site 46: hypermarket new malden · site 46: hypermarket new malden floodplain compensation storage...

AECOM London Borough of Merton Level 2 Strategic Flood Risk Assessment

60471781 Final Report January 2017

SITE 46: HYPERMARKET NEW MALDEN

1) SFRA SITE AREA

Site ID 46

Site Address Burlington Road, West Barnes, New Malden, KT3 4

Site Area 3.50 ha

Local Plan:

Site allocation or designation

(Sites and Policies Plan 2014)

No

Current Use Tesco Superstore Retail [A1 Use Class]).

Proposed Use Existing use on-site or Employment use (B Use Class).

Vulnerability Less Vulnerable (Commercial); Water Compatible (outdoor sports); More Vulnerable (Residential)

2) SUMMARY OF LEVEL 1 FLOOD RISK

Flood risk from rivers

Pyl Brook flows in a westerly direction adjacent to the northern site boundary in an open channel. Some sections of Pyl Brook in the

surrounding area are culverted. Beverley Brook flow s in a northern direction approximately 400-500 metres to the west.

Proportion of potential

development site within

Flood Zone

Flood Zone 3b Flood Zone 3a Flood Zone 2 Flood Zone 1 Area Benefiting of Defences

34 % 21 % 3 % 42 % 0 %

Flood risk from all other sources Limitations

Risk of flooding to the

potential development

site and surrounding

area

Surface Water flooding:

(uFMfSW)

Low Risk

1 in 1000 year (0.1%

annual probability)

The uFMfSW data does not show the

susceptibility of individual properties to surface

water flooding. The uFMfSW also does not take

into account the details of the existing drainage

system.

Groundwater flooding:

(BGS Susceptibility to

Groundwater Flooding)

Medium Risk

Potential for groundwater

flooding to occur at

surface, but no historic

records of groundwater

flooding

The dataset cannot be used on its own to

indicate risk of groundwater flooding and should

not be used to inform planning decisions at a site

scale. It is suitable for use in conjunction with a

large number of other factors, e.g. records of

previous incidence of groundwater flooding, to

establish relative risk of groundwater flooding.

Historic records of flooding

Historic records of

flooding from each

source within a 100m

radius of potential

development site

Fluvial records Surface water

records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 3 0 0 0 0

(Contains Ordnance Survey data © Crown copyright and

database right 2016. Contains Environment Agency data ©

Environment Agency and database right 2016).




3) LEVEL 2 ASSESSMENT

The fluvial hazard, depth and velocity outputs used in the Level 2 SFRA assessment and mapped below are based on the Environment

Agency modelling of the Beverley Brook (2009) and are provided for the 1% AEP plus Climate Change event1.

Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity

1 It is important to note that any future site specific FRA would be required to assess this site against the updated climate change allowances (London

Borough of Merton Level 2 SFRA, Section 1.4).













4) RECOMMENDATIONS AND POLICIES

Development

Layout and

Sequential

Approach

All current development is to be demolished. Development should be steered away from Flood

Zone 3b Functional Floodplain and set back at least 8 metres from the Pyl Brook along the

northern edge of the site. Where land within Flood Zone 3b must be developed, Water Compatible

development (i.e. the football stadium or public open space) should be located in the north where

there is greatest hazard. Less Vulnerable development (e.g. parking, retail units, refuse storage

etc.) should be located across the south where there is moderate hazard. Areas of lower risk, and

“No Hazard”, should be used for More Vulnerable development (i.e. residential units and hospitality

facilities).

Measures to manage surface water on the site should be considered early in the site masterplan

to enable inclusion of attenuation SuDS where possible.

Self-contained residential basements and bedrooms at basement level are not permitted in areas

that have ‘potential for groundwater to occur at the surface’ without appropriate mitigation (BGS

Susceptibility to Groundwater Flooding). Less Vulnerable basements, basement extensions and

conversions, such as plant, car parking etc, must provide safe internal access to higher floors

situated above levels derived from the fluvial modelling. Further ground investigations, such as

site specific boreholes, would be required at this site to confirm the likelihood of groundwater

occurrence.

Section 9.2

Finished Floor

Levels

For the current development site (without mitigation), modelling of Beverley Brook identifies that

during the flood event with 1% AEP (1 in 100 year) including an allowance for climate change, there

are small areas in the north that are at risk of flooding to depths of over 1 metre. The area

surrounding this is at risk of flooding up to 1 metre. There are areas in the south of the site that are

at risk of flooding to depths of up to 0.5m. The central area of site has flood risk depths of <0.1m.

The Water Compatible and Less Vulnerable site developments do not need to raise finished flood

levels with regard to policy. Instead they can be designed to be floodable, which will help minimise

the impact of the development of the displacement of floodwater and the risk of flooding the

surrounding area.

For the More Vulnerable site developments a minimum freeboard of 300mm is required above the

1% annual probability (1 in 100 year) including climate change fluvial flood level. Therefore if it is

necessary to locate More Vulnerable development within this zone finished floor levels must

adhere to this policy.

Section 9.3

Flood

Resistance

In those areas where flood depths may reach up to 0.6 metres, it is recommended that flood

resistant measures are implemented to keep the water out. This should be applied to development

in the southern area where depths are between 0.25-0.5m. This can be achieved by:

• Using materials and construction with low permeability.

• Land raising.

• Landscaping e.g. creation of low earth bunds (subject to this not increasing flood risk to

neighbouring properties).

• Raising thresholds and finished floor levels e.g. porches with higher thresholds than main

entrance.

• Flood gates with waterproof seals.

• Sump and pump for floodwater to remove waste faster than it enters.

Section 9.4

Flood

Resilience

Where flood depth is over 0.6 metres (in the north) the strategy for design should be to allow water

through the property to avoid risk of structural damage. This may be achieved through:

• Use materials with either, good drying and cleaning properties, or, sacrificial materials that can

easily be replaced post-flood.

• Design for water to drain away after flooding.

• Design access to all spaces to permit drying and cleaning.

• Raise the level of electrical wiring, appliances and utility metres.

• Coat walls with internal cement based renders; apply tanking on the inside of all internal walls.

• Ground supported floors with concrete slabs coated with impermeable membrane.

• Tank basements, cellars or ground floors

Section 9.5

Safe

Access/Egress

The site is accessed from Beverley Way to the west of the site or Bushey Road in the east. In the

event of widespread flooding associated with the Pyl Brook, there is potential that Bushey Road

may become flooded and inaccessible. In order to make sure the occupants/residents of the site

evacuate safely it is necessary to prepare a Flood Warning and Evacuation Plan (FWEP), described

further below.

Section 9.7




Floodplain

Compensation

Storage

Some of this site is located within the outline of the 1% annual probability (1 in 100 year) flood

event including an allowance for climate change. Where proposed development results in an

increase in building footprint in this zone, the developer must ensure that it does not impact upon

the ability of the floodplain to store water and that it does not impact upon floodwater flow

conveyance. Any loss in floodplain storage must be compensated for on and level for level,

volume for volume basis in an area that does not already flood and is within the site boundary. The

area of this site defined as Flood Zone 1 could be used for this function.

Section 9.9

Flow Routing New development should not adversely affect flood routing and thereby increase flood risk

elsewhere (including surrounding area). On this site, opportunities should be sought to make

space for water, such as:

• Removing boundary walls or replacing with other boundary treatments such as hedges,

fences (with gaps).

• Create under-croft car parks or consider reducing ground floor footprint and creating an open

area under the building to allow flood water flow.

• Where proposals include floodable outbuildings or garages, design the external walls to

enable the free flow of floodwater.

Section

9.12

Flood Warning

and

Evacuation

Plan

A Flood Warning and Evacuation Plan (FWEP) must be prepared for the site, detailing how flood

warning will be provided how the safety of occupants and access to/from the development will be

ensured and what will be done to protect development and contents. The FWEP should consider

arrangements for the evacuation of basement car parks. Where possible, the FWEP should also

detail the length of time before the site becomes inaccessible by emergency vehicles.

Flood Warning Areas

The local area is covered by the Environment Agency Flood Warning Areas for ‘Beverley Brook at

West Barnes’. Residents of the site should ensure they are signed up to the Environment Agency

Flood Warning system.

Emergency Rest Centres

The closest designated emergency rest centre for this site is the Raynes Park High School, which

is less than 100m north.

Section

9.14

Surface Water

Management

Current risk of flooding

The site is within Drainage Catchment 30, which is distributed across three London Boroughs,

including: Merton, Kingston and Sutton. It drains much of Worcester Park, Motspur Park and West

Barnes.

The uFMfSW indicates that the site and surrounding area is at low risk of surface water flooding.

However, there are areas of medium to high risk. There have been three previous reported

incidents of surface water flooding held by Merton Council in this location.

Indicative Existing Runoff Rate: 16.1 l/s (1 in 1 year), 60.3 l/s (1 in 100 year)

Indicative Greenfield Runoff Rate: 7 l/s

Level 2

Appendix B

SuDS Suitability

Reference to the SWMP Appendix C2 Figure 4 identifies that (prior to the completion of a site

investigation to determine precise local conditions) it is uncertain if infiltration of surface water

into the ground is possible at this location; therefore a site investigation is required to assess the

potential use of infiltration SuDS prior to the development of a Drainage Strategy for the site.

If infiltration SuDS are not feasible at this site then other SuDS techniques should be considered,

including: green roofs, filter strips, detention basins and ponds, as well as permeable surfacing in

combination with tanked systems.

Alternatively, if infiltration of surface water into the ground is possible then infiltration SuDS could

be installed, including: infiltration basins and trenches.

Section

10.3 and

10.9

Drainage Strategy and Approvals

Merton Council will require a Drainage Strategy to be prepared outlining the surface water

management for the site, runoff rates and consideration of SuDS in line with the London Plan

policy 5.13, the mayor’s Design and construction SPG and Merton’s Local Plan policies.

Where it is not possible to achieve greenfield runoff rates in accordance with the London Plan

policy 5.13 and Design and Construction SPG (April 2014), then justification must be provided.

Arrangements for the future maintenance and adoption of the drainage system must be made and

detailed in the Drainage Strategy.

Any potential diversions and/or discharges into a sewer or main river must be agreed with Thames

Water or Environment Agency, respectively.

Section

10.6




Indicative Unit Costs

Green roofs ~ £90/m2.

Permeable paving ~ £30-50/m2.

Filter strips £2-4m2.

Detention basin £15-50m3.

Concrete storage tank £449-518/m3.

Infiltration trench £55-65 /m3.

Infiltration basin £10-15 /m3.

Section

10.4

5) EXCEPTION TEST CONSIDERATIONS

The NPPF states that there are two parts to the Exception Test that must be passed for development to be allocated or permitted:

1) “it must be demonstrated that the development provides wider sustainability benefits to the community that outweigh

flood risk” and

2) “demonstrate that the development will be safe for its lifetime taking account of the vulnerability of its users, without

increasing flood risk elsewhere, and, where possible, will reduce flood risk overall”.

This development site consists of a mixture of site uses and a varied risk of flooding. The Water Compatible uses should be located

in areas with Significant Hazard, the Less Vulnerable where there is Moderate Hazard and the More Vulnerable where there is No

Hazard. If More Vulnerable development cannot be avoided within the 1% AEP (1 in 100 year) including an allowance for climate

change, then finished floor levels must be raised accordingly. Depending on the modelled flood depth, flood resistant and resilient

measures should be employed to mitigate the potential impacts of flooding. SuDS should be incorporated into the building design in

order to reduce the risk of increasing flood risk elsewhere. There is potential that floodwaters will limit dry routes out of the local area,

therefore it is necessary to prepare a FWEP for residents / occupants of the site detailing steps to evacuate the site prior to the onset

of flooding. Therefore, on this basis, it is likely that this site would pass the Exception Test.



SITE 47: 265 WEST BARNES LANE

1) SFRA SITE AREA

Site ID 47

Site Address 265 West Barnes Lane, New Malden, KT3 6

Site Area 1.29 ha

Local Plan:



No

Current Use Office uses

Proposed Use This is a scattered employment site, so change of use should be for employment (B Use Class) or

community use (D1 Use Class). Other uses would be considered in accordance with the Council’s

Local Plan.

Vulnerability More Vulnerable (Residential)



The site is located immediately south of Pyl Brook, where the river flows in an open channel from the southeast to the west. In the

northeast corner Pyl Brook is joined by a culverted ordinary watercourse flowing in from the north.



Flood Zone


9 % 6 % 41 % 44 % 0 %




site and surrounding area

Surface Water

flooding:

(uFMfSW)

Low Risk

1 in 1000 year (0.1%

annual probability)





system.

Groundwater

flooding:


Groundwater

Flooding)

Medium Risk



surface, with three

previous records of

surface water flooding.









Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 3 0 0 0 0









Agency modelling of Pyl Brook (2009) and are provided for the 1% AEP plus Climate Change event2.

Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity
















Development

Layout and

Sequential

Approach

A sequential approach to site layout should be used. There are small areas in the north west of the

site which are within Flood Zone 3b and 3a of the Pyl Brook. There is a large area of Flood Zone 2

across the centre of the development site. The northwest corner is at “Significant Hazard” and the

rest of the site is at either No or Low hazard.

The Pyl Brook borders the northern site boundary therefore all development should be set back at

least 8m from the river.

More Vulnerable development should be located away from the area of greatest flood risk.









occurrence.

Section 9.2

Finished Floor

Levels

For the current development site (without mitigation), modelling of the Pyl Brook identifies that

during the flood event with 1% AEP (1 in 100 year) including an allowance for climate change there

is a very small area in the north west corner that is at risk of flooding up to 0.5m.

For More Vulnerable development, a minimum freeboard of 300mm is required above the 1% AEP

(1 in 100 year) including climate change fluvial flood level, which should be achievable for the large

part of the site. Less Vulnerable uses (e.g. car parking), do not need to be raised with regards to

policy.

Section 9.3

Flood

Resistance

It is recommended that flood resistant construction methods should be considered, including use

of construction materials with low permeability, raising property thresholds, using landscaping to

manage surface water and fluvial floodwater.

Section 9.4

Flood

Resilience

It is recommended that flood resilient measures should also be considered on the site. These

measures are appropriate where modelled flood depths are greater than 0.6m3. The strategy

should be to allow water into the building, but to implement careful design in order to minimise

damage and allow rapid re-occupancy. For example, concrete flooring and waterproofing building

materials such as timber joists and render and flood resilient air brick covers.

Section 9.5

Safe

Access/Egress

Access to the site is provided via West Barnes Lane to the north east of the site. In the event of

widespread flooding associated with the Pyl Brook there is potential that dry routes out of the local

area to a safe place of refuge may be limited. It will therefore be necessary to prepare a Flood

Warning and Evacuation Plan (FWEP), described further below.

Section 9.7

Floodplain

Compensation

Storage

This site is located within the outline of the 1% annual probability (1 in 100 year) flood event

including an allowance for climate change. Within this area, new development must not result in a

net loss of flood storage capacity. The eastern side of the site is outside this zone and therefore

should be considered for potential compensatory storage.

Section 9.9





fences (with gaps).

• Create under-croft car parks or consider reducing ground floor footprint and creating an open




Section

9.12

Flood Warning

and

Evacuation

Plan




arrangements for the evacuation of basement car parks. Where possible, the FWEP should also

detail the length of time before the site becomes inaccessible by emergency vehicles.

Flood Warning Areas





The closest designated emergency rest centre for this site is the Raynes Park High School, which

is approximately 100 metres away.

Section

9.14

3 Department for Communities and Local Government (2007) Improving the flood performance of new buildings, Flood resilient construction.




Surface Water

Management


The site is located within Critical Drainage Area (CDA) Group7_002, which is an area with localised

flooding issues. The potential development must not increase flood risk to other areas in the CDA.

The site is within Drainage Catchment 30, which is distributed across three London Boroughs,

including: Merton, Kingston and Sutton. It drains much of Worcester Park, Motspur Park and West

Barnes.

The uFMfSW indicates that the site and surrounding area is at low risk of surface water flooding.

There are no reported incidents of flooding held by Merton Council in this location; however, there

have been three previous surface water flood incidents.

Indicative existing runoff rate: 5.9 l/s (1 in 1 year), 22.2 l/s (1 in 100 year)


Level 2

Appendix B

SuDS Suitability



into the ground is possible at this site, further investigation is required to assess the potential use

of infiltration SuDS. This will need to be confirmed prior to the development of a Drainage Strategy

for the site.

If infiltration SuDS are not feasible at this site then the SuDS techniques that should be considered

include green roofs, filter strips, detention basins and ponds, as well as permeable surfacing in

combination with tanked systems.

Alternatively, if infiltration of surface water into the ground is possible at this site location then

infiltration basins and trenches could be installed.

Section

10.3 and

10.9




policy 5.13, the Mayor’s Design and construction SPG 2014 and Merton’s Local Plan policies.







Section

10.6









Section

10.4




flood risk” and



For this development site, the most vulnerable development should be located in areas of no hazard, away from Flood Zone 3b in the

northwest. Pyl Brook flows along the northern boundary of the site, therefore any new development should be built at least 8 metres

from the river. There is potential that dry routes out of the local area to a safe place of refuge may be limited and it is therefore

necessary to prepare a FWEP for residents / occupants of the site detailing steps to evacuate the site prior to the onset of flooding.

Resilient construction techniques and the incorporation of SuDS should also be considered in order to reduce the risk of increasing

flood risk elsewhere. On this basis, it is likely that this site would pass the Exception Test.



SITE 48: CHAMPION HOUSE

1) SFRA SITE AREA

Site ID 48

Site Address Champion House, Burlington Road, New Malden, Greater London, KT3 4NB

Site Area 0.76 ha

Local Plan:



Designated Employment Area

Current Use Commercial (Timber Merchant)

Proposed Use Commercial (Timber merchant) (B Use Classes)

Vulnerability Less Vulnerable



The site is at risk from Beverley Brook and Pyl Brook which flow to the west and the north respectively. Both flow in open channels.



Flood Zone


0 % 0 % 81 % 19 % 0 %


Risk of flooding to

the potential

development site and

surrounding area


(uFMfSW)

High Risk

1 in 30 year (3.33% AEP)





system.




Medium Risk





flooding









Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 2 0 0 2 1









Agency modelling of Beverley Brook (2009) and are provided for the 1% AEP plus Climate Change event4.

Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity






(Contains Ordnance Survey data © Crown copyright and database right

2016. Contains Environment Agency data © Environment Agency and

database right 2016).








In accordance with the NPPF, Less Vulnerable development is considered compatible within Flood Zone 2 and does not require the

application of the Exception Test. However, given the risk of fluvial and surface water flooding to the area surrounding the site, the

principles of the Exception Test should still be considered when developing on this site, namely:


flood risk” and



The following information and recommendations are therefore provided for consideration.

Development

Layout and

Sequential

Approach

The majority of the site is located within Flood Zone 2 associated with the Beverley Brook. There

is a small area of Flood Zone1. Development should be steered towards the areas of Flood Zone

1. The incorporation of SUDS into the site design should be considered early in the master

planning process.

Self-contained residential basements and bedrooms at basement level are not permitted in

areas that have ‘potential for groundwater to occur at the surface’ without appropriate mitigation

(BGS Susceptibility to Groundwater Flooding). Less Vulnerable basements, basement extensions

and conversions, such as plant, car parking etc, must provide safe internal access to higher

floors situated above levels derived from the fluvial modelling. Further ground investigations,

such as site specific boreholes, would be required at this site to confirm the likelihood of

groundwater occurrence.

Section 9.2

Finished Floor

Levels

The site is above the 1% AEP (1 in 100 year) flood event including an allowance for climate

change, therefore there are no requirements in terms of policy for finished for levels. Given the

potential for surface water flooding in the area, coupled with historic records of surface water

flooding, it may be prudent to consider threshold levels and finished floor levels in relation to

potential surface water ponding on the site.

Section 9.3

Safe

Access/Egress

In the event of a 0.1% AEP (1 in 1000 year) flood event, access via the normal route (Burlington

Road) may be limited. Therefore it is necessary to provide a Flood Warning and Evacuation Plan

(FWEP) for the site.

Section 9.7

Flood Warning

Areas

A Flood Warning and Evacuation Plan (FWEP) should be prepared for the site, detailing how flood

warning will be provided how the safety of occupants and access to/from the development will

be ensured and what will be done to protect development and contents. Where possible, the

FWEP should also detail the length of time before the site becomes inaccessible by emergency

vehicles.

Flood Warning Areas





The closest designated emergency rest centre for this site is Raynes Park High School,

approximately 300m east of the site, within the Merton Borough.

Section 9.14

Surface Water

Management


The site is located within Critical Drainage Area (CDA) Group7_001, which is an area with

localised flooding issues. The potential development must not increase flood risk to other areas

in the CDA.

The site is within Drainage Catchment 30, which is within the London Boroughs of Merton,

Kingston and Sutton.

The uFMfSW indicates that the site and surrounding area is at high risk of surface water flooding.

There are five previous records of flood incidents held by Merton Council for this location, two of

which are from surface water flooding.


Indicative Greenfield Runoff Rate:5 l/s

Level 2

Appendix B

SuDS Suitability


investigation to determine precise local conditions) infiltration of surface water into the ground is

potentially uncertain and requires further investigation.

If unsuitable the techniques which should be considered include green roofs, filter strips,

detention basins and ponds, as well as permeable surfacing in combination with tanked systems.

If infiltration SuDS are suitable then infiltration basins and/or trenches could be considered.

Section 10.3

and 10.9







policy 5.13, the mayor’s Design and construction SPG (2014) and Local Plan policies.



Arrangements for the future maintenance and adoption of the drainage system must be made

and detailed in the Drainage Strategy.

Any potential diversions and/or discharges into a sewer or main river must be agreed with

Thames Water or Environment Agency, respectively.

Section 10.6









Section 10.4



SITE 49: BURLINGTON ROAD

1) SFRA SITE AREA

Site ID 49

Site Address 197 Burlington Road, New Malden, KT3 4NA

Site Area 0.22 ha

Local Plan:



Designated Employment Area

Current Use Restaurant (A3)

Proposed Use Restaurant

Vulnerability More Vulnerable



The Beverley Brook flows to the west of the development site and Pyl Brook to the north, both as open channels.



Flood Zone


0 % 0 % 95 % 5 % 0 %





Surface Water

flooding:

(uFMfSW)

High Risk

1 in 30 year (3.33% AEP)





system.

Groundwater

flooding:


Groundwater

Flooding)

Medium Risk





flooding









Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 2 0 0 3 1







3) RECOMMENDATIONS

In accordance with the NPPF, Less Vulnerable development is considered compatible within Flood Zone 2 and does not require the




flood risk” and




Development

Layout and

Sequential

Approach

The development site is almost entirely Flood Zone 2 of Beverley Brook; therefore it is difficult to

apply a Sequential Approach to site layout as all development will be within this Flood Zone.







occurrence.

Section 9.2

Finished Floor

Levels

The site is above the 1% AEP (1 in 100 year) flood event including an allowance for climate change,

therefore there are no requirements in terms of policy for finished for levels. However, it is good

practice to raise finished floor levels a minimum of 300mm above the 1% AEP (1 in 100 year),

especially as the site is at high surface water flood risk.

Section 9.3

Safe

Access/Egress

Access/Egress to the site is provided via West Barnes Lane in the south or Beverley Way in the

northeast. In the scenario of a very extreme event the driest route to safety would be south down

Beverley Way.

Section 9.7

Flood Warning

Areas

Flood Warning Areas





The closest designated emergency rest centre for this site is Raynes Park High School,

approximately 300m east of the site, within the Merton Borough.

Section

9.14

Surface Water

Management




The site is within Drainage Catchment 30, which is within the London Boroughs of Merton,

Kingston and Sutton.

The uFMfSW indicates that the site and surrounding area is at high risk of surface water flooding.

There are five previous records of flood incidents held by Merton Council for this location, three of

which are from surface water flooding.

Indicative Existing Runoff Rate: 1 l/s (1 in 1 year), 3.8 l/s (1 in 100 year)


Level 2

Appendix B

SuDS Suitability



potentially uncertain and requires further investigation.

If unsuitable the techniques which should be considered include green roofs, filter strips,

detention basins and ponds, as well as permeable surfacing in combination with tanked systems.

If infiltration SuDS are suitable then infiltration basins and/or trenches could be considered.

Section

10.3 and

10.9




policy 5.13, the Mayor’s Design and construction SPG (2014) and Merton’s Local Plan policies.







Section

10.6












Section

10.4



SITE 50: LAND ADJ TO BUSHEY ROAD

1) SFRA SITE AREA

Site ID 50

Site Address 84-88 Bushey Road, Raynes Park, SW20 0JH

Site Area 2.63 ha

Local Plan:



Yes. Designated Employment Area

Current Use The site consists of relatively large scale industrial buildings ranging between two and five storeys in

height and open parking areas. To the west is the A3 ‘Beverley Way’ dual carriageway and to the south is

Bushey Road (A298). To the east of the site is a “Pets at Home” store and, beyond that, a primary school.

To the north, on the opposite side of Bodnant Gardens, are two storey houses.

The site consists of two separate ownerships. There is a vacant 5 storey office toward the southern end

(Apex House), a storage and distribution unit (Safestore) located centrally and a light industrial use to the

rear (Racetech). The other section consists of the vacant art deco former Thales Avionics offices and

warehouse, with a separate industrial unit to the rear ion the northeast corner.

Proposed Use Employment led mixed use:

An employment-let mixed use scheme, research and development, light industrial appropriate in a

residential area and storage or distribution that may include an appropriate mix of any of the

following: bulky goods retail, car show room and school.

Vulnerability Less Vulnerable (Commercial uses), More Vulnerable



The Pyl Brook flows from the southeast to the west just south of the development site through a series of culverts and open

channels. The Pyl Brook then confluences Beverley Brook to the southwest of the site, on the opposite side of the Kingston By Pass.



Flood Zone


1 % 8 % 0 % 91 % 0 %


Risk of flooding

to the potential

development

site and

surrounding

area

Surface Water

flooding:

(uFMfSW)

Medium Risk

Between 1 in 100 year (1% annual

probability) and 1 in 30 year (3.3%

annual probability)

The uFMfSW data does not show the susceptibility

of individual properties to surface water flooding.

The uFMfSW also does not take into account the

details of the existing drainage system.

Groundwater

flooding:

(BGS Susceptibility

to Groundwater

Flooding)

Medium Risk

To the northwest there is potential for

groundwater flooding to occur below the

surface. In the southeast there is potential

for ground water flooding to occur at the

surface. There are no previous records of

groundwater flooding in this area.

The dataset cannot be used on its own to indicate

risk of groundwater flooding and should not be

used to inform planning decisions at a site scale. It

is suitable for use in conjunction with a large

number of other factors, e.g. records of previous

incidence of groundwater flooding, to establish

relative risk of groundwater flooding.


Historic records of

flooding from each source

within a 100m radius of

potential development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 1 0 0 0 0

(Contains Ordnance Survey data © Crown

copyright and database right 2016. Contains

Environment Agency data © Environment

Agency and database right 2016).






Agency modelling of the Beverley Brook (2009) and are provided for the 1% AEP plus Climate Change event5.

Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity



















Development

Layout and

Sequential

Approach

The majority of the development site is not within the floodplain; however, there is a small area in

the south of the site which is designated as Flood Zone 3a associated with the Pyl Brook.

Modelling shows that flood depths in this area of Flood Zone 3a may reach up to 0.5m during the

1% AEP flood event including an allowance for climate change.

The proposed development includes a variety of uses, with varying vulnerability classifications. All

built development should be steered away from the area of Flood Zone 3a, in order to preserve

areas of floodplain storage. Where this is not possible, it should be ensured that the most

vulnerable elements of the development, i.e. the school, is located within an area of Flood Zone 1,

and the areas of Flood Zone 3a are retained as flood storage areas, or used for landscaped areas,

car parking, or Less Vulnerable commercial uses.

As there is a medium risk of surface water flooding to this area, measures to manage surface

water across the whole development site, in a coordinated manner, should be considered early in

the site masterplan to enable inclusion of attenuation SuDS where possible.







occurrence.

Section 9.2

Finished Floor

Levels

Across the majority of the site, within Flood Zone 1, finished floor levels will not need to be raised.

In the southern part of the site, Less Vulnerable developments can be designed to be floodable

instead of raising floor levels, and this may be beneficial to help minimise the impact of the

development on the displacement of floodwater and the risk of flooding to the surrounding area.

However, it is strongly recommended that internal access is provided to upper floors (first floor or

a mezzanine level) to provide safe refuge in a flood event. Such refuges will have to be permanent

and accessible to all occupants and users of the site and a FWEP should be prepared to document

the actions to take in the event of a flood (see below).

There is no set guidance for the setting of finished floor levels of development in relation to

surface water flood risk, and this should be considered in the design of surface water

management measures for the site.

Section 9.3

Flood

Resistance

In the southern section of the site, which is designated Flood Zone 3a, there is a risk of flooding up

to 0.5m, it is recommended that the development should attempt to keep water out. This may be

achieved by using materials with low permeability, flood resilient designs as well as ensuring there

is access to all spaces to permit drying and cleaning.

Section 9.4

Safe

Access/Egress

Even during a flood event there remains dry access to safe land via Bodnant Gardens to the north

of the site. Evacuation to the south must be avoided. To ensure the correct evacuation route is

taken, it is necessary to prepare a Flood Warning and Evacuation Plan (FWEP).

Section 9.7

Floodplain

Compensation

Storage

Where proposed development results in an increase in building footprint, the developer must

ensure that it does not impact upon the ability of the floodplain to store water and that it does not

impact upon floodwater flow conveyance.

The southern part of the site is located within the outline of the 1% AEP (1 in 100 year) flood event

including an allowance for climate change. Within this area, new development must not result in a

net loss of flood storage capacity, and floodplain compensation storage must be provided on a

level for level, volume for volume basis for any raise in ground levels.

Section 9.9


elsewhere (including surrounding area). This site is largely outside of the floodplain therefore

there should not be much influence on the flow routing. However, any development within the area

of Flood Zone 3a in the south of the site should consider the following methods to ensure to make

space for water:

Removing boundary walls or replacing with other boundary treatments such as hedges, fences

(with gaps).

Create under-croft car parks or consider reducing ground floor footprint and creating an open


Where proposals include floodable outbuildings or garages, design the external walls to


Section

9.12




Flood Warning

and

Evacuation

Plan

A Flood Warning and Evacuation Plan (FWEP) should be prepared for the site to ensure the correct

direction of evacuation is applied. Where possible, the FWEP should also detail the length of time

before the site becomes inaccessible by emergency vehicles.

Flood Warning Areas


West Barnes’. Occupants of the site should ensure they are signed up to the Environment Agency



The closest designated emergency rest centre for this site is the Raynes Park High School,

approximately 200m south east.

Section

9.14

Surface Water

Management




The site is within Drainage Catchment 29, which starts in the London Borough of Sutton but is

predominately within the Borough of Merton. It drains much of Rosehill, Morden Park and West

Barnes.

The uFMfSW indicates that the site and surrounding area is at medium risk of surface water

flooding. The majority of the site is categorised by a low surface water flood risk, however, in the

northwest of the site there is an area of high risk. There is one previously reported incident of

surface water flooding held by Merton Council in this location.


Indicative Greenfield Runoff Rate: 5.3 l/s

Level 2

Appendix B

SuDS Suitability



into the ground is possible at this site, further investigation is required to assess the potential use

of infiltration SuDS. This will need to be confirmed prior to the development of a Drainage Strategy

for the site.

If infiltration SuDS are not feasible at this site then the SuDS techniques that should be considered

include green roofs, filter strips, detention basins and ponds, as well as permeable surfacing in

combination with tanked systems. Alternatively, if infiltration of surface water into the ground is

possible at this site location then infiltration basins and trenches could be installed.

Section

10.3 and

10.9








detailed in the Drainage Strategy. Any potential diversions and/or discharges into a sewer or main

river must be agreed with Thames Water or Environment Agency, respectively.

Section

10.6









Section

10.4




flood risk” and



The majority of this development site is not at risk of fluvial flooding. Careful site planning should be undertaken to incorporate SuDS

measures to deliver effective surface water management across the site and surrounding area. There is a small area that intersects

Flood Zone 3a, and therefore the potential impacts of flooding should be mitigated by safeguarding this area as open space, using it

for car parking or other Less Vulnerable uses, and using resilient construction techniques. Therefore, on this basis, it is likely that this

site would pass the Exception Test.



SITE 51: TOOTING FOOTBALL CLUB

1) SFRA SITE AREA

Site ID 51

Site Address Tooting & Mitcham United FC, Imperial Fields, Bishopsford Road, Morden, SM4 6BF

Site Area 5.10 ha

Local Plan:



No

Current Use Football Stadium and leisure facilities (D2)

Proposed Use The site is metropolitan Open Land (MOL): small scale structures to support outdoor open space

uses

Vulnerability Water Compatible/Less Vulnerable (Commercial)



The River Wandle flows the east of the development site as a series of open channels in a north westerly direction. One of the

tributaries (ordinary watercourse) flows adjacent to the eastern boundary of the development site.



Flood Zone


36 % 31 % 12 % 21 % 0 %





Surface Water

flooding:

(uFMfSW)

Medium Risk

Between 1 in 100 year

(1% annual probability)

and 1 in 30 year (3.3%

annual probability)





system.

Groundwater

flooding:


Groundwater

Flooding)

Medium Risk





flooding









Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 1 0 1 0 0









Agency modelling of the River Wandle (2015) and are provided for the 1% AEP plus Climate Change event6.

Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity
















Development

Layout and

Sequential

Approach

A sequential approach to site layout should be used. The centre section of the site intersects

the Functional Floodplain. The northernmost part and some areas in the southeast are at

“Significant Hazard”. The middle of the site is defined as “Low Hazard”. The southwest border

is within Flood Zone 1 and has “No Hazard”.

The current site use is a mixture of Water Compatible (i.e. the football ground) with some Less

Vulnerable (e.g. car parking) and a few More Vulnerable (i.e. hospitality) development. Re-

development of this site should ensure to keep the Water Compatible uses within the

Functional Floodplain and the More Vulnerable developments within Flood Zone 1 in the

southwest.

Measures to manage surface water on the site should be considered early in the site

masterplan to enable inclusion of attenuation SuDS where possible.


areas that have ‘potential for groundwater to occur at the surface’ without appropriate

mitigation (BGS Susceptibility to Groundwater Flooding). Less Vulnerable basements,

basement extensions and conversions, such as plant, car parking etc, must provide safe

internal access to higher floors situated above levels derived from the fluvial modelling.

Further ground investigations, such as site specific boreholes, would be required at this site to

confirm the likelihood of groundwater occurrence.

Section 9.2

Finished Floor

Levels

For the current development site (without mitigation), modelling of the River Wandle identifies

that during the flood event with 1% AEP (1 in 100 year) including an allowance for climate

change there is a large area to the north west at risk of flooding up to 1 metre. There are

extents in the northwest and southeast at risk of flooding up to 0.5 metres. Towards the centre

of the site there is risk of flooding up to 0.25 metres.

Finished Flood Levels of Less Vulnerable development do not need to be risen with regard to

policy, instead they can be designed to be floodable using appropriate construction material

and building layout. For the More Vulnerable site developments a minimum freeboard of

300mm is required above the 1% annual probability (1 in 100 year) including climate change

fluvial flood level. Therefore if it is necessary to locate More Vulnerable development within

this zone finished floor levels must adhere to this policy.

Section 9.3

Flood

Resistance

For flood depth up to 0.6 metres it is recommended that flood resistant measures are

implemented to keep the water out. This should be applied to development in the central area

where depths are between 0.25-0.5m. This can be achieved by:

• Using materials and construction with low permeability.

• Land raising.

• Landscaping e.g. creation of low earth bunds (subject to this not increasing flood risk to

neighbouring properties).

• Raising thresholds and finished floor levels e.g. porches with higher thresholds than

main entrance.

• Flood gates with waterproof seals.

• Sump and pump for floodwater to remove waste faster than it enters.

Section 9.4

Flood Resilience Where flood depth is over 0.6 metres (in the northwest) the strategy for design should be to

allow water through the property to avoid risk of structural damage. This may be achieved

through:

• Use materials with either, good drying and cleaning properties, or, sacrificial materials

that can easily be replaced post-flood.




• Coat walls with internal cement based renders; apply tanking on the inside of all internal

walls.


• Tank basements, cellars or ground floors

Section 9.5

Safe

Access/Egress

Access to the site is provided via Bishops Ford Road to the south west of the site. In the event

of widespread flooding associated with the River Wandle, there is potential that dry routes out

of the local area to a safe place of refuge may be limited. It will therefore be necessary to

prepare a Flood Warning and Evacuation Plan (FWEP), described further below.

Section 9.7

Floodplain

Compensation

Storage

Part of this site is located within the outline of the 1% AEP (1 in 100 year) flood event including

an allowance for climate change. Within this area, new development must not result in a net

loss of flood storage capacity. Any loss in floodplain storage must be compensated for on and

level for level, volume for volume basis in an area that does not already flood and is within the

site boundary. The area of this site (in the southwest) defined as Flood Zone 1 could be used

for this function.

Section 9.9




Flow Routing Any new development should not adversely affect flood routing and thereby increase flood

risk elsewhere (including surrounding area). On this site, opportunities should be sought to

make space for water, such as:


fences (with gaps).



• Potential overland flow paths should be determined and appropriate solutions proposed

to minimise the impact of the development, for example by configuring road and

building layouts to preserve existing flow paths and improve flood routing, whilst

ensuring that flows are not diverted towards other properties elsewhere.

Section 9.12

Flood Warning

and Evacuation

Plan



be ensured and what will be done to protect development and contents. Where possible, the

FWEP should also detail the length of time before the site becomes inaccessible by

emergency vehicles.

Flood Warning Areas

The local area is covered by the Environment Agency Flood Warning Areas for ‘River Wandle

at Morden’. Residents of the site should ensure they are signed up to the Environment Agency



The closest designated emergency rest centre for this site is Vestry Hall, approximately 1

kilometre north of the site.

Section 9.14

Surface Water

Management


The site is within Drainage Catchment 36, which is predominantly within London Borough of

Merton; with a slight intersect with the London Borough of Sutton. It is a comparatively small

drainage catchment, draining Poulter Park, a school and Moreton Green.

The uFMfSW indicates that the site is at low to medium surface water flooding, with areas of

high risk in the north. There are two flood incident reports held by Merton Council in this

location, one of which was from surface water and the other sewer flooding.



Level 2

Appendix B

SuDS Suitability


investigation to determine precise local conditions) infiltration of surface water into the ground

is potentially unsuitable for the site. This will need to be confirmed prior to the development of

a Drainage Strategy for the site.

Techniques which should be considered include green roofs, filter strips, detention basins and

ponds, as well as permeable surfacing in combination with tanked systems.

Section 10.3

and 10.9




policy 5.13, the mayor’s Design and construction SPG 2014 and Local Plan policies.




and detailed in the Drainage Strategy. Any potential diversions and/or discharges into a sewer

or main river must be agreed with Thames Water or Environment Agency, respectively.

Section 10.6







Section 10.4







flood risk” and



The re-development of this site has various vulnerability classifications. Water Compatible development should be located where the

site is at significant hazard. The More Vulnerable site uses should be located within Flood Zone 1. If it is essential to build any More

Vulnerable development with the flood hazard areas then finished floors levels must be raised appropriately. Any development within

the floodplain should use relevant flood resistant and/or resilient measures to mitigate the potential impacts of flooding. SuDS should

be incorporated where possible to reduce the risk of flooding to the surrounding area. In an event of a flood dry access to the site

may with restricted, therefore it is necessary to prepare a FWEP for the occupants of the site, detailing the steps to evacuate the site

prior to the onset of flooding. Therefore, on this basis, it is likely that this site would pass the Exception Test.



SITE 52: WIMBLEDON GREYHOUND STADIUM

1) SFRA SITE AREA

Site ID 52

Site Address Plough Lane, SW17 0BL

Site Area 5.26 ha

Local Plan:



Yes. Site proposal 37. Planning permission granted.

Current Use Greyhound stadium (D2 Use Class) and car park (Sui Generis Use Class). Wimbledon Greyhound

Stadium, its associated parking areas, Christopher’s Squash Club and commercial uses (café,

office and motor cycle workshop).

Allocated use Intensification of sporting activity (D2 Use Class) with supporting enabling development.

Developments that facilitate more sporting activity may be enabled by more viable uses, subject

to meeting planning policy, evidence and consultation (allocation includes Volante site to the east

(37a)).

Proposed Use Proposed development (planning application 14/P4361): demolition of existing buildings and

erection of a 20,000 seat football stadium (initially 11,000 seat) with hospitality and coach parking,

pedestrian street, 1,273 m2 retail unit, 1,730 m2 squash and fitness club, 602 residential units with

basement parking, refuse storage, 297 car parking spaces, cycle parking, and associated

landscaping/open space and servicing.






Flood Zone


0 % 98 % 2 % 0 % 0 %


Risk of flooding to

the potential


surrounding area


(uFMfSW)

High Risk

1 in 30 year (3.33%

AEP)

The uFMfSW data does not show the susceptibility of

individual properties to surface water flooding. The

uFMfSW also does not take into account the details of

the existing drainage system.




Medium Risk

Potential for

groundwater flooding

to occur at surface, but

no historic records of


The dataset cannot be used on its own to indicate risk of

groundwater flooding and should not be used to inform

planning decisions at a site scale. It is suitable for use in

conjunction with a large number of other factors, e.g.

records of previous incidence of groundwater flooding,

to establish relative risk of groundwater flooding.


Historic records of

flooding from each source

within a 100m radius of

potential development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

1 2 0 9 Internal 1 0










Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity
















Development

Layout and

Sequential

Approach

It is recommended that a sequential approach to site layout should be used. The majority of the

development site is within Flood Zone 3a of the River Wandle, with small areas of Flood Zone 2

within the current Wimbledon greyhound stadium. More Vulnerable elements of the development

(residential properties) should be located in areas with low hazard to the south east and south west

of the site. For the current development site (without mitigation), modelling of the River Wandle

identifies that during the flood event with 1% AEP (1 in 100 year) including an allowance for climate

change there are small areas within the current greyhound stadium and to the east of it at risk of

flooding to depths of 1.5m. Areas to the north, centre and south of the development site are at

risk of flooding to depths up to 1m.

Uses with lower vulnerability should be located to the northern and central areas of the

development site, and inside the greyhound stadium footprint.









occurrence.

Section 9.2

Finished Floor

Levels

For More Vulnerable development, a minimum freeboard of 300mm is required above the 1% AEP

(1 in 100 year) including climate change fluvial flood level. For Less Vulnerable uses (such as

commercial development), finished floor levels do not need to be raised with regards to policy,

however, for this site it is recommended that a minimum freeboard of 300mm is provided above

the 1% AEP (1 in 100 year) including climate change fluvial flood level.


surface water flood risk. The site is at high risk of surface water flooding and it is considered that

the finished floor level requirement for fluvial flood levels would also protect the property from a

0.33% AEP (1 in 30 year) surface water flood event.

Section 9.3

Flood

Resistance

It is recommended that flood resistant construction methods should be considered, including use

of construction materials with low permeability, raising property thresholds, using landscaping to

manage surface water and fluvial floodwater.

Section 9.4

Flood

Resilience

It is recommended that flood resilient measures should also be considered on the site. These



damage and allow rapid re-occupancy. For example, concrete flooring and waterproofing building

materials such as timber joists and render and flood resilient air brick covers.

Section 9.5

Safe

Access/Egress

Access to the site is provided via Wimbledon Road to the east of the site. In the event of

widespread flooding associated with the River Wandle, there is potential that dry routes out of the

local area to a safe place of refuge may be limited. Due to the proximity of this site to the Merton

council’s administration boundary, some areas of refuge need to be considered within LB

Wandsworth. It will therefore be necessary to prepare a Flood Warning and Evacuation Plan

(FWEP), described further below.

Section 9.7

Floodplain

Compensation

Storage


ensure that it does not impact upon the ability of the floodplain to store water and that it does not

impact upon floodwater flow conveyance.

This site is located within the outline of the 1% AEP (1 in 100 year) flood event including an

allowance for climate change. Within this area, new development must not result in a net loss of

flood storage capacity. Due to the site lying wholly within the floodplain it will not be possible to

provide floodplain compensation storage within the site boundary. The extent of any increase in

building footprint should therefore be reduced as much as possible.

The use of flood voids may be considered to mitigate any loss of floodplain storage.

Section 9.9




Removing boundary walls or replacing with other boundary treatments such as hedges, fences

(with gaps).

Create under-croft car parks or consider reducing ground floor footprint and creating an open




Section

9.12

8 Department for Communities and Local Government (2007) Improving the flood performance of new buildings, Flood resilient construction.




Flood Warning

and

Evacuation

Plan




arrangements for the evacuation of car parks. Where possible, the FWEP should also detail the

length of time before the site becomes inaccessible by emergency vehicles.

Flood Warning Areas

The local area is covered by the Environment Agency Flood Warning Areas for ‘River Wandle at

Wimbledon’. Residents of the site should ensure they are signed up to the Environment Agency



Due to the proximity of this site to the Merton council’s administration boundary, the closest

designated emergency rest centre for this site is the Lola Jones Hall and Tooting Leisure Centre,

both within the London Borough of Wandsworth.

Section

9.14

Surface Water

Management



flooding issues. The potential development must not increase flood risk to other areas in the CDA,

in particular the electricity substation in Copper Mill Lane.


Wandsworth, and which drains much of Summerstown and Tooting Graveney. The uFMfSW

indicates that the site and surrounding area is at medium to high risk of surface water flooding.

There are no reported incidents of flooding held by Merton Council in this location.

Indicative Existing Runoff Rate: 23.4l/s (1 in 1 year), 87.7l/s (1 in 100 year)

Indicative Greenfield Runoff Rate: 10.5l/s

Level 2

Appendix B

SuDS Suitability



potentially unsuitable for the site. This will need to be confirmed prior to the development of a

Drainage Strategy for the site.



Section

10.3 and

10.9




policy 5.13, the mayors Design and construction SPG 2014 and Merton’s Local Plan policies.





Development will require major diversion of an existing Thames Water storm water culvert. Any

potential diversions and/or discharges into a sewer or main river must be agreed with Thames


Section

10.6







Section

10.4




flood risk” and



For this development site, the most vulnerable development should be located in areas of low hazard. There is potential that dry

routes out of the local area to a safe place of refuge may be limited and it is therefore necessary to prepare a FWEP for residents /

occupants of the site detailing steps to evacuate the site prior to the onset of flooding. The potential impacts of flooding should be

mitigated through careful site layout, resilient construction techniques, and incorporation of SuDS, to reduce the risk of increasing

flood risk elsewhere. Therefore, on this basis, it is likely that this site would pass the Exception Test.



SITE 53: VOLANTE, SUMMERSTOWN

1) SFRA SITE AREA

Site ID 53

Site Address 46-76 Summerstown, London, SW17 0BH

Site Area 0.23 ha

Local Plan:



Yes. Site proposal 37a.

Current Use Industrial use

Allocated use

Intensification of sporting activity (D2 Use Class) with supporting enabling development.

Developments that facilitate more sporting activity may be enabled by more viable uses, subject

to meeting planning policy, evidence and consultation (allocation with Wimbledon Greyhound

Stadium (site 37).






Flood Zone


0 % 100 % 0 % 0 % 0 %


Risk of flooding to

the potential


surrounding area


(uFMfSW)

Medium Risk

Between 1 in 100 year (1%

annual probability) and 1 in

30 year (3.3% annual

probability)





system.



Groundwater Flooding

data)

Medium Risk





flooding


indicate risk of groundwater flooding and

should not be used to inform planning

decisions at a site scale. It is suitable for use in

conjunction with a large number of other

factors, e.g. records of previous incidence of

groundwater flooding, to establish relative risk

of groundwater flooding.


Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 0 0 0 0 0








The fluvial hazard, depth and velocity outputs used in the Level 2 SFRA assessment and mapped below are based on the

Environment Agency modelling of the River Wandle (2015) and are provided for the 1% AEP plus Climate Change event9.

Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity
















Development

Layout and

Sequential

Approach

The development site is uniformly within Flood Zone 3a of the River Wandle. More Vulnerable

elements of the development (including residential properties) should be located in areas with

low hazard to the centre and southern part of the site. Modelling of the River Wandle identifies

that during the flood event with 1% annual probability (1 in 100 year) including an allowance for

climate change the south east of the site is at risk of flooding depths of at least 0.15 – 0.25m,

compared to greater depths of 0.3m - 0.45m to the north west of the site.

Uses with lower vulnerability should be located along the north western edge of the site.

Measures to manage surface water on the site should be considered early in the site

masterplan to enable inclusion of attenuation SuDS where possible.





internal access to higher floors situated above levels derived from the fluvial modelling. Further

ground investigations, such as site specific boreholes, would be required at this site to confirm

the likelihood of groundwater occurrence.

Section 9.2

Finished Floor

Levels

A minimum freeboard of 300mm should be set above the 1% annual probability (1 in 100 year)

including climate change fluvial flood level for More Vulnerable development such as housing.

For this site, the greatest flooding depth is approximately 0.45m in the north west of the site,

therefore it is recommended that finished floor levels are set in the region of 9.66 metres

Above Ordnance Datum (mAOD).


surface water flood risk. The site is at medium risk of surface water flooding and it is

considered that the finished floor level requirement for fluvial flood levels would also protect

the property from a 0.1% annual probability (1 in 1,000 year) surface water flood event.

Section 9.3

Flood

Resistance

Flood resistant construction methods should be considered on the site to minimise the impact

of floodwaters directly affecting any buildings and provide occupants time to take steps to

protect contents if necessary.

Section 9.4

Flood Resilience Flood resilient measures should also be considered on the site. These measures are

appropriate where modelled flood depths are greater than 0.6m10. The strategy should be to

allow water into the building, but to implement careful design in order to minimise damage and

allow rapid re-occupancy. For example concrete flooring and waterproofing building materials

such as timber joists and render and flood resilient air brick covers.

Section 9.5

Safe

Access/Egress

Access to the site is provided via Wimbledon Road to the east of the site and via

Summerstown and Garratt Lane to the north,. In the event of widespread flooding associated

with the River Wandle, there is potential that dry routes out of the local area to a safe place of

refuge may be limited. It will therefore be necessary to prepare a Flood Warning and

Evacuation Plan (FWEP), described further below.

Section 9.7

Floodplain

Compensation

Storage


ensure that it does not impact upon the ability of the floodplain to store water and that it does

not impact upon floodwater flow conveyance.

This site is located within the outline of the 1% annual probability (1 in 100 year) flood event

including an allowance for climate change. Within this area, new development must not result

in a net loss of flood storage capacity. Due to the location of the site wholly within the

floodplain it will not be possible to provide floodplain compensation storage within the site

boundary. The extent of any increase in building footprint should therefore be reduced as

much as possible. The use of flood voids may be considered to mitigate any loss of floodplain

storage.

Section 9.9




Removing boundary walls or replacing with other boundary treatments such as hedges,

fences (with gaps).

Create under-croft car parks (which are designed to flood in extreme events through voids

or louvres) or consider reducing ground floor footprint and creating an open area under the

building to allow flood water flow.



Section

9.12

10

Department for Communities and Local Government (2007) Improving the flood performance of new buildings, Flood resilient construction.




Flood Warning

and Evacuation

Plan


warning will be provided, how the safety of occupants and access to/from the development will

be ensured and what will be done to protect development and contents. The FWEP should

consider arrangements for the evacuation of basement car parks. Where possible, the FWEP

should also detail the length of time before the site becomes inaccessible by emergency

vehicles.

Flood Warning Areas


Wimbledon’. Residents of the site should ensure they are signed up to the Environment

Agency Flood Warning system.


Due to the proximity of this site to the Merton Council’s administration boundary, the closest

designated emergency rest centre for this site the Lola Jones Hall and Tooting Leisure Centre,

both within the London Borough of Wandsworth.

Section

9.14

Surface Water

Management



localised flooding issues. The potential development must not increase flood risk to other

areas in the CDA, in particular the electricity substation in Copper Mill Lane.


Wandsworth, and which drains much of Summerstown and Tooting Graveney. The uFMfSW

indicates that the site and surrounding area is at medium risk of surface water flooding. There

are no reported incidents of flooding held by Merton Council in this location.



Level 2

Appendix B

SuDS Suitability



is potentially unsuitable for the site. This will need to be confirmed prior to the development of

a Drainage Strategy for the site.



Section

10.3 and

10.9




policy 5.13, the mayor’s Design and construction SPG 2014 and Merton’s Local Plan policies.







Section

10.6







Section

10.4




flood risk” and



For this development site, the most vulnerable development should be located in areas of low hazard. There is potential that dry

routes out of the local area to a safe place of refuge may be limited and it is therefore necessary to prepare a FWEP for residents /

occupants of the site detailing steps to evacuate the site prior to the onset of flooding. However, the potential impacts of flooding

can be mitigated through design and layout and resilience construction, incorporating SuDS and other flood mitigation measures,

to reduce the risk of increasing flood risk elsewhere. Therefore, on this basis, it is likely that this site would pass the Exception Test.



SITE 54: PLOUGH LANE SUBSTATION

SFRA SITE AREA

Site ID 54

Site Address Plough Lane, Wimbledon SW17 0BL

Site Area 3.28 ha

Local Plan:



No

Current Use Borough owned land that has remained largely dormant and derelict for a number of years. It

contains a pair of houses fronting Durnsford Road, a large warehouse and a 3 storey office

building with under croft parking. All are in a poor state of repair.

Proposed Use Redevelopment of the site involving the erection of buildings ranging in height from 3 to 7 storeys, above

covered car parking, to provide 570 flats (335 x 1 bedroom, 186 x 2 bedroom and 49 studio flats) of

which 171 units would be for affordable housing; 2400 square metres of commercial floor space (Food

and drink – Class A3), Business use (Class B1) and non-residential institutional use (Class D1); provision

of 518 car parking spaces; alteration to existing vehicular access and formation of new vehicular access

from Plough Lane; alterations to existing public highways including junction improvements; provision of

publicly accessible open space, riverside walk and landscaping.

Vulnerability Less Vulnerable, More Vulnerable



The River Wandle flows northwards adjacent to the western side of the development site as an open channel.



Flood Zone


0 % 57 % 37 % 6 % 0 %


Risk of flooding to

the potential

development site

and surrounding

area

Surface Water

flooding:

(uFMfSW)

Medium Risk

Between 1 in 100 year (1%

annual probability) and 1 in 30

year (3.3% annual probability)

The uFMfSW data does not show the susceptibility of

individual properties to surface water flooding. The

uFMfSW also does not take into account the details of

the existing drainage system.

Groundwater

flooding:

(BGS Susceptibility

to Groundwater

Flooding)

Medium Risk


flooding to occur at surface,

but no historic records of


The dataset cannot be used on its own to indicate risk of

groundwater flooding and should not be used to inform

planning decisions at a site scale. It is suitable for use in

conjunction with a large number of other factors, e.g.

records of previous incidence of groundwater flooding,

to establish relative risk of groundwater flooding.



from each source within a

100m radius of potential

development site

Fluvial

records

Surface water

records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 0 0 0 0 0










Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity
















Development

Layout and

Sequential

Approach


that during the flood event with 1% AEP (1 in 100 year) including an allowance for climate change

the northern extent of the development site is at risk of flooding up to 1 metre with the area

south of this is at risk of flooding up to 0.5 metres. The rest of the site is at low flood hazard.

The River Wandle flows along the western site boundary and therefore all development should

be set back at least 8 metres from the river. A sequential approach to site layout should be

used. Development with the lowest vulnerability (i.e. public open space) should be located in the

area with significant flood risk in the north east. The more vulnerable residential properties

should be located in the area of no hazard, in the western half of the site. Any development that

is within the Flood Zone 3a should ensure that commercial, less vulnerable uses are located on

the ground floor and residential apartments are located above. Measures to manage surface

water on the site should be considered early in the site masterplan to enable inclusion of

attenuation SuDS where possible.



(BGS Susceptibility to Groundwater Flooding). Less Vulnerable basements, basement

extensions and conversions, such as plant, car parking etc, must provide safe internal access to

higher floors situated above levels derived from the fluvial modelling. Further ground

investigations, such as site specific boreholes, would be required at this site to confirm the

likelihood of groundwater occurrence.

Section 9.2

Finished Floor

Levels

For all new More Vulnerable development (i.e. the residential flats), finished floors levels should

be set a minimum of 300mm above the 1% AEP flood level (1 in 100 year) including climate

change. Any residential development in the “Significant Hazard” zone should ensure that

sleeping accommodation is restricted to the first floor or above to offer the required ‘safe

places’.

Internal ground floors below this level could however be occupied by the Less Vulnerable

commercial floor space, business use or car parking facilities, as there is no requirements in

terms of policy for finished floor levels and Less Vulnerable development.

Section 9.3

Flood

Resistance

As a new development, the main mitigation methods will be the site layout out, raising of finished

floor levels and the provision of suitable access/egress. However, if it is necessary to build in the

“Significant Hazard” area then flood resistant measures should be employed for the ground floor

uses. This includes the use of construction materials with low permeability, raising property

thresholds, using landscaping to manage floodwaters and use of devises such as air vent covers

to keep floodwaters out.

Section 9.4

Flood Resilience Where there is “Significant Hazard”, Less Vulnerable uses should be located on the ground floor

(e.g. car parking, offices, food and drink establishments). These properties should be designed

with flood resilience in mind, such as:

• Use materials with either, good drying and cleaning properties, or, sacrificial materials that

can easily be replaced post-flood.




• Coat walls with internal cement based renders; apply tanking on the inside of all internal

walls.


• Tank ground floors with water resistant membranes (particularly relevant for under croft

car parking).

• Use plastic water resistant internal doors.

Section 9.5

Safe

Access/Egress

Access to the site is provided via Copper Mill Lane leading onto Wimbledon Road to the south of

the site. In a flood event it is likely that dry access will be limited, therefore it is necessary to

prepare a Flood Warning and Evacuation Plan (FWEP), described further below.

Section 9.7

Floodplain

Compensation

Storage


ensure that it does not impact upon the ability of the floodplain to store water and that it does

not impact upon floodwater flow conveyance. Similarly, where ground levels are elevated to

raise a development out of the fluvial floodplain, compensatory floodplain storage within areas

that currently lie outside the floodplain must be provided to ensure that the total volume of the

floodplain storage is not reduced.

This site is located almost entirely within the outline of the 1% AEP (1 in 100 year) flood event

including an allowance for climate change. Therefore offsite floodplain storage should be

considered or the potential use of flood voids.

Section 9.9








fences (with gaps).

Create under-croft car parks or consider reducing ground floor footprint and creating an

open area under the building to allow flood water flow.



Section

9.12

Flood Warning

and Evacuation

Plan




consider arrangements for the evacuation of basement car parks. Where possible, the FWEP


vehicles.

Flood Warning Areas


Wimbledon’. Residents and occupants of the site should ensure they are signed up to the

Environment Agency Flood Warning system.


The closest designated emergency rest centre for this site is Christ the King, which is located

approximately 700 metres to the north west.

Section

9.14

Surface Water

Management



localised flooding issues. The potential development must not increase flood risk to other areas

in the CDA, in particular the electricity substation in Copper Mill Lane.


Wandsworth, and which drains much of Summerstown and Tooting Graveney.

The uFMfSW indicates that the site and surrounding area is at medium to high risk of surface

water flooding. There are no reported incidents of flooding held by Merton Council in this

location.



Level 2

Appendix B

SuDS Suitability



is potentially unsuitable for the site. This will need to be confirmed prior to the development of a

Drainage Strategy for the site. Techniques which should be considered include green roofs,

filter strips, detention basins and ponds, as well as permeable surfacing in combination with

tanked systems.

Section

10.3 and

10.9








and detailed in the Drainage Strategy. Any potential diversions and/or discharges into a sewer or

main river must be agreed with Thames Water or Environment Agency, respectively.

Section

10.6







Section

10.4







flood risk” and



For this development site, the most vulnerable development should be located in areas with “No Hazard” or above ground floor level.

Any Less Vulnerable development that is located in areas with greater risk should ensure to adopt careful site layout, resilient

construction techniques and incorporate SuDS to reduce the risk of increasing flood risk elsewhere. It is likely that in a flood event

dry access to and from the site will be limited; therefore it is necessary to prepare a FWEP for residents/occupants detailing steps to

evacuate the site proper to the onset of flooding. Therefore, on this basis, it is likely that this site would pass the Exception Test.



SITE 55: WIMBLEDON STATION

1) PROPOSED DEVELOPMENT

Site ID 55

Site Address Wimbledon Station, Wimbledon, SW19

Site Area 3.41 ha

Local Plan:



No

Current Use Railway Station and Retail (A use class)

Proposed Use Safeguarded for Crossrail2




The River Wandle flows northwards, approximately 1.5km to the east of Wimbledon Station. The site is not shown to be at risk of

fluvial flooding from the River Wandle.



Flood Zone


0 % 0 % 0 % 100 % 0 %





Surface Water

flooding:

(uFMfSW)

High Risk

1 in 30 year ((3.33 AEP)

The uFMfSW data does not show the susceptibility

of individual properties to surface water flooding.

The uFMfSW also does not take into account the

details of the existing drainage system.

Groundwater

flooding:


Groundwater

Flooding)

Medium Risk

Potential for


to occur at surface, but

no historic records of


The dataset cannot be used on its own to indicate

risk of groundwater flooding and should not be

used to inform planning decisions at a site scale. It

is suitable for use in conjunction with a large

number of other factors, e.g. records of previous

incidence of groundwater flooding, to establish

relative risk of groundwater flooding.


Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 5 0 0 0 0


copyright and database right 2016.

Contains Environment Agency data ©

Environment Agency and database right

2016).



SITE 55: WIMBLEDON STATION

3) RECOMMENDATIONS

In accordance with the NPPF, More Vulnerable development is considered compatible within Flood Zone 1, and does not require the




flood risk” and




Development

Layout and

Sequential

Approach

The site is shown to be located entirely within Flood Zone 1.

Early consideration of potential surface water flow paths across the site should be made, to

inform the most effective design for SuDS on the site.





internal access to higher floors situated above levels derived from the fluvial modelling. Further

ground investigations, such as site specific boreholes, would be required at this site to confirm

the likelihood of groundwater occurrence.

Section 9.2

Finished Floor

Levels

The site is located above the 1% AEP (1 in 100 year) flood event including an allowance for

climate change, therefore there are no requirements in terms of policy for finished for levels. Section 9.3

Surface Water

Management


The site is shown to be located within Critical Drainage Area 8 identified within the SWMP. The

potential development on the site must not increase flood risk within the CDAs.

The site is located across Drainage Catchment 18. The uFMfSW indicates that the site is at

high rise of surface water flooding. There are 5 reported incidents of surface water flooding

held by Merton Council in this location.



Level 2

Appendix B

SuDS Suitability


investigation to determine precise local conditions) the potential for infiltration of surface

water into the ground is uncertain.

Techniques which should be considered on this site include green roofs, filter strips, detention

basins and ponds, as well as permeable surfacing in combination with tanked systems.

Section 10.3

and 10.9




policy 5.13, the mayor’s Design and construction SPG (2014 and Merton’s Local Plan policies.


policy 5.13) and mayor’s Design and Construction SPG (April 2014), then justification must be

provided.





Section 10.6







Section 10.4



SITE 56: 12 RAVENSBURY TERRACE

SFRA SITE AREA

Site ID 56

Site Address 12A Ravensbury Terrace, Wimbledon Park, SW18 4RL

Site Area 0.10 ha

Local Plan:



Yes. Site proposal 64

Current Use Office and vacant warehouse use (B Use Class)

Proposed Use Office (B use class) and residential (Use Class C3)




The site is located south of a confluence between the River Wandle and an ordinary watercourse. The River Wandle flows from south

to north to the east of the site. The ordinary watercourse flowing in from the west is culverted until it reaches the site.



Flood Zone


20 % 45 % 35 % 0 % 0 %





Surface Water

flooding:

(uFMfSW)

High Risk

1 in 30 year (3.33% AEP)





system.

Groundwater

flooding:


Groundwater

Flooding)

Medium Risk





flooding









Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 0 0 0 0 0

(Contains Ordnance Survey data © Crown copyright

and database right 2016. Contains Environment

Agency data © Environment Agency and database

right 2016).







Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity
















Development

Layout and

Sequential

Approach

The River Wandle flows along the eastern edge of the site, and a portion of the site is designated

Flood Zone 3b Functional Floodplain. Development within the functional floodplain must have an

appropriate vulnerability use (i.e. Water Compatible) and must not increase flood risk overall.

For the remainder of the site, all development should be set back at least 8m from the edge of

the River Wandle and a sequential approach to site layout should be used based on vulnerability

classification. For the current development site (without mitigation), modelling of the River

Wandle identifies that during the flood event with 1% AEP (1 in 100 year) including an allowance

for climate change the north eastern corner is a risk of flooding up to 1m and the rest of the site

up to 0.5m. The lowest hazard is located to the west of the site; this is where the most vulnerable

parts of the development, such as residential accommodation, should be located.

Measures to manage surface water on the site should be considered early in the sites

devlopment proposal to enable inclusion of attenuation SuDS where possible.








Section 9.2

Finished Floor

Levels



the north eastern corner is a risk of flooding up to 1m and the rest of the site up to 0.5m.

For More Vulnerable residential development, a minimum freeboard of 300mm is required above

the 1% AEP (1 in 100 year) including climate change fluvial flood level.

For Less Vulnerable development there are no requirements in terms of policy for finished floor

levels. Instead, development of this vulnerability can be designed to be floodable, which will also

minimise the impact of the development on the displacement of floodwater and the risk of

flooding to the surrounding area. If this strategy is employed then a clear Flood Warning and

Evacuation Plan (FWEP) should be provided to ensure occupants of the site can access safe

refuge in a flood, especially as the entire site is within the floodplain.


surface water flood risk. The site is at high risk of surface water flooding and it is considered

that the finished floor level requirement for fluvial flood levels for residential development would

also protect property from a 0.33% AEP (1 in 30 year) surface water flood event.

Section 9.3

Flood

Resistance

It is recommended that flood resistant construction methods should be considered, including

use of construction materials with low permeability, raising property thresholds, using

landscaping to manage surface water and fluvial floodwater.

Section 9.4

Flood Resilience It is recommended that flood resilient measures should also be considered on the site. These



damage and allow rapid re-occupancy. For example, concrete flooring and waterproofing

building materials such as timber joists and render and flood resilient air brick covers.

Section 9.5

Safe

Access/Egress

The eastern side of the development site is designated Flood Zone 2; therefore access off the

site can be achieved via Haslemere Avenue which joins the site at this point.

The surrounding area is either a Flood Zone 2 or 3a. A FWEP should be prepared for the site.

Access and egress to the site should be made via Haslemere Avenue, to the southwest, as this

leads to an area of high ground located above the floodplain.

Section 9.7

Floodplain

Compensation

Storage

This site is located within the outline of the 1% AEP (1 in 100 year) flood event including an

allowance for climate change. Within this area, new development must not result in a net loss of

flood storage capacity. Due to the site lying wholly within the floodplain it will not be possible to

provide floodplain compensation storage within the site boundary. The extent of any increase in

building footprint should therefore be reduced as much as possible. The use of flood voids may

be considered to mitigate any loss of floodplain storage.

Section 9.9

13









fences (with gaps).

Create under-croft car parks or consider reducing ground floor footprint and creating an

open area under the building to allow flood water flow.



Section

9.12

Flood Warning

and Evacuation

Plan


warning will be provided and how the safety of occupants and access to/from the development

will be ensured as well as what will be done to protect development and contents. The FWEP

should consider arrangements for the evacuation of basement car parks. Where possible, the

FWEP should also detail the length of time before the site becomes inaccessible by emergency

vehicles.

Flood Warning Areas


Wandsworth’. The developer need to ensure that residents of the site are signed up to the

Environment Agency Flood Warning system and set out in the FWEP how this will be achieved. .


Due to the proximity of this site to the Merton council’s administration boundary, the closest

designated emergency rest centre for this site is Earlsfield Library, within the London Borough of

Wandsworth.

Section

9.14

Surface Water

Management



Merton with the northern district in Wandsworth. It drains much of Wimbledon Park and the

surrounding area.

The uFMfSW indicates that the site itself is at low risk to surface water flooding, however, the

area to the east of the site is at high risk of surface water flooding. There are no reported

incidents of flooding held by Merton Council in this location.

Indicative existing runoff rate: 0.5 l/s (1 in 1 year), 1.7 l/s (1 in 100 year)


Level 2

Appendix B

SuDS Suitability







Section

10.3 and

10.9











Section

10.6







Section

10.4







flood risk” and



This is a relatively small development site located immediately adjacent to the River Wandle. More Vulnerable development should

be set back from the edge of the river with an undeveloped buffer zone of at least 8m width. The potential impacts of flooding should

be mitigated through the raising of finished floor levels and flood resistant construction methods. A FWEP should be prepared to

establish an evacuation plan via Haslemere Avenue to higher ground to the southwest of the site. Careful consideration should be

made of the management of surface water from on the site to ensure no increased flood risk to adjacent to areas. On this basis it is

likely that the site would pass the Exception Test.



SITE 57: HASLEMERE INDUSTRIAL ESTATE

1) SFRA SITE AREA

Site ID 57

Site Address Haslemere Industrial Estate, 20 Ravensbury Terrace

Site Area 0.78 ha

Local Plan:



Yes. Site proposal 70

Current Use Business and industrial (B1)

Proposed Use Business/light industrial (B1) or suitable employment led redevelopment.

Vulnerability Less Vulnerable (commercial), More Vulnerable



The River Wandle flows from the south to north past the north eastern corner of the development site as an open channel. Just north

of the development site the Wandle is joined by a tributary, which is a culverted ordinary watercourse.



Flood Zone


4 % 51 % 42 % 3 % 0 %





Surface Water

flooding:

(uFMfSW)

Medium Risk

Between 1 in 100 year

(1% annual probability)

and 1 in 30 year (3.3%

annual probability)





system.

Groundwater

flooding:


Groundwater

Flooding)

Medium Risk





flooding









Historic records of

flooding from each


radius of potential

development site


records

Groundwater

records

Sewer

records

Multiple source

records

Other

0 0 0 0 0 0



Environment Agency data © Environment Agency

and database right 2016).







Flood Hazard Rating

Maximum Flood Depth

Maximum Velocity
















Development

Layout and

Sequential

Approach

A sequential approach to site layout should be used. Half the development site is defined as

Flood Zone 3 and the other half is within Flood Zone 2 associated with the River Wandle.

Development should be set back 8m from the edge of the River Wandle, and areas to the north

west of the site where the hazard rating is lower should be developed in preference to the rest of

the site.



the south and east of the site is at risk of flooding up to 1 metre. The area adjacent to this is at

risk of flooding up to 0.5 metres. Development should be steered towards areas where flood

depths are lower. Only uses with lower vulnerability should be considered in these southern and

eastern locations.










Section 9.2

Finished Floor

Levels

There is typically no requirement for setting finished floor levels for Less Vulnerable

developments. Less Vulnerable developments can be designed to be floodable instead of

raising floor levels, and this may be beneficial to help minimise the impact of the development on

the displacement of floodwater and the risk of flooding to the surrounding area. However, it is

strongly recommended that internal access is provided to upper floors (first floor or a mezzanine

level) to provide safe refuge in a flood event. Such refuges will have to be permanent and

accessible to all occupants and users of the site and a FWEP should be prepared to document

the actions to take in the event of a flood (see below).


surface water flood risk. The site is at medium risk of surface water flooding and it is considered

that measures to mitigate the risk from fluvial flooding would also protect the property during a

surface water flood event.

Section 9.3

Flood

Resistance

The use of flood resistant construction methods may be appropriate across parts of the site.

Measures include the use of construction materials with low permeability, raising property

thresholds, using landscaping to manage surface water and fluvial floodwater.

Section 9.4

Flood Resilience It is recommended that flood resilient measures should be considered for the majority of the

site, where modelled flood depths are greater than 0.6m15. Measures associated with the ‘Water

Entry Strategy’ should be adopted, which is to allow water into the building, but to implement

careful design in order to minimise damage and allow rapid re-occupancy. For example, raising

of electrical appliances, use of concrete flooring and waterproofing building materials such as

timber joists and render and flood resilient air brick covers.

Section 9.5

Safe

Access/Egress

Access to the site is provided via Haslemere Avenue to the northwest of the site. In the event of

widespread flooding associated with the River Wandle, there is potential that dry routes out of

the local area to a safe place of refuge may be limited. It will therefore be necessary to prepare a

Flood Warning and Evacuation Plan (FWEP), described further below.

Section 9.7

Floodplain

Compensation

Storage

The majority of this site is located within the outline of the 1% AEP (1 in 100 year) flood event

including an allowance for climate change. Within this area, new development must not result in

a net loss of flood storage capacity. Due to the site lying wholly within the floodplain it will not be

possible to provide floodplain compensation storage within the site boundary. The extent of any

increase in building footprint should therefore be reduced as much as possible. The use of the

Water Entry Strategy will also enable temporary storage of floodwater.

Section 9.9





fences (with gaps).



Section

9.12

15





Flood Warning

and Evacuation

Plan




consider arrangements for the evacuation of associated car parks. Where possible, the FWEP


vehicles.

Flood Warning Areas


Wandsworth’. Residents of the site should ensure they are signed up to the Environment

Agency Flood Warning system.


Due to the proximity of this site to the Merton Council’s administration boundary, the closest

designated emergency rest centre for this site is Earlsfield Library, northeast of the site within

the London Borough of Wandsworth.

Section

9.14

Surface Water

Management



Merton, however, the northern extent lies within the London Borough of Wandsworth. It drains

much of Wimbledon Park and the surrounding area.

The uFMfSW indicates that the site is at medium risk to surface water flooding along the

southeast extent, with high risk in the south. There are no reported incidents of flooding held by

Merton Council in this location.



Level 2

Appendix B

SuDS Suitability







Section

10.3 and

10.9











Section

10.6







Section

10.4




flood risk” and



The site is within either Flood Zone 2 or 3a, however, because the development site will be characterised by non-residential (i.e. Less

Vulnerable) buildings, the potential hazard caused by flooding can be mitigated through flood resilient ‘Water Entry Strategy’. This

includes careful site layout, resilient construction techniques, and incorporation of SuDS, to allow controlled flooding of Less

Vulnerable buildings and the avoidance of increasing flood risk elsewhere. If this approach is selected, then it is particularly important

to prepare a FWEP for the occupants of the site. This will detail the steps to evacuate the site and protect the contents of the

property prior to the onset of flooding. On this basis, it is likely that this site would pass the Exception Test.

site 46: hypermarket new malden · site 46: hypermarket new malden floodplain compensation storage...

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