Page 85 - Hillingdon SuDS DESIGN & EVALUATION

9.5.4.3 Making allowances for interception losses

As a rule of thumb, where the total wetted
area of SuDS components equates to at least
25% of the development area (all buildings
and hard surfaces) then it is acceptable to Detailed Design
make an allowance for interception losses.
For more detailed analysis methods
This loss can be applied within storage
calculations by reducing the rainfall depths see SuDS Manual Section 24.8
by 5mm.

9.5.4.4 Defining infiltration rates

The specified infiltration test methodology For example, tests should not be undertaken
should be representative of the proposed 1.5m below ground level when shallow
design. infiltration is proposed from permeable
pavement, rain gardens or basins which will
The depth of water and depth of test trench
be located close to ground surface.
below ground level should seek to replicate
the attributes of the proposed infiltration
system.

Bromsgrove Civic Centre re-development. 80
Permeable block and slab paving with a central grass detention basin
provide a fully integrated infiltrating SuDS scheme.

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