Page 87 - Hillingdon SuDS DESIGN & EVALUATION

9.5.4.6 Accounting for Climate Change

Future predictions suggest that more surface, the designer should evaluate likely
extreme rainfall events will occur with greater flood volumes, depths and velocities to
regularity. ensure there is no significant risk to
development or people. Generally, depths Detailed Design
To make allowance for this within SuDS less than 0.25m will not present a risk, but
calculations the current industry approach is steep parts of sites may generate high
to factor up rainfall intensities for Climate velocities which may be unsuitable.
Change Allowance.
Table 2 from the DEFRA Guidance on climate
Flows in excess of the storage capacity of
change is replicated below with additional
SuDS components should be directed along advisory notes on how the upper end and
modified flow routes. When the sensitivity
central projections should be applied:
test indicates potential for flows across the

Design life Design life Design life
2015-2039 2040-2069 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 10% 20% 40% 82
incorporated into design (i.e
significant flood depths on site
during this event could present a
danger to people)

Central Projection

These represent the Minimum
climate change allowances that can
be adopted where sensitivity tests 5% 10% 20%
demonstrate that no unacceptable
flood risks are introduced by not
allowing for Upper End Projections.

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