- 17th May 2017
- Posted by: Joanne Woodhouse
- Category: News
The Rivers Trust have recently released a report that we created for them on Natural Flood Management (NFM).
The study was developed alongside Lancaster University and United Utilities. It investigates NFM in a tiered approach across the Eden, Kent and Derwent catchments in Cumbria. It aims to help prioritise where different NFM measures are likely to be more effective.
Barry Hankin, Head of Environmental Modelling at JBA, commented, “There are still considerable uncertainties in modelling catchment processes at the large scale, and a lack of observational evidence. However, it is possible to scale known physical effects up, such as frictional losses and additional storage, using robust physically based modelling. This helps understand the effectiveness of nature-based solutions at a whole catchment scale.
“We have been able to do this upscaling of the impacts of very distributed nature-based measures at a fine, 2m resolution. We have also assessed their combined effect for 500km2 catchments by taking advantage of technological advances. Our very fast 2d flow model, JFLOW, solves the full shallow water equations on graphics cards.”
In the Rivers Trust press release David Johnson commented: “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.”
The strategic modelling was used to produce a suite of interactive maps which should be used in combination with the user guide. The maps list the different assumptions and limitations and highlight relative changes to the runoff hydrographs.
The Runoff Attenuation Feature (RAF) NFM measures, identified using JRAFF and JFLOW, were useful to identify locations to model in more detail. They also provide a starting point for more detailed modelling studies.
The detailed modelling shows there is an optimum, ‘intermediate’ retention time for RAFs of around 10 hours where storage is more limited. Longer drain-down times may be acceptable where opportunities are more widespread. The detailed modelling was compared with the strategic modelling. Whilst there were obvious differences in terms of JFLOW focussing on overland flow and DT modelling the whole hydrograph, there were similarities in terms of the potential for NFM to help regulate flooding.
Want to know more?
There’s more information on our Catchment and River Restoration webpage on working with natural processes.