Land-use, Sediment and Flood Risk

1. Land-use, Sediment and Flood Risk delivered by: Colin Thorne, Nottingham University on behalf of: FRMRC Sediment Research Team

2. UPLAND CATCHMENTS Catchment Sediment Yields: natural vs intensive pasture Pontbren Experimental Catchments Melin-y-grug Coarse sediment yield 12x greater Fine sediment yield 5x greater Most excess sediment generated from withinchannel network Pen-y-cwm Henshaw, A.J. (2009) Impacts of land use changes and land management practices on upland catchment sediment dynamics: Pontbren, mid-Wales. Unpublished PhD thesis. University of Nottingham. Available online at http://riverscience.wikidot.com/alex-henshaw

3. UPLAND CATCHMENTS Increased Sedimentation in Engineered vs Natural Channels River Wharfe: sedimentation in engineered channels can lead to significant increases in flood risk. Review of Foresight on Future Flooding commissioned by Sir Michael Pitt (Evans et al., 2008) stated that:  “approximately a year and a half of aggradation produced an increase in the flooded area equivalent to nearly half a century of the impact of climate change on catchment runoff.” E.K Raven et al. 2010. Understanding sediment transfer and morphological change for managing upland gravel-bed rivers. Progress in Physical Geography 34(1) 23-45.

4. Cumbrian floods - 2009 Sediment and vegetation reduced conveyance capacity of engineered channels; Bank scour damaged properties; Bed scour led to the collapse of bridges and loss of life; Extensive overbank deposition of coarse sediments damaged farmland. TRAGIC EVIDENCE

5. LOWLAND CATCHMENTS Land use and Sediment Dynamics in the River Tone Complex fines deposition – especially at structures Elevated sediment yields Localised coarse sedimentation

6. SEDIMENT FUTURES Modelling future erosion, sediment and morphological responses to changes in climate and land use Strategic land use management can substantially reduce erosion and sediment yields Land use changes buffer rivers from the worst impacts of climate change Uncertainties are high and further research is needed 2050sintensive Baseline 2050s current 2050s tree strips

7. SEDIMENT & FLOOD VICTIMS • “Drop & collect” questionnaires & interviews: • Carlisle (2005) • Cockermouth (2009) • Boscastle (2004), Lostwithiel, St Blazey (2010) • Cockermouth: initial results • 55 respondents stated damage costs • mean damage/household = £83,000 • 52% of damage attributed to water • 30% of damages attributed to sediment • 18% of damage attrributed to debris • 85 respondents rated life satisfaction • (0 = extremely dissatisfied; 1 = extremely satisfied) • Interviews & thematic analyses : • High anxiety concerning future flooding • Stakeholders believe that sediment management for Conservation pre-empts sediment management for Flood Control

8. TAKE HOME MESSAGES • Sediment-related flood risks and damages are significant and flood victims recognise this. • Land use management can substantially increase or decrease sediment-related flood risks. • Unless we act, future sediment impacts are likely to increase due to climate change. • Sediment management for flood risk reduction must be aligned with environmental legislation.

9. ACKNOWLEDGEMENTS FRMRC Sediment Researchers and Advisors Paul Bates - Bristol University Paul Brewer – Aberystwyth University Tom Coulthard - Hull University Simon Gosling – Nottingham University Stuart Lane – Université de Lausanne Mark Macklin - Aberystwyth University Suresh Surendran – Glamorgen University Adrian Collins - ADAS Mervyn Bramley – Independent Jon Rees - NERC Mike Thorn – Independent David Brown - Environment Agency Jim Walker - Environment Agency Sean Longfield - Environment Agency Alex Henshaw – Queen Mary, London Nick Wallerstein – Heriot-Watt University Emma Raven – Durham University Ian Dennis – Royal Haskoning Gemma Harvey – Queen Mary, London Jorge Rameirez - - Hull University Phil Soar – Portsmouth University Jenny Mant – River Restoration Centre Clifford Williams – Environment-Agency Chris Parker - University West of England Steve Dangerfield – Nttm University Tim Meadows – Nottingham University Andy Wallis - Black and Veatch