In the aftermath of the horrendous flooding in the North of England, the Environment Agency had to undertake the huge task of assessing the damage the flooding caused to defences. Repairs to culverts, embankments and flood walls had to be undertaken and debris from rivers – including trees, heavy boulders and even cars – had to be removed, not to mention repairs and replacements of structures such as footbridges and riverside buildings in parts of Yorkshire.
Big clear up
In Yorkshire, the entire year’s budget for maintaining flood defences was spent in just two months in the aftermath of December 2015’s floods – a figure of £7.5 million. This sum finances a huge programme of work that involves specialists such as civil engineers, modellers and hydrologists to plan the schedule of work and provide the specialist skills to carry it out.
Cumbria also experienced terrible flood conditions and a special group, the Cumbrian Floods Partnership, has been set up to take a wide-ranging look at what improvements to the region’s flood defences can be implemented. This would include examining the possibility of managing river flows.
Cumbria has already experienced a flood alleviation scheme following the severe floods of 2009. In Thacka Beck, on the edge of Penrith, £5.6 million was spent replacing culverts under the streets and a flood storage reservoir around the size of 30 Olympic size swimming pools was constructed upstream of the town to hold back flood waters.
What else could prevent or minimise flooding?
As above, water storage is a possible option. The Penrith example reduced flooding from a 20% chance to less than one, according to the Cumbria Wildlife Trust.
Opinions are divided regarding the effectiveness of dredging – indeed, some opponents argue it can actually make things worse by increasing the speed of flow and causing a situation where water flows overwhelm defences.
Restore rivers to natural courses
Several rivers have been straightened over the years to improve their navigability, but this has the effect of increasing flow with possible risks as described in dredging above. By restoring the natural bends to rivers, not only would flow reduce but it would effectively increase their length to help delay flow.
A key element to effective flood prevention. Again, the Penrith example shows how improving the under street culverts considerably lessened the flood risk, so drainage channels play an important part so existing ones need clearing and more need constructing in the obviously vulnerable areas.
Another problem is where water actually goes. Over time, more and more land has been covered with hard surfaces as towns and cities have expanded, so water simply runs off instead of being absorbed naturally into the soil.
As a result, drainage systems become overwhelmed with the sudden influx of heavy volumes of water. Since 2010 and the Flood Act, builders have been obliged to landscape developments so water from hard surfaces goes into open ground rather than being channelled directly into drainage systems.
Sustainable drainage schemes are becoming popular. These consist of permeable surfaces designed to drain water away, and the strategic placement of plants and trees to absorb water along with ponds and effective water courses all help built up areas manage rainfalls.
The implications for towns and cities
As discussed, sustainable drainage is becoming popular and is very important for towns and cities that are already battling with growth and the increase in ‘hard surfaces’. London is already undergoing significant upgrades to its water management capabilities with the impending construction of the twenty-plus mile long Thames Tideway Tunnel.
The increased flood risk
Flooding is a very real problem likely to get worse unless prevention measures keep up. The issue of increased development causing water runoff from hard surfaces is going to increase as development continues, and there’s also the issue of climate change. In general, it’s expected that rain will fall in shorter but harder bursts in the future which is exactly the wrong type for flood prevention.
Fraser Ruthven is the Marketing Associate for London Drainage Facilities, one of London’s leading drainage companies. London Drainage provides a wide range of drainage diagnostic and repair services in and around London.