DRAINAGE, PLUMBING & WATER SUPPLY
to be effective throughout the life of the
development. The NPPF changes are designed
to eliminate the potential for SuDS to be left
unadopted or unmaintained.
A poor or imprecise maintenance schedule can
lead to a reluctance by the adopting authority to
take on the SuDS. Incorporating manufactured
devices can help to demonstrate a robust
maintenance schedule for the life of the drainage.
Using a management train can also protect
sensitive features. For example, a hydrodynamic
separator can be deployed upstream of a sediment
forebay to prevent a pond or wetland from silting
up. So, the pond continues to operate at the
designed hydraulic capacity and maintenance
visits are much less frequent.
Engineering and environmental objectives are best
achieved when they work hand-in-hand. Fresh
ways of thinking about SuDS can enable delivery
of workable and cost-effective schemes that
benefit the environment.
All SuDS are engineered, even those that use
vegetation and operate above-ground, but lowimpact
does not have to mean low-tech. In future,
we will see the SuDS toolbox expanded further
as ‘smart’ internet-enabled technologies provide
opportunities to monitor performance of the
drainage system and provide alerts to indicate
when maintenance is necessary, or to control
the operation of rainwater harvesting systems.
New technological ideas and innovations, such
as cloud-connected sensors and instrumentation,
will add to the possibilities to deliver the best
possible drainage performance.
So, when it comes to specifying SuDS in a
development, it should no longer be a question of
And, where there is a will, there is almost
certainly a way to provide multifunctional benefits
to keep the planners happy.
8 | BUILDING PRODUCTS
The preference for multifunctional benefits aims
to encourage developers to use above-ground
features to double-up as public amenities like
playing fields or pocket parks, and provide
biodiversity for wildlife.
However, the first priority for engineers and
developers is not to pursue environmental
ideals: the drainage design must be achievable,
commercially-viable and capable of being built to
time and to budget.
The good news is that, with a pragmatic
attitude, it really can be possible to achieve
drainage that delivers the best of both worlds.
There will be very few cases where cost, landtake,
or ground conditions cannot be overcome,
some with good, old-fashioned, common-sense
engineering and well-informed specification.
The SuDS toolbox
SuDS use a sequence of devices and techniques
to mimic natural drainage processes as closely as
possible. Unfortunately, a tendency has grown up
to polarise approaches as either ‘hard’ or ‘soft’ to
distinguish between manufactured and vegetative
devices, and they can be perceived as alternatives
of varying merit effectively in competition with
The good news is, there is a growing acceptance
that SuDS offer a broad and expanding toolbox
that can be applied to achieve the best possible
performance, appropriate to the site conditions.
Furthermore, the drainage design may incorporate
a management train of several components.
Let’s consider a below-ground attenuation
system used for storing excess water to prevent
flooding. Choosing modular geocellular storage
with a honeycombed structure will deliver a
very high void rate, so that the space needed is
minimised, with consequent savings on materials
and excavation costs. With a high compressive
strength, the drainage is sufficiently load-bearing
to be used under roads or car parks, or underneath
amenity areas to maximise the development
potential. Choosing underground storage made
from recycled PVC reduces carbon footprint and
could also help developers to achieve a higher
In some cases, for example, in a heavily built-up
urban environment where flood storage is
needed below a shopping centre or tower
block, above-ground features could be simply
impossible. However, in other cases, using
below-ground attenuation can actually enable
a drainage design to incorporate above-ground
features like a pond or swale, while still achieving
the required hydraulic capacity and performance
in the space available.
Below-ground storage can be incorporated
underneath a dry pond or detention basin. This
may enable the amenity to be used for most of
the time; let’s say as a playing field, and designed
to flood only infrequently during severe storm
events. Alternatively, the underground tank can
provide an overflow ensuring that a pond or
wetland continues to operate efficiently and the
resident wildlife is protected. Both these solutions
are becoming increasingly common.
With all that rainwater collected, why not also
recycle it? Storage tanks can save rainwater for
re-use in irrigation schemes or can be integrated
into domestic or commercial rainwater harvesting
SuDS use a sequence of
devices and techniques
to mimic natural
systems. This can be especially advantageous in a
commercial or retail development where the water
could be used for toilet flushing, for example.
In some developments, treating stormwater is a
requirement because of the heavy pollutant load
in the runoff, or the sensitivity of the receiving
watercourse. By designing a management train
of drainage features, devices can be incorporated
to deal with the pollutants. Installing a treatment
device such as a hydrodynamic vortex separator is
very effective at removing the silts and sediments
that carry pollutants with them.
The NPPF revisions also formalise the need for
developers to demonstrate minimum operating
standards for SuDS and how they will continue
Below ground modular geocellular storage with a honeycombed structure will deliver a very high void rate, minimising the
space needed, with consequent savings on materials and excavation costs. With a high compressive strength, the drainage is
sufficiently load-bearing to be used under roads, car parks or amenity areas