land-use, sediment and flood risk · 2020-01-23 · sediment impacts on conveyance, channel...
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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 – Super Work Package 5
UPLAND CATCHMENTS
Pontbren experimental catchment
WP 5.1 Modelling flood impact of upland land use change
contact: [email protected]
Pontbren was a unique 6-year field experiment performed through collaboration between scientists, farmers and decision-makers.
3
Land use, Infiltration and Runoff
Arrows demonstrate
relative magnitudes
At the field scale, effects of land-use on surface runoff are
strong and responsive to management changes
WP 5.1 Modelling flood impact of upland land use change
contact: [email protected] 4
Land-use Runoff and Farm-scale Flooding
At farm scale, the effect of land-use on flows and flood peaks is clear
WP 5.1 Modelling flood impact of upland land use change
contact: [email protected]
Flow gauges Low ‘T’ indicates faster flow responses
Land use
5
Upland land use change impacts on peak flows
Models allow analysis of the effects of field-scale land management on flood peaks
Scenario: Tree shelterbelts over 10% of the catchment
WP 5.1 Modelling flood impact of upland land use change
contact: [email protected]
Median change: -5%
Uncertainty range: -2 to -11%
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WP 5.1 Modelling flood impact of upland land use change
contact: p.e.o‘[email protected]
Land-use impacts on downstream flood peaks in Large Catchments
Peat: blocked Peat: drained Peat: intact Good Fair Poor Pre-change Post-change
Modelled impact on peak is small, only a few percent, but uncertainty is high
95% prediction bounds
7
Land use Management has no visible effects on
Hydrographs and Flood Risks
At the large catchment scale River Hodder: Empirical evidence
Land-use and Flooding: Summary
Minimum/(no?) effect
Maximum effect
Incr
easi
ng
scal
e Increasing return period
How the Drainage Network Controls Flood Impacts at Large Catchment Scale
• Hydrodynamic Dispersion: channel friction attenuates Flood Peaks and their impacts.
• Geomorphological Dispersion: configuration of network controls arrival times and impacts at Flood Receptor locations.
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
Sediment Impacts on Conveyance, Channel Stability and Habitats
Channel
migration
Channel conveyance capacity
Water quality Habitat degradation
2002-2004 aggradation
2050s climate scenario Present
1-in-0.5 year flood +12.2% +5.7% Combined: +38.2%
Lane et al. (2007)
WP 5.2 Modelling sediment impacts of upland land use change
contact: [email protected]
River Wharfe investigation shows that
sedimentation in channels with stabilised
banks 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 riversProgress in Physical Geography 34(1)
23-45.
Context: reconciling goals for flood risk management and ecological status
National trends in ecological indices in managed reaches:
• Reduced instream habitat
heterogeneity • Reduced riparian habitat
complexity
Harvey, G. L. and Wallerstein, N. P. (2009) Exploring the interactions between flood defence maintenance works and river habitats: the use of River Habitat Survey data. Aquatic Conservation: Marine and Freshwater Ecosystems 19: 689-702.
Lowland Catchments
Distributed hydrological model for the River Tone
WP 5.3 Modelling flood impact of lowland land use change contact: [email protected]
…Interflow
Reservoir
…Vegetation
…Topography
…Soil
…Baseflow
Reservoir
River (Channel flow model)
Slower/Deeper Baseflow
Precipitation
Evapotranspiration
Canopy Interception
Root Zone Model
Interflow Storages
Baseflow Storages
INFILTRATION
INTERFLOW (H)
PERCOLATION (V)
Water Movement Procedures Vertical Data Layers
(MIKE SHE/11)
Grid size – 100 metres
Overland Flow Model
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Lowland land use change scenarios
Woodland
planting
scenario
Flood
retention
storage
scenario
WP 5.3 Modelling flood impact of lowland land use change contact: [email protected]
The model shows limited impact of woodland planting, but greater impacts from distributed flood retention storage
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Land use and Sediment Dynamics in the River Tone
Halse Water
114 T/km2/yr Halse Water GS
10,000 T/yr Ham Weir
6,000 - 16,000 River Tone River Tone
64 T/km2/yr
13,000 T/yr 70 T/km2/yr 57 T/km
2/yr
10,000 - 15,500 20,900 T/yr 18,000 T/yr 17,000 T/yr
19,000 - 25,500 12,000 - 27,000 12,000 - 27,000
Bishops Hull GS
Upper River Tone
Downstream of Taunton
22,500 - 29,000 21,000 - 29,000
83 T/km2/yr 80 T/km
2/yr 60 T/km
2/yr
25,000 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
sedimentation – especially
at structures
Elevated
sediment yields Localised coarse
sedimentation
Options for Modelling, Predicting and Managing Sediment-Related Flood Risk:
FRMRC Sediment Toolbox
Halse Water
90 T/km2/yr Halse Water GS
8,000 T/yr Bathpool
(estimated)
River Tone River Tone
75 T/km2/yr 41 T/km
2/yr 28 T/km
2/yr
15,000 T/yr 12,000 T/yr 8,000 T/yr
(SS No. 609) (SS No. 295) (SS No. 146)
Bishops Hull GS
Upper River Tone
Downstream of TauntonUpstream of Taunton Taunton
24,000 T/yr 12,000 T/yr 4,000 T/yr
River Tone
41 T/km2/yr 14 T/km
2/yr
Knapp
Bridge
83 T/km2/yr
(SS No. 113) (SS No. 182)
New
Bridge
(SS No. 445)
French
Weir
Firepool
Weir
River Tone River Tone
Sediment Yield Analysis
Change in Stream Power d/s
0.00
10.00
20.00
30.00
40.00
50.00
60.00
0.0 1000.0 2000.0 3000.0 4000.0 5000.0 6000.0 7000.0 8000.0 9000.0 10000.0 11000.0 12000.0 13000.0
Chaniage (m)
Sp
ecif
ic S
tream
Po
wer
(Wm
-2)
Stream Power Screening
FRMRC Sediment Toolbox
ST:REAM
Sediment Transport:
Reach Equilibrium
Assessment
Method
HEC-RAS/SIAM
ISIS-Sediment
CAESAR – Cellular Automaton Evolutionary Slope
and River model
Modelling future erosion, sediment and morphological responses to changes in climate and land use
Baseline
2050s tree strips
2050s current
2050s intensive
Selective woodland planting can reduce flood peaks in small catchments
Strategic land use management can substantially reduce erosion and sediment yields
Land use changes buffer rivers from the worst impacts of climate change
SEDIMENT FUTURES
Modelling future sediment yields at Pontbren
Baseline (1961-90)
2050s (low
emissions)
2050s (medium
emissions)
2050s (high
emissions)
Present-day (with Pontbren tree strip planting)
- +9.3% +28.3% +35.3%
1990s (pre-Pontbren tree strip planting)
+4.1% +15.3% +30.0% +53.8%
Tree strips planted in all grazed pastures
-58.2% -37.6% -22.4% -11.4%
Climate scenario
Land use scenario
Predicted change in 30 year sediment yield from baseline climate/present-day land use scenario (percentages represent difference in median sediment yield calculated from 50 UKCP09 weather generator rainfall sequences)
WP 5.1 Impact of upland land use on sediments contact: [email protected]
Climate change predicted to amplify catchment sediment yield but
problems could be offset through changes in land use
management.
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Habitat Connectivity
Hydrology
Farm productivity
Sediment
Transport
Trade off Layer
POLYSCAPE Multi-functional Land-
use Management - areas are beneficial to
all services
SWP 5 Land use management negotiation tool
contact: [email protected]
FRMRC
Sediment Tool
Box
A range of sediment
methods and models
is available.
The relative
contributions of
interpretative and
analytical approaches
vary, but all methods
and models require
both.
OPTIONS FOR MODELLING AND MANAGING
SEDIMENT-RELATED FLOOD RISK
Project
Success
Management
Resources
Management
ResourcesStakeholder
Attitudes
Stakeholder
Attitudes
ScienceScience
Credibility
Cognizance
Constraints
Support
ComplexitySimplicity
Project
Success
Management
Resources
Management
ResourcesStakeholder
Attitudes
Stakeholder
Attitudes
ScienceScience
Credibility
Cognizance
Constraints
Support
ComplexitySimplicity
Successful
uptake depends
not only on the
strength of the
science base but
also availability of
management
resources to
apply the
method/model
and stakeholder
attitudes.
Does Sediment Really Matter?
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.
DOES SEDIMENT MATTER?
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
The Foresight project found that
“a clash between FRM and
environmental objectives could
lead to a 3-fold increase in flood
risk in the 2050s, rising to a
4-fold increase in the 2080s”
(Evans et al. 2008).
They concluded that:
“under Global Sustainability,
lower climate change and
economic growth combined with
greater environmental
consciousness result in River
Vegetation and Conveyance,
Environmental Regulation, and
River Morphology and Sediment
Supply topping the table in the
2050s.”
Environmental Regulation and Flood Risk
Management
FRMRC TAKE HOME MESSAGES
1. Land use is significant to downstream flood risk and flood victims understand this even if not all hydrologists do.
2. Land use management can substantially increase or decrease flood and sediment-related flood risks.
3. Unless we act, future flood and sediment impacts are likely to increase due to climate and land use changes.
4. Land use management for flood risk reduction must be properly aligned with agricultural, environmental and
planning policies and legislation.
Some key outputs
Academic Outputs Numerous journal articles and conference papers Doctoral Theses from multiple individuals
Books and Book Chapters Flood Risk Science and Management (Pender and Faulkner, 2010) Flood Risk: Planning, design and management of flood defence infrastructure (Sayers, 2012) 20 Research fact Sheets 10 User-focused FRMRC Reports and Guides 4 Construction Industry Research & Information Association Technical Reports
Tools Models, code, algorithms Optimisation methods, risk analysis frameworks, uncertainty analyses, sediment toolbox
Data All datasets (with meta-date where available) are free to download
Practitioner and Stakeholder Events 9 Practitioner and Stakeholder Workshops 8 International Research Dissemination Conferences – including this one
Pender G. and
Faulkner H. (2010)
Flood Risk Science
and Management
Wiley Blackwell,
Chichester, UK
Sayers P. (2012)
Flood Risk:
Planning, design
and management of
flood defence
infrastructure
Thomas Telford,
London
Construction Industry Research Information Association
Technical Reports:
1. Framework for assessing uncertainty in fluvial flood risk mapping
2. Predicting and managing flood risk associated with debris at structures
3. Performance based inspection of flood defences
4. Land use management and flooding – guidance on prediction and implementation
Catchment Inundation Modelling
• Modelling of flood risk to people and property
• Visualizing uncertainty: Organization and communication of probabilistic flood inundation data
• Strategic planning: Decision analysis for strategic planning
• Inundation modelling: parallelisation of two dimensional hydraulic models
• Inundation modelling: benchmarking a new fast inundation model to support uncertainty analysis
• Coping with sea level rise uncertainties in the Thames Estuary
• Rapid flood inundation modelling
Coastal Inundation Modelling
• Coastal processes and flooding: From offshore waves to coastal overtopping
• Coastal processes and flooding: Long term cliff erosion modelling
• Coastal processes and flooding: Dredging impact analysis
• Beach profile prediction: Use of advanced statistical techniques
• Inundation modelling – coastal flooding: Improved storm surge forecasting
Urban Flood Modelling
• Urban flooding: Health impacts of urban flooding
• Urban pluvial flood modelling: Improved short term rainfall & urban flood prediction
• Urban flood modelling: Improved simulation of gulley hydraulics
• Urban flooding: Feasibility of whole life costing of non-structural measures
• Integrating urban flood modelling & social vulnerability at the local scale: GIS-based Flood Risk Assessment Tool
Infrastructure
• Infrastructure monitoring: Quantitative assessment of asset surface topography
• Infrastructure management: Predicting and managing flood risk associated with debris at structures
• Flood risk asset management: Optimised flood risk management strategies
• Infrastructure management: Broad scale integration of coastal flood and erosion risk models
• Breach formation: Rapid methods of assessment
Land use, Sediment and Flood Risk
• Effects of rural land management on flood risk: New simulation methods to quantify local and catchment scale impacts
• Catchment sediment dynamics and flood risk: Impacts of upland agricultural land management on catchment sediment dynamics at Pontbren, mid-Wales
• Wetland land use management: Modelling approaches for a multi-scaled, nested catchment
FRMRC End-user Workshops
FRMRC End-user Workshops
FRMRC Collaborative Workshops