SuDS in London - a guide

1.1 Planning for SuDs
Controlling stormwater quantity and water
quality to mitigate flooding and the risk of
pollution respectively are the main drivers
for SuDS.
Potential flooding is not limited to large
one in 100 year storms; flooding in urban
areas often results from the more frequent
and intense rainfall we are experiencing in
the Capital as a result of climate change.
When localised flooding happens, it is
usually linked to surface water flows
exceeding the capacity of the drainage
system. It is therefore important to
slow down the flow rate or hold the
rainfall back, whether that be within
developments or the public realm.
The London Sustainable Drainable Action
Plan (LSDAP) also seeks to reduce surface
water flows into the sewer network
through a series of wide-ranging actions.
SuDS are crucial to help achieve this;
they also reduce risk and address policies
dealing with current and future flood
issues in a sustainable and cost effective
way (London Plan Policy 5.12).
Ideally, SuDS need to be delivered
in a coordinated and integrated
manner, subject to the constraints and
considerations set out in this document.
The additional benefits that can arise from
SuDS in the public realm and streetscape
are discussed throughout this chapter.
They can contribute positively to the
character of the streets, open spaces and
parks in the Capital, as well as address
flood risk and pollution concerns.
The aim for the reduction in flow rate
– or ‘betterment’ – is to achieve levels
that emulate a greenfield site which is
supported by the London Plan (Policy
5.13). Although greenfield rates are not
always achievable, the London Sustainable
Design and Construction SPD reports
that ‘most developments referred to the
Mayor have been able to achieve at least
50% attenuation of the site’s surface water
runoff at peak times’.
Surface water flooding is the greatest short-term flood risk to London
8 1 Principles of SuDS