Hillingdon SuDS Design & Evaluation Guide

9.5.4.6 Accounting for Climate Change
Future predictions suggest that more
extreme rainfall events will occur with greater
regularity.
To make allowance for this within SuDS
calculations the current industry approach is
to factor up rainfall intensities for Climate
Change Allowance.
Flows in excess of the storage capacity of
SuDS components should be directed along
modified flow routes. When the sensitivity
test indicates potential for flows across the
surface, the designer should evaluate likely
flood volumes, depths and velocities to
ensure there is no significant risk to
development or people. Generally, depths
less than 0.25m will not present a risk, but
steep parts of sites may generate high
velocities which may be unsuitable.
Table 2 from the DEFRA Guidance on climate
change is replicated below with additional
advisory notes on how the upper end and
central projections should be applied:
Detailed Design
Design life
2015-2039
Design life
2040-2069
Design life
2070-2115
Upper End Projection
Carry out sensitivity test. Where
unacceptable flood risk to site or
adjacent sites is identified Upper
End Projection allowances must be
incorporated into design (i.e
significant flood depths on site
during this event could present a
danger to people)
10% 20% 40%
82
Central Projection
These represent the Minimum
climate change allowances that can
be adopted where sensitivity tests
demonstrate that no unacceptable
flood risks are introduced by not
allowing for Upper End Projections.
5% 10% 20%
Design Note:
Climate Change should be considered for both attenuation storage and conveyance
calculations.
London Borough of Hillingdon SuDS D & E Guide
© 2018 McCloy Consulting & Robert Bray Associates