Page 108 - Hillingdon SuDS DESIGN & EVALUATION

Detailed Design 9.7.2 What water quality design should demonstrate

Effective treatment is provided through
For effective treatment of runoff SuDS
provision of source controls and a
should be designed to:
management train.
■
reduce the frequency of runoff by
incorporating interception losses
■
maximise travel time along the
management train

■ ■ trap a range of contaminates
minimise impacts from accidental spillage.

9.7.3 Hazard and mitigation risk assessment

Prior to 2015, SuDS water quality design ■ On low to medium risk sites where
adopted the ‘treatment train’ approach. This discharge is to surface water – apply
inferred that treatment was provided by ‘Hazard and Mitigation’ Indices approach

allowing run-off to pass through a series of to identify the number of SuDS
suitable SuDS components prior to components required (CIRIA SuDS Manual
103 discharge. This method remains robust if Section 26.7.1).
applied correctly, but has been refined by the
■ For medium risk sites where discharge is
2015 CIRIA SuDS Manual which adopts a
via infiltration, undertake risk screening to
‘Source-Pathway-Receptor’ approach, with
establish whether infiltration will be
the extent of analysis required associated
permitted and apply the Indices approach
with the level of risk.
to identify the number of SuDS
The varying levels of assessment are components required prior to infiltration
identified as follows: (CIRIA SuDS Manual Section 26.7.2).

■ For High Risk sites, there is likely to be a
requirement for a discharge licence. The
Environment Agency will outline level of
assessment required and discharge water
quality parameter compliance limits.

Design Note:

Table 26.15 of the 2015 SuDS Manual denotes that conventional gully and pipe drainage
provide zero treatment.

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