Hillingdon SuDS Design & Evaluation Guide

Local SuDS requirements
21
6.0
Landscape Character
Local SuDS requirements for
Hillingdon
Hillingdon is London’s second largest
borough, by area, covering 42 sq. miles (109
sq. kilometres) with a population of 273,936
according to the 2011 Census.
The borough has a distinctive character with
its combination of suburban streets and
shopping centre’s, industrial land, major office
developments and large areas of open land,
historic woodland and inland waterways
including 4,960 hectares of Green Belt.
The River Colne borders the borough to the
west and the Yeading Brooks which are more
fast flowing becoming the River Crane to the
east. The River Pinn is a particularly fast
responding watercourse. There are a large
number of ordinary watercourse crisscrossing
the area.
Despite remaining one of London’s greenest
boroughs, Hillingdon has a pivotal role in the
economic success of the capital being the
home of Heathrow Airport, as well as
managing the environmental impacts of the
area such as air quality and noise that
appropriate planting within SuDS schemes
can and should help address.
The area is served by separate surface water
and foul sewers however the information on
the condition, location and appropriate sizing
of the sewerage provision is poor and may
need to be investigated.
Landscape geology
The dominant solid geology within Hillingdon
is the London Clay Formation. To the north of
the Borough, within the vicinity of Ruislip and
Northwood, outcrops of the Lambeth group
(formerly known as the Woolwich and
Reading beds) occur within river valleys.
Along the western boundary of London and
Hillingdon you find the beginning of some
areas of Chalk are located within the vicinity
of the River Colne, which identify the edge of
the London basin.
However the depth at which London Clay
band can be found varies considerably. In
the southern area of Hillingdon there are drift
deposits overlying the solid geology. These
consist of pockets of Langley Silt (sandy clay
and silt ’brick earth‘) overlying the River
Terraced Deposits (mainly gravels). To the
north of the A40 drift deposits are limited to
pockets of Glacial Sand and Gravel, Along the
line of river channels, alluvial deposits are
located and in some areas the underlying
solid formation has been exposed.
Although a predominant clay geology results
in much lower infiltration rate, this does not
prevent the use of SuDs within a
development, however it reinforces the need
for SuDs to be integrated within design at an
early stage and the appropriate tests
undertaken to understand the site specific
infiltration rates.
London Borough of Hillingdon SuDS D & E Guide
© 2018 McCloy Consulting & Robert Bray Associates