SuDS in London - a guide

It is helpful to engage the local community
in SuDS development from the outset,
particularly during retrofits. Local
knowledge can help shape the design,
while allowing people to appreciate what
the SuDS components do. This also
offers potential for the local community
to take ownership, by helping to
manage and maintain SuDS as part of
their neighbourhood.
In London, operational constraints on
management and maintenance vary
between the busiest streets (managed by
TfL) and the 95% that are maintained by the
boroughs. Not all SuDS features will meet
the criteria of Local Highway Authorities to
adopt maintenance responsibilities, which
needs to include long-term costs.
Maintenance requirements can be
simplified by using well thought-out
designs. In a rain garden, for example, soil
specification and plant species selection
should meet the specific demands of the
SuDS, site characteristics and geotechnical
conditions. Maintenance requirements will
vary depending on the time of year.
For a detailed guide to SuDS maintenance,
refer to CIRIA C753 The SuDS Manual,
Chapter 32 (Operation and maintenance).
Component specific maintenance
Green walls: most versions require
irrigation. This must be maintained
rigorously. Failure of an irrigation system
will result in the death of the green wall,
reducing the attractiveness of the area
and increasing replanting costs. Lowmaintenance
green walls planted directly
into the ground can be just as effective.
Sweeping: detritus and sediment from
pedestrian and traffic use can
accumulate quickly. This can lead to a
build-up of sediments to clog systems,
such as joints for permeable pavements.
Sweeping regimes need to support the
SuDS components.
Geotextiles: Many SUDS components
incorporate specific geotextiles to separate
materials to separate materials to some
extent. These tend to blind/clog over
time, reducing infiltration/percolation
rates. There is little long-term test data
from the UK for public/urban situations;
designers should be aware of the longterm
maintenance risks that geotextiles
may pose.
Compacting: for landscaped SuDS to be
effective, they must be protected from
both vehicle and pedestrian overrun. As a
minimum, structural edges are generally
necessary alongside soft SuDS that interface
with pavements. Where edges adjoin
carriageways or parking bays, high/double
kerbs and or >450mm wide paved aprons
should be provided for access to parked
cars without walking in the soft feature.
Salting: where soft SuDS receive runoff
containing de-icing salts, good subdrainage
is essential to prevent salt
accumulation from harming plants. Subdrainage
allows most salts to drain through
during the winter months when plants
are dormant. Salt tolerant plants should
still be selected and the ground must not
become compacted.
Geocellular drainage: while useful for
creating below-ground surface water
reservoirs or rooting zones for street
trees, geocells are complex and potentially
dangerous. There are various design,
certification, supervision, testing and
maintenance issues that require emphasis
if they are to be used safely
and appropriately.
Highway structures and geo-technical
structures must be designed, checked and
supervised under relevant eurocodes. Most
Highway Authorities will wish to manage
this via their Geotechnical and Highways
Structures technical approvals process.
64 3 SuDS components