Case study:Investigating the Impacts of Upland Land Use Management on Flood Risk at Pontbren, Wales

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Location: 52° 39' 17", -3° 23' 38"
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Project overview

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Status Complete
Project web site http://www.therrc.co.uk/sites/default/files/projects/27_pontbren.pdf
Themes Economic aspects, Flood risk management, Habitat and biodiversity, Hydromorphology, Land use management - agriculture, Monitoring
Country Wales
Main contact forename Tom
Main contact surname Nisbet
Main contact user ID
Contact organisation Forest Research
Contact organisation web site http://www.forestresearch.gov.uk/
Partner organisations Imperial College London, Centre for Ecology & Hydrology, Pontbren Farmers' Cooperative, Coed Cymru, Environment Agency, Countryside Council for Wales, Forestry Commission
Parent multi-site project
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Project summary

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The aim of this research project on the Pontbren catchment in north Wales (Photo 1 and Map 1) was to improve understanding of how changes in upland land management impact on flood risk at the catchment scale. Experimental plots were established to measure the effects of sheep grazing and tree planting on soil structure and the generation of flood run-off. The data from these plots were used to derive parameter values and uncertainty bounds for a multi-scale modelling methodology. The model was applied to the headwater catchment to predict the impact of alternative land use practices on flood flows. Results showed that land management can have a major effect on run-off processes, providing scope for targeted interventions to significantly reduce flood risk in low permeability, upland landscapes at local scales. Soil infiltration rates were found to be 67 times higher within woodland plots and shelterbelts planted on improved grassland compared with grazed pasture; this reduced measured surface run-off volumes by an average of 78% compared with the control. These differences were quick to develop, becoming apparent within one year of sheep exclusion and tree planting. This was partly explained by the removal of the grazing pressure on the soil, which reduced run-off volumes by 48%, and partly by the action of tree rooting and growth, which was responsible for the remaining 30% decrease. Modelling predicted that planting tree strips across 7% of the 12km2 headwater catchment could reduce a severe flood (return period of 180 years) by an average of 5%. The effect of complete afforestation was much greater, reducing the same flood peak by an average of 36%.

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Catchment and subcatchment



Site

Name Afon Gafenni
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Heavily modified water body No
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Protected species present No
Invasive species present No
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River corridor land use
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Project background

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Project started 2005
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Funding sources EPSRC, Pontbren Farmers' Cooperative, Lottery Fund, Welsh Government

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Reasons for river restoration

Mitigation of a pressure Flood risk management
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Measures

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Floodplain / River corridor establishment of woodland
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Monitoring

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