Tree planting can reduce flood risk, finds study

Planting more trees can help prevent flooding in towns by 20 per cent - when used alongside other natural flood defences, according to a new study.

 

 
11th March 2016
Photo credit: iStock

Researchers from the Universities of Southampton and Birmingham found that the strategic planting of trees was effective in flood management.

The study, funded by the Environment Agency (EA) and published in the journal Earth Surfaces Processes and Landforms, also found that natural flood management helps to improve water quality, preventing erosion and storing carbon.

Woodland creation was found to contribute to managing flood risk to communities downstream alongside other flood risk management measures.

Ben Lukey, flood risk manager at the Environment Agency, said: The Environment Agency is already working with partners to use natural flood management measures - such as tree planting - in our flood defence work and have found that they can make an effective contribution when used alongside other, more traditional, flood defences.

“Natural flood management can deliver more benefits than just reducing flood risk – such as improving water quality, preventing erosion and in some cases storing carbon, but it is not suitable in all locations, so we only use it where there are clear flood risk benefits.”

However, the EA also warned that the findings were not a “silver bullet”, as natural methods would not be suitable for all locations, and that more tree cover was unlikely to have prevented larger scale floods that took place in the UK at the end of 2015. 

As part of the study, researchers analysed a whole river catchment in the New Forest over an area of 100 square kilometres, upstream of the town of to understand how tree planting, river restoration and logjams might affect the ‘peak height’ of a flood in a downstream urban location.

Using a digital terrain model of the landscape and a hydrological model simulation the scientists found that planting trees on the floodplain and increasing the number of logjams, across 10-15 per cent of the total river length could reduce the peak height of a potential flood in the town by 6 per cent once the trees had grown for 25 years.

Dr Simon Dixon, from the University of Birmingham’s Institute of Forest Research (BIFoR), lead author of the study, said: ‘"As our research shows, targeted tree planting and restoration can contribute to reducing flood risk.  We believe that tree planting can make a big contribution to reducing flood risk, and should be part of a wider flood risk management approach, including conventional flood defences.  Tree planting would represent an extra element that helps to slow down the arrival of rain water to vulnerable locations."

Natural flood schemes, such as Belford in Northumberland and Pickering in North Yorkshire, show that natural flood management is most effective in smaller river catchments with smaller floods. 

Additionally, they discovered that for more extensive floodplain forest and river restoration, trees resulted in a reduction in flood peak height of up to 20 per cent.  The researchers have predicted that as the trees age and the forests become more mature there are larger reductions in flood peak height. 

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