Hillingdon SuDS Design & Evaluation Guide
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9.6.6 The importance of protected openings<br />
There are no minimum thresholds for<br />
<strong>SuDS</strong> components such as permeable<br />
attenuated flow rates in <strong>SuDS</strong> design.<br />
pavements, bioretention or filter drains are<br />
Previously the drainage industry has applied pre-filtered, and assuming collection through<br />
a minimum flow rate of 5 l/s but this does not perforated pipes or similar, the flow control<br />
take into account the need in <strong>SuDS</strong> for low opening requires little additional protection.<br />
flow rate controls and the design of<br />
Open <strong>SuDS</strong> components such as swales,<br />
protected openings.<br />
ponds and basins, require additional<br />
Small sites and sub-catchments of larger protection. One way to provide this<br />
sites may need to meet minimal outflow flow protection is to use a stainless steel basket<br />
rates. Flows can be controlled down to 0.5 filled with 80-150mm stone with the<br />
– 2 l/s using small openings (15-20mm<br />
connecting pipe opening set within the stone<br />
diameter) with shallow depth of storage. to prevent floating debris reaching the flow<br />
control.<br />
Detailed <strong>Design</strong><br />
A stainless steel mesh basket filled with 80-<br />
150mm aggregate forms an effective<br />
protection for pipe openings. Note the pipe<br />
opening has a mesh guard to stop stone<br />
migrating through the pipe.<br />
98<br />
Key points to be considered when designing<br />
protected openings:<br />
pass over the outlet as water rises in the<br />
<strong>SuDS</strong> component.<br />
■■<br />
Protection to the opening should be of a<br />
■■<br />
Openings in the protective screen should<br />
reasonable surface area to allow for<br />
be smaller than the orifice opening size,<br />
accumulation of litter and vegetation<br />
thus any residual silt passing through<br />
across the surface of the protection.<br />
protective screen will pass through the<br />
■■<br />
Outlets in open structures should be<br />
orifice opening.<br />
located on a slope to encourage debris to<br />
London Borough of <strong>Hillingdon</strong> <strong>SuDS</strong> D & E <strong>Guide</strong><br />
© 2018 McCloy Consulting & Robert Bray Associates