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Geoff Darch* on climate change and how we can prepare for future flooding.

England and Wales are still mopping up from the latest, and one of the most severe flood episodes of the past century.  It is now seven years since the autumn floods of 2000, when The Guardian headline warned 'Climate change: it's with us now'. Once again, the newspaper has postulated that global warming is to blame.  Scientists have been cautious in attributing the unusual rainfall to anything other than natural variability, but such events are providing early insight into future impacts.

UK summers are projected by most climate models to be drier on average, but the atmosphere will be capable of delivering more intense storms if moisture is available.  In winter rainfall is projected to increase significantly, compounded by increased storm intensity.  This is likely to lead to more severe flooding, occurring later in the season once higher autumn soil moisture deficits have been replenished.

The events this summer have highlighted the knock-on effects that flooding has on infrastructure.
The Mythe Water Treatment Works supplies water to 140,000 homes in Gloucestershire.  In July it was inundated by water from the Rivers Severn and Avon and supply of potable water was lost for 17 days.  Homes in the area also suffered power cuts and the Environment Agency and the military protected successfully a key electrical sub-station supplying power to 600,000 homes.  Elsewhere, rail travel was disrupted severely by flooding. In late June water reached platform level at Glasgow's Queen Street Station.  In Ludlow, a road bridge was destroyed, severing a gas main and causing several explosions as street lights fell into the water, and leading to the collapse of a house.

Minimising such impacts relies on locating key infrastructure in areas at low risk of flooding. This requires robust planning and an accurate understanding of flood risk.  Inevitably, much of our infrastructure is situated in areas at high risk of flooding.  Over time renewal will ensure some is relocated, but some will remain at risk.  Recognizing and managing this risk is the new challenge.

For buildings, flood resistance (dry-proofing) and flood resilience (wet-proofing) are strategies for reducing the damage caused by flooding. Recent events have highlighted the importance of ensuring water and electricity supplies are not disrupted by flooding. Away from rivers there is a need to improve the design of urban areas to manage better surface run-off from exceptional rainfall events.

Flood defences can fail or be exceeded, whilst pluvial flooding can occur in areas behind defences with pumped/tide locked drainage.  In these cases flood resilience means ensuring flood resistance measures are incorporated into the design of new buildings.  Improved design of the urban environment allows flood waters, or the temporary exceedence of drainage capacity, to be managed by controlled flooding, avoiding property.

For key infrastructure retrospective flood-proofing may be justified. However, for existing properties, financial and structural constraints may mean that reducing damage through resilience is more practical than avoiding damage through means of resistance.  The effectiveness of these measures is tempered by the variability of individual properties and the need for sufficient, accurate, flood warnings for the timely installation of property-scale temporary flood defences. 

Climate change predictions indicate that the hydrological cycle will intensify and become more variable in the UK, creating the conditions for greater droughts and floods.  We can adapt to these changes and although this will require an increase in resources, proactive adaptation will save money, livelihoods and lives in the long-term.

*Geoff Darch is Senior Consultant at Atkins and was the winner of this year's River and Coastal Group Young Members' Competition. Richard Breakspear, Assistant Consultant at Entec UK Ltd; Paul Crossley, Hydraulic Modeller/Project Manager at  Halcrow; and Jo Miejluk, Operations Delivery Technical Support Team Member One at the  Environment Agency, contributed to the article.  The contributors are young members and organizers of the River and Coastal Group Young Members' weekend.