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Forests and flooding

The RFS supports moves to increase understanding of how trees and woodlands can help alleviate flooding, either in small scale local schemes or as part of wider scale integrated flood defence measures.

 Flooding Hottopic 170216Wn Ctwilson
RFS working for greater understanding of how trees and woodlands can prevent flooding such as this in Cumbria - picture Ted Wilson

Our policies state that forestry provides many non-market ecosystem services such as climate change mitigation, flood control, habitat conservation and landscape enhancement. We believe these should be supported by public finances where it is not possible to establish a market incentive to deliver these services.

Ted Wilson, RFS Education Manager, sits on the Cumbria Flood Partnership which is a committee set up in December 2015 after flooding devastated parts of Cumbria. The committee is chaired by Forestry Minister Rory Stewart.

Ted has also given a talk summarising the benefits that trees and woodlands can have in flood alleviation at a national conference addressing the issue of flooding and community resilience. The event was organised by the Public Policy Exchange in London on 20 January 2016

There is already significant understanding of the ways that trees can influence the natural soil and water processes in British wooded catchments. This knowledge is supported by evidence from field research and modelling exercises which suggest woodland cover has a beneficial influence and the potential to reduce flood flows within catchments under <100 km2.

However, the evidence is not so clear for larger catchments or at a larger scale, due to the more restricted presence of woodland and its variable distribution. We believe:

  • Forestry has the potential to make a significant and positive impact as part of a flood management strategy for Britain, especially in smaller and medium sized catchments upstream from high risk communities.
  • The greatest benefits will come where woodland creation and woodland management is combined with other measures within catchments and across the landscape. 

How trees and woods influence flooding 

Trees can contribute to flood risk reduction in a number of ways:

  • Physiology - trees generally evaporate more water than grassy/shorter vegetation, which can reduce the volume of flood water draining from the land.
  • Soils - soils under woodland tend to be better structured than under other land uses, enabling more rainfall to enter and drain through the soil. This promotes the retention of water within soils and delays its passage to watercourses.
  • Resistance - trees, shrubs and deadwood along stream sides and within floodplains exert a greater drag on flood waters compared to grass, delaying flood flows.
  • Erosion - tree cover can decrease soil erosion and the delivery of sediment to watercourses, which helps reduce siltation and thereby increases the capacity of river channels to convey flood waters downstream.