Page 93 - Updated SuDS Design & Evaluation Guide-Newham V3 Spreads

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Detailed Design 9.5.6 Managing runoff rates from Detailed Design

Brownfield sites

On Brownfield sites (also known as Previously
Developed Land or PDL), if infiltration of the 1
in 100 year rainfall event is not possible, the
rate of discharge should be reduced to
greenfield runoff rates. Where greenfield
rates cannot be achieved, the designer must

demonstrate why reduction in rate is not
achievable. The designer will be required to
demonstrate that they have explored all
options for storage including the use of
storage on roofs (e.g. blue-green roofs),
permeable pavements, and the use of
appropriately designed underground storage.
(NSTS S3 and S6.)

Not all planning applications comprise a
complete redevelopment of the site, and only
a small parcel of the overall site may be
planned for re-development. On such
occasions LLFA will not expect the entire
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development to be returned to greenfield
runoff status.

In these circumstances LLFA will not accept

the combining of the greenfield runoff rate
for the development parcel with the existing
impermeable runoff rate from the remainder Designers should provide the following:
of the site when the designer is undertaking
storage calculations. ■ the net increase in impermeable area

The existing development remaining intact ■ greenfield runoff rates are calculated
and the parcel of land proposed for based on the area of the redevelopment
development should be treated separately in parcel and not the wider development
terms of calculations and drainage strategy.
■ storage requirements for additional
impermeable area based on outflow
controlled to greenfield rates for the
Facing: The Islington, Ashby Grove Raingarden.
A raingarden for a single property with control development parcel.
tube and overflow that can manage the 1 in 100
year return period rainfall event.

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