Page 102 - Updated SuDS Design & Evaluation Guide-Newham V3 Spreads

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Detailed Design 9.6.5 Flow controls for SuDS Silt is trapped at source in SuDS components 9.6.6 The importance of protected openings Detailed Design

SuDS components such as permeable
There are no minimum thresholds for
Attenuation storage within sub-catchments
pavements, bioretention or filter drains are
attenuated flow rates in SuDS design.
and settles out along the management train.
and along the management train can require
pre-filtered, and assuming collection through
Where slow movement of flow is maintained
Previously the drainage industry has applied
several flow controls. Flow controls come in
perforated pipes or similar, the flow control
throughout, floating debris that easily blocks
a minimum flow rate of 5 l/s but this does not
many forms including orifice plates, slot or
opening requires little additional protection.
outlets is not driven against openings; as is
take into account the need in SuDS for low
V-notch weirs and vortex controls. Any type
flow rate controls and the design of
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.
ponds and basins, require additional
can direct floating debris past the outlet as
protection. One way to provide this
Small sites and sub-catchments of larger
The rate of flow of water through SuDS
the storage structure fills. protected openings. Open SuDS components such as swales,
components is slow as it is restricted to sites may need to meet minimal outflow flow protection is to use a stainless steel basket
‘greenfield rates’ of runoff through each flow rates. Flows can be controlled down to 0.5 filled with 80-150mm stone with the
control. There should always be an overflow – 2 l/s using small openings (15-20mm connecting pipe opening set within the stone
arrangement to deal with blockage or diameter) with shallow depth of storage. to prevent floating debris reaching the flow
exceedance of the design storm. control.
A stainless steel mesh basket filled with 80-
150mm aggregate forms an effective
protection for pipe openings. Note the pipe
opening has a mesh guard to stop stone
migrating through the pipe.

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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 Key points to be considered when designing pass over the outlet as water rises in the
Hollington School are very easy to unblock.
protected openings: SuDS component.

■ Protection to the opening should be of a ■ Openings in the protective screen should
reasonable surface area to allow for be smaller than the orifice opening size,
accumulation of litter and vegetation thus any residual silt passing through
across the surface of the protection. protective screen will pass through the
orifice opening.
■ Outlets in open structures should be
located on a slope to encourage debris to

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