Page 27 - Merton SuDS DESIGN & EVALUATION
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responsibility of Thames Water. However, in Local SuDS Specific Requirements
the extreme northern parts of the borough
there is combined sewer system. Many of the SuDS are an extremely important tool to help
surface water sewers discharge locally into manage the risk of flooding. They are the
the river network. Thames Water has a duty preferred drainage method across Merton.
as a statutory water undertaker to provide All planning applications and Drainage
clean water in the central and northern areas Strategies are expected to follow the range
of the borough and Sutton and East Surrey of policies set out within the London Plan Local SuDS requirements
Water provide clean water services to the and Merton’s Local Plan.
southern part of the borough. Thames Water Merton’s adopted Local Plan consists of the
are responsible for receiving surface water Core Strategy (2011), Sites and Policies Plan
drainage from development which discharge and Policies Map (2014) and the South
via adopted sewers and for maintaining trunk London Waste Plan (2012). A new Local Plan
sewers into which the majority of the is in the process of being prepared by
highway drainage in Merton connects. Merton, which will replace the Core Strategy
and Sites and Policies Plan and Policies Map.
Several flood events in the borough have
occurred as a result of high water levels in All planning applications should have
the River Wandle, Graveney, Beverley Brook consideration and regard to policy DM F2
and Pyl Brook, blocking storm water outfalls (SuDS and wastewater) within Merton’s Sites
and causing water to back up in the sewer and Policies Plan.
system and highway drainage. Across Merton, In Merton, discharge rates for new
trash screens and culverts have the potential developments should be restricted to 22
to become blocked by items such as plant Greenfield runoff rates. For brownfield sites,
debris and rubbish. runoff rates should not be more than three
times the calculated greenfield rate, in line
Plans for regeneration, development and
intensification within London Borough of with the London Plan’s Sustainable
Merton may present a challenge to the Construction and Design SPG (Section 2.5.2).
existing drainage systems. However, it also Large potential development areas with a
affords a crucial opportunity to address number of new allocation sites should look to
long-standing issues and problems relating to develop a strategy for providing a joint SuDS
surface water flooding and pressure points scheme. This should be on an integrated and
on the drainage system through strategic strategic scale and where necessary would
infrastructure improvements and upgrades to require the collaboration of all developers
the drainage system through the involved in implementing a specific expansion
implementation of SuDS and slowing the flow area or site.
of runoff at source. The Drainage Catchment areas, identified and
mapped in Merton’s Strategic Flood Risk
Assessment (SFRA), should be considered
for development sites that are not directly at
London Borough of Merton SuDS D & E Guide © 2018 McCloy Consulting & Robert Bray Associates
