There are two principal reasons for freshwater flooding. The first, obviously, is heavy rainfall. Second, perhaps less obviously, is the way in which land and rivers respond to this rainfall. We believe that the restoration of some of Britain’s missing ecosystems could play a major role in the prevention and mitigation of the kind of floods now blighting Cumbria and parts of Scotland.
If the uplands, where most of our rain falls, are kept bare, rainwater flashes off them. Tree cover greatly increases the rate at which it is absorbed by the soil. This means that instead of rushing off the hills and into the nearest river, it is released more slowly, and the flood peaks are likely to be lower.
Studies of the Pontbren Project in mid-Wales, where shelter belts of trees were planted across sheep pastures, discovered that water infiltrates into the soil under the trees at 67 times the rate at which it infiltrates into the soil under the pasture. The reason appears to be that the tree roots create channels down which the water can flow, allowing the soil to function as a sponge. By contrast, heavy grazing, as a result of the removal of deep vegetation and compaction of the soil by the feet of livestock, ensures that the land is much less permeable.
One research paper arising from these studies estimates that reforesting just 5% of the land reduces flood peaks by around 29%, while full reforestation would reduce them by some 50%.
The management of rivers can also have a major impact on the speed and severity of flooding. During the last devastating floods in Cumbria, in 2009, river managers noted a massive difference in the response of the St John’s Beck in Thirlmere, which had been canalised and straightened, and the River Liza in Ennerdale, that had been allowed to rewild: to braid and meander naturally, to form islands and accumulate banks of stone and woody debris.
The St John’s Beck suffered a massive pulse of floodwater, roaring down the river valley. The River Liza was still clear and fordable the day after the downpour had occurred. The obstructions in the river slowed and filtered the water. Dredging, canalisation and embankment speed the flow of water downstream, while ecological restoration turns out to be as good for people as it is for wildlife.
One cost-free solution to flooding is allowing beavers to return to our rivers. The dams they build and woody debris they pull into the water can have a powerful influence in slowing the flow. Following the reintroduction of beavers to Belgium, one study found a significant lowering of peak flow downstream of dams, and an increase in the interval between major floods.
Claims are often made that soils are saturated and incapable of taking more water. But in many cases the problem appears to be not saturation, but compaction as a result of careless land management – too many livestock or the use of heavy machinery in wet weather, for example. The photograph heading up this article illustrates this. One field is covered in surface water, creating the impression that it is saturated, while its neighbours are not. The problem in this case is clearly compaction, rather than saturation.
The Westminster government is spending £2.3 billion in flood defence over the course of this parliament. Much of this spending takes the form of hard infrastructure, such as channels, walls and barrages. We believe that in some places flooding can be prevented much more cheaply and with less disruption, through better management of land and rivers.
A major study by Forest Research, an arm of the Forestry Commission, found that tree planting, both in the hills and along watercourses, could significantly reduce flooding, soil erosion and water pollution. It concluded:
“There is a need to increase incentives for woodland planting by making these better reflect the full range of water and other benefits.”
In its 2015 progress report to Parliament, the Committee on Climate Change noted that:
“Some forms of farming practices are exacerbating flood risk. Although the area of agricultural land protected by flood defences is increasing, some forms of farming practices are potentially exacerbating flood risk, increasing the need for dredging and watercourse management downstream.”
“Land management practices can play a role in reducing the likelihood of flooding through their effect on the water cycle. Approaches include upland water storage, peatland restoration, the management of run-off from cropped land, and riparian tree planting.”
In reaction to this weekend’s floods in Cumbria, a spokeswoman for the Environment Agency said:
“Climate change is happening now and we must build resilience and adapt to the changes that are unavoidable.”
We believe that rewilding has a crucial role to play in Britain’s efforts to adapt to climate change. The restoration of river catchments and the rivers themselves could help save homes and lives, as well as providing magnificent and enthralling habitats for wildlife and natural wonders for people to enjoy.