DRAIN APPENDIX E - OPTIONS ASSESSMENT

CDA DESCRIPTION

London Borough: Critical Drainage Area ID: Group 7_018 (Summerstown) (Lead)

(Other) Description: This CDA is located in and includes Cemetery and Wimbledon Stadium Business Centre. The main flow path into Summerstown flows through the cemetery from the east and eventually ponds in Summerstown around Wimbledon Stadium. There is also a flow path along Upper Tooting Road flowing south westerly and Road (A217).

The western and south-western CDA area is located within an iPEG area. Flood Risk Categorisation: All Sources Property Count: 3,392 residential and 218 non-residential properties >0.03m 50 residential properties >0.5m Critical Infrastructure: • Copper Mill Lane Electricity Substation • • Franciscan Primary School • St Boniface RC Primary School • Electricity Substation (Hebdon Road) • Tooting Broadway Station • Broadwater Primary School • Fircroft Primary School • Garratt Park School • Springfield Hospital Validation: • There are several records of surface water flooding across this CDA, predominantly from the heavy rainfall event in July 2007. Flooded areas include Graveney School, Franciscan Primary School, Tooting Library, St Boniface RC Primary School, Tooting Broadway Station, Tooting High Street, Herlwyn Gardens, Broadwater Primary School, Fircroft Primary School, Garratt Park School, Maskell Road and Springfield Hospital. • There are over 140 sewer flooding incidents within the wider postcode areas, in which the CDA is located. • There are two groundwater flooding records within the CDA. Local Flood Risk Zones • North Tooting Graveney – pluvial modelling results indicate dispersed areas of ponding of surface water in the vicinity of Tooting High Street, Upper Tooting Road, Broadwater Road and Totterdown. • Wimbledon Stadium Business Park – pluvial modelling and historical flooding records indicate that surface water ponds here during heavy rainfall. The area also lies within Flood Zone 3a of the . • Copper Mill Lane Electricity Substation - pluvial modelling indicates that surface water could pond in this vicinity to a depth of 0.2m during the 1% AEP rainfall event. Figures: Figure 3.8.5a – Surface Water Flood Depth (1% AEP) Figure 3.8.5b – Surface Water Flood Hazard (1% AEP) DRAIN LONDON APPENDIX E - OPTIONS ASSESSMENT

STAGE 1 - MEASURES IDENTIFICATION

Critical Drainage Area ID: Group 7_018 (Summerstown)

Measure Opportunity Assessment Description Location / Specific Details Comments

To be identified on site-by-site basis when opportunities arise but likely to be limited Green Roof G Generic Measure Throughout CDA - large buildings (potential retrofit) and for new development. opportunity for implementation of measure within the CDA.

Likely to be limited due to geology. Further investigation is needed to assess the infiltration Soakaways a Generic Measure Throughout CDA potential due to geology.

Further investigation will be required to determine drainage arrangements and discharge for Swales g Generic Measure Throughout CDA swales - may be limitied due to geology.

Likely to be limited due to geology. Further investigation is needed to assess the infiltration Permeable Paving a Generic Measure Throughout CDA potential due to geology. RCE RCE

SOU Rainwater Harvesting G Generic Measure. For all new development and retrospectively. Throughout CDA To be identified on site-by-site basis.

A strategically located detention basin could be constructed to manage the surface water from Detention Basins r N/A Likely to have limited space in the CDA for these to be implemented. the upstream catchment of the CDA.

A strategically located pond could be constructed to manage the surface water from the Ponds and Wetlands R N/A Likely to have limited space in the CDA for these to be implemented. upstream catchment of the CDA.

Other 'Source' Measures N/A

Ashvale Road, Undine Street, Valnay Street, Rogers Road, Strathdon Drive, Upper Tooting Increasing Capacity in Drainage Systems G The existing drainage system capacity could be increased to accommodate storm water Road and Deeside Road.

Separation of Foul and Surface Water Sewers G The combined sewers within this CDA could be separated to allow for more capacity. As above To be identified on site-by-site basis.

Generic Measure. More regular inspection of the current sewer system to remove debris and Improved Maintenance Regimes G Throughout CDA To be identified on site-by-site basis. improve conveyance.

Part of Garratt Green could be constructed as a detention basin. Managing Overland Flows (Online Storage) a Online flood storage The playing field to the east of Streatham cemetery that would control surface water running Limited opportunities for online storage given the residential nature of this CDA. off onto Rogers Road.

Manage overland flow paths to drain to proposed flood storage area from Wimbledon

PATHWAY PATHWAY Managing Overland Flows (Preferential Flowpaths) a Streets could be lowered or kerbs raised to create a flow path. To be identified on site-by-site basis. Stadium Business Park (Siward Road and Riverside Road) and the surrounding area.

Land Management Practices R N/A N/A Not applicable due to CDA being heavily urbanised.

Deculverting Watercourse(s) R N/A N/A The CDA contains no main rivers or ordinary watercourses.

Other 'Pathway' Measures N/A

Given the nature of the flooding in the CDA, it is unlikely this measure could be effectively Improved Weather Warning a Dependent on location and storm event duration. Depending on the timings of the storm event evacuation of these properties could be possible. implemented.

Planning Policies to Influence Development G Generic Measure Throughout CDA For all new development.

The residential area to the west of Streatham Cemetery, Upper Tooting, Ashvale Road, Temporary or Demountable Flood Defences g Household flood resistance / resilience measures could be installed. To be identified on site-by-site basis. Undine Street, Valnay Street and Rogers Road.

Will be dependent on engagement opportunities with community. In areas with a large Social Change, Education and Awareness g Generic Measure Throughout CDA migration of population it will be difficult to undertake / pass on information from one property RECEPTOR RECEPTOR owner to another.

The residential area to the west of Streatham Cemetery, Upper Tooting, Ashvale Road, Improved Resilience and Resistance Measures G Property level resilience measures To be identified on site-by-site basis. Undine Street, Valnay Street and Rogers Road.

Other 'Receptor' Measures N/A DRAIN LONDON APPENDIX E - OPTIONS ASSESSMENT

STAGES 2 and 3 - OPTIONS IDENTIFICATION AND SHORT LISTING

Critical Drainage Area ID: Group 7_018 (Summerstown)

Standard Measures Short listing Options SOURCE PATHWAY RECEPTOR

Option No. Option (Scheme Category) Comments Social Overall Technical Economic Objectives Environmental Appropriate Measures Available? Take to Detailed Forward Option Assessment? Green Roof Soakaways Swales Permeable Paving Rainwater Harvesting Detention Basins Ponds and Wetlands Other 'Source' Measures Increasing Capacity in Drainage Systems Separation Foul andof Surface Water Sewers Improved Maintenance Regimes Managing Overland Flows (Online Storage) Managing Overland Flows (Preferential Flowpaths) Land Management Practices Deculverting Watercourse(s) Other 'Pathway' Measures Improved Weather Warning Planning Policies Influence to Development Temporary or Demountable Defences Flood Social Change, Education and Awareness Improved Resilience and Resistance Measures Other 'Receptor' Measures

1 Do Nothing  2 -1 -2 0 -2 -3  In line with PAG the 'do nothing' option (no intervention and no maintenance) and 'do minimum' (continuation of current practise) should be taken forward to the detailed options assessment. 2 Do Minimum  2 0 -1 0 -1 0 

This option will be relatively easy to implement by increasing the regularity of the existing maintenance regime. It is however only likely to see localised flooding 3 Improved Maintenance G N/A  2 1 1 0 1 5  benefits.

To implement this option into new developments would be relatively simple through planning policy. Once an area has been identified as being in a critical drainage 4 Planning Policy G  2 2 0 1 1 6  area policies to manage the surface water on the site are already in place. These could be reiterated in forthcoming policy documents.

There are some opportunities to implement small scale SuDS measures throughout the CDA. None of the options are considered technically difficult but may be 5 Source Control, Attenuation and SUDS G a g a G N/A R  1 1 1 1 1 5  limited in terms of the benefits they can deliver.

6 Flood Storage / Permeability r R N/A a R N/A  1 1 0 1 1 4  here are limited opportunities to implement these measures in the CDA.

7 Separate Surface Water and Foul Water Sewer Systems G  1 -2 0 0 1 0  This is technically possible, but the cost of carrying out sewer separation over a large geographic area is not viable. The cost-benefit ration is likely to be negative.

8 De-culvert / Increase Conveyance R N/A  0

Much of the flooding in this CDA is adjacent to roads and there this option is likely to have a positive cost-benefit ratio. However, there are no additional 9 Preferential / Designated Overland Flow Routes a N/A  2 2 0 0 1 5  environmental benefits.

This option could protect properties from flooding through the installation of flood barriers on the doors of properties. But there may be local resistance to the uptake 10 Community Resilience a g g G N/A  2 1 1 0 1 5  of the barriers and the success of the barriers relies on human intervention and the dissemination of appropriate flood warnings. It is also a costly exercise to fit multiple properties with demountable barriers and/or property level resilience measures.

This option could be considered for schools and infrastructure predicted to flood to greater depths in the CDA . However, it is likely to be achieved in combination 11 Infrastructure Resilience g N/A  2 1 1 0 1 5  with improved education / awareness and small scale SuDS measures such as rainwater harvesting.

A local increase in drainage capacity on Gaskell Street is technically feasible and will achieve local flood alleviation and potentially more widespread flood alleviation. 12 Other - Improvement to Drainage Infrastructure G N/A  2 1 1 0 1 5  However, there would be no environmental benefits.

 0  Investigate local drainage capacity in Tooting High Street, Upper Tooting Road, Broadwater Road and Totterdown area. 13 Other or Combination of Above

 0  Confirm resilience of Copper Mill Lane Electricity Substation