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FLOOD RISK ASSESSMENT

Lewisham Shopping Centre

Flood Risk Assessment

October 2024

For Planning

P0 18 Oct 2024 For Planning L Harding F Labbé F Labbé

Appendix

Appendix G: Thames Water Asset Records vii

Appendix H: Drainage Strategy Drawings viii

Appendix I: Maintenance and Management Plan ix

1 Introduction

This Flood Risk Assessment (FRA) has been prepared to support the Hybrid Planning Application for the comprehensive, phased redevelopment of land at Lewisham Shopping Centre and adjacent land

The structure of this FRA follows the checklist included in the National Planning Policy Guidance (NPPG) on Flood Risk and Coastal Change[1]

This FRA includes all necessary supporting documents, a validation checklist is included in Appendix A including reference to the relevant part of this document.

This document should be read in conjunction with the Sustainable Drainage Strategy also prepared by Expedition.

2 Development Site and Location

2.1 Where is the development site located?

The 6.93ha site located within the London Borough of Lewisham, in Southeast London The site is bound to the west and south by Molesworth St (A21), to the east by Lewisham High Street and to the north by Rennell Street (A20). West of Molesworth Street is the railway line and Ravensbourne River as well as a mix of green space, residential and commercial buildings.

The Lewisham DLR and railway stations are located, respectively, approximately 170m and 240m north of the site. Northeast of the site is a Police Station, east of Lewisham High Street which is then followed by shops and commercial premises running south beyond the southern tip of the site The River Quaggy runs along the north-east of the site, on the opposite side of Lewisham High Street. The site is centred at postcode SE13 0HB and on OS grid reference 38239, 75543

2.2 What is the current use of the site?

The site currently comprises the Shopping Centre, which includes a range of retail units, a multi-storey car park, the 18-storey vacant former Lewisham House office building, the vacant leisure box and Riverdale Hall, as well as commercial properties on the High Street. The existing Shopping Centre was built in 1977.

Figure 1: Site location

2.3 Which Flood Zone is the site within?

The Environment Agency (EA) flood map shows the northern half of the site to be within Flood Zone 3, as shown on Figure 3.

Figure 2: Aerial view of the site

Figure 3: Environment Agency flood map

A strategic Flood risk Assessment (SFRA) has been prepared for the London Borough of Lewisham by AECOM in 2018 [2]. Map 004 of the SFRA (Appendix B) suggests that approximately half of the site would be in Flood Zone 3, and approximately a third of the site would be in Flood Zone 3b, the “functional flood plain” of the River Ravensbourne and River Quaggy This is also shown on the Environment Agency (EA) flood map.

Predicted flood levels have been received from the EA as part of a Product 4-7 data request. These levels are based on the results of the River Ravensbourne Model[3], carried out by CH2M Hill for the EA in 2015 to map flood risk on the River Ravensbourne catchment. They have been compared with the results of a detailed topographical survey and a measured building survey of the existing shopping centre (Appendix C) which has been summarised in Table 1. In several places, the predicted flood levels were found to be lower than the surveyed existing ground levels within the building. This suggests that the EA flood map for planning and SFRA flood map are inaccurate in places. As discussed with the EA and LLFA (refer to meeting minutes in Appendix D) this is explained by the strategic flood mapping produced by the EA being based on relatively coarse LIDAR data, which is inaccurate when the site is occupied by buildings.

(see Figures 4 and 5)

Table 1: Fluvial flood levels, refer to Figure 4 and 5 for node locations.

[1] Location found not to be subject to fluvial flooding for up to the 1 in 100 year + 20% event.

[2] Note that the existing pavement to the west of node 8 is at +9.77mAOD which is above the flood level of +9.68 mAOD and therefore protects the adjacent internal areas from flooding.

A revised flood map for the site has been produced and is shown in Figure 5, mapping predicted fluvial flood levels onto a ground model generated on the results of the detailed topographical survey. This shows that approximately 10% of the site area is now in Flood Zone 3, most of which is in Flood Zone 3b.

The mapping of Flood Zone 3b has been based on the 1:30 year flood envelope, in line with latest guidance from NPPG and in consultation with the LLFA.

This approach has been agreed with the EA and LLFA in consultation meetings on 21st December 2023, 30th January 2024 and 29th May 2024 (Appendix D).

3 Development Proposals

3.1 What are the development proposal(s) for this site? Will this involve a change of use of the site and, if so, what will that change be?

This hybrid planning application is for the comprehensive, phased redevelopment of land at Lewisham Shopping Centre and adjacent land, comprising:

Full planning application (within Phase 1a) comprising the demolition of existing buildings, structures and associated works to provide a mixed-use development including the erection of a Co-Living building (Sui Generis) up to 23 stories in height (Plot N1), and a residential building (Class C3) up to 15 stories in height (Plot N2), associated residential ancillary spaces as well as town centre uses (Class E (a, b, c, d, e, f, g (i, ii)); and Sui Generis) together with public open space, public realm, amenity space and landscaping, car and cycle parking, highway works and the formation of new pedestrian and vehicle accesses, existing shopping centre interface works (the ‘Phase 1a Finish Works’), service deck modifications, servicing arrangements, site preparation works, supporting infrastructure works and other associated works

Figure 4 (left): EA flood extents

Figure 5 (right): Revised flood map based on site topography

Outline planning application (all matters reserved) for a comprehensive, phased redevelopment, comprising demolition of existing buildings, structures and associated works to provide a mixed-use development including:

• The following uses:

o Living Uses, comprising residential (Class C3) and student accommodation (Sui Generis);

o Town Centre Uses (Class E (a, b, c, d, e, f, g (i, ii)) and Sui Generis); and,

o Community and Cultural uses (Class F1; F2; and Sui Generis)

• Public open space, public realm, amenity space and landscaping works;

• Car and cycle parking;

• Highway works;

• Formation of new pedestrian and vehicular accesses, permanent and temporary vehicular access ramps, service deck, servicing arrangements and means of access and circulation within the site;

• Site preparation works;

• Supporting infrastructure works;

• Associated interim works;

• Meanwhile and interim uses; and,

• Other associated works.

The proposed masterplan is shown in Figure 6, Figure 7 and Figure 8. Proposed drawings are included in Appendix E

Highways works proposals include the maintenance and local improvements of the existing infrastructure to improve connectivity and quality of access into and around the development They do not include significant changes to the existing drainage arrangement or finished levels. As such these works do not affect flood risk are not covered by this FRA.

Figure 6: Illustrative Proposed Masterplan, Studio Egret West

Figure 7: Illustrative Landscape Proposals, Studio Egret West (Full height of buildings not shown)

Figure 8: Illustrative Masterplan, Studio Egret West

3.2 In terms of vulnerability to flooding, what is the vulnerability classification of the proposed development?

In accordance with Annex 3 of NPPF[4], highways works are classified as essential infrastructure, living uses are classified as more vulnerable and all other parts of the proposals are classed as less vulnerable. No residential development is proposed on the ground floor of proposed buildings, but overall, the vulnerability classification of the proposed development is taken as more vulnerable. This is compatible with Flood Zones 1 to 3a, in accordance with Table 2 of NPPG[1]

Some of the existing buildings to the north of the site are within Flood Zone 3b, the functional floodplain where commercial and residential development would not usually be permitted. These building footprints cover a total area of 5,100m2 This is generally described as “developed Flood Zone 3b”.

As part of the scheme, it is proposed to redevelop these buildings, with a total built footprint in Flood Zone 3b of 5,000m2 No increase in built footprint within Flood Zone 3b is proposed. However, to maximise placemaking opportunities, the quality of the public realm to the north of the site and access to the station to promote sustainable mobility, it is proposed to open the space between existing buildings at the north of the site. As such, it is proposed to slightly reduce and amend the layout of the built footprint from current in Flood Zone 3b. This is shown in Appendix F

This approach will not increase flood risk within the site or locally and has been accompanied by level-bylevel floodplain storage compensation calculations as discussed in Section 6.7. This has been agreed with the EA and LLFA (Appendix D).

3.3 What is the expected or estimated lifetime of the proposed development likely to be?

For the purpose of assessing the risk of flooding, the residential element has an estimated lifetime of at least 100 years in line with NPPG[1]. The non-residential element would generally have a shorter design life, but as the residential is above the non-residential element; for the purpose of assessing flood risk, the lifetime of the development is taken as 100 years.

4 Sequential Test

In accordance with the NPPF[4]the Sequential Test must be applied by the local planning authority for any proposed development in areas at risk of flooding

This site has been designated to be re-developed in existing and emerging Lewisham Local Plans, under reference Central Area Site Allocation 2 in the Lewisham Local Plan: Submission Version (January 2023) This site allocation seeks comprehensive mixed-use redevelopment comprising compatible main town centre, commercial, community and residential uses As part of the preparation of the new Local Plan, Sequential testing has been carried out [5] This has established that no other location in areas with lower flood risk were suitable for the proposed development

5 Climate Change

5.1 How is flood risk at the site likely to be affected by climate change?

Climate change is predicted to increase rainfall intensities, which will in turn increase the risk of surface water and fluvial flooding.

The following climate change allowances have been considered as part of this flood risk assessment, in line with NPG and latest DEFRA mapping of climate change allowances for the London Management Catchment.

• +35% increase in rainfall intensities on the 1:30 year rainfall event (Upper End allowance to 2070s horizon);

• +40% increase in rainfall intensities on the 1:100 year rainfall event (Upper End allowance to 2070s horizon); and,

• +17% increase in fluvial flows (Central allowance to the 2080s horizon).

This FRA is based on the results of the River Ravensbourne Model [3] carried out by CH2M Hill for the EA in 2015 to map flood risk on the River Ravensbourne catchment A +17% increase in fluvial flow had not been modelled at the time, but the modelling work included a +20% increase in fluvial flow scenario. As agreed with the EA and the Lead Local Flood Authority (LLFA) (refer to minutes in Appendix D), a +20% increase in fluvial flows has conservatively been assumed in this FRA

6 Site Specific Flood Risk

6.1 What is/are the main source(s) of flood risk on the site?

A review of the main potential sources of flooding that could affect the development has been carried out, considering the key sources of flooding defined in the National Planning Policy Framework (NPPF)[4]

6.1.1 Fluvial

The EA and SFRA flood maps in Section 2.2 and Appendix B, show that the northern part of the site is at risk of fluvial flooding, and that part of the site falls in the functional floodplain (Flood Zone 3b) of the River Ravensbourne and River Quaggy. This mapping has been refined using more detailed site topography as detailed in Section 2.2. The extent of the site at risk of flooding and in the functional floodplain is reduced as shown on Figure 5

The risk of fluvial flooding is however significant for part of the site and mitigations measures have been developed to ensure occupants are safe and the development does not increase flood risk elsewhere. These mitigation measures are described in Sections 6.6 to 6.8.

Map 010 of the SFRA (Appendix B) identifies that the site is within the Flood Warning Area and the Flood Alert Area.

6.1.2 Tidal

The River Ravensbourne and River Quaggy are not tidal at the site. The Thames Tidal Upriver Breach flood maps (Maps 012a-d, Appendix B) within the SFRA [2] does not show any risk of flooding to the site As such there is no risk of tidal flooding to the site.

6.1.3

Pluvial and Sewer Flooding

In urban areas, where impermeable surfaces typically drain to sewers, pluvial flooding tends to occur as a consequence of sewer surcharging or poor drainage. Pluvial and sewer flood risks have therefore been considered together in this FRA

The EA surface water flood risk map (Figure 9) shows that there is a high risk of flooding to the north of the site around the highways. There are also localised areas of medium and low risk within the rest of the site. Elsewhere the annual probability of surface water flooding is less 0.1% The SFRA[2] surface water flood map 005 (Appendix B), is consistent with this.

As shown in Figure 10, a network of existing Thames Water surface water and combined sewers run along surrounding streets and across the existing Lewisham Shopping Centre. This system also includes private secondary networks within the site connecting to the Thames Water sewers Thames Water Asset Records are included in Appendix G.

Map 005 of the 2018 Lewisham SFRA [2] (Appendix B) identifies the site as in a local critical drainage area. This is defined as a surface water catchment which drains to a local flood risk zone (LFRZ).

6.1.1

Groundwater

Map 007 of the SFRA [2] (Appendix B) identifies the site to have limited potential for groundwater flooding to occur.

A Ground Investigation Report was prepared in December 2022 by WSP [6] following geotechnical ground investigation in 2022 by Ground Engineering Ltd. British Geological Survey maps and borehole logs have also been reviewed to understand existing ground conditions.

Figure 9: EA Surface Water Flood Map

A summary of the geological profile extracted from the ground investigation is shown in Table 2.

*Alluvium was found in the east of the site (WS16 and WS17) with an average top level of +6.89 mOD and average thickness of 1.35m) and in the west of the site (RH1) with a recorded top level of +4.58 mOD and a recorded thickness of 0.5m.

** Bullhead beds only recorded in RH1, BH1, BH4 and BH11. NP – Top/thickness of strata not proven (NP) during the site-specific investigation works.

Table 2: Summary of the geological profile on site, WSP 2022

Groundwater monitoring between May 2022 and August 2022 found groundwater to be present in the Thanet Sand, with average groundwater levels to be at +1.2mAOD, circa 7.5m below ground levels. Groundwater was found to be shallowest in the southeast of the site with max levels of +2.57mAOD and lowest in the northwest with max levels of +0.27mAOD.

Relatively low groundwater levels are understood to be associated with historic groundwater abstraction. This confirms that there is no significant risk of groundwater flooding to the site.

Figure 10: Existing site drainage arrangement

6.1.2

Water Infrastructure

As shown in the EA reservoir flood map in Figure 11, in the event of a reservoir breach, the northern part of the site would be subject to flooding When this is combined with fluvial flooding conditions, the whole site would be flooded

The SFRA also identifies this risk in Map 08 (Appendix B) and outlines that this flooding would be due to failure of the Sutcliffe Park and Weigall Road Flood Storage Areas in Greenwich The SFRA [2] states that ‘risk of failure is very low due to rigorous safety and inspection regimes in place for all designated reservoirs’. The mitigations measures developed for the fluvial flooding will also deal with the reservoir flood risk when river levels are in normal conditions.

6.1.3

Conclusions

The north of the site is subject to fluvial flooding. The predicted fluvial flood extents have been revised based on detailed site topography. The northern part of the site and surrounding streets are also subject to surface water flooding and flooding associated with a failure of the water storage infrastructure. These risks are broadly similar in extent and severity to the fluvial flood risk and will be mitigated in similar ways.

6.2 What is the probability of the site flooding?

As shown in Figure 5, the revised fluvial flood map shown areas to the far north of the site to be in Flood Zone 3b, with a 3.33% or greater annual probability of fluvial fooding. A small part of the site falls in Flood Zone 3a with an annual probability of fluvial flooding of 1% or greater. The rest of the site is within Flood Zone 1 and has an annual probability of fluvial flooding of less than 0.1%.

Figure 11: EA Reservoir flood map

Figure 9 shows areas in the north of the site to have an annual probability of surface water flooding of 3.33% or greater The localised areas of medium and low risk within the rest of the site have annual probabilities of flooding of between 1% and 3.33%, and between 0.1% and 1%, respectively. Elsewhere the annual probability of surface water flooding is lower than 0.1%

The residual probability of flooding associated with a failure of the Sutcliffe Park and Weigall Road Flood Storage Areas in Greenwich is very low. This has not been quantified in the SFRA.

6.3 Are you aware of any other sources of flooding that may affect the site?

No other sources of flood risk have been identified.

6.4 What is the expected depth and level for the design flood?

Table 1 summarises the predicted fluvial flood levels and depths of flooding for the existing condition across the site. In the northwest corner of the site adjacent to the existing Lewisham House, predicted flood depths for the 1 in 100 year + 20% fluvial design flood are up to 0.73m. At the northeast corner of the site, near the junction between Lewisham Hight Street and Rennel Street predicted flood depths are up to 0.53m.

6.5 Are properties expected to flood internally in the design flood and to what depth? Internal flood depths?

The main Lewisham Shopping Centre building is not expected to flood during the 1:100 year +20% design flood event, or from surface water flooding

Buildings to the north of the Shopping Centre would be flooded during severe fluvial events. As far as practical and as agreed with the EA and LLFA, finished levels have been raised above the 1:30 year fluvial flood levels, but this has not been possible everywhere where building levels are to tie into existing levels of surrounding streets.

Table 3 below summarises proposed finished floor levels and flood depths for different events in the buildings that would be subject to flooding. No residential dwellings are proposed on the ground floor of any of the buildings. Reference should be made to architectural drawings in Appendix E for details of proposed finished floor levels in buildings at the north of the site.

Mitigation measures for these buildings are described in the following section.

Table 3: Proposed finished floor levels and flood depths

6.6 How will the development be made safe from flooding and the impacts of climate change, for its lifetime?

Several flood risk mitigation measures have been adopted to protect the proposed development from flooding. This includes:

• Setting finished floor levels in relation to design flood levels, considering use class.

• Temporary flood protection and flood resilience measures where finished floor levels cannot be raised above design flood levels.

• Safe emergency access and egress

The predicted fluvial flood levels for the 1:100 year + 20% event are estimated from available flood maps to be higher than surface water flood levels. They are also estimated to be similar to flood levels from a reservoir failure when river levels are in normal condition. As such mitigation measures have been developed considering the fluvial flood levels, and these measures will also mitigate the other flood events. The extreme scenario of a reservoir failure combined with a fluvial flood event will generate greater depths of flooding, but the probability of this combined event is very low. This is discussed separately hereafter.

6.6.1 Finished Floor Levels (FFLs)

No residential dwellings are proposed on the ground floor of any buildings. The lowest residential dwellings will be one storey above ground levels. As such, proposed residential FFLs are well above good practice requirements of 600mm above the 1 in 100 year + 20% fluvial flood level.

Most ground floor FFLs within the shopping centre and proposed buildings will be above the fluvial flood levels for the design 1:100 year + 20% event, except for parts of Block N1, Block N2 and Lewisham House to the north of the site. As discussed in Section 6.2, these levels have been set where possible above the 1:30 year flood level. Building FFLs are shown on the architectural drawings in Appendix E. Table 3 in Section 6.5 summaries the building FFLs that are below design flood levels and flood depths for the 1:100 year +20%. Mitigation measures for these buildings are discussed in Section 6.6.2.

Residential dwellings will be adequately protected against a reservoir flooding event combined with fluvial flooding. Relatively high FFLs in the shopping centre and most buildings would result in shallow depths of flooding and low velocities within the buildings in such extreme event. The risk to life will be low and mitigated by the safe egress and access strategy described in Section 6.6.3. Furthermore, the mitigation measures proposed for the buildings at the north (N1, N2 and the extension to Lewisham House) will significantly mitigate the risk of flooding for an extreme event combining fluvial flooding and reservoir failure.

6.6.2

Temporary flood protection and flood resilience measures

As described above some of the ground floor commercial units, residential lobbies, utility areas and plantrooms within buildings to the north of the site will be subject to fluvial flooding. The proposals have been developed to raise ground floor levels where possible above the 1 in 30 year flood level, to minimise the frequency of flooding. Temporary flood protections will be provided at doors to ground floor units at risk (demountable defences) to protect against events greater than 1 in 30 year and up to 1 in 100 year +20%.

The site is within the EA Flood Warning Area and the Flood Alert Area (Appendix B), and the building management will be connected to the EA flood warning system, to help ensure demountable flood defence are deployed. The residential building occupants will also be encouraged to receive warnings directly via SMS.

Flood resilience measures will also be implemented, including robust finishes designed to withstand water damage and for ease of cleanup. Power sockets, services and sensitive plants will be set above design flood 1:100 year +20% level. Sensitive plants will be set on a plinth or on finished floor level a minimum of 300mm above the design flood level.

6.6.3

Safe access and egress

A strategy has been developed to ensure occupants can safely egress and emergency services can effectively access the buildings during a 1:100 year + 20% fluvial flood event. As shown in the proposals drawings (Appendix E), most residential buildings will have access to the two-level podium public park, which is connected to Lewisham High Street and the southern part of Molesworth Street that will not be flooded. Residents and occupants from buildings to the north of the site will also have access to dry areas within the Northern Square. For the 1:100 year +20% event, routes to these areas will be through shallow depths of flooding typically no greater than 70mm and low velocities as flood waters would not run through the square but back-up from Rennel Street. This will connect to the podium and surrounding streets that are not flooded. Residents and building occupants within the northern part of the site not able to walk through shallow depth of water will also be able to take refuge in communal areas on the upper floors of the buildings. This approach has been discussed with the EA and LLFA (Appendix D)

As mentioned earlier, the building management will sign up to the EA flood warning system and residents will be encouraged to receive warnings directly via SMS, to help ensure they can prepare for flood events and where necessary evacuate the buildings before occurrence of the flood.

In the event of reservoir flooding combined with fluvial flooding, occupants will also be able to take refuge on the upper floors of the building and on the landscape podium.

6.7 How will you ensure that the development and any measures to protect the site from flooding will not cause any increase in flood risk off-site and elsewhere? Have you considered the impacts from climate change, over the expected lifetime of the development?

6.7.1 Flood plain storage compensation

To prevent any increase in flooding off-site, any loss of floodplain storage volume has been compensated on a level-by-level and volume-by-volume basis, in line with NPPG. The flood storage lost to the west of the site has been compensated by lowering levels within the Northern Square and connecting these levels to flooded area along Rennell Street

An analysis has been undertaken to compare the existing and proposed topographies against the design fluvial flood event. Flood volumes have been estimated in 200mm bands from the design flood level (z) Existing and proposed buildings have been omitted from the calculations. This approach has been agreed with the EA and LLFA (Appendix D). Anticipated flood depths for the existing and proposed condition are illustrated in Figure 12 Volumes are summarised in Table 4

This shows that for all level bands existing floodplain storage is either matched or increased. As such, the development will not increase flood risk elsewhere and will result in a small reduction of flood risk.

Table 4: Flood compensation volumes

6.7.2 Overland flow routes

The primary mechanisms of fluvial flooding are associated with overtopping of the banks of the River Ravensbourne to the west and the River Quaggy to the east of the site. As shown on the revised flood map in Figure 5, at present there are no fluvial overland flow routes through the site. Flood water follows the main road and street corridors, with typical flow velocities of up to 1m adjacent to existing buildings according to the EA flood modelling data.

As shown in Figure 12, this pattern of flow will be broadly maintained. There will be no throughflow across the Northern Square and as such minimal anticipated changes to the main overland flow route from the Ravensbourne River to the west. Flows are expected to enter the Northern Square from the east and north in areas not previously submerged. Flood waters will back up into the Northern Square from flooded streets to occupy the floodplain storage area within reduced levels. This is not anticipated to materially affect overland flow routes.

6.8 Are there any opportunities offered by the development to reduce the causes and impacts of flooding?

As discussed in Section 6.6, the proposed mitigation measures will mitigate any impact of the development on off-site flooding, but there are no opportunities to reduce fluvial flooding to surrounding communities and facilities.

Figure 12: Existing (left) and proposed (right) flood depths for the 1 in 100 year + 20% fluvial event

However as discussed in the following sections, as peak surface water discharge rates to the local sewers will be reduced from current and the 1:100 year + 40% pluvial event will be contained on site, surface water and sewer flooding will be reduced.

7 Surface Water Management

7.1 What are the existing surface water drainage arrangements for the site?

At present most of the site is impermeable, with no noticeable soft landscape area. All stormwater is discharged to the sewer network. There are no known methods of stormwater attenuation on the site.

A 229mm dia surface water sewer runs across the north of the site and discharges into the River Quaggy. It is anticipated that this takes surface water drainage flows from Lewisham House, the northern end of the Shopping Centre including Riverdale Hall, and from the ramped access to the Shopping Centre.

A network of combined sewers runs through the Shopping Centre, connecting to the 686mm x 610mm sewer running from west to east and joining the deep trunk sewer along Lewisham High Street to the east of the site.

7.2 If known, what (approximately) are the existing rates and volumes of surface water run-off generated by the site?

Current surface water runoff rates have been estimated using the Modified Rational Method. As the site consists of majority roofs with some hardstanding areas, a volumetric runoff coefficient of 0.85 has been assumed for all surfaces As stormwater flows are not attenuated, the 15-minute storm has been considered critical to calculate peak surface water runoff rates, outlined in Table 2

The calculations are based on FEH 2022 rainfall depths of 7.6mm, 23.3mm and 30.1mm for the 1 in 2, 1 in 30 and 1 in 100 year 15-minute storms, respectively.

The existing stormwater discharge volume for the 1:100 year 6 hour storm has been estimated as 3,400m3

7.3 What are the proposals for managing and discharging surface water from the site, including any measures for restricting discharge rates?

Reference should be made to the Sustainable Drainage Strategy, also prepared by Expedition, to accompany the planning application for the proposed development. This is briefly summarised hereafter.

Table 5: Current surface water runoff rates

7.3.1

Strategic principles

The key strategic principles of the Sustainable Drainage Strategy accompanying this planning application are summarised below:

• Adopting the most sustainable disposal route for surface water drainage flows, in line the London Plan [7] Policy SI13 and with the drainage hierarchy set out by the SUDS Manual CIRIA C753 [8]

• Flood resilience and no increase in flood risk off-site. Peak discharge limited to peak greenfield runoff rate in line with London Plan [7] Policy SI 13 and LLFA requirements.

• Control runoff at source, maximise opportunities for enhancement of the landscape and biodiversity and control pollution following best practice in line with The SUDS Manual CIRIA C753 [8]

• Management of stormwater flows in efficient multi-function open water bodies integrated with green infrastructure.

• Effective management and maintenance of the drainage infrastructure to ensure performance over design life in line with SUDS Manual CIRIA C753 [8]

• Smart harvesting of rainwater for irrigation of the podium landscape planting

7.3.2 Overview of drainage system

An overview of the surface water drainage strategy is included in Figure 13 and in Appendix H

The nature of the ground suggests that infiltration may be feasible, subject to infiltration testing, groundwater levels and contamination. However given the relative density of the proposed development and need to maintain a sufficient distance between soakaways and buildings, soakways and infiltration basisns will not be feasible as primary disposal route for surface water.

Permeable pavement is proposed where suitable in parts of the proposed development. The aspiration is to let surface water flows infiltrate to ground. However as the site is currently occupied by buildings, it is not possible to carry out infiltration testing until after demolition of these buildings. The system has therefore been designed assuming no infiltration from the pavement system, and controlled discharge to the sewer. If infiltration was found to be feasible these systems will be designed to maximise infiltration to ground. This approach has been agreed with the LLFA (Appendix D)

Discharge to the River Quaggy will be maximised, reusing an existing surface water drainage connection.

Consideration has been given to create a new outfall in the Quaggy to maximise discharge to the river but this was found to not be feasible due to large utility constraints along Lewisham High Street. Opportunity for direct discharge to the River Ravensbourne are limited

As such the rest of the site will drain to the existing Thames Water combined sewer network at four connection points around the site.

Peak discharge will be limited to greenfield rates of 40.9 l/s for the 1 in 30 year + 35% rainfall event and 56.7 l/s for the 1 in 100 year + 40% event.

Run-off will be controlled at source, with green roofs, extensive soft landscape of the two-level podium and permeable pavement and SUDS features at ground level. Raingardens and filter drains will also form part of the strategy as well as two attenuation ponds within the Northern Square, with permanent water enhancing amenity and biodiversity. These features will also contribute to intercepting diffuse urban pollutants at source, in line with established best practice from the SUDS Manual CIRIA C753 [8]

A number of Thames Water sewers will be diverted or decommissioned as part of the works.

Figure 13: Surface water drainage strategy

7.3.3 Proposed surface types

The proposed surface types are shown in the landscape drawings in Appendix E. Associated areas are outlined in Table 6. In the south of the site (catchments E1, E2 and E3) it is assumed that 50% of hardstanding is permeable. It is assumed that 70% of all podium is planted. These assumptions have been coordinated with the masterplan design team.

Table 6: Proposed surface areas

7.3.4 Design criteria

The surface drainage system has been designed for:

• No surface water flooding for all events up to 1 in 30-year return period, in line with BS EN 752;

• No flooding of buildings and containment on site extreme events up to the 1 in 100-year return period, in line with NPPF.

The climate change allowances discussed in Section 5 have been applied.

7.4 How will you prevent run-off from the completed development causing an impact elsewhere?

As described in the Sustainable Drainage Strategy, all surface water drainage flows from the main site will be discharged to the Thames Water network at greenfield rate. This will result in a net reduction of peak flows to the network of 917 l/s and 1179 l/s for the 1 in 30 and 1 in 100 year events, considering the effects of climate change in the proposed condition. This equated to approximately a 95% reduction in peak discharge

The stormwater discharge volume for the 1:100 year 6 hour event has been quantified as 2,500m3, resulting in a 10% reduction from current.

Rainfall events up to the 1 in 100 year + 40% event will be contained within the site, as outlined in Section 7.3.2. At present these flows overspill onto roads and adjacent public realm contributing to the surface water flooding issues.

7.5 Where applicable, what are the plans for the ongoing operation and/or maintenance of the surface water drainage systems?

A maintenance and management plan has been developed to ensure that the performance of the drainage system is maintained over its entire design life. This is included in Appendix I This has been based on guidance from the SUDS Manual (CIRIA C753). It covers all private elements of the system including: green roofs, raingardens, bio-swales, pond and drainage pipework.

8 Occupants and Users of the Development

8.1 Will the development proposals increase the overall number of occupants and/or people using the building or land, compared with current use?

The site does not currently include any residential dwellings, but a number of working occupants within the existing facilities. The proposed redevelopment of the site will result in a significant number of residents and an increased number of people coming to visit and work within the Shopping Centre.

8.2 Will the proposals change the nature or times of occupation or use, such that it may affect the degree of flood risk to these people?

The proposed redevelopment of the site will result in a significant number of new residents, with 24-hour occupation of the site.

8.3 Where appropriate, are you able to demonstrate how the occupants and users that may be more vulnerable to the impact of flooding will be located primarily in the parts of the building and site that are at lowest risk of flooding?

Section 6.6.1 outlines how FFLs have been set to make the development safe from flooding. All residential dwellings will be on the first floor and above. As such, residents will be adequately protected from flooding. Mitigations measures are proposed to protect working occupants and shopping visitors from flooding as described in Section 6.6.

9 Exception Test

As part of the site falls within Flood Zone 3, residential dwellings are subject to the Exception Test as set out in Table 2 of NPPG.

9.1 Would the proposed development provide wider sustainability benefits to the community? If so, could these benefits be considered to outweigh the flood risk to and from the proposed development?

The existing Shopping Centre is in need of regeneration. The proposed development will support meeting strategic policies within the Local Plan through the provision of needed community, commercial and residential spaces.

The development proposes to bring green infrastructure into the heart of Lewisham, with the creation of a large park on a podium, and significant opportunities for sustainable water management.

In line with the 2014 Lewisham Town Centre Local Plan the proposals will encourage healthy lifestyles through the maintenance, protection and improvement of the supply of publicly accessible open space and incorporation of additional recreational and open space.

9.2 How can it be demonstrated that the proposed development will remain safe over its lifetime without increasing flood risk elsewhere?

This Flood Risk Assessment has assessed flood risks from all relevant sources and proposed a number of mitigation measures to ensure the development and its working occupants and residents are safe, and that the development does not increase flood risk elsewhere. This includes consideration of finished floor levels in relation to flood levels, temporary demountable flood protection, flood resilience measures, safe emergency access and egress, flood compensation and consideration of the impact on overland flows.

9.3 Will it be possible to for the development to reduce flood risk overall?

As described in Sections 6.6 and 6.7 the proposed development will incorporate flood resilience measures and drainage infrastructure which will mitigate the risk of flooding to the site, its future occupants as well as the adjacent streets and neighbourhoods.

Peak surface water discharge rates to the local sewers will be reduced from current and the 1:100 year + 40% pluvial event will be contained on site. Surface water and sewer flooding will therefore be reduced.

10 Residual Risk

10.1 What flood related risks will remain after the flood risk management and mitigation measures have been implemented?

The main residual risk of flooding is associated with a failure or exceedance of the site’s drainage system. This risk associated system will be mitigated by ensuring a robust and regular maintenance schedule in line with CIRIA 753.

A residual risk of flooding is also associated with demountable defences not being deployed on time on the ground floor units to the north of the site. This will be mitigated by the flood resilience measures described in Section 6.6.

The proposed topography has been designed so that for exceedance events excess surface water will be routed away from buildings, as shown in Figure 14. This is discussed further in Section 4.7 of the Sustainable Drainage Strategy.

10.2 How, and by whom, will these risks be managed over the lifetime of the development?

The site will be managed by an Estate Manager and the maintenance of the surface water drainage will fall under their remit. This includes SUDS features, the below ground drainage system and connection to the Thames Water network. Adoptable sewers will be managed by Thames Water

11 FRA Credentials

11.1 Who has undertaken the flood risk assessment?

This Flood Risk Assessment has been produced by Lana Harding, a Civil Engineer at Expedition Engineering. It has been reviewed by Fred Labbé, Director at Expedition Engineering.

11.2 When was the flood risk assessment completed?

This assessment was completed in October 2024

Figure 14: Surface water exceedance routes

12 References

[1] Ministy of Housing, Communities & Local Government, “National Planning Policy Guidance, Flood risk and coastal change,” 2022.

[2] AECOM, “London Borough of Lewisham Strategic Flood Risk Assessment Level 1 Report,” 2018.

[3] CH2M Hill, “Ravensbourne Rmeodelling Study,” Environment Agency, 2015.

[4] Ministry of Housing, Communities & Local Government, “National Planning Policy Framework,” 2022.

[5] Lewisham Council, “Lewisham Local Plan Sequential and Exception Tests Paper,” 2023.

[6] WSP, “Lewisham Shopping Centre, Ground Investigation Report,” December 2022.

[7] Greater London Authority, “The London Plan,” Greater London Authority, London, 2021.

[8] CIRIA, “CIRIA SuDS Manual C753,” CIRIA, 2015.

Appendix A: Validation Checklist

The table below summarises the requirements for the Flood Risk Assessment as agreed with the Local Planning Authority and how they have been addressed in this document.

The study should include:

A site-specific Flood Risk Assessment (FRA) identifying the sources of flooding and assessing the risk to and from the development, demonstrating how they will be managed and mitigated. The assessment needs to take climate change into account.

Where a safe and dry means of escape cannot be provided a Flood Evacuation Management Plan will also be necessary to detail how a building would operate safely during a flood event and ensure the safety of all occupiers including those working in any commercial space.

Topographical survey of the existing and proposed sites, with contours demonstrating the flow of surface water across the site.

Details of areas of permeable and impermeable land for both existing and proposed site.

Proposals should be informed by a suitable qualified specialist. Mitigation proposed in the FRA will need to be incorporated into the plans (i.e. finished floor levels, living roofs etc).

References in document

Sources of flooding and associated risks are covered in sections 6.1 and 6.2.

Proposed management and mitigation of flood risk is covered in sections 6.5 to 6.7 and Section 7.

Refer to sections 6.6.2 and 6.6.3.

Refer to section 10.1

Refer to section 7.1 and 7.3.3 and landscape plans in Appendix E.

Refer to section 11.1 and masterplan proposals in Appendix E.

Appendix B: SFRA Flood Maps

Appendix C: Topographic Survey

Appendix D: EA and LLFA meeting minutes correspondence

Consultation meeting with Environment Agency – 21 Dec 2023

1927 - Lewisham Shopping Centre Regeneration

Reason for Issue For Information

Date 21 Dec 2023

Attendees:

Expedition (EXP) – Fred Labbé, Lana Harding

Author L Harding

Date Issued 10 April 2024

Studio Egret West (SEW) – Andrew Furzeland, Martin Lee

Landsec (LS) - Karen McCormick

Environment Agency (EA) – Kayleigh Wyatt, Ericka Johnston, Michael Wilkinson, Aidan Anderson

Minutes and Key Actions:

Item Notes

These minutes should be read in conjunction with the slides presented during the meeting.

1 Introduction

The purpose of the meeting was to introduce the project to the Environment Agency (EA) and discuss the key strategic principles that the project team proposes to adopt to deal with and mitigate the risk of flooding The intention is for the project team to work alongside the EA throughout the pre-planning design stage to ensure flood risk is adequately managed and mitigated on the site and not increased elsewhere.

The development site is the existing Lewisham Shopping Centre, adjacent to the River Ravensbourne to the west and River Quaggy to the east. The two rivers join to the north of the site at Lewisham Gateway

It is proposed to redevelop the site with a new shopping centre including commercial and retail units on the ground and first floors under a two-level podium deck forming an extensive public park. Residential development is proposed above the commercial units and around the park that will form a green spine to the development

Actions

2 Flood Map

EXP presented the EA flood map for planning and the flood map extracted from the Strategic Flood Risk Assessment (SFRA). These maps show that approximately half of the site is in Flood Zone 3, with approximately a third of the site in Flood Zone 3b (“functional flood plain”)

EXP have compared the predicted flood levels received from the EA as part of a Product 4-7 request with the results of a detailed topographical survey within the existing shopping centre building. In several places, the predicted flood levels were found to be lower that the existing ground levels within the building. This suggests that the EA flood map for planning and SFRA flood map are inaccurate in places

The EA noted that these flood maps are based on a strategic assessment at river catchment level, based on LIDAR ground level data and are not always accurate at site level, in particular in densely built-up areas as is the case for the existing shopping centre, where internal levels are generally interpolated.

EXP proposed a revised flood map for the site, mapping predicted fluvial flood levels onto a ground model generated based on the results of the detailed topographical survey. This shows that approximately 10% of the site area is now in Flood Zone 3, most of which is in Flood Zone 3b.

The EA confirmed that using a more accurate flood map built on detailed topography would be the right approach and recommended engaging with the Lead local Flood Authority (LLFA) to confirm the definition and revised extent of Flood Zone 3b.

The EA also indicated that the Ravensbourne flood model is currently being updated. This modelling work is anticipated to be complete in April 2024. The planning submission and supporting Flood Risk Assessment (FRA) will need to be based on the latest predicted flood levels available at that time. The EA will keep EXP and the project team updated on progress.

3 Fluvial flood risk mitigation

EXP presented the proposed approach to mitigate flood risk to the development and ensure that flood risk elsewhere is not increased, considering the following:

1. Compatibility of development proposals with flood zones

2. No net loss of fluvial flood plain storage

3. No significant impact on fluvial overland flow routes

4. Finished floor levels above flood levels

5. Emergency access and egress

EXP to engage with LLFA.

EA to update on progress in updating Ravensbourne flood model.

Built footprint in Flood Zone 3b

EXP indicated that existing buildings and car park ramps within Flood Zone 3b (functional floodplain where commercial and residential development would not be permitted) included an area of circa 5,100m2

As part of the scheme, a built footprint in Flood Zone 3b of circa 5,000m2 is proposed.

No increase in built footprint within Flood Zone 3b is proposed. However, to maximise place making opportunities and the quality of the public realm, it is proposed to open up the space between buildings at the north of the site to create a square well connected to Lewisham Gateway and public transport infrastructure. As such, it is proposed to slightly amend the layout of the built footprint in Flood Zone 3b.

The EA indicated that in principle any redevelopment of existing buildings in Flood Zone 3b should stay within the existing built footprint. But they recognised the significant place making benefits of the proposed approach and that the impact on flood risk would likely be negligible.

The EA also noted that the introduction of residential spaces, even on higher floors, would increase the vulnerability to flooding.

The EA recommended engaging with the LLFA (Martin O’Brien and Marcus Gayle) to discuss the proposed changes to the built footprint in Flood Zone 3b and introduction of residential use on higher floors, before a follow-up meeting with both the EA and LLFA to review the proposal.

The EA recommended also confirming the definition of Flood Zone 3b with the LLFA and how existing buildings are considered.

Fluvial floodplain storage

EXP indicated that the development will result in no net loss of fluvial floodplain storage, level by level, up to the 1:100 year + climate change flood level.

The “central” climate change allowance for the 2080’s epoch in the London Management Catchment is 17% increase in river peak flows. This scenario has not been modelled as part of the Ravensbourne flood mapping work. It is therefore proposed to conservatively use the +20% scenario which has been modelled. The EA confirmed this was acceptable.

EXP outlined that the current development proposals resulted in a loss of 1:100 year +20% flood envelope of circa 900m2 if existing ground levels were maintained. It is proposed to compensate for this loss by lowering proposed levels within the public realm to the north of the site. Level by level and volume by

EXP to discuss proposed modifications to the built footprint in Flood Zone 3b with the LLFA

volume analysis will be carried. The EA confirmed that this was acceptable as an approach

Finished floor levels

EXP indicated that no residential units are proposed on the ground floor and as such all residential FFLs will be well above good practice requirements of 300mm above the 1:100 year + 20% flood levels.

Some of the ground floor commercial units, residential lobbies, utility areas and plantrooms within buildings to the north of the site will be subject to fluvial flooding.

EXP indicated that the strategy for these buildings would be to:

• Raise ground floor levels where possible above the 1:30 year flood level, to minimise the frequency of flooding.

• Provide temporary flood protections at doors to ground floor units at risk, for events greater than 1: 30 year and up to 1:100 year +20%.

• Implement flood resilience measures, including consideration on finishes, and setting power sockets, services and sensitive plants above design flood levels.

The EA agreed with this proposed approach and the raising of FFLs above the 1:30 year flood level.

Emergency access and egress

EXP indicated that most residential buildings would have access to the two-level podium public park, which is connected to Lewisham and the southern part of Molesworth Street that will not be flooded.

Residents and occupants from buildings to the north of the site will either walk through relatively shallow depths of flooding (250-300mm for the 1:100 year +20% event) to reach the podium or surrounding streets or take refuge in communal areas on upper floors.

discuss emergency access with the LLFA 4

The EA indicated that this strategy was generally acceptable but that the preference was generally to not rely on residents taking refuge on upper floors of residential buildings. They recommended engaging with the LLFA on the emergency access strategy.

Surface Water Drainage

EXP outlined the proposed sustainable surface water drainage strategy, for information as part of a holistic approach to flood risk and water resource management, noting that this was the remit of the LLFA.

At present the site is mostly impermeable and drains to the River Quaggy through an existing Thames Water surface water sewer to the north of the site, and to local combined sewers.

Infiltration drainage is unlikely to be feasible as a main disposal source for surface water, but opportunities will be explored for localised infiltration from porous pavement of SuDS systems.

It is proposed to maximise discharge to the River Quaggy though the existing surface water sewer from the northern part of the site. The southern part of the site will drain to the combined sewer system.

Peak discharge will be limited to greenfield runoff rates and reuse existing outfalls. The EA confirmed that discharge into the Quaggy at greenfield runoff rate would be acceptable.

Run-off will be controlled at source, with green roofs, extensive soft landscape of the two-level podium and permeable pavement. This will also contribute to intercepting diffuse urban pollutants at source, in line with established best practice from the SUDS Manual (CIRIA C753).

Attenuation is proposed in multi-function systems, using green infrastructure where possible, including rain gardens and bio-retention systems at ground level and the significant storage capacity within the podium drainage system.

As part of a circular approach to sustainable water management and to minimise impact on local water resources, it is also proposed to use a smart weathercontrolled system to manage the retention and release of water from the stormwater attenuation system. This would allow harvesting rainwater for irrigation of the podium landscape, and potentially flushing of WCs in some buildings, without the need for dedicated storage and associated embodied carbon impacts.

The EA indicated that they would be supportive of such approach to reduce pressure on water resources and questioned the reliability of the weather prediction system. EXP noted that this technology has been in use for over 15 years in the US and mainland Europe, and uses both accurate weather prediction and live rainfall monitoring.

The EA also indicated that the risk of groundwater contamination should be assessed and mitigated. EXP noted that this would be considered as part of the Environmental Impact assessment

5 River Ravensbourne

EXP indicated that a review of the impact of the development on the river corridor is being carried out, considering pollution and flooding.

6

Considering that the drainage system of the existing shopping centre will have been designed several years ago to standards of pollution control now superseded, it is anticipated that the development proposals will have a significant beneficial effect on pollution loads. The pollution control strategy will follow established best practice from the SUDS Manual (CIRIA C753) and any loading bay will include robust treatment. The proposed landscape podiums and green roofs replacing existing roofs will also significantly reduce diffuse pollution loads.

Limiting discharge to greenfield runoff rate will have a beneficial effect on fluvial flood risk. Any loss of fluvial flood plain storage will be compensated level by level.

A high-level overshadowing assessment has been carried out. This found that the development proposals do not increase overshadowing of the river corridor. The EA noted that this was encouraging and that their Fisheries and Biodiversity Team would welcome this to be included as part of the planning submission

AOB

The EA noted that the proposed redline extends over the culverted River Quaggy and indicated that any works over and around culverts should be carefully managed

LS clarified that the proposed works around the Quaggy are primarily highways surfacing works, with no significant work at depth and that any impact on the culvert or watercourse should be negligible.

LS and EXP confirmed that an assessment of Biodiversity Net Gains (BNG) will be included as part of the planning application. The scheme will aim at maximising BNG and given the current nature of the site, the minimum requirements of 10% BNG will easily be achieved

Consultation meeting with Lewisham LLFA – 30 Jan 2024

1927 - Lewisham Shopping Centre Regeneration

Reason for Issue For Information

Date 30 Jan 2024

Attendees:

Author L Harding

Date Issued 10 April 2024

LLFA – Louisa Orchard, David Robinson, Marcus Gayle, Gwilym Jones

Landsec (LS) – Jon Watson, Rebecca Allwood

QUOD – Mattew Sherwood, Ben Ford

Studio Egret West (SEW) – Andrew Furzeland, Martin Lee

Expedition (EXP) – Fred Labbé, Lana Harding

Minutes and Key Actions:

Item Notes

These minutes should be read in conjunction with the slides presented during the meeting.

1 Introduction

The purpose of the meeting is to introduce the project to Lewisham LLFA and discuss the key strategic principles that the project team proposes to adopt as part of a sustainable drainage strategy and to mitigate the risk of flooding The intention is for the project team to work alongside the LLFA pre-planning, to ensure sustainable drainage principles are embedded in the development proposals and flood risk is adequately managed and mitigated on the site and not increased elsewhere.

The project team also consulted with the EA, with an initial meeting in December 2023

Actions

The development proposes green infrastructure into the heart of Lewisham, with significant opportunities for sustainable water management

2 Flood Map

EXP have compared the predicted flood levels received from the EA as part of the Product 4-7 data pack with the results of a detailed topographical survey of the existing shopping centre. In several places, the predicted flood levels were found to be lower than the existing ground levels within the building. This suggests that the EA flood map for planning and SFRA flood map are inaccurate in places These flood maps are based on a strategic assessment of fluvial flood risk at river catchment level, based on LIDAR ground level data and are not always accurate at site level, in particular in densely built-up areas as is the case for the existing shopping centre, where internal levels are generally interpolated.

EXP proposed a revised flood map for the site, mapping predicted fluvial flood levels onto a ground model generated based on the results of the detailed topographical survey This shows that approximately 10% of the site area is now in Flood Zone 3, most of which is in Flood Zone 3b.

EXP explained that this was raised with the EA who accepted the inaccuracy of the flood zones and confirmed that the approach was acceptable The EA recommended engaging with the LLFA to confirm the definition and revised extent of Flood Zone 3b.

The EA had advised that their fluvial flood models are currently being revised and that new results would be available in April 2024 The planning application will need to be based on latest available fluvial modelling results at the time of submission.

The LLFA also accepted the proposed approach to developing a site-specific more accurate flood map

3 Fluvial flood risk mitigations

EXP outlined the following proposed flood risk mitigation measures:

• Compatibility of development with flood zone

• Flood plain storage

• Overland flow

• Finished floor levels

• Emergency access and egress

Compatibility of development with flood zone

As part of the scheme, a built footprint in Flood Zone 3b of circa 5,000m2 is proposed.

The LLFA agreed that this approach was acceptable and as it would not increase flood risk on the catchment

EXP confirmed that to the approach will focus on not increasing flood risk to existing buildings adjacent to and around the site, and that temporary flood protection measures will be provided where necessary to mitigate flood risk.

Flood plain storage

EXP indicated that the development will result in no net loss of fluvial floodplain storage, level by level, up to the 1:100 year + climate change flood level.

Compensation of any loss of flood plain storage will be provided level-by-level and volume-by-volume by partially lowering the Northern Square

PMN – The LLFA have confirmed that existing and proposed buildings should be omitted from the flood plain volume compensation calculations. Email dated 2nd February 2024.

Overland flow

EXP indicated that the development proposals would not have any significant impact on fluvial overland flow routes that could result in an increased risk of flooding elsewhere

Finished floor levels

Some of the ground floor commercial units, residential lobbies, utility areas and plantrooms within buildings to the north of the site will be subject to fluvial flooding.

EXP indicated that the strategy for these buildings would be to:

• Raise ground floor levels where possible above the 1:30 year flood level, to minimise the frequency of flooding.

• Provide temporary flood protections at doors to ground floor units at risk, for events greater than 1: 30 year and up to 1:100 year +20%.

• Implement flood resilience measures, including consideration on finishes, and setting power sockets, services and sensitive plants above design flood levels.

The LLFA agreed with this proposed approach and the raising of FFLs above the 1:30 year flood level in ground floor units

Emergency access and egress

Residents and occupants from buildings to the north of the site will also have access to dry areas within the Northern Square, through shallow depth of flooding typically no greater than 70mm for the 1:100 year +20% event. This will connect to the podium and surrounding streets that are not flooded

Residents and building occupants of buildings within the northern part of the site not able to walk through shallow depth of water will also be able to take refuge in communal areas on the upper floors of the buildings.

The LLFA had no concern with the proposed approach

Surface Water drainage

EXP outlined the existing surface water drainage arrangement of the site The site is mostly impermeable Its northern part drains to a 225mm dia. Thames Water surface water sewer that discharges into the River Quaggy. The rest of the site drains to the local network of combined sewers.

The 2023 emerging Lewisham Local Plan identifies the site as being within a critical drainage area. The proposals will require a drainage strategy and flood risk assessment to be submitted at planning.

EXP have proposed the following sustainable drainage principles for the scheme:

1. Most sustainable disposal route for surface water run-off in line with London Plan Policy SI13.

2. Flood resilience and no increase in flood risk off-site. Peak discharge limited in line with London Plan Policy SI 13 and LLFA requirements.

3. Source control measures to minimise runoff at source, and control pollution in line with SUDS Manual.

4. Attenuation in efficient multi-function open water bodies integrated with green infrastructure

5. Maintenance of drainage system to ensure performance over design life in line with SUDS Manual

6. Smart harvesting of rainwater / water retention

Disposal route

The site ground condition generally consists of Kempton Park Gravels over London Clay. Infiltration rates are expected to be relatively good.

Infiltration drainage is not feasible as a primary disposal route, due to spatial constraints, high groundwater levels and potential contamination risks. However, permeable pavement systems will be considered as part of an approach to reduce runoff at source.

Opportunities for harvesting of rainwater are also considered as discussed below.

Restriction of surface water runoff

EXP indicated that the drainage system will be designed for no surface water flooding for the 1 in 30 year +35% event and for containment on site with no flooding for the 1 in 100 year + 40% event. The London Plan requires restriction of surface water runoff to greenfield rates.

The LLFA confirmed that discharge to the sewer system peak discharge should be limited to greenfield rates, matching discharge for the 1:1, 1:30 and 1:100 greenfield runoff rate. Limiting peak discharge to Qbar is not required.

For the proposed discharge to the River Quaggy, the LLFA suggested exploring whether discharge could be unattenuated. Given the scale of the River Quaggy catchment it may be preferable to discharge unattenuated, and early before occurrence of the peak in the river system, rather than discharging at lower rate over a longer period and adding to the peak. The LLFA noted that the expected time of peak river flow is expected to be 5 or 6 hours from the start of the storm event.

This would be beneficial to reduce flood risk on the river catchment and would reduce cost and carbon associated with attenuation infrastructure. Such an approach has

been successfully adopted on the London 2012 Olympic Park, Meridian Water and other projects within the River Lea, and the Brentford Lock West project at the bottom of the River Brent catchment.

EXP will review the catchment hydrology and capacity of the existing Thames Water outfall into the River Quaggy

FEH 22 data will be used for drainage design and attenuation sizing.

Source control measures

Stormwater attenuation

At podium level attenuation is proposed in modular podium storage, typically 150mm deep. Initial calculations show that, for restriction of discharge from the whole site to greenfield rate, the majority of attenuation required can be provided in the podium.

Maintenance

Recognising the importance of maintenance to ensure continued performance of the drainage system, a maintenance schedule will be prepared as part of the drainage strategy, building on best practice form the SUDS Manual and clearly confirming responsibilities

Water circularity

EXP outlined that use of Hydrorock attenuation systems could also be used at ground level offering storage and passive irrigation in a low carbon solution.

EXP outlined that the strategy will be developed to consider anticipated non potable demands which will be quantified in the next stages prior to planning

The LLFA noted that large irrigation demands are expected considering the extent of proposed planting on podium

The LLFA confirmed that the overall strategy would meet their requirements and was a good holistic approach to sustainable water management

River Ravensbourne

The LLFA questioned whether potential opportunities to improve connectivity along the River Ravensbourne corridor between Riverdale Sculpture Park and Cornmill Gardens were being explored

EXP noted that a potential opportunity discussed previously would be to install a suspended boardwalk under the railway bridges The impact on flood risk would need to be considered, but this could be a carbon efficient and cost effective way of improving connectivity.

The LLFA noted that impact on flood risk could potentially be mitigated elsewhere.

SEW/EXP to sketch and test potential options for discussion

6 AOB

The EA suggested a joint follow-up meeting with EA and LLFA to review the proposals as they develop The LLFA agreed that this would be a good way to coordinate consultation. Quod and EXP to arrange.

SEW/EXP

Quod/EXP

Consultation meeting with Lewisham LLFA – 29 May 2024

1927 - Lewisham Shopping Centre Regeneration

Reason for Issue For Information

Date 29 May 2024

Attendees:

LLFA – Louisa Orchard, Marcus Gayle

Author L Harding/ L Lester

Date Issued 22 July 2024

EA – Ericka Johnston, Kayleigh Wyatt, Aidan Anderson, Michael Wilkinson

Landsec (LS) – Rebecca Allwood, Karen McCormick

QUOD – Mattew Sherwood, Ben Ford

Ploughman Craven (PC) - Tony Selwyn

Studio Egret West (SEW) – Andrew Furzeland, Martin Lee

Expedition (EXP) – Fred Labbé, Lana Harding, Lauren Lester

Minutes and Key Actions:

Item Notes

These minutes should be read in conjunction with the slides presented during the meeting.

1 Introduction

The purpose of the meeting was to discuss the proposals for Lewisham Shopping Centre with the Lead Local Flood Authority (LLFA) and Environment Agency, reviewing key scheme developments since previous engagement with the EA on 21st December 2023 and the LLFA on 30th Jan 2024.

The meeting focused on the sustainable drainage strategy and fluvial flood risk mitigations Feasibility of improving connectivity along the Ravensbourne corridor was also be discussed.

The development site is the existing Lewisham Shopping Centre, adjacent to the River Ravensbourne to the west and River Quaggy to the east. The two rivers join to the north

Actions

of the site at Lewisham Gateway. Ground levels at the north of the site are approx. 2m lower than at the south of the site

The development proposes to bring green infrastructure into the heart of Lewisham, with significant opportunities for sustainable water management, particularly within the proposed park.

It is proposed to phase the development as presented. Phase 1A to the northeast, including blocks N4 and N2 will be delivered first Phase 1B to the northwest includes redevelopment of the existing Lewisham House.

The current programme is to submit for planning at the end of summer 2024. Phase 1A is to be submitted as a detailed planning application, with the remaining phases submitted as part of an outline planning application

Some of the points discussed at the previous meeting consultation meetings with the EA and LLFA were represented to recapitulate on agreed principles and context. These minutes also cover these points for completeness.

2 Flood Map

EXP presented the EA flood map for planning and the flood map extracted from the Strategic Flood Risk Assessment (SFRA). These maps suggest that approximately half of the site would be n Flood Zone 3, and approximately a third of the site would be in Flood Zone 3b (“functional flood plain”)

As presented previously, EXP have compared the predicted flood levels received from the EA as part of the Product 4-7 data pack with the results of a detailed topographical survey of the existing shopping centre. In several places, the predicted flood levels were found to be lower than the existing ground levels within the building. This suggests that the EA flood map for planning and SFRA flood map are inaccurate in places

This approach has been previously accepted by the EA and LLFA, and was confirmed as acceptable.

The EA queried node 8 on the revised flood map (slide 14). This was shown to be outside of the flood extents for the 1in100 + 20% flood extents but below the predicted flood level.

PMN – Existing pavement to the west of node 8 is at +9.77mAOD which is above the flood level of +9.68 mAOD and therefore protects the adjacent internal areas from flooding. The proposed flood envelope is therefore correct.

3 Fluvial flood risk mitigations

EXP outlined the following proposed flood risk mitigation measures:

• Compatibility of development with flood zones

• Flood plain storage

• Overland flow

• Finished floor levels

• Emergency access and egress

Compatibility of development with flood zone

As part of the scheme, a built footprint in Flood Zone 3b of circa 5,000m2 is proposed. This has been remeasured and confirmed following the latest scheme developments.

No increase in built footprint within Flood Zone 3b is proposed. However, to maximise placemaking opportunities and the quality of the public realm, it is proposed to open up the space between buildings at the north of the site to create a square well connected to Lewisham Gateway and public transport infrastructure. As such, it is proposed to slightly amend the layout of the built footprint in Flood Zone 3b.

The LLFA previously agreed that this approach was acceptable and as it would not increase flood risk on the catchment

EXP confirmed that the approach will focus on not increasing flood risk to existing buildings adjacent to and around the site, and that temporary flood protection measures will be provided where necessary to mitigate flood risk.

The LLFA confirmed that this is acceptable as long as the benefits of relocation of the spaces can be justified as part of the planning application. The EA confirmed that this would be acceptable to them if acceptable to the LLFA

Flood plain storage

EXP outlined that the development will result in no net loss of fluvial floodplain storage, level-by-level and volume-by-volume, up to the 1:100 year + climate change flood level.

EXP presented results from the flood compensation analysis, with use of 200mm level bands from the design flood level. The analysis shows that compensation is provided by partially lowering the Northern Square.

EXP clarified that “relative level bands” offset from the inclined flood water surface have been used, rather than “absolute level bands”

The EA indicated that this would be acceptable in principle, as the flood compensation storage is in a similar area to the lost storage. They will review the approach and confirm acceptability following the meeting.

In an email dated 2nd February 2024, the LLFA confirmed that existing and proposed buildings should be omitted from the flood plain volume compensation calculations. This was confirmed in the meeting.

Overland flow

EXP indicated that the development proposals would not have any significant impact on fluvial overland flow routes that could result in an increased risk of flooding elsewhere

The EA requested that an assessment of impact on overland flow routes is included in the FRA. This does not necessarily require rerunning the fluvial flood model The EA noted that consideration of flow velocities is important.

Finished floor levels

Some of the ground floor commercial units, residential lobbies, utility areas and plantrooms within buildings to the north of the site will be subject to fluvial flooding.

EXP indicated that the strategy for these buildings would be to:

• Raise ground floor levels where possible above the 1:30 year flood level, to minimise the frequency of flooding.

• Provide temporary flood protections at doors to ground floor units at risk (demountable defences), for events greater than 1:30 year and up to 1:100 year +20%.

• Implement flood resilience measures, including consideration on finishes, and setting power sockets, services and sensitive plants above design flood levels.

As agreed previously, the LLFA confirmed that this approach was acceptable

The EA would not object to commercial properties sitting below 1:30 levels but requires justification as to why this is the case (e.g. tying to existing levels, etc.).

The EA recommended considering the ease of deployment of the demountable defences and noted that resilience measures should be prioritised.

The EA further advised that 600mm above design flood level is generally required rather than the previously typical 300mm for residential properties. EXP explained that as no residential accommodation is proposed on the ground floor this would be achieved. EXP to confirm minimum freeboard achieved above 1:100+20% flood level for the residential units.

Emergency access and egress

Residents and occupants from buildings to the north of the site will also have access to dry areas within the Northern Square (block N4). For the 1:100 year +20% event, routes to this area route will be subject to shallow depth of flooding typically no greater than 70mm. This will connect to the podium and surrounding streets that are not flooded.

Residents and building occupants within the northern part of the site not able to walk through shallow depth of water will also be able to take refuge in communal areas on the upper floors of the buildings.

The LLFA had no concern with the proposed approach The EA requested that flow velocities are also considered.

EXP confirms the FRA will comment on flow velocities.

Surface Water drainage

As outlined previously, EXP proposed the following sustainable drainage principles for the scheme:

1. Most sustainable disposal route for surface water run-off in line with London Plan Policy SI13.

2. Flood resilience and no increase in flood risk off-site. Peak discharge limited in line with London Plan Policy SI 13 and LLFA requirements.

3. Source control measures to minimise runoff at source, and control pollution in line with SUDS Manual.

4. Attenuation in efficient multi-function open water bodies integrated with green infrastructure

5. Maintenance of drainage system to ensure performance over design life in line with SUDS Manual

6. Smart harvesting of rainwater / water retention

Disposal route

The site ground condition generally consists of Kempton Park Gravels over London Clay. Infiltration rates are expected to be relatively good.

EXP outlined that infiltration drainage is not anticipated to be feasible as a primary disposal route, due to spatial constraints, high groundwater levels and potential contamination risks. However, permeable pavement systems will be considered as part of an approach to reduce runoff at source.

The LLFA noted that infiltration through permeable pavements is generally considered acceptable closer to the buildings (less than 5m) as the infiltration is more distributed.

As agreed previously with the LLFA, infiltration testing will be carried out after demolition of buildings currently occupying the site. The strategy for planning will assume no infiltration but attenuation through the permeable pavement sub-base If following infiltration testing, before start of construction, infiltration was found to be feasible, the strategy will be updated to incorporate infiltration, subject to LLFA consent.

Direct Discharge to the river

Given the location of the site at the downstream end of the catchments of both the River Quaggy and River Ravensbourne, it may be preferable to discharge unattenuated, and early before occurrence of the peak in the river system, rather than discharging at lower rate over a longer period and adding to the peak flow condition. This would be beneficial to reduce flood risk on the river catchment and would reduce cost and carbon associated with attenuation infrastructure. This approach was suggested by the LLFA previously and has been adopted by EXP on similar projects.

EXP have extracted flow and level hydrographs from the fluvial models for the 1 in 100 year + 20% flood events Peak river flow at the site occurs approximately 7 hours after start of the storm for the River Quaggy and approx. 3-4 hours for the River Ravensbourne.

EXP indicated that the existing 225mm surface water outfall into the River Quaggy at the North of the site would not have the capacity to take the unattenuated flow to the Quaggy. A 600mm diameter pipe would be required.

EXP presented the outcome of a feasibility study to install a new outfall into the Quaggy. This would include micro-tunelling or pipe jacking.

The route across Lewisham High Street is particularly constrained, including a medium pressure gas main (SNG, 762mm) and trunk sewer (Thames Water, 2130mm OD) perpendicular to the proposed new route. EXP presented an indicative cross section, identifying that only approx. 500mm is available vertically between the two utilities Thames Water have confirmed that 500mm clearance from the trunk sewer would be required. Therefore, installing a new 600mm dia pipe is not feasible. Multiple smaller pipes would not be feasible either and would require large access shaft for installation in a very congested area,

Discharge to the Ravensbourne through the existing surface water to the south of the site has also been considered. This 225mm pipe already collects flows from a relatively

large catchment and would not be able to accommodate unattenuated discharge from the site. Existing pipe levels would make any connection from the site challenging. This, as well as existing utilities along Molesworth Street would also make a new outfall not feasible.

Peak discharge limit and design criteria

In line with policy and as agreed previously, discharge will be limited to greenfield runoff rate. For the 4.32ha site, this is 40.7l/s for the 1in30 year event and 56.1l/s for the 1in100 year event.

EXP presented the proposed catchment plan and connection points. It is proposed to connect into the existing Thames Water network at 5 locations around the site. The restricted rate discharged into each connection point will be distributed according to the associated catchment. It is proposed to maximise discharge to the River Quaggy though the existing surface water sewer from the northern part of the site.

The drainage system will be designed for no surface water flooding for the 1 in 30 year +35% event and for containment on site with no flooding for the 1 in 100 year + 40% event. FEH 22 data will be used for drainage design and attenuation sizing.

Source control measures

Run-off will be controlled at source, with green roofs, extensive soft landscape of the two-level podium and permeable pavement. Permeable pavement will be extensive across the Northern and Southern Squares, as well as in the podiums. Raingardens will also form part of the strategy. This will also contribute to intercepting diffuse urban pollutants at source, in line with established best practice from the SUDS Manual (CIRIA C753).

EXP presented a concept sketch for the Northern Square which will incorporate permeable pavement, raingardens and other soft landscaped areas with attenuation ponds which will effectively drain the north

Raingardens will be provided adjacent to the highway in Molesworth Street. EXP noted these are partially within the site’s boundary and partially within the public realm. The LLFA noted that this is a TfL highway so engagement with TfL will be required to ascertain ownership and maintenance. Current but stop locations to be considered EXP to join LLFA in engaging with highway teams and TfL

The LLFA noted that a conceptual design has been submitted for a sculpture park in the Southwest which will incorporate SuDS features and overland flow routes. This has been submitted to the GLA for review in July 2024, but if approved it can present opportunities to connect the developments’ surface water management.

Stormwater attenuation

EXP presented the stormwater attenuation proposals throughout the site. Attenuation is proposed in multi-function systems, using green infrastructure where possible, including

rain gardens and bio-retention systems at ground level. At podium level attenuation is proposed in modular podium storage, typically 150mm deep. Initial calculations show that, for restriction of discharge from the whole site to greenfield runoff rate, the majority of attenuation required can be provided in the podium. Podium storage is therefore significant in the overall strategy.

EXP presented the proposed ponds in the Northern Square and proposed connection points. EXP confirmed that the storage for the 30-year and 100-year (+ climate change) events are optimised across all SuDS features after defining the catchments and flow rates. The underground tanks in the Northern Square (3 no.) are provided to supplement the raingardens, ponds and permeable pavement storage. A similar arrangement is proposed in the southern catchments.

EXP confirmed that network hydraulic modelling will be undertaken for the detailed planning application.

EXP and SEW noted that the proposed SuDS and landscape features will be developed further.

The LLFA confirmed that the proposed strategy holistically aligns with expectations.

Water circularity

As part of a circular approach to water management and to minimise impact on local water resources, it is also proposed to use a smart weather-controlled system to manage the retention and release of water from the stormwater attenuation system. This would allow harvesting rainwater for irrigation of the podium landscape, and potentially flushing of WCs in some buildings, without the need for dedicated storage and associated embodied carbon impacts.

At ground level, the use of rockwool attenuation blocks such as Hydrorock is proposed as a low carbon alternative to plastic crates. The systems can be integrated with rainwater harvesting and used for passive irrigation. EXP noted that the system works through an operated valve controlling storage.

EXP confirmed that water balance modelling will be completed to validate the smart harvesting approach. Water will be harvested from two tanks: one in the North and the other in the South

The LLFA previously confirmed that the overall strategy would meet their requirements and was a good holistic approach to sustainable water management

River Ravensbourne and Corridor

EXP presented the outcome of a study to improve connectivity along the River Ravensbourne corridor between Riverdale Sculpture Park and Cornmill Gardens Different approaches have been considered, and it was found that a footbridge span over the railway lines would be very challenging

EXP tested a potential option of installing a suspended boardwalk under the railway bridges. The impact on flood risk would need to be considered, but this could be a carbon efficient and cost-effective way of improving connectivity. Proposed boardwalk structures could be floating or ballasted and resting on the riverbed.

The EA noted that the channel is near capacity and a boardwalk would reduce already limited capacity, and that the proposals would require careful hydraulic analysis The EA would not rule out options to increase flood storage upstream to mitigate potential impacts, although this would likely require large volumes which would not be available within the Sculpture Park

Opportunity for providing additional fluvial storage further upstream within Ladywell fields, or elsewhere, could potentially be considered.

Appendix E: Proposed Development Plans

Appendix F: Flood Zone 3b mapping

Existingbuiltfootprintatgroundlevel

Builtfootprintatgroundlevel

Projectionongroundofpodiumfootprint (additionaltobuildingfootprint)

1in100+20%climatechangefloodextents

1in30floodextents(FloodZone3b)

Reducedlevelsfromcurrenttocompensatefor lossofvolume

Floodmodellingnode

Appendix G: Thames Water Asset Records

Groundwise Searches Ltd Suite 8 Chichester House

45Chichester Road

SOUTHEND ON SEA SS1 2JU

Search address supplied Lewisham Shopping Centre, Molesworth Street SE13 7HF

Your reference URO6409.1JS

Our reference ALS/ALS Standard/2019_3946982

Search date 5 February 2019

From 1 September 2018 Thames Water Property Searches will be increasing the price of its Asset Location Search in line with RPI at 3.23%.

For further details on the price increase please visit our website: www.thameswater-propertysearches.co.uk

Please note that any orders received with a higher payment prior to the 1 September 2018 will be non-refundable.

Thames Water Utilities Ltd Property Searches, PO Box 3189, Slough SL1 4WW DX 151280 Slough 13

searches@thameswater.co.uk www.thameswater-propertysearches.co.uk

0845 070 9148

Search address supplied: Lewisham Shopping Centre, Molesworth Street, SE13 7HF,

Dear Sir / Madam

An Asset Location Search is recommended when undertaking a site development.It is essential to obtain information on the size and location of clean water and sewerage assets to safeguard against expensive damage and allow cost-effective service design.

The following records were searched in compiling this report: - the map of public sewers & the map of waterworks. Thames Water Utilities Ltd (TWUL) holds all of these.

This searchprovides maps showing the position, size of Thames Water assets close to the proposed development and also manhole cover and invert levels, where available.

Please note that none of the charges made for this report relate to the provision of Ordnance Survey mapping information. The replies contained in this letter are given following inspection of the public service records available to this company. No responsibility can be accepted for any error or omission in the replies.

You should be aware that the information contained on these plans is current only on the day that the plans are issued. The plans should only be used for the duration of the work that is being carried out at the present time. Under no circumstances should this data be copied or transmitted to parties other than those for whom the current work is being carried out.

Thames Water do update these service plans on a regular basis and failure to observe the above conditions could lead to damage arising to new or diverted services at a later date.

Contact Us

If you have any further queries regarding this enquiry please feel free to contact a member of the team on 0845 070 9148, or use the address below:

Thames Water Utilities Ltd

Property Searches PO Box 3189 Slough SL1 4WW

Email: searches@thameswater.co.uk Web: www.thameswater-propertysearches.co.uk

Waste Water Services

Please provide a copy extract from the public sewer map.

The following quartiles have been printed as they fall within Thames' sewerage area:

TQ3875NW

TQ3875SW

Enclosed is a map showing the approximate lines of our sewers. Our plans do not show sewer connections from individual properties or any sewers not owned by Thames Water unless specifically annotated otherwise. Records such as "private" pipework are in some cases available from the Building Control Department of the relevant Local Authority.

Where the Local Authority does not hold such plans it might be advisable to consult the property deeds for the site or contact neighbouring landowners.

This report relates only to sewerage apparatus of Thames Water Utilities Ltd, it does not disclose details of cables and or communications equipment that may be running through or around such apparatus.

The sewer level information contained in this response represents all of the level data available in our existing records. Should you require any further Information, please refer to the relevant section within the 'Further Contacts' page found later in this document.

For your guidance:

• The Company is not generally responsible for rivers, watercourses, ponds, culverts or highway drains. If any of these are shown on the copy extract they are shown for information only.

• Any private sewers or lateral drains which are indicated on the extract of the public sewer map as being subject to an agreement under Section 104 of the Water Industry Act 1991 are not an ‘as constructed’ record. It is recommended these details be checked with the developer.

Clean Water Services

Please provide a copy extract from the public water main map.

The following quartiles have been printed as they fall within Thames' water area:

TQ3875NW

TQ3875SW

Enclosed is a map showing the approximate positions of our water mains and

associated apparatus. Please note that records are not kept of the positions of individual domestic supplies.

For your information, there will be a pressure of at least 10m head at the outside stop valve. If you would like to know the static pressure, please contact our Customer Centre on 0800 316 9800. The Customer Centre can also arrange for a full flow and pressure test to be carried out for a fee.

For your guidance:

• Assets other than vested water mains may be shown on the plan, for information only.

• If an extract of the public water main record is enclosed, this will show known public water mains in the vicinity of the property. It should be possible to estimate the likely length and route of any private water supply pipe connecting the property to the public water network.

Payment for this Search

A charge will be added to your suppliers account.

Further contacts:

Waste Water queries

Should you require verification of the invert levels of public sewers, by site measurement, you will need to approach the relevant Thames Water Area Network Office for permission to lift the appropriate covers. This permission will usually involve you completing a TWOSA form. For further information please contact our Customer Centre on Tel: 0845 920 0800. Alternatively, a survey can be arranged, for a fee, through our Customer Centre on the above number.

If you have any questions regarding sewer connections, budget estimates, diversions, building over issues or any other questions regarding operational issues please direct them to our service desk. Which can be contacted by writing to:

Developer Services (Waste Water)

Thames Water Clearwater Court

Vastern Road

Reading

RG1 8DB

Tel: 0800 009 3921

Email: developer.services@thameswater.co.uk

Clean Water queries

Should you require any advice concerning clean water operational issues or clean water connections, please contact:

Developer Services (Clean Water)

Thames Water Clearwater Court

Vastern Road

Reading

RG1 8DB

Tel: 0800 009 3921

Email: developer.services@thameswater.co.uk

n/a 11.61 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 10.37 n/a n/a n/a 18.54 21.13 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 12.4 n/a n/a n/a n/a n/a n/a n/a n/a

n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 5.04 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 5.68 n/a n/a n/a 6.66 7.62 n/a n/a 8.7 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 7.26 n/a n/a n/a 16.41 18.33 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 9.15 n/a n/a n/a n/a n/a n/a n/a n/a

n/a n/a

n/a

8.56 n/a n/a 8.9 8.29 9.23 8.43 8.83 8.68 8.26 n/a 8.07 n/a n/a n/a n/a n/a n/a n/a n/a 8.48 9.25 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 8.12 n/a n/a n/a n/a n/a n/a 4.79 n/a n/a n/a n/a 5.36 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 6.25 n/a n/a n/a 6.72 n/a n/a n/a 6.44 n/a n/a n/a n/a 4.7 6.78 n/a 6.82 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 4.32 5.16 4.24 5.39 7.34 3.12 n/a n/a 5.01 n/a n/a n/a n/a n/a n/a n/a n/a 3.96 6.74 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 5.82 n/a

8.66 8.74

n/a 6.67 6.62 6.15 8.65 8.65 8.62 8.69 8.65 8.69 8.65 8.69 7.91 8.38 8.18 8.65 8.65 8.65 7.9 7.79 7.17 n/a n/a n/a 8.57 8.75 5.36 8.54 8.61 7.52 7.17 8.67 n/a 8.62 7.135 6.26 8.58 n/a 8.74 8.73 8.64 7.12 n/a 8.8 8.8 8.59 8.63 8.85 n/a 6.915 6.86 7.3 6.71 5.66 5.57

8.65 n/a n/a 6.79 n/a n/a n/a n/a 7.19 n/a 7.46 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 5.92 n/a 6.19 6.95 6.67 8.75 8.38 8.48 8.43 8.48 8.48 8.21 n/a 10.2 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 18.43 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 8.52 8.26 6.84 6.11 5.75 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 7.41 n/a n/a n/a n/a n/a n/a n/a n/a n/a 9.57 n/a 9.48 n/a n/a

n/a n/a n/a n/a n/a n/a n/a 10.6 10.86 n/a n/a n/a n/a 10.71 10.64 n/a n/a 10.42 n/a 10.46 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 10.95 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 9.61 n/a n/a n/a n/a n/a n/a n/a n/a n/a 9.11 n/a n/a n/a n/a 8.97 n/a n/a n/a 17.52 n/a n/a n/a 13.87 9.28 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 9.14 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 8.88 9.78 n/a n/a n/a n/a 7.89 7.76 n/a n/a 7.99 n/a 7.94 n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a 8.96 n/a n/a n/a n/a n/a n/a n/a n/a

The position of the apparatus shown on this plan is given without obligation and warranty, and the accuracy cannot be guaranteed. Service pipes are not shown but their presence should be anticipated. No liability of any kind whatsoever is accepted by Thames Water for any error or omission. The actual position of mains and services must be verified and established on site before any works are undertaken.

ALSSewerMapKey

PublicSewerTypes (Operated&MaintainedbyThamesWater)

Foul: Asewerdesignedtoconveywastewaterfromdomesticand industrialsources toa treatmentworks.

SurfaceWater: Asewerdesignedtoconveysurfacewater(e.g.rain water fromroofs,yardsandcarparks) toriversorwatercourses.

Combined: Asewerdesignedtoconveybothwastewaterandsurface water fromdomesticandindustrialsources toa treatmentworks.

TrunkSurfaceWater

StormRelief

VentPipe

ProposedThamesSurface WaterSewer

Gallery

SurfaceWaterRising

Main

SludgeRisingMain

Vacuum

TrunkFoul

TrunkCombined

Bio-solids(Sludge)

ProposedThamesWater FoulSewer

FoulRisingMain

CombinedRisingMain

ProposedThamesWater RisingMain

SewerFittings

Afeatureinasewerthatdoesnotaffecttheflowinthepipe.Example:avent isa fittingas the functionofaventis toreleaseexcessgas.

AirValve

DamChase

Fitting

Meter

VentColumn

OperationalControls

Afeatureinasewerthatchangesordivertstheflowinthesewer.Example: Ahydrobrakelimits the flowpassingdownstream.

ControlValve

DropPipe

Ancillary

Weir

End Items

Endsymbolsappearatthestartorendofasewerpipe.Examples:an UndefinedEndatthestartofasewerindicatesthatThamesWaterhasno knowledgeofthepositionofthesewerupstreamofthatsymbol,Outfallona surfacewatersewerindicates that thepipedischargesintoastreamorriver.

Outfall

UndefinedEnd Inlet

Notes:

1)Alllevelsassociatedwith theplansare to OrdnanceDatumNewlyn.

2)Allmeasurementson theplansaremetric.

3)Arrows(ongravityfedsewers)orflecks(onrisingmains)indicatedirectionof flow.

4)Mostprivatepipesarenotshownonourplans,asinthepast,thisinformationhas notbeenrecorded.

5)‘na’or‘0’onamanholelevelindicates thatdataisunavailable.

6)Thetextappearingalongsideasewerlineindicatestheinternaldiameterof thepipeinmilimetres.Textnexttoamanholeindicatesthemanhole referencenumberandshouldnotbetakenasameasurement.Ifyouare unsureaboutanytextorsymbologypresentontheplan,pleasecontacta memberofProperty Insighton0845 070 9148.

Thames Water Utilities Ltd, Property Searches, PO Box 3189, Slough SL1 4W, DX 151280 Slough 13 T 0845 070 9148 E searches@thameswater.co.uk I www.thameswater-propertysearches.co.uk

OtherSymbols

Symbolsusedonmapswhichdonot fallunderothergeneralcategories

Public/PrivatePumpingStation /

Changeofcharacteristicindicator(C.O.C.I.)

InvertLevel

Summit

Areas

Linesdenotingareasofundergroundsurveys,etc.

Agreement

OperationalSite

Chamber

Tunnel

ConduitBridge

OtherSewerTypes

FoulSewer

CombinedSewer

(Not OperatedorMaintainedbyThamesWater)

CulvertedWatercourse

SurfaceWaterSewer

Gulley

Proposed

AbandonedSewer

ALS Water Map Key

Pipes

DistributionMain: Themostcommonpipeshownonwatermaps. Withfewexceptions,domesticconnectionsareonlymadeto distribution mains.

TrunkMain: Amaincarryingwaterfromasourceofsupplytoa treatmentplantorreservoir,orfromonetreatmentplantorreservoir toanother.Alsoamaintransferringwaterinbulktosmallerwater mains used for supplying individual customers.

SupplyMain: Asupplymainindicatesthatthewatermainisused as a supply for a single property or group of properties.

FireMain: Whereapipeisusedasafiresupply,thewordFIREwill be displayed along the pipe.

MeteredPipe: Ameteredmainindicatesthatthepipeinquestion supplieswaterforasinglepropertyorgroupofpropertiesandthat quantityofwaterpassingthroughthepipeismeteredeventhough there may be no meter symbol shown.

TransmissionTunnel: Averylargediameterwaterpipe.Most tunnelsareburiedverydeepunderground.Thesepipesarenot expectedtoaffectthestructuralintegrityofbuildingsshownonthe map provided.

ProposedMain: Amainthatisstillintheplanningstagesorinthe processofbeinglaid.Moredetailsoftheproposedmainandits reference number are generally included near the main. Water

Hydrants

Operational Sites

Booster Station

Other

Other (Proposed)

Pumping Station

Service Reservoir

Shaft Inspection

TreatmentWorks

Unknown

WaterTower

End Items

Symbol indicating what happens at the end of a water main.

Blank Flange

Capped End

Emptying Pit

Undefined End

Manifold

Customer Supply Fire Supply

Other Symbols

Data Logger

Up to 300mm (12”) 900mm (3’)

300mm - 600mm (12” - 24”) 1100mm (3’ 8”)

600mm and bigger (24” plus) 1200mm (4’)

Thames Water Utilities Ltd, Property Searches, PO Box 3189, Slough SL1 4W, DX 151280 Slough 13 T 0845 070 9148 E searches@thameswater.co.uk I www.thameswater-propertysearches.co.uk

Other Water Pipes (Not Operated or

Maintained by Thames Water)

OtherWaterCompanyMain: Occasionallyotherwatercompany waterpipesmayoverlaptheborderofourcleanwatercoverage area.Thesemainsaredenotedinpurpleandinmostcaseshave the owner of the pipe displayed along them.

PrivateMain: Indiatesthatthewatermaininquestionisnotowned byThamesWater.Thesemainsnormallyhavetextassociatedwith them indicating the diameter and owner of the pipe.

(Operated & Maintained by Thames Water)

Appendix H: Drainage Strategy Drawings

CONNECTIONPOINTFOR BLOCKN1COURTYARD (DRAINAGEOFCATCHMENT A3FORSITEWIDEDRAINAGE STRATEGY).PEAKDISCHARGE LIMITEDTO1.9l/s.

CONNECTIONTOEXISTINGTHAMESWATER

SURFACEWATERSEWERFROMDRAINAGE CATCHMENTA1OFSITEWIDEDRAINAGE STRATEGY.INVERTLEVELTBCBYSURVEYOF EXISTINGTHAMESWATERSEWER.

HYDROBRAKEFLOWRESTRICTIONDEVICETO LIMITFLOWRATETOMAXIMISESTORAGEIN PONDFEATURESFORTHE1IN100+40% RAINFALLEVENT

SMARTWEATHER-CONTROLLEDRETENTIONAND RELEASEOFWATER,TOMINIMISETOPPING-UP REQUIREMENTSINTOOPENWATERFEATURES. SUMMERRETAINEDLEVELINDRYPERIODTOBE 200mmHIGHER(7.7mAOD)THANNORMAL WINTERRETAINEDLEVEL(7.5mAOD)

HYDROBRAKEFLOWRESTRICTIONDEVICE

TOLIMITFLOWRATETO17.5l/sFORTHE1 IN100YEAR+40%RAINFALLEVENT.

STUBFORFUTURECONECTIONOF RETROFITTEDANDEXTENDEDLEWISHAM HOUSE.PEAKDISCHARGELIMITEDTO 2.1l/sFOR1:100+40%RAINFALLEVENT (DRAINAGECATCHMENTB2OFSITEWIDE DRAINAGESTRATEGY).

260mATTENUATIONTANK HYDROROCKD320HDUNITS1000mm DEEP.

CL:8.0mAOD IL:6.20mAOD

PERMEABLEPAVEMENTWITHATTENUATIONIN300mm GRANULARSUB-BASE(TRAFFICCATEGORY4TOBS7533) ANDCONTROLLEDDISCHARGETOSEWERSYSTEM.AIM TOMAXIMISEINFILTRATIONTOGROUND,SUBJECTTO INFILTRATIONANDGROUNDCONTAMINATIONTESTING, ANDESTABLISHINGGROUNDWATERLEVELS.PROVIDES 15m3OFSTORAGE.

SUDSFEATURESINTEGRATEDINTOPLANTEDAREAS

PROVIDINGAPPROXIMATELY20m3ATTENUATION FORTHE1IN100+40%RAINFALLEVENT.FLOW RATESFOREACHFEATURERESTRICTEDTO MAXIMISESTORAGE.

CONNECTIONFROMPODIUMDRAINAGEOUTLETS. ABOVEGROUNDCONNECTIONBYMEPENGINEER. RODDINGACCESSATBASEOFABOVEGROUNDPIPE. PODIUMANDASSOCIATEDDRAINAGESUBMITTEDAS PARTOFOUTLINEPLANNINGAPPLICATION

RWPDISCHARGESTOPODIUMBYMEPENGINEER

INTERNALLAYOUTTOBECOORDINATEDWITH STRUCTURALANDMEPENGINEERS

RODDINGACCESSATENDOFRUNTOBE COORINATEDWITHINTERNALLAYOUT

EXTENTOF1IN100YEAR +40%ATTENUATION 7.9mAOD TOTALATTENUATION VOLUME:110m

INDICATIVEEXTENTOF1 IN30YEAR+30% ATTENUATION 7.7mAOD TOTALATTENUATION VOLUME:80m

REFERTOBLOCKN1's CIVILENGINEERS IN-GROUNDDRAINAGE DESIGN.DRAWING 2210000-EWP-ZZ-00-SK-C-001

SMARTWEATHER-CONTROLLEDRETENTION ANDRELEASEOFWATER,FOR COST-EFFECTIVEANDCARBONEFFICIENT HARVESTINGOFRAINWATER.MANHOLE CHAMBERTOINCLUDE600mmDEEPSILTTRAP

BOUNDARYCHANNELDRAINWITH RODDINGACCESS CL8.2mAOD

PERMANENTAMENITYAND BIODIVERSEPONDS

225mmDIACONNECTIONFROM BLOCKN2AT7.14mAODINVERT

RAINGARDENFEATURESTO PROVIDE80mOFSTORMWATER ATTENUATION.MIN.FINISHED LEVEL7.6mAOD,MIN800mmOF SOILOVER300mmGRANULAR DRAINAGELAYER.

MANHOLECHAMBERTO INCLUDE600mmDEEP SILTTRAP

PROVISIONFORCONNECTIONOF CHANNELDRAINSATBASEOF STAIRS(SUBMITTEDASPARTOF OUTLINEPLANNINGAPPLICATION)

REFERTOBLOCKN2's CIVILENGINEERS IN-GROUNDDRAINAGE DESIGN.DRAWING LSC-WSP-N2-ZZ-DR-CV-527101

LEWISHAMHOUSE RUNOFFFROMEXTENSIONTOBERESTRICTEDTO GREENFIELDRUNOFFRATES.

EXTENTOFEXISTINGBUILDINGTODISCHARGE UNRESTRICTED

PEAKDISCHARGEFROMRETROFITTED ANDEXTENDEDLEWISHAMHOUSETOBE RESTRICTEDTO2.1L/SFORTHE1IN100 YEAR+40%EVENT

RENNELLSTREET MOLESWORTH STREET

IMPROVEMENTOFPUBLICREALM ALONGHIGHWAYPARTLYWITHINAND BEYONDOWNERSHIPBOUNDARY,TO DRAINTOSUDSRAINGARDENS. ADOPTIONTOBECOORDINATEDWITH TFLHIGHWAYS.

CP3 PEAKDISCHARGERESTRICTED TO1L/SFORTHE1IN100YEAR+ 40%EVENT

EXISTINGDRAINAGE ARRANGEMENTOFHIGHWAY WILLNOTBEAFFECTEDBY PROPOSEDHIGHWAYWORKS

RODDINGACCESSATENDOFRUNTOBE COORDINATEDWITHINTERNALLAYOUT

PEAKDISCHARGERESTRICTEDTO 17.5L/SFORTHE1IN100YEAR+40% EVENT

PEAKDISCHARGEFROMD2 RESTRICTEDTO7.5L/SFOR THE1IN100YEAR+40%EVENT

FORDETAILSOFNORTHERN SQUARESURFACEWATER DRAINAGEREFERTOEXPEDITION DRAINAGEDRAWING LSC-EXP-ZZZ-ZZZ-DR-C-00001

LEWISHAM

EXISTINGBUILDINGSASSUMEDTODRAIN TOLOCALSEWERSASCURRENT

STREET

REFERTOBLOCKN1'sCIVILENGINEERS IN-GROUNDDRAINAGEDRAWING 2210000-EWP-ZZ-00-SK-C-001FORDETAILS

RODDINGACCESSATENDOFRUNTOBE COORDINATEDWITHINTERNALLAYOUT

REFERTOBLOCKN2'SCIVILENGINEERS IN-GROUNDDRAINAGEDRAWING LSC-WSP-N2-ZZ-DR-CV-5271011FORDETAILS

CONNECTIONPODIUMDRAINAGEOUTLETS.RODDING ACCESSATBASEOFABOVEGROUNDPIPE. ABOVEGROUNDROUTETOBECOORDINATEDWITH WSP/SEW

RUNOFFFROMCOURTYARDTOBEATTENUATED INPERMEABLEPAVEMENTANDROUTEDNORTH TONETWORKINNORTHERNQUARTER

EXISTINGDRAINAGE ARRANGEMENTOFPAVEMENT ALONGHIGHWAYTOBE MAINTAINEDASCURRENT

PEAKDISCHARGEFROMC1 RESTRICTEDTO10.3L/SFORTHE 1IN100YEAR+40%EVENT

PEAKDISCHARGEFROME1 ANDE2COMBINED RESTRICTEDTO11.0L/SFOR THE1IN100YEAR+40%EVENT

RODDINGACCESSATENDOFRUNTOBE COORDINATEDWITHINTERNALLAYOUT

PEAKDISCHARGEFROME3 RESTRICTEDTO5.4L/SFOR THE1IN100YEAR+40%EVENT

PEAKDISCHARGEFROMD2 RESTRICTEDTO7.5L/SFOR THE1IN100YEAR+40%EVENT

EXISTINGDRAINAGE ARRANGEMENTOF HIGHWAYWILLNOTBE AFFECTEDBYPROPOSED HIGHWAYWORKS

RODDINGACCESSAT ENDOFRUNTOBE COORDINATEDWITH INTERNALLAYOUT

E2

RODDINGACCESSATENDOFRUNTOBE COORDINATEDWITHINTERNALLAYOUT

EXISTINGDRAINAGE ARRANGEMENTOFPAVEMENT ALONGHIGHWAYTOBE MAINTAINEDASCURRENT

D2 C1 E1 E3

155m3ATTENUATIONIN HYDROROCKD320HDUNITS 1000mmDEEP.

PEAKDISCHARGEFROMC1 RESTRICTEDTO10.3L/SFORTHE 1IN100YEAR+40%EVENT

CP4

TOTALPEAKDISCHARGE RESTRICTEDTO34.3L/SFORTHE 1IN100YEAR+40%EVENT

150m3ATTENUATIONHYDROROCK D320HDUNITS1000mmDEEP.

ASSUMED50%OFHARDSTANDINGINCATCHMENTSE1,E2ANDE3 ASPERMEABLE PAVEMENTWITHATTENUATIONIN300mmGRANULARSUB-BASE (TRAFFICCATEGORY4TOBS7533)ANDCONTROLLEDDISCHARGE TOSEWERSYSTEM.AIMTOMAXIMISEINFILTRATIONTOGROUND, SUBJECTTOINFILTRATIONANDGROUNDCONTAMINATION TESTING,ANDESTABLISHINGGROUNDWATERLEVELS.

RETAINEDBUILDINGSTO DRAINTOEXISTING SEWERSYSTEMAS CURRENT

IMPROVEMENTOFPUBLICREALM ALONGHIGHWAYPARTLYWITHIN ANDBEYONDOWNERSHIP BOUNDARY,TODRAINTOSUDS RAINGARDENS.ADOPTIONTOBE DISCUSSEDWITHTFLHIGHWAYS.

140m3ATTENUATIONIN HYDROROCKD320HDUNITS 1000mmDEEP.

CONNECTIONPOINTFOR BLOCKN1COURTYARD (DRAINAGEOFCATCHMENT A3FORSITEWIDEDRAINAGE STRATEGY).PEAKDISCHARGE LIMITEDTO1.9l/s.

CONNECTIONTOEXISTINGTHAMESWATER SURFACEWATERSEWERFROMDRAINAGE CATCHMENTA1OFSITEWIDEDRAINAGE STRATEGY.INVERTLEVELTBCBYSURVEYOF EXISTINGTHAMESWATERSEWER.

HYDROBRAKEFLOWRESTRICTIONDEVICETO LIMITFLOWRATETOMAXIMISESTORAGEIN PONDFEATURESFORTHE1IN100+40% RAINFALLEVENT

STUBFORFUTURECONECTIONOF RETROFITTEDANDEXTENDEDLEWISHAM HOUSE.PEAKDISCHARGELIMITEDTO 2.1l/sFOR1:100+40%RAINFALLEVENT (DRAINAGECATCHMENTB2OFSITEWIDE DRAINAGESTRATEGY).

260mATTENUATIONTANK HYDROROCKD320HDUNITS1000mm DEEP.

CL:8.0mAOD IL:6.20mAOD

SUDSFEATURESINTEGRATEDINTOPLANTEDAREAS PROVIDINGAPPROXIMATELY20m3ATTENUATION FORTHE1IN100+40%RAINFALLEVENT.FLOW RATESFOREACHFEATURERESTRICTEDTO MAXIMISESTORAGE.

PROVISIONOFSTUBSTOCONNECTTOPODIUMDRAINAGE OUTLETSONCECOMPLETEATALATERPHASE.

RWPDISCHARGESTOEXISTINGCOMBINEDWATER SEWERBEFOREPODIUMISCONSTRUCTED

INTERNALLAYOUTTOBECOORDINATEDWITH STRUCTURALANDMEPENGINEERS.

EXTENTOF1IN100YEAR +40%ATTENUATION 7.9mAOD TOTALATTENUATION VOLUME:110m

INDICATIVEEXTENTOF1 IN30YEAR+30% ATTENUATION 7.7mAOD TOTALATTENUATION VOLUME:80m

REFERTOBLOCKN1's CIVILENGINEERS IN-GROUNDDRAINAGE DESIGN.DRAWING 2210000-EWP-ZZ-00-SK-C-001

SMARTWEATHER-CONTROLLEDRETENTION ANDRELEASEOFWATER,FOR COST-EFFECTIVEANDCARBONEFFICIENT HARVESTINGOFRAINWATER.MANHOLE CHAMBERTOINCLUDE600mmDEEPSILTTRAP

BOUNDARYCHANNELDRAINWITH RODDINGACCESS CL8.2mAOD

PERMANENTAMENITYAND BIODIVERSEPONDS

225mmDIACONNECTIONFROM BLOCKN2AT7.14mAODINVERT

RAINGARDENFEATURESTO PROVIDE80mOFSTORMWATER ATTENUATION.MIN.FINISHED LEVEL7.6mAOD,MIN800mmOF SOILOVER300mmGRANULAR DRAINAGELAYER.

MANHOLECHAMBERTO INCLUDE600mmDEEP SILTTRAP

PROVISIONFORCONNECTIONOF CHANNELDRAINSATBASEOF STAIRS(SUBMITTEDASPARTOF OUTLINEPLANNINGAPPLICATION)

REFERTOBLOCKN2's CIVILENGINEERS IN-GROUNDDRAINAGE DESIGN.DRAWING LSC-WSP-N2-ZZ-DR-CV-527101

PROPOSEDINFILLSLABTODRAINTO EXISTINGCOMBINEDSEWERSYSTEM REUSINGEXSITINGCONNECTION.TOBE COORDINATEDWITHMEPENGINEER

EXISTINGCOMBINEDMH2501

Appendix I: Maintenance and Management Plan

Maintenance and Management for Lewisham Shopping Centre

This document should be read in conjunction with the Sustainable Drainage Strategy. This maintenance and management guidance is for Lewisham Shopping Centre Maintenance of the drainage system will be carried out by the Estate Manager. As construction has not yet commenced, the process of finalising the management company contract has not yet commenced. The developer will ensure that the measures as outlined below form part of the management company contact details, for the sustained maintenance of all SuDS features on site.

The drainage system includes drainage pipework, hydro-brakes, filter drains, ponds, pervious pavements, and raingardens. The maintenance and management of these are described as per CIRIA C753 guidance

Access to these features is provided across the Site. Vehicle access is provided across the Site through paved and unpaved roadways and all manhole covers are unobstructed. There is sufficient space across the Site for both workers and equipment. Litter and debris should regularly be cleared as part of general landscape maintenance to ensure unobstructed access. Further, 1m clear level ground around access covers/manholes is provided to support routine maintenance

Maintenance and Management Guidance as per CIRIA C753

The indicative maintenance requirements for each proposed SuDS component is given below, taken from CIRIA report C753 “The SuDS Manual”.

Drainage Pipes

MAINTENANCE

Regular Maintenance

Occasional Maintenance

Hydro-brake

Remove sediment and debris from inspection chambers and flow control chambers

Cleaning of gutters and any filters on downpipes

Annually

Remove any root ingress As required

CCTV survey of drains to check alignment, cracking and joint displacement 10 year intervals

Regular inspections Visual inspection of each unit

Monthly for first 3 months and then six monthly

Occasional maintenance Clear out blockages within the system As required

Remedial actions

The pivoting bypass door can be opened to allow the system to drain in the event to a blockage As required

Filter Drains

MAINTENANCE

SCHEDULE

Regular Maintenance

Occasional Maintenance

REQUIRED ACTION

Remove litter (including leaf litter) and debris from filter drain surface, access chambers and pre-treatment devices

FREQUENCY

Monthly (or as required)

Inspect filter drain surface, inlet/outlet pipework and control systems for blockages, clogging, standing water and structural damage Monthly

Inspect pre-treatment systems, inlets and perforated pipework for silt accumulation, and establish appropriate silt removal frequencies

Remove sediment from pre-treatment devices

Remove or control tree roots where they are encroaching the sides of the filter drain, using recommended methods (eg NJUG 2007 or BS 3998:2010)

At locations with high pollution loads, remove surface geotextile and replace, and wash or replace overlying filter medium

Clear perforated pipework of blockages

Six monthly

Six monthly (or as required)

As required

Five yearly (or as required)

As required

Pond

MAINTENANCE

SCHEDULE

Regular Inspections

Occasional maintenance

Remedial actions

REQUIRED ACTION

Remove litter and debris

Cut the grass – public areas

Cut the meadow grass

Inspect marginal and bankside vegetation and remove nuisance plants (for first 3 years)

Inspect inlets, outlets, banksides, structures, pipework etc for evidence of blockage and/or physical damage

Inspect water body for signs of poor water quality

Inspect silt accumulation rates in any forebay and in main body of the pond and establish appropriate removal frequencies; undertake contamination testing once some build-up has occurred, to inform management and disposal options

Check any mechanical devices, eg penstocks

Hand cut submerged and emergent aquatic plants (at minimum of 0.1m above pond base; include max 25% of pond surface)

Remove 25% of bank vegetation from water’s edge to a minimum of 1m above water level

Tidy all dead growth (scrub clearance) before start of growing season (Note: tree maintenance is usually part of overall landscape management contract)

FREQUENCY

Monthly (or as required)

Monthly (during growing season)

Half yearly (spring, before nesting season, and autumn)

Monthly (at start, then as required)

Monthly

Monthly (May-October)

Six monthly (half yearly)

Annually

Remove sediment from any forebay. Every 1-5 years (or as required)

Remove sediment and planting from one quadrant of the main body of ponds without sediment forebays.

Remove sediment from the main body of big ponds when pool volume is reduced by 20%

Repair erosion or other damage

Replant, where necessary

Aerate pond when signs of eutrophication are detected

Realign rip-rap or repair other damage

Repair / rehabilitate inlets, outlets and overflows.

Every 5 years (or as required)

With effective pre-treatment, this will only be required rarely, eg every 25-50 years.

As required

Pervious Pavement

MAINTENANCE SCHEDULE

Regular Maintenance

Occasional Maintenance

REQUIRED

Remedial Actions

Brushing and vacuuming (standard cosmetic sweep over whole surface)

Stabilise and mow contributing and adjacent areas

Removal of weeds or management using glyphosphate applied directly into the weeds by an applicator rather than spraying

Remediate any landscaping which, through vegetation maintenance or soil slip, has been raised to within 50mm of the level of the paving

Remedial work to any depressions, rutting and cracked or broken blocks considered detrimental to the structural performance or a hazard to users, and replace lost jointing material

Rehabilitation of surface and upper substructure by remedial sweeping

Once a year, after autumn leaf fall, or reduced frequency as required, based on site-specific observations of clogging or manufacturers recommendations – pay particular attention to areas where water runs onto pervious surface from adjacent impermeable areas as this area is most likely to collect the most sediment

As required

As required – once per year on less frequently used pavements

As required

Monitoring

As required

Every 10-15 years or as required (if infiltration performance is reduced due to significant clogging)

Inspect for evidence of poor operation and/or weed growth – if required, take remedial action Monthly

Inspect all silt accumulation rates and establish appropriate brushing frequencies Annually

Monitor inspection chambers Annually

Bioretention systems (Rain gardens)

MAINTENANCE SCHEDULE

Regular inspections

Regular maintenance

Occasional maintenance

Remedial actions

REQUIRED ACTION

FREQUENCY

Inspect infiltration surfaces for silting and ponding, record de-watering time of the facility and assess standing water levels in underdrain (if appropriate) to determine if maintenance is necessary Quarterly

Check operation of underdrains by inspection of flows after rain Annually

Assess plants for disease infection, poor growth, invasive species etc and replace as necessary Quarterly

Inspect inlets and outlets for blockage Quarterly

Remove litter and surface debris and weeds Quarterly (or more frequently for tidiness or aesthetic reasons)

Replace any plants, to maintain planting density As required

Remove sediment, litter and debris build-up from around inlets or from forebays

Quarterly to biannually

Infill any holes or scour in the filter medium, improve erosion protection if required As required

Repair minor accumulations of silt by raking away surface mulch, scarifying surface of medium and replacing mulch As required

Remove and replace filter medium and vegetation above

As required but likely to be >20 years

Temple Chambers

3-7 Temple Avenue

London EC4Y 0HA

+44 (0)20 7307 1000 www.expedition.uk.com info@expedition.uk.com