The storms that have been battering the UK since the end of October 2013 are set to make the 2013-14 winter the wettest on record (compared to the winters of 2010/2011 and 2011/2012 which were amongst the driest on record). By mid-February, more than 5,000 homes and businesses had been flooded and many rivers in southern England had reached their highest ever recorded levels. Rainfall records were broken in December and again in January, with the first half of February also wetter than usual. Floods and storm surges have caused millions of pounds worth of damage, with the south west of England particularly severely hit. And yet should we be surprised? Although the last widespread floods were in 2007, there are floods every year somewhere in the UK.
There have been calls for the dredging of rivers, as though this is the magic bullet. Of course dredging a river does allow it to hold more water, but it is primarily a tool for improving navigation and dredging one area of a river just moves the problem more quickly downstream. Land management practices in upland areas means that surface water runs off rapidly into river tributaries, when we should be slowing it down, and holding it on the hills, allowing it to infiltrate back into the ground to recharge aquifers. To do this we need to incentivise farmers to plant trees on our uplands to slow down runoff. At the same time we need to allow rivers to flood onto their floodplains (in the areas where we haven’t built) and to pay farmers to store water on their lands during high river levels.1
There is still reluctance amongst engineers and water companies to move away from an infrastructure led approach to surface water management (e.g. the insistence on concrete attenuation tanks and pipes on new developments). By concentrating on this as the only solution and ignoring the bigger picture, our sewers are still overwhelmed during storm events and our aquifer levels drop rapidly if the periods between rainfall events are longer than usual. It is becoming more and more obvious that a sustainable water management strategy needs to be put into place that mitigates the extremes of floods and droughts rather than the piecemeal reaction of sandbags and hosepipe bans that happens now.
Water Sensitive Urban Design (WSUD)
Just as we need to slow down water movement in our uplands we need to do the same within our built environment. Our stormwater sewers are designed to remove rainwater as quickly as possible, whereas what we should be doing is to design that water into our urban landscapes. We need to embrace the WSUD concept for our towns and cities, an integrated approach that considers all elements of the water cycle and their interconnections. This includes managing:
- Water demand and supply
- Wastewater and pollution
- Rainfall and runoff
- Watercourses and water resources
- Flooding and water pathways
WSUD highlights the fact that surface water management is linked to reduction in flooding damage and more resilience during times of little rainfall.2
Sustainable Drainage Systems (SuDS)
SuDS are one part of WSUD and are designed to attenuate, treat and dispose of rainwater where it falls (ideally by infiltrating it back into the ground to recharge ground waters) rather than moving it rapidly away from the site into underground drains where it causes downstream problems, whether that is adding to rising river levels or causing combined sewers to overflow and raw sewage spills into rivers or the sea. In a SuDS system if stormwater needs to be moved it is transported above ground in swales to a series of SuDS basins and ponds. By keeping water above ground on a site in this way, biodiversity is improved as insects, birds and animals that are not found in the absence of water will arrive. In the summer these bodies of water provide localised cooling and (somewhat controversially) places for children to play. There are some excellent examples of SuDS designed into new developments (The Triangle, Swindon and the Upton urban extension in Northampton to name just two).
Of course, we need to retrofit SuDS too. This is less straightforward due to lack of space but can be done. Well-designed green roofs and green walls (classified as source control within a SuDS design) cool the urban environment, retain stormwater, and provide biodiversity. We can decouple rainwater downpipes from sewers and run them into tree pits, or rain gardens.3 We need to replace the current situation of impermeable roadway and paved front gardens by retrofitting rain gardens into our streets in place of road gulleys; they will provide additional runoff treatment and storage, reduce pollution and downstream flooding and improve urban ecology. There are many excellent examples in the US, with a few now in the UK.
The one silver lining from all these clouds? Well, this “right kind of rain” means that aquifer levels across the south and south east of England are at their highest for many years (most being classified notably high or exceptionally high) and reservoirs across most of the UK are near to 100% full. It is unlikely there will be any water shortages this summer. But what we need is a realisation that it’s important to keep our water sources as full as possible by sensible use of water so that if we have a dry winter next year it won’t put pressure on our water supplies. And at the same time we need to introduce sustainable stormwater solutions to mitigate flooding if case we have another wet winter.
Published in Green Building Magazine, Spring 2014
Notes
- George Monbiot has written an excellent article on how farmers are rewarded under the Common Agricultural policy for clearing their fields of all vegetation.www.monbiot.com/2014/01/13/drowning-in-money/
- This is a good introduction to WSUD from CIRIA.www.ciria.org/service/Home/AM/ContentManagerNet/ContentDisplay.aspx?Section=Home&NoTemplate=1&ContentID=25286
- There is a perfect example of this where my niece lives. The building at the rear of her garden runs all its rainwater into a small flower bed where there is a bay tree growing, and all the water disappears. In the next street my lawn takes run-off from nowhere yet has standing water on it.