Managing the landscape to control flooding: Evidence from recent UK research

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Megan Palmer
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1 Managing the landscape to control flooding: Evidence from recent UK research Neil McIntyre, Howard Wheater, Caroline Ballard, Nataliya Bulygina, Beth Jackson Brian Reynolds, Miles Marshall, Imogen Solloway, Zoe Frogbrook John Ewen, Enda O Connell, Greg O Donnell, Josie Geris Ian Cluckie, Jong Sook Park, Colin Thorne, Alex Henshaw, Stephen Dangerfield Fergus Sinclair, Tim Pagella Imperial College London, CEH Bangor, Newcastle University Swansea University, Nottingham University, University of Wales Bangor NERC Grant: NE/F001134/1

2 Question addressed What are the effects of rural land use management on local scale and catchment scale floods? NERC Grant: NE/F001134/1

3 Scope of this presentation Planting and removal of trees in upland UK Removal of existing woodland Strategically placed tree strips NERC Grant: NE/F001134/1

4 Scope of this presentation Grassland and moorland restoration in upland UK Reducing or increasing grazing pressures Drainage management

5 Case studies The Pontbren catchment in upland central Wales The Hodder catchment in upland north-west England NERC Grant: NE/F001134/1

6 Pontbren plot experiments C Tree-planted plot Ungrazed plot Grazed plot UG T Overall, experiments showed large reductions in surface flows in the plots after planting trees

7 Pontbren catchment scenarios (6 to 12 km 2 ) NERC Grant: NE/F001134/1

8 SCENARIO Pontbren catchment scenarios Catchment Area (km 2) (6 to 12 km 2 ) CHANGED AREA IMPACT ON PEAK FLOW FREQUENT FLOOD EVENT (T<2 years) CHANGE IN PEAK FLOW UNCERTAINTY BOUNDS Removal of trees 12 7% increase 13% 6 to 18% Tree strips 12 8% decrease 29% 48 to 13%

9 SCENARIO Pontbren catchment scenarios Catchment Area (km 2) (6 to 12 km 2 ) CHANGED AREA IMPACT ON PEAK FLOW FREQUENT FLOOD EVENT (T<2 years) CHANGE IN PEAK FLOW UNCERTAINTY BOUNDS Removal of trees 12 7% increase 13% 6 to 18% Tree strips 12 8% decrease 29% 48 to 13% Heavy sheep grazing 6 88% increase 11% 3 to 22%

10 SCENARIO Pontbren catchment scenarios Catchment Area (km 2) (6 to 12 km 2 ) CHANGED AREA IMPACT ON PEAK FLOW FREQUENT FLOOD EVENT (T<2 years) CHANGE IN PEAK FLOW UNCERTAINTY BOUNDS Removal of trees 12 7% increase 13% 6 to 18% Tree strips 12 8% decrease 29% 48 to 13% Heavy sheep grazing 6 88% increase 11% 3 to 22% EXTREME FLOOD EVENT (T>100 years) Tree strips 12 8% decrease 5% 11 to 2%

11 Hodder catchment scenarios (25 km 2 )

12 Hodder catchment scenarios (25 km 2 ) SCENARIO Catchment Area (km 2) CHANGED AREA IMPACT ON PEAK FLOW CHANGE IN PEAK FLOW UNCERTAINTY BOUNDS FREQUENT FLOOD EVENT (T<2 years) Unblocking drains 25 ~10% no change 0% 1 to 2% Return to intact moorland 25 ~10% no change 0% 2 to 2%

13 Hodder (260km 2 ) catchment scenarios 95% prediction bounds HP Pre-change Peat: blocked Peat: drained Peat: intact Good Fair Poor HP Post-change Impact on peak is small, only a few percent, but considerable uncertainty

14 14 Impacts of land use management on sediments at Pontbren

15 Conclusions Strategic tree planting and grassland/moorland restoration can have significant beneficial effects on flood flows However, the beneficial effects are likely to be marginal at medium to large scales (e.g. York, Tewksbury) for realistic degrees of change, and by themselves these measures should not be relied upon to manage flood risk

16 Conclusions The full benefits of tree planting and grassland/moorland restoration may only become clear when the interactions between flows, sediment regulation and other ecosystem services are understood and taken into account Although substantial progress has been made under recent research programmes, uncertainty is high and predictions cannot yet be safely made for most catchment types. Investment in field experiments and modelling is needed.

Land use management effects on flood flows and sediments - guidance on prediction

Land use management effects on flood flows and sediments - guidance on prediction Who we are Established in 1960, CIRIA is a highly regarded, industry-responsive, not for profit research and information