Page 29 - Merton SuDS Design and Evaluation Guide

Local SuDS requirements
paths to areas downstream that are at risk applied in all development situations,

from surface water flooding and could be although individual site constraints may limit
impacted by the development. Mitigation the potential of some sites achieving full
measures, such as attenuation measures, benefits for all functions. The variety of SuDS
should be used in the upper catchment areas available allows planners and designers to
to prevent increased risk to the downstream make full potential of the local land and
sites. consider the needs of local people when Local SuDS requirements
implementing the drainage design. The
Policy 5.13 in the London Plan sets out the wishes of all the relevant stakeholders needs
drainage hierarchy that developers should to be balanced in additional to the risk
follow for managing surface water in London associated with each design option.
Boroughs. The London Plan drainage Developers are strongly recommended to use
hierarchy is set out in Section 2.5.1 of this to the council’s pre-application planning
SFRA. Generally the aim should be to advice service.
discharge surface water run-off as high up
the following hierarchy of drainage options as
reasonably practicable. Where possible,

stormwater should be managed in small,
cost-effective landscape features located
within small subcatchments, rather than
being conveyed to and managed in large
23 systems at the bottom of drainage areas. 24

The passage of water between stages of the
SuDS management train should be
considered through the use of natural
conveyance systems (e.g. swales and filter
trenches) wherever possible. Pipework and
sub-surface proprietary produce may still be
required, especially where space is limited.
Pre-treatment (i.e. the removal of silt and
sediment loads) and maintenance is vital to
ensure the long-term effectiveness of SuDS.

Overland flow routes will also be required to
convey and control floodwaters safely and
effectively during extreme flood events.
Generally, the greater the number of
techniques used in a series the better the
performance is likely to be and the lower the
risk of overall system failure. SuDS can be
Facing Page: Baltic Close, Merton

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