Journalist, George Monbiot sparked criticism from farmers when he asserted that flooding in the UK was not just predictable but predicted, and concluded, “We need flood prevention as well as flood defence. This means woodland and functioning bogs on the hills. It means dead wood and gravel banks and other such obstructions in the upper reaches of the streams (beavers will do such work for nothing). It means pulling down embankments to reconnect rivers to their floodplains, flooding fields instead of towns. It means allowing rivers to meander and braid. It means creating buffer zones around their banks: places where trees, shrubs, reeds and long grass are allowed to grow, providing what engineers call hydraulic roughness.”
The Wildlife Trusts appear in agreement, “flooding needs to be addressed through a range of solutions, but working with nature rather than against it is the key to a more flood resilient future.”
However, in an article in The Guardian in January, Jeremy Biggs, Director of the Freshwater Habitats Trust, warned against seeing tree planting as a panacea and disputed the earlier assertion of Geoffrey Lean in the Independent, that working with nature had helped Pickering to avoid flooding over Christmas. Lean, however, has restated his argument on his blog and confirmed the evidence for his conclusions. The disagreement centres mainly around which sources are used to confirm rainfall in and around the Yorkshire town over the Christmas period, although Biggs’ warning, not to see tree planting as the only answer (other natural and conventional methods can also be complimentary), should not be disregarded.
April’s Budget 2016 announced additional spending on flood defences of over £700m by 2020-21. Emily Gosden, Energy Editor of the Telegraph responded, “households at risk of flooding face missing out on £700 million of new funding for defences, after ministers said they wanted to spend the cash on “more imaginative” projects such as planting trees and protecting big businesses and mobile phone networks.”
But what this article fails to make clear is that tree planting is a key component of natural flood defences. This is supported by a recent study for the Environment Agency, which found that trees can slow the rush of rainwater and save properties from flooding. However, the report also warns that natural flood prevention methods do not always work. A joint report between Confor (Confederation of Forest Industries) and Forest Research (Forestry Commission) has also concluded that planting productive woodland in specific areas of the UK could reduce the risk of flooding.
The Woodland Trust agree with the case for trees, “There is so much potential for trees and woods, alongside other natural approaches, to contribute to the way in which flood risk is managed in this country – especially for communities that are unlikely to ever see Government funding for traditional flood risk schemes.”
The UK is one of the least wooded countries in Europe - perhaps the floods will spur action to address this as we grow to better understand and appreciate the many ecosystem services (see p. 8 of Forest Matters May), such as water management, that trees and forests provide.
How do trees aid flood prevention?
- Removing and reducing water - Less rain reaches the soil and instead lands on leaves - rain that does reach the soil is absorbed by tree roots and released from leaf pores. Some water evaporates from the leaves.
- Speeding up soak away and slowing down run off - Water soaks away up to 60 times faster into woodland soils than grazed pasture.
- Slowing the flow - Trees, shrubs and woody debris at the side of streams and on flood plains act as a drag on flood waters, slowing the flow and enhancing flood storage.
- Protecting soils - Roots protect soil from erosion by binding it together, reducing the amount of soil that runs off into streams and rivers and the need for dredging.
This article was originally published in May Forest Matters, our bi-monthly e-magazine.
Sources - National Flood Forum, The Guardian, Wildlife Trusts, The Guardian, The Independent, Geoffrey Lean, The Telegraph, BBC, Forestry Commission, Woodland Trust, Tilhill Forestry