Category Archives: Farming

Underwater UK: how to stop floods by planting trees

The Thames is higher than I’ve ever seen it – seagulls swim on the football fields, my route to work is underwater, and thousands of homes face the misery of flooding.

With this kind of extreme weather likely to occur more often in future, how can we adapt? It is human nature to look for big engineering solutions, and many are calling for more dredging, so that rivers can discharge faster, as well as for higher flood walls and sea defences. These options certainly have a part to play, but there could be far greater benefits from a more subtle ‘soft engineering’ approach – working with nature rather than against it.

A thoughtful article by George Monbiot tells the fascinating story of a small group of Welsh hill farmers who rebelled against the standard practice of chopping down trees, grubbing up hedges and digging drainage ditches – advocated in order to cram more sheep onto the land. In the words of the article, “It made no economic sense, the animals had nowhere to shelter, and the farmers were breaking their backs to wreck their own land.”

Instead, the Pontbren farmers planted shelter belts and woodlands using 120,000 native trees, and restored 16 miles of hedges. They created 12 new ponds, and protected natural wetlands instead of draining them. Although their main aim was to return to traditional farming methods and protect wildlife, the changes had another important effect. Heavy rain running down the hills simply disappeared when it reached the belts of trees. Research has now shown that the land planted with trees soaks up 67 times more water than traditional grazed pasture, and the amount of water running off the land is reduced by 78%. In fact, even though only 5% of the land was planted with trees, this was capable of reducing peak flows downstream by 29%.

In contrast, much of the engineering work traditionally carried out on UK rivers can actually make flooding worse. Dredging and straightening rivers, and building high banks that separate them from their flood plains, allows water to shoot straight down from the hills into the nearest town. A more intelligent approach is to allow rivers to form natural features such as meanders, braids and ox-bow lakes, which slow down the passage of the water and allow more of it to soak into the surrounding land, as well as trapping logs and boulders which can damage bridges and houses.

Dredging and building hard defences may be a necessary part of the solution in some cases, but it also causes further adverse impacts – damaging the ecosystem of the river and its floodplain, and using fuel and cement that result in further pollution and greenhouse gas emissions.

Softer approaches, in contrast, have multiple co-benefits. Planting trees stores carbon, thus helping to mitigate climate change and alleviate the risk of future extreme weather events. Trees stabilise the soil, thus reducing the amount of sediment swept into rivers, protecting the soil and improving water quality. By adding nutrients as leaves fall and rot, trees improve soil fertility. And they provide shade and shelter for livestock, and habitats for wildlife. Perhaps most remarkably, one study in Latin America showed that trees even make cows happier – it seems that they feel more secure with shrubs and trees to hide behind.

As well as protecting against flooding, trees can help to reduce the risk of droughts. By slowing down the passage of water to the sea and increasing absorption into the soil, trees allow water to be stored in the soil and vegetation, and more water is diverted to replenish underground aquifers.

In a future of more storms, floods and droughts as well as threats to biodiversity and food security, it makes sense to invest in solutions that tackle all these problems at once, rather than the false promise of dredging that can make matters worse in the long term.