URBAN DRAINAGE
Time for action on flooding
Should rainwater harvesting be compulsory if flood risks are high? With global warming changing weather patterns
– and causing increased rainfall – it’s a no-brainer, says Mike Norton, technical director for Kingspan Water
T
here is very little argument with the
assertion that flood risks continue to rise
for millions of properties. Building is
extending on to marginal areas around river
valleys where more hard surface areas (roofed
areas, paths and roads) cause higher volumes of
rainwater to flow into the watercourses.
Allied to this, global warming is changing
weather patterns, causing increased rainfall and
raised sea levels. But are we, as an industry,
doing all we can to minimise those risks? Are we
considering all the questions that climate change
is posing us, particularly around water usage and
effective drainage? Do we need to look at more
united, holistic solutions than we are currently for
new build developments?
Suds and rainwater harvesting
As building has expanded on to more marginal
areas, the need to incorporate Sustainable Urban
Drainage Systems (SUDS) into a development to
achieve planning permission has increased.
Planning policy statement, PPS25 now
requires planning authorities to undertake
strategic flood risk assessments as part of their
development planning – a welcome step
forward. An interesting recent development from Rainwater harvesting only has an impact when every house on an estate has a system
Kingspan Water’s point of view has been the
steady rise in the enquiries for rainwater chances of flooding. A typical tank for a three- The future
harvesting equipment, not so much to reduce person home is around 2.8m3; if the size of the I would like to work with the regulators and the
reliance on treated mains water, but to attenuate tank is increased to create freeboard (unused water companies to develop a unified, long-term
water on site, as part of SUDS schemes. capacity) of, say, 6m3, fed by the downpipe plan, linking together water usage and flood
Could it be that rainwater harvesting will from the roof guttering, the amount of surface management. We need fresh, joined up thinking,
provide the answer to two pressing issues: water run off from that property can be joined up planning, and joined up action. Existing
flooding, and reducing our huge (non- significantly reduced. Built-in vermin traps and and emerging techniques can save water and
sustainable) per capita water usage? filters will prevent the stored tank water contribute to managing flood risks for new build
becoming contaminated. properties. If we must build on flood plains then
BS8515 and attenuation But rainwater harvesting doesn’t have much building regulations and planning should require
Rainwater recycling systems can act as an impact if it is installed in just a few houses on an that SUDS, rainwater harvesting and greywater
effective form of attenuation scheme. By estate built on a flood plain: every house in that recycling techniques are incorporated into
capturing rainwater from the roof via the development will need an individual system, or planning requirements. Not just on a few
guttering, and storing it on site, a rainwater alternatively, multi-user tanks can be used to properties, but all those within a development.
harvesting system can reduce surface run off service several properties. These should link in with the Code for
during heavy rainfall. Furthermore, by passing the Sustainable Homes and BREEAM assessments.
recycled water indirectly via re-use applications “If we must build on flood And the next stage – engaging the customer in
(such as washing machines) to the foul system
plains, building regulations
this process – can only be achieved by
rather than the storm drains, it can reduce the education and effective communication, with an
flood risk associated with overflowing surface and planning should require emphasis on how it can both save their money
water drains.
that SUDS and rainwater
and their environment.
BS8515, the recently published rainwater
harvesting British Standard, describes how it is harvesting are in the For more information, visit
possible to use an oversized rainwater harvesting
planning requirements”
www.kingspanwater.com/domestic_rainwater
tank for flood water attenuation, to lessen the _harvesting.htm, or call 01296 633139
September 2009 Water & Wastewater Treatment 37