Page 27 - Merton SuDS Design and Evaluation Guide

6.0 Local SuDS requirements for responsibility of Thames Water. However, in Local SuDS Specific Requirements
Local SuDS requirements
the extreme northern parts of the borough
SuDS are an extremely important tool to help
Merton
there is combined sewer system. Many of the
surface water sewers discharge locally into
promoted to limit the opportunity for surface
the river network. Thames Water has a duty manage the risk of flooding and should be
water to enter the foul and combined sewer
Landscape Character flows north through the centre of the as a statutory water undertaker to provide networks, to avoid foul/sewer flooding. They
Borough and its main tributary, the River clean water in the central and northern areas
The London Borough of Merton is located in Graveney, forms the Borough’s eastern of the borough and Sutton and East Surrey are the preferred drainage method across Local SuDS requirements
the south west of Greater London and covers boundary. Water provide clean water services to the Merton. All planning applications and
an area of approximately 37km2. The main southern part of the borough. Thames Water Drainage Strategies are expected to follow
urban centres within Merton are Wimbledon, Geology are responsible for receiving surface water the range of policies set out within the
Raynes Park, Colliers Wood, Morden and drainage from development which discharge London Plan and Merton’s Local Plan.
Mitcham, which are comprised of mostly The underlying bedrock of Merton is almost via adopted sewers and for maintaining trunk Merton’s adopted Local Plan consists of the
commercial and residential land uses. entirely London Clay, with a small area of sewers into which the majority of the Core Strategy (2011), Sites and Policies Plan
Claygate Member and Bagshot Formation to
The majority of the Borough is low lying the northwest. The majority of the superficial highway drainage in Merton connects. and Policies Map (2014) and the South

except the area in the north west, namely deposits are various River Terrace Deposits Several flood events in the borough have London Waste Plan (2012). A new Local Plan
Wimbledon and Wimbledon Common, where (gravel, sandy and clayey in part), which occurred as a result of high water levels in is in the process of being prepared by
elevations reach 55m above Ordnance differentiate on the basis of altitude but are the River Wandle, Graveney, Beverley Brook Merton, which will replace the Core Strategy
Datum. The rest of London Borough of geologically similar. These can be sub-divided and Pyl Brook, blocking storm water outfalls and Sites and Policies Plan and Policies Map.
Merton is lower lying at 18-35mAOD, with into Taplow Gravel Formation and Hackney and causing water to back up in the sewer In Merton, discharge rates for new
gentle slopes associated with the floodplains Gravel Member which are located in the system and highway drainage. Across Merton, developments should be restricted to
of the River Wandle and Beverley Brook Mitcham area; Kempton Park Grave in Merton trash screens and culverts have the potential Greenfield runoff rates. For brownfield sites,
21 catchments. and New Malden and Black Park Gravel is to become blocked by items such as plant runoff rates should not be more than three 22

located on the higher ground at Wimbledon. debris and rubbish.
The Borough is generally urbanised and has times the calculated greenfield rate, in line
large areas of impermeable surface, with the Ribbons of Alluvium (mainly sand, silt and Plans for regeneration, development and with the London Plan’s Sustainable
clay) are distributed along the River Wandle
main town centres interspersed by large intensification within London Borough of Construction and Design SPG (Section 2.5.2).
areas of green open space, namely and Beverley Brook. Merton may present a challenge to the Large potential development areas with a
Wimbledon Park, Wimbledon Common, Ground investigations have shown a shallow existing drainage systems. However, it also number of new allocation sites should look to
Bushey Mead, Morden Park, Morden Hall Park perched groundwater layer is common across affords a crucial opportunity to address develop a strategy for providing a joint SuDS
and Mitcham Common. significant parts of the borough, due to the long-standing issues and problems relating to scheme. This should be on an integrated and

presence of the underlying London Clay. This surface water flooding and pressure points strategic scale and where necessary would
The Borough contains four main river require the collaboration of all developers
watercourses; Beverley Brook, Pyl Brook, perched groundwater layer can result in on the drainage system through strategic involved in implementing a specific expansion
groundwater ingress to basements if tanking
River Wandle and River Graveney. The infrastructure improvements and upgrades to area or site.
Beverley Brook forms the western boundary is not appropriate or up to standard. the drainage system through the
of the London Borough Local Drainage and Sewer Network implementation of SuDS and slowing the flow The Drainage Catchment areas, identified and
of runoff at source. mapped in Merton’s Strategic Flood Risk
of Merton and its main tributary, the Pyl The waste water drainage infrastructure Assessment (SFRA), should be considered
Brook flows northwest through the southwest across the borough is generally a separate for development sites that are not directly at
corner of the Borough. The River Wandle surface and foul sewer system which is the risk of surface water flooding, to identify flow

London Borough of Merton SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates London Borough of Merton SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates