Www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1 Land-use, Sediment and Flood Risk delivered by: Colin Thorne, Nottingham University on behalf of: FRMRC.
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www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1
Land-use, Sediment and Flood Risk
delivered by:Colin Thorne, Nottingham University
on behalf of:
FRMRC Sediment Research Team
Catchment Sediment Yields: natural vs intensive pasture
Coarse sediment yield 12x greater
Fine sediment yield 5x greater
Most excess sediment generated from within
channel network
Pontbren Experimental Catchments
Melin-y-grug
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 Unpublished PhD thesis.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
UPLAND CATCHMENTS
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.”
Increased Sedimentation in Engineered vs Natural Channels
UPLAND CATCHMENTS
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.
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
Land use and Sediment Dynamics in the River Tone
Halse Water
114 T/km2/yr Halse Water GS10,000 T/yr Ham Weir6,000 - 16,000 River Tone River Tone
64 T/km2/yr
13,000 T/yr 70 T/km2/yr 57 T/km2/yr10,000 - 15,500 20,900 T/yr 18,000 T/yr 17,000 T/yr
19,000 - 25,500 12,000 - 27,000 12,000 - 27,000Bishops Hull GS
Upper River Tone
Downstream of Taunton
22,500 - 29,000 21,000 - 29,000
83 T/km2/yr 80 T/km2/yr 60 T/km2/yr25,000 T/yr 23,900 T/yr
Sediment Yield (Best Fit with limits)
Upstream of Taunton
River Tone River Tone River Tone
French Weir
Firepool Weir
Knapp Bridge
New Bridge
Taunton
LOWLAND CATCHMENTS
Complex fines deposition – Complex fines deposition – especially at structures especially at structures
Elevated Elevated sediment yieldssediment yields
Localised coarse Localised coarse sedimentationsedimentation
Modelling future erosion, sediment and morphological responses to changes in climate and land use
Baseline
2050s tree strips
2050s current
2050s intensive
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
SEDIMENT FUTURES
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
TAKE HOME MESSAGES
1. Sediment-related flood risks and damages are significant and flood victims recognise this.
2. Land use management can substantially increase or decrease sediment-related flood risks.
3. Unless we act, future sediment impacts are likely to increase due to climate change.
4. Sediment management for flood risk reduction must be aligned with environmental legislation.
FRMRC Sediment Researchers and AdvisorsAlex Henshaw – Queen Mary, LondonNick Wallerstein – Heriot-Watt UniversityEmma Raven – Durham UniversityIan Dennis – Royal HaskoningGemma Harvey – Queen Mary, LondonJorge Rameirez - - Hull University Phil Soar – Portsmouth UniversityJenny Mant – River Restoration CentreClifford Williams – Environment-AgencyChris Parker - University West of EnglandSteve Dangerfield – Nttm UniversityTim Meadows – Nottingham UniversityAndy Wallis - Black and Veatch
Paul Bates - Bristol UniversityPaul Brewer – Aberystwyth University Tom Coulthard - Hull UniversitySimon Gosling – Nottingham UniversityStuart Lane – Université de LausanneMark Macklin - Aberystwyth UniversitySuresh Surendran – Glamorgen
UniversityAdrian Collins - ADASMervyn Bramley – Independent Jon Rees - NERCMike Thorn – IndependentDavid Brown - Environment AgencyJim Walker - Environment AgencySean Longfield - Environment Agency
ACKNOWLEDGEMENTS
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