A new modelling study, commissioned by The Rivers Trust, shows that extensive and appropriately located Natural Flood Management (NFM) could make a significant difference to flood flows which would compliment traditional engineering measures.
The Rivers Trust has been working with JBA Consulting, Lancaster University and United Utilities to investigate how extensive NFM in large recently flooded catchments could have reduced flood flows in extreme storms, such as Storm Desmond in December 2015, which caused an estimated £500million of damage.
Working in four river catchments, a series of maps have been developed which quantify the potential flood-reducing benefits of NFM. A critical part of the study was to quantify the uncertainty in the predictions so that we understand how much confidence can be placed in NFM. These maps and the associated uncertainty analyses are already being used to inform the planned delivery and evaluation of £3M of NFM investment by rivers trusts and other organisations.
Image - Modelled flows in the Eden catchment without (blue) and with (pink) NFM. Five scenarios were modelled so that catchment managers could understand the uncertainty in these predictions. This graph shows the results from the most optimistic scenario.
David Johnson from The Rivers Trust, said: “Catchment management of flood risk needs a long term plan which includes both traditional engineering and extensive NFM delivery. The Rivers Trust approach is to understand, maintain and add to a catchment’s natural capacity to reduce flooding, using the available evidence.”
Dr Nick Chappell of Lancaster University, said: “Our modelling techniques demonstrated that by adding a range of NFM measures at many key locations in the landscape, significant reductions to flood peaks on large rivers may be produced. The research showed these benefits could potentially be produced, even for an event as extreme as Desmond, though our work highlighted the need for new experimental evidence addressing changes in rainfall interception losses through such extreme storms.”
This study provides new evidence that will help move catchments towards a longer term approach to the management of flood risk, which will also benefit water resources, water quality and nature.
Funding for this work has been provided through the Environment Agency’s support for the Catchment Based Approach, the EU LIFE IP Natural Course programme, United Utilities and the NW RFCC.