The impact of floodplain degradation on flooding in the UK

Entwistle, NS; Heritage, G

Abstract

A review of floodplain functioning in the north of England following the winter storms of 2015 was conducted
using high resolution aerial imagery of the events captured using drone and helicopter survey during and
immediately after the flooding. This revealed that for the most part 100% of the floodplain area was inundated.
Sediment left across floodplains from the 2015 flood events areas suggest high floodplain velocities (> 1.5
m/s). GIS analysis of land use mapping for valley bottom areas across England reveal part of the cause for
these unnaturally high velocities is the near complete loss of natural rough floodplain surfaces, having been
replaced by a hydraulically smoother managed arable/grassland mix. The review has revealed extensive and severe degradation of floodplain systems in England and it is highly likely that similar results would be found
for floodplains across the rest of the UK, both upland and lowland areas are equally impacted and the result is
an almost complete loss of natural floodplain functioning. River restoration remains concentrated on in-channel
activity, however, the push for natural flood management offers an opportunity to restore our floodplains with an associated improvement in ecological value and flood driven functionality. The research presented here suggests that it is not lack of floodplain storage space in the upper catchment, rather the decreased efficiency of floodplain areas to retard flow which is leading to increased downstream flood risk.
Floodplain reconnection, vegetative naturalization and selective grazing reduction are required to begin to
restore upstream floodplain flood function helping alleviate flooding pressure downstream.

Citation

Entwistle, N., & Heritage, G. The impact of floodplain degradation on flooding in the UK. Presented at 37th IAHR World Congress, Kuala Lumpur, Malaysia

• Presentation Conference Type: Other
• Conference Name: 37th IAHR World Congress
• Conference Location: Kuala Lumpur, Malaysia
• End Date: Aug 18, 2017
• Publication Date: Aug 13, 2017
• Deposit Date: Sep 8, 2017
• Publicly Available Date: Nov 13, 2017
• Publisher URL: http://www.iahrworldcongress.org/
• Additional Information: Event Type : Conference; Funders : Coop Insurance; Projects : Impact of Floodplain Degradation on Flooding in the UK