Page 102 - Hillingdon SuDS DESIGN & EVALUATION

Detailed Design 9.6.5 Flow controls for SuDS Silt is trapped at source in SuDS components

Attenuation storage within sub-catchments
and settles out along the management train.
and along the management train can require
Where slow movement of flow is maintained
several flow controls. Flow controls come in
throughout, floating debris that easily blocks
many forms including orifice plates, slot or
outlets is not driven against openings; as is
V-notch weirs and vortex controls. Any type
the case with conventional drainage. Simple
of flow controls can be prone to blockage
design features such as sloping headwalls
unless the opening is protected.
can direct floating debris past the outlet as
The rate of flow of water through SuDS
the storage structure fills.
components is slow as it is restricted to
‘greenfield rates’ of runoff through each flow
control. There should always be an overflow
arrangement to deal with blockage or
exceedance of the design storm.

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Orifice flow control chambers such as this one
by Controflow are simple, reliable,
cost-effective and easy to maintain.

Flow controls in the landscape can make
interesting features and help tell the story of
how the system works. Although more prone
to blockage, features such as this slot weir at
Hollington School are very easy to unblock.

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