development of the Ferrier Estate as part of the wider Kidbrooke Development Area has been promoted over a number of years with Outline Planning Permission for the scheme granted in March 2009. 3.2.2 A number of Planning Conditions were imposed on the site, several relate to flood risk and drainage as follows:

¢ Supplementary flood risk assessments shall be submitted to, and approved by, the Local Authority for each development phase (with the exception of phase 1) prior to development commencing in that phase. These documents shall be prepared in accordance with the latest national guidance and the latest available information on flood risk and climate change.

¢ Development shall not begin on each development phase (with the exception of phase 1) until a surface water drainage scheme based on sustainable drainage principles and an assessment of the hydrological and hydrogeological context of the development, has been submitted to and approved in writing by the local planning authority. The scheme should achieve surface water discharge at the greenfield runoff rate, for flood events up to and including the 1 in 100 year plus climate change critical duration storm event. The scheme shall subsequently be implemented in accordance with the approved details before the development is completed.

¢ There shall be no structures, fences and overhanging structures such as balconies within 8 metres of the culvert edge of the Lower Kid Brook main river, unless otherwise agreed upon in writing by the Local Planning Authority. 3.2.3 No development is proposed within Flood Zones 2 or 3 as part of the Phase 2 development scheme. All development is proposed within Flood Zone 1. 3.2.4 PPS25 Annex F paragraph F6 states that ‘Surface water arising from a developed area should, as far as practicable, be managed in a sustainable manner to mimic the surface water flows arising from the site prior to the proposed development,

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while reducing the flood risk to the site itself and elsewhere, taking climate change into account. This should be demonstrated as part of the flood risk assessment.’ 3.2.5 Full details of the proposed drainage strategy for the Phase 2 development scheme can be found in Section 6.

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4 Assessment of Potential Sources of Flooding to the Development Site

4.1 ENVIRONM ENT AGENCY COM M UNICATIONS 4.1.1 The Environment Agency has supplied records of historical information regarding flooding from the overflowing River Quaggy in 1968 affecting the site, details regarding the completed Flood Alleviation Scheme in the area and the modelling results from the Detailed Flood Risk Mapping Study undertaken in October 2006. The levels and flood extents for the area were provided by the Environment Agency 23rd January 2008. 4.1.2 Following detailed discussions with the Environment Agency during the determination period for the Outline Application further modelling work was undertaken by WSP to take into consideration the potential flood risk emanating from the Lower Kid Brook Culvert. This work found that the highest flood level in the vicinity of the Phase 2 Area during a 1 in 100 + 20% increase in flow to be 19.98m AOD, approximately 1.6m below the lowest ground level in Phase 2. 4.1.3 The table below identifies the various flood risk sources which could impact on the Phase 2 development area. Table 4.1 Flood Source Identification

Definition of the Flood LIKELIHOOD Hazard Source – Very Likely, Possible, Negligible Fluvial A detailed mapping provided by the Environment Agency confirmed that the Phase 2 Development lies outside of the 1 in 100 year and the 1 in 1,000 year flood extents. Flood Risk – Negligible Coastal - Sea The Phase 2 Site is situated approximately 4.5km south of the Barrier. Flood Risk - Negligible Coastal - Estuarine Flood Risk - Negligible Pluvial / sheet run off Existing high density development Flood Risk - Possible Sewer - SWS, FWS, Thames Water confirmed no records of flooding in the area; , CS, CSO however, TFL records suggest that some of the surrounding roads could be at risk. Flood Risk - Possible Groundwater The Environment Agency has confirmed that they have no records of any groundwater flooding within a 500m radius of the overall Kidbrooke site. The Phase 2 site is not located within or near to a groundwater Source Protection Zone (SPZ). Flood Risk - Negligible Dam Breach The key flood defence for the overall Kidbrooke Site is the Sutcliffe Park Flood Alleviation Scheme. The retained water level is at ground level. The development is believed to be

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on ground higher than the retained level. Flood Risk – Negligible Canal There are no known canals within the vicinity of the overall Kidbrooke site. Flood Risk - Negligible Major Water Main A 200mm water main is indicated along Weigall Road and runs through the eastern half of the Kidbrooke site. Flood Risk - Negligible

4.2 FLUVIAL 4.2.1 The site is a minimum of 1.6m above the highest flood level in the River Quaggy during a 1 in 100 + 20% allowance for climate change event. The table below shows the respective flood levels from both models. River Quaggy

Table 4.2 Flood Levels Level mAOD Node Reference Location 5 year 20 year 100 year 100 year +20% EA Detailed Kidbrooke modelling 19.5 19.66 19.95 20.06 Park Road 06343NODEK105 WSP 2D modelling Eltham Green - - - 19.98 06343NODEQ4612D Bridge

4.3 OVERLAND FLOW S 4.3.1 Flooding of the western section of the overall Kidbrooke development site from overland flow routes from areas north of the site is unlikely to occur as the overland flow is likely to be intercepted by Moorhead Way and the Bexleyheath railway line, conveying the water in the east direction away from the site. 4.3.2 The area immediately to the north of Phase 2, Phase 5, could generate overland flow. Levels along the boundary between the two phases will be designed to provide flow routes towards the MOL and to the south through the proposed development. 4.3.3 Overland flows from areas to the west of the site are unlikely to occur given the topography of the surrounding area. 4.3.4 Overland flows from areas to the east of the site are likely to be intercepted by Kidbrooke Park Road and conveyed south towards the River Quaggy away from the proposed Phase 2 development area. 4.3.5 Land falls to the south so overland flows from this direction will not occur. 4.4 SEW ER FLOODING 4.4.1 Thames Water sewer records confirm the existence of both surface and foul water sewers in the vicinity of the site. Refer to Section 2 for a detailed description of these sewers and Appendix E for an extract of the existing sewers in the vicinity of the site.

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4.4.2 As part of the consultation for the overall Kidbrooke Flood Risk Assessment, Thames Water were contacted to request historic flooding records. Thames Water confirmed that their records show no incidents of any flooding as a result of surcharging sewers in the vicinity of the development site. 4.4.3 Greenwich Council’s Highway Department also confirmed that they have no recorded knowledge of any public highways flooding in the vicinity of the site. 4.4.4 Transport for London (TfL) did provide some records of flooding associated with the overall Kidbrooke development site. TfL stated that there had been 1 flooding event associated with Eltham Road, 2 events for Kidbrooke Park Road, 8 events for Rochester Way Relief Road and 5 events for the Rochester Way Roundabout. Further details of these flood events could be provided, however, one of the key aims of the strategy is to improve pedestrian and vehicular connectivity with the surrounding communities. 4.4.5 Of the events listed above the potential risks at Kidbrooke Park Road could impact on the Phase 2 area. However the development phase includes an alternative access routes to Weigall Road. Paragraph 7.4.1 discusses safe access and egress in more detail. 4.5 GROUNDW ATER FLOODING 4.5.1 The Phase 2 part of the overall Kidbrooke Development is shown to be underlain by London Clay from the British Geological Survey (BGS) Maps, which protects the site from groundwater flooding. 4.5.2 The Environment Agency confirmed that their records show no entries of any Groundwater Flooding for the whole Kidbrooke Site and within a 500m radius.

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5 Probability

5.1 FLOOD ZONE 5.1.1 A copy of Table D1 Environment Agency Probability Flood Zones can be found in Appendix D. According to the Environment Agency’s Flood Risk Mapping the proposed Phase 2 area is situated within Flood Zone 1. 5.2 EXISTING FLOOD M ITIGATION M EASURES 5.2.1 The Sutcliffe Park Flood Alleviation Scheme to the south of the site has recently been completed providing 85,000m3 of flood storage to mitigate the risks of flooding to the whole Kidbrooke Development Area. 5.3 EFFECTS OF EXISTING M ITIGATION ON FLOOD LEVELS AND PROBABILITY 5.3.1 The predicted flood level from the Environment Agency’s detailed modelling takes into consideration the existing mitigation at Sutcliffe Park at the Phase 2 area during for the 100 year event is 19.95m AOD at Kidbrooke Park Road. The ground levels within the Phase 2 and Extra Care Unit areas range approximately between 28.0mAOD and 21.5mAOD, a minimum of 1.6m above the predicted flood level. 5.4 EXISTING RATES AND VOLUM ES OF RUN-OFF GENERATED BY THE SITE

5.4.1 See Appendix E for the methodology and calculations of runoff rates. 5.4.2 The total site area for the Phase 2 Planning Application is approximately 5.57 hectares, of which the main built area, approximately 75% is currently hard surfacing, the assessment of existing impermeable area is shown on WSP Drawing 2229/PH2/D/201 provided in Appendix E. The proposed Phase 2 Site currently comprises the existing Sala House, Clegg House and Goldmark House as part of the Ferrier Estate, which are to be demolished as part of this Phase of development. 5.4.3 A survey of the existing drainage system was undertaken in August 2008 by ELS Land Surveys Limited an extract of which is provided in Appendix B. The key surface water drainage routes have been identified and the catchments draining to each system determined. The Phase 2 Site of the overall Kidbrooke Development drains to a manhole on Weigall Road, which is assumed to drain through the sports centre to the River Quaggy. The existing catchments are shown on WSP Drawing 2229/PH2/D/203 also provided in Appendix E. 5.4.4 The existing surface water run-off from the application site based on a crude approximation is 580.7 l/s (2.78 x 50mm/hr x 5.57ha x 75%) for the annual 5 minute rainfall event and approximately 1671.2 l/s (2.78 x 143.9mm/hr x 5.57ha x 75%) for the 1 in 100 year rainfall event. This demonstrates the considerable volume of runoff that would be generated from the existing site. 5.4.5 Whilst the above considers the runoff from the Phase 2 area, there is also contributing runoff from the Phase 5 to the north. The approved drainage strategy for the site utilises large swales as linear detention basins which have been sized to attenuate runoff from the new development to Greenfield rates. The swales that will serve the whole of the western half of the development including Phase 5 will be constructed as part of this phase, the allowable discharge rates have therefore, been calculated based on the completed development. This will still represent a significant reduction on the overall rate.

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5.4.6 The rainfall intensities used for the approximate existing calculations are obtained from Table 1(a) of the TRRL Report LR 595 in Appendix E. The summary of the rates of run off are shown in the table below; Table 5.1 Existing and Proposed Discharge Rates

Peak rates of flow at discharge point - litres per second

Return Period 30 Yr 100 Yr 100 Yr + 30 %

(l/s) (l/s) climate change (l/s)

(l/s)Condition

Pre-development Phase 2 & Extra Care Units – 1,402.1 1,785.2 2,320.9

West of Kidbrooke Park Road

Permitted rate of Phase 2 & Extra Care Units – 75.7 106.6 106.6

discharge (IoH124 West of Kidbrooke Park Road

Greenfield Estimates) (including allowance for Phase 5)

Calculated rate of Phase 2 & Extra Care Units – 103.0 103.0

discharge West of Kidbrooke Park Road

(including allowance for Phase 5)

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6 Climate Change

6.1 DEVELOPM ENT LIFESPAN 6.1.1 Based on a typical lifespan for this type of development of 100 years the contingency allowances for climate change set out in Table B2 of PPS25 applicable to this site are 30% for the peak rainfall intensity and 20% for the peak river flow. 6.1.2 See Appendix D for a copy of Table B2 6.1.3 The development site is a minimum of 1.6m above the nearest 1 in 100 + 20% flood level of 20.06m AOD. 6.1.4 The previous approved drainage strategy is designed to restrict the runoff to that of a Greenfield during a 1 in 100 year plus 30% climate change. Therefore the effects of climate change have been taken into account as required by PPS25 and it has been shown that there is no significant increase in flood risk to the development due to climate change.

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7 Flood Risk Management Measures

7.1 FLUVIAL 7.1.1 The detailed modelled flood extents provided by the Environment Agency show the site to lie outside of the 1 in 100 year + 20% increase for climate change flood plain. The 2D modelling work completed by WSP shows the site to be approximately 1.6m above the predicted flood levels including a 20% allowance for climate change. 7.2 SURFACE W ATER DRAINAGE 7.2.1 A fundamental principle of sustainable development in terms of flood defence is the reduction of surface water runoff from the new or redevelopments. 7.2.2 Paragraph F10 of Annex F of PPS25 states that “the surface water drainage arrangements for any development site should be such that volumes and peak flow rates of surface water leaving a developed site are no greater than the discharge rates prior to the proposed development. Any increase in runoff above the discharge limit must be stored or attenuated on site.” 7.2.3 Given the density of the existing site, a significant amount of benefit has been afforded by the ability of the masterplan to accommodate SUDS storage measures to attenuate up to the 1 in 100 year + 30% increase in storm event to Greenfield runoff rates in accordance with the London Plan and the Kidbrooke Development SPD. 7.2.4 The approach in developing the drainage strategy for the site was to utilise SUDS to create amenity and ecological enhancement across the MOL. As part of the original Phase 2 Development Scheme and the overall design of the Kidbrooke MOL area; it was proposed to incorporate linear detention basins or swales along the eastern boundary of the Phase 2 Development Site. These swales were designed to store all surface water runoff from the proposed development area before discharging at a controlled rate to the existing outfall located south of the proposed Phase 2 Site, on Weigall Road. 7.2.5 However, demands on the use of the MOL have developed as the scheme has evolved and the previous available space for the proposed swales has been reduced as a consequence. The main issue is the key sustainability driver to reuse as much of the excavation and demolition arisings as possible on site to minimise the volume of waste disposed of to landfills. This means that the proposed levels are be increased across the whole development site including the MOL area. Given the constraints in tying the proposed levels into the surrounding area the space on site which can be raised is limited which has meant that the MOL proposed levels have increased further with a resultant reduction in swale widths. As such, only 3 linear ponds are to be utilised on the western side of the site, providing a total volume of approximately 2400m3 for attenuation. 7.2.6 The Masterplan has been reviewed in detail and areas of Tanked Pervious Pavements are now proposed underneath the car parking spaces as part of the Phase 2 Drainage Strategy to provide additional storage to replace the volume lost due to the raising of land along the MOL area. 7.2.7 The proposed tanked pervious pavements and swales will include online orifice controls to restrict discharge from the site, and maximise the full storage potential of the pervious pavements and ponds before discharging to the existing connection and ultimately out-falling into the River Quaggy located south of the Phase 2 Site and west of Sutcliffe Park.

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7.2.8 A Cellular Storage system covering an area of approximately 265m2 has also been proposed underneath the locally equipped area for play (LEAP) providing some attenuation for the estimated runoff from the Phase 5 area of the Kidbrooke Development. 7.2.9 The Greenfield runoff rates have been determined in accordance with IoH124 and factored with the FSR growth curves to generate the restricted runoff rates for the 1 in 100 year flood event for the catchment, including the allowance for Phase 5. Applying these discharge rates allowed storage volumes for each phase of the development to be determined. A copy of the Greenfield runoff calculations and storage estimates are provided in Appendix E. 7.2.10 The proposed drainage strategy storage areas has been modelled in Microdrainage as a dry swale , pervious paving and oversized pipes to demonstrate the ability of the masterplan to accommodate the storage required. The drainage strategy is shown on WSP Drawing no. 2229/PH2/D/205 presented in Appendix E. 7.2.11 It has been confirmed by Greenwich Council that SUDS within the MOL will be adopted and maintained as part of the parkland in perpetuity. 7.3 OVERLAND FLOW ROUTES 7.3.1 Runoff from the Phase 5 area north of the site has been incorporated in the design of the drainage system. Furthermore, levels across the site will be designed to divert flows south towards the River Quaggy. 7.4 ACCESS & EGRESS DURING FLOOD 7.4.1 The main existing vehicular access to the west side of the Ferrier Estate is via a junction on Weigall Road leading to Eltham Road. 7.4.2 It is also an intention of the scheme that the connectivity to the surrounding communities to the east and west of the site be improved. These areas lie outside of the Environment Agency flood risk mapping which is considered to represent the residual risk on site. 7.5 GROUNDW ATER 7.5.1 The Environment Agency has confirmed that they have no groundwater level information for the Phase 2 Development Site, although shallow water should be expected in the southern portion of the overall Kidbrooke Site. 7.5.2 The Environment Agency has confirmed that their records show no entries of any Groundwater Flooding for the site and within a 500m radius.

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8 Residual Risk

8.1 OVERLAND FLOW ROUTES 8.1.1 In the event that the onsite drainage system is exceeded, road levels will be designed to ensure that overland flow is diverted to the central MOL area and to the south replicating the existing system. 8.2 FLUVIAL River Quaggy

8.2.1 The Phase 2 Development Site is not affected by the 1 in 100 year + 20% allowance for climate change flood event in either the EA’s detailed flood mapping or the recent 2D modelling work as the EA and modified by WSP. 8.3 SEW ER AND HIGHW AY FLOODING 8.3.1 Whilst Thames Water and Greenwich Council’s Highway Department have confirmed that they have no recorded knowledge of any public highways flooding in the vicinity of the site as discussed in Section 4.4.4 TfL have confirmed there have been several events in the vicinity of the Phase 2 Site as follows:

¢ 1 event on Eltham Road,

¢ 2 events for Kidbrooke Park Road,

¢ 8 events for Rochester Way Relief Road

¢ 5 events for the Rochester Way Roundabout. 8.3.2 Unfortunately further details of these events could not be obtained. Of the locations listed above the events on Kidbrooke Park Road could impact on the development however the Phase 2 area will be provide alternative routes to the west and south to Weigall Road.

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9 Conclusion and Recommendations

9.1 CONCLUSIONS 9.1.1 The development proposals are for a mixed use redevelopment of the existing Ferrier Estate as part of the Phase 2 area of the Kidbrooke Regeneration Project. Phase 2 comprises a total of approximately 627 residential units and 107 extra care units. 9.1.2 The development proposals comply with the approved Flood Risk Assessment. 9.1.3 The Environment Agency supplied detailed modelled flood mapping, which indicates that the Phase 2 part of the Kidbrooke Site lies outside of Flood Zones 3 and 2, therefore all proposed development types within the proposed area is adequate. 9.1.4 The development proposals include a high quality SUDS scheme providing water quality, amenity and ecological enhancements as well as attenuating the predicted 1 in 100 year + 30% allowance for climate change storm event to the Greenfield Runoff Rate. 9.1.5 The proposed Phase 2 Development Site is located in Flood Zone 1. In the event of an overtopping or failure of the alleviation scheme, safe access and egress from the site is obtained via Weigall Road to the south. 9.1.6 Therefore the proposals are robust in terms of flood risk and continue to comply with PPS25.

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Appendices, Figures & Tables

Appendix A References

Ms Julia Greene Our ref: SL/2009/105469/01-L01 WSP Development & Transport Your ref: JT/2229 Mountbatten House Basing View Date: 04 September 2009 Basingstoke Hampshire RG21 4HJ

Dear Julia

KIDBROOKE REGENERATION PROJECT PHASE 2 DESIGN

Thank you for your letter dated 12th August 2009 regarding the Phase 2 proposals. We understand flood risk assessment (FRA) addendum will be submitted to support a reserved matters planning application for Phase 2.

Please find below our comments and advice on the flood risk proposals in your letter:

Phase 2 – West of Kidbrooke Park Road: Surface water flood risk

The Environment Agency accept the principle of the revised design to the phase 2 area to the west of Kidbrooke Park Road, as long as the site still discharges to the linear detention basins and continues to provide sufficient attenuation for all return periods up to and including the 1 in 100 year plus 30% climate change.

Phase 2a – North East of Kidbrooke Park Road and the Adhikaar Centre

It is noted that, for the phase 2 area north east of Kidbrooke Park Road and the Adhikaar Centre, you are proposing oversized pipes and tanked pervious pavements as an interim measure to attenuate surface water run-off for all return periods. The Environment Agency considers piped/tanked systems should only be considered if it can be justified that all sustainable options in the SUDS hierarchy are not possible. We would not usually support these techniques, so we would expect this to be clearly explained and justified in the FRA. We will be able to comment further on this once we have seen further detail of the proposals and the FRA.

Fluvial flood Risk

The Environment Agency accept the proposed finish floor levels for phase 2 to be set at a minimum of 300mm above the 1 in 100 year plus climate change flood level, or 300mm above the ground level - whichever is greater.

For your information, although it is not yet finalised, our latest 2D model extents for the Ravensbourne have shown that phase 2 is not affected by fluvial flooding for all return periods.

We hope this is helpful. We will be able to provide further comments and advice once further details are submitted. We look forward to being consulted on the flood risk assessment and the forthcoming planning application.

Please contact me if you have any queries.

Environment Agency Eastbury House, 30-34 Albert Embankment, London, SE1 7TL. Tel: 020 7091 4003, fax: 020 7091 4090 Yours sincerely

Ms Charlotte Amor Major Projects Officer

Direct dial 020 7091 4005 Direct fax 020 7091 4090 Direct e-mail [email protected]

Environment Agency Eastbury House, 30-34 Albert Embankment, London, SE1 7TL. Tel: 020 7091 4003, fax: 020 7091 4090

Docum ents referred to for Data

WSP Flood Risk Assessment November 2008

WSP Flood Risk Addendum 1 January 2009

WSP Flood Risk Addendum 2 June 2009

PPS25 – Development and December 2006 Flood Risk

PPS25 – Development and June 2008 Flood Risk Practice Guide

SFRA None available

Greenwich Unitary July 2006 Development Plan

Kidbrooke Supplementary June 2008 Planning Document

Flood Risk Mapping Received from EA December 2007

Environment Agency – A River EA document Reborn

The London Plan February 2004

List of Consultees

Consultee Office Response received at time of drafting report Y/N Environment South East Thames Office Y Agency

Appendix B Existing Site

Appendix C Proposed Development