Is infrastructure the answer to flood defenses?
The winter of 2015 saw northern parts of Britain battered by storms that unleashed record-breaking rainfall and brought devastating flooding to towns and countryside alike.
The Cumbrian fells were the worst affected. Over 340mm of rain fell in 24 hours on 5 December, the highest amount of documented in UK rainfall records.
The severe flooding that followed was exacerbated by the previous month’s heavy rainfall in the same region, which ensured already very wet ground conditions.
However, with designated floodplains, river catchment areas and flood defense schemes, why has so much devastation been caused to tens of thousands of UK homes?
In the wake of Storm Frank, the BBC reported on what we as a nation have done to contribute to the havoc caused.
The first and potentially most important topic is the development of properties on flood plains. Since 2011, housing in areas where flooding is likely has grown at a rate of 1.2 per cent per annum, amounting to a total of four million residential properties at risk of flooding in England.
The BBC further reported on the ongoing argument over river dredging (or lack thereof) and the straightening of river meanders that negates the natural effect of slowing water flow.
A particularly hot topic – one which is causing dispute amongst the scientific community and parliamentary figures – is the destruction of upland habitats for agricultural gain. Trees, bushes and plants act as a natural flood defense in times of excessive rainfall as their roots loosen the surrounding soil, thus allowing water to drain away more easily.
A hillside habitat comprising thick, unspoiled vegetation releases water more slowly than a bare and compacted hillside. Removal of such habitats, which have often been cleared for or by animal grazing, becomes particularly problematic if it is upstream of a main river. In its natural state the habitat would slow the movement of water, reducing the risk of flooding further down the line.
Whilst some, including the former environment minister Lord Rooker, argue that the re-wilding of these areas by planting trees and letting dense vegetation re-grow could help to slow the flow of rivers and therefore reduce the risk of flooding, others in the scientific community contest the idea.
Professor Alan Jenkins, deputy director of the Centre for Ecology and Hydrology, told the BBC that “there is no compelling scientific evidence” that rewilding works. He went on to say that we “should be looking at the concept of integrated catchment management” and a mix of solutions, but “with these huge rainfall events one has to look more towards concrete infrastructure.”
The intensity of rainfall and the size of a catchment are indeed important considerations when determining the best flood defense solutions.
But it is also important not to confuse a lack of evidence with the absence of adequate data. As such, coordinated catchment scale investigations to better understand relationships between land management and river flow, in both floods and droughts, need to be better promoted and funded by the scientific community and regulatory authorities.
Faced with an ever-increasing population and major housing boom, the increased use of flood plain land will inevitably become an ever bigger problem in the future. Flood defense and river catchment schemes will need to adapt and adjust to allow for appropriate mitigation, but so too will planning and agricultural policies. Farmers are already reluctant to allow the re-growth of vegetation on their upland plots as EU rules state “land covered in permanent ineligible features” such as ponds, dense scrub and woodland can be “disqualified from farm subsidies.”
With further robustly coordinated scientific investigation, however, we may find that this non-concrete, naturally derived environment is an essential part of the solution everyone is looking for.
APEM Inc is a global environmental consultancy providing independent advice and guidance to support government and environmental regulatory guidelines