Alex Stephenson talks about rain, droughts and how we cope with both.
As half the UK was officially declared in drought -what happened? The rains came. We seem to be being beset by drought and deluge in equal measure. It’s clear that drought does not mean an end to surface water flooding.
Much progress has been made with Sustainable Drainage Systems (SuDS) in the UK in recent years, but there is no room for complacency. Flooding during the past week has no doubt been exacerbated by a ground hardened by drought which will prevent surface water infiltrating through the soil.
Climate experts are predicting that global warming will make our weather patterns more prone to extremes of drought and intense rainfall in future. That means more strain on our stormwater drainage infrastructure, making the need to control peak flows greater than ever.
The changing weather gives us very short memories, but it wasn’t that long ago when our TV screens were full of scenes of flooding. Remember the Summer of 2007? The floods then claimed 14 lives, caused £3.2 billion worth of damage, and affected 48,000 homes and 6,000 businesses. Two thirds of those floods were attributed to surface water.
The floods were an impetus for big changes for the building industry in terms of designing and installing drainage on new developments. The Flood and Water Management Act (FWMA) 2010 will make Sustainable Drainage Schemes compulsory for new developments where they serve more than one property.
New Local Authority SuDS Approving Bodies (SABs) are due to begin approving schemes according to new National SuDS Standards from October this year. The Standards, together with a set of more detailed guidelines still to be published, set out expectations for controlling both the flow, quantity and quality of stormwater runoff.
The National SuDS standards set out the expectations according to important SuDS principles – including dealing with water as close as possible to where it falls, managing water on the surface and providing a public amenity value where possible.
The conditions for controlling the flow and quantity of surface water discharge from the development with the aim of returning the site to greenfield conditions are laid out.
Critically, for the first time there are now also regulations regarding the control of the quality of surface water and a requirement for treatment to be provided to deal with silts, sediments and pollutants in runoff. The extent of the treatment required will depend on the site conditions.
There has been a tendency to view SuDS schemes as ‘green’ or natural features, but in fact a full ‘toolbox’ of techniques, both engineered and natural is available. There are a wide range of SuDS that can be sold by the builders’ merchant to meet SuDS standards, for example Vortex Flow Controls , stormwater storage and treatment products such as those provided by Hydro International.
Alex Stephenson is director of Hydro International UK Stormwater Division and chair of the British Water SuDS Focus Group. www. Engineering Nature’s Way.co.uk – a means of sharing knowledge and experience about SuDS.