Alex Fraser and Sim Reaney - Durham University€¦ · Case Studies of this approach ... • 8km2...
Transcript of Alex Fraser and Sim Reaney - Durham University€¦ · Case Studies of this approach ... • 8km2...
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Catchment management, SuDS and NFM for
flood mitigation. Tutta Beck, County Durham
Alex Fraser1&2 and Sim Reaney1
1, Durham University, 2, Northumberland County Council
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Introduction
This presentation will:
� Introduce research aims
� Discuss the problems within the study site
� Outline the risk mapping and targeting approach
� Demonstrate methods and preliminary results from CRUM3
simulations
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Why Natural Flood Management &
Catchment Based Approach? � Winter 2015-16 events demonstrated last line approach to flood
management unsustainable
� Environment Agency and DEFRA funding towards Natural Flood
Management and catchment management
� Targets ‘flashy’ hydrograph
� Multiple Benefits
� NFM can enhance fluvial ecology (EdenDTC)
� Amenity Value (Thacka Beck, Penrith; Holnicote, Somerset)
� Maintenance can form part of Land Management Practices
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Case Studies of this approach Demonstration test catchments and examples of LLFA projects
� Land Management/CSF approach (ALFA, Eden DTC, Durham
University)
� Channel management, upstream storage (Pickering, EA, FC &
Durham University)
� Runoff attenuation (Belford, EA & Newcastle University)
� Floodplain Storage (NT Holnicote Estate, DEFRA & JBA)
� Attenuation, slowing flow (Hepscott, Northumberland County
Council, EA
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Research Aims
� Develop an innovative approach to managing catchment
hydrology
� Use risk mapping to target hydrological simulations
� Provide outputs that satisfy funding regulations
� Long term management advice, land management to
mitigate flood risk supporting farming and rural economy.
� Increase resilience across the catchment
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Tutta Beck Catchment
Location
• 40 miles South of Newcastle
• Adjacent to the A66 Transpennine trunk road
Hydrology
• 8km2 sub-catchment of the River Tees
• Gravel bed watercourse with a flashy flow
regime
Characteristics
• Predominantly agricultural
• Heritage Designations at receptor (scheduled
Ancient Monument, Ancient Parkland, Listed
Buildings)
Twin Arch Culvert 3.2mx1.5m
Ancient Monument Confined Channel
Receptor
2x 90⁰ direction changes Observed overflow
Unsuitable Flood Barrier option
Opportunities to manage catchment for flood alleviation instead
Flood Plain Storage?
Woody Debris
Intercepting Runoff?
Ditch Blocking?
Land cover change?
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Research Approach � Output driven approach
CRUM3
Assess land management techniques using a Catchment
Based Approach, NFM and SuDS for Flood Mitigation.
Existing land cover
Land cover weighting
The GLUE approach
Model Sensitivity Analysis
SCIMAP-Flood
Flood Risk
Generation Hydrological Connectivity
Stakeholder Engagement
Parish Council Meeting
LLFA Meeting
Land Owner/Farmer
Communication
Natural Flood Management, Catchment Sensitive Farming & SuDS
Literature
Scenario Development
Catchment Modelling
Submit to Durham County Council for Detailed Design
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SCIMAP-Flood Risk based mapping tool assessing catchment
characteristics and likelihood of rapid connectivity to
watercourse.
(Pearson, 2016)
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SCIMAP Flood
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Using SCIMAP to target
simulations
For a new catchment SCIMAP offers the opportunity to
support initial field assessments and identify areas that
have a higher risk factor than others.
Greater resolution than hydrological modelling to better
drive simulations
The results can be used to generate scenarios for detailed
simulation of
• Woodland for flood alleviation • Large Woody Debris dams
• Ponds and Attenuation features
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Simulation scenarios
� Woodland for flood risk
� Rainfall intercepted by canopy
� Increase infiltration
� Intercept overland flow
� Large Woody Debris
� Slow the flow
� Attenuation
� Reduce and elongate the flood hydrograph
� SuDS attenuation
� Volumetric storage
� Slow Flow
Minnesota Dept. Agriculture
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CRUM3 - Overview
� Fully distributed across the
landscape (apx. every 50 m)
� Detailed process
representation
� 1D vertical
� 2D landscape routing
� 1D channel flow
� Detailed Outputs
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Vertical Processes
� Interception
� Evapotranspiration
� Runoff/overland flow
� Infiltration
� Soil flow
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2D Representation
� Terrestrial and fluvial
representations
� Multiple flow routing on the
landscape
� Muskingum-Cunge river
flow routing
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Example outputs:
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Validation of the CRUM3 Model
for Tutta Beck
� Model performs well
� Max Nash Sutcliff 0.76
� Observed Modelled Peak
ratio 0.97
� An ensemble of 25 models
taken forward into
scenarios
� Captures the predictive
uncertainty of the model
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CRUM3 Summary � Fully spatially distributed catchment hydrological
simulation model
� Detailed physical process representation
� Predicts changes in flood peak and general catchment
hydrological behaviour
� Suitable to testing natural flood risk management
mitigation features
� Next slides show the results from scenarios developed
using SCIMAP-Flood and from stakeholder engagement…
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Land cover change simulation
● Intercept rainfall
● Increase surface roughness,
improve infiltration, improve soil
structure
Vegetation can provide mitigation in a number of ways:
Botanic gardens of South Australia Minnesota Dept. Agriculture
● Riparian buffer strips intercept
overland flow reducing
connectivity to watercourses
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Blanket Land Use Change Results
� Greatest reduction
through deciduous
landcover
� Arable increases
discharge
� Most simulations have
little impact on sum of
discharges meaning
little change in fluvial
environment
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Buffer Strip Land Use Change Results
• Buffer strip simulation 50m
around cells classified as
channel to disconnect
runoff
• Greatest reduction through
Deciduous woodland
• Most simulations have little
impact on sum of discharges
meaning little change in
fluvial environment
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CSF Flood Risk Targeted Woodland
• Reduces peak discharge under
all events (~0.5m3s-1 at Mean)
• Second most effective
reduction of mean discharge
• Strategy supported by
Catchment Sensitive Farming
funding initiative
• Little impact on sum of
discharges meaning negligible
change in fluvial environment
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Large Woody Debris Simulation
� Disturbing in channel flows
(Hepscott, Belford, Stroud)
� Promoting flooding of the
floodplain (Pickering)
� Restricting discharge and
attenuation (Pickering)
Large woody debris can provide mitigation in multiple ways-
Hepscott Burn (Northumberland
County Council) Pickering (Odoni et al., 2010)
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Large Woody Debris Results
� Large woody debris is simulated
as a flow restriction
� Little disturbance in sum of
discharge
� Flood plain discharges offer
greatest reduction but would
have greatest cost
� Arable features little reduction
o Minimal contribution to discharge
o Require lower flow restriction
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LWD – Targeting the Upper
Catchment
� Targeting dams to the
upper catchment
� Aim to slow the flow and
remove water from the
flood peak
� Maximum discharge through
dam of 0.75 m3 s-1 Black – catchment outline Blue – river channel network
Red – locations of dams
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LWD – Targeting the Upper Catchment • 0.13m3s-1 reduction in
peak flow
• Principle of
disconnecting the upper
catchment from the peak
flows
• Little impact on sum of
discharges meaning
negligible change in
fluvial environment
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Image Courtesy Nick Barber, Durham University
SuDS Attenuation (Ponds/Basins)
� Ditch of the Future
Structures (Eden DTC)
Towcett Farm
� Online/offline structures
(Belford)
� SuDS Systems
SuDS/attenuation can function in multiple ways-
Eden DTC, Image Courtesy Nick Barber, Durham University
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SuDS Simulation � Capturing around 0.01%
catchment within a single
structure reduces all
discharge figures by mean
of 0.1m3s-1.
� Simulation developed
through manipulation of
DEM
� Little impact on sum of
discharges meaning
negligible change in fluvial
environment
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Summary of Results
90th Percentile Mean 10th Percentile
Control Run results 6.5 6.3 5.8
Berm 1m High 6.4 6.2 5.7
CSF Targetting 5.9 5.7 5.3
Blanket Changes Arable 7.0 6.4 6.2
Blanket Changes Improved Grazing 6.8 6.3 5.7
Blanket Changes Coniferous 6.7 6.3 5.9
Blanket Changes Rough Grazing 6.5 5.9 4.7
Blanket Changes Deciduous 6.5 5.7 4.6
Watercourse Buffers Improved Grazing 6.6 5.9 5.5
Watercourse Buffers Coniferous 6.4 5.9 5.5
Watercourse Buffers Rough Grazing 6.4 5.8 5.1
Watercourse Buffers Deciduous 6.1 5.7 5.0
Arable 3m3s-1 6.5 6.3 5.8
Arable 4m3s-1 6.4 6.1 5.7
Arable 5m3s-1 6.4 6.1 5.7
Floodplain 4m3s-1 4.2 4.2 4.2
Floodplain 5m3s-1 5.2 5.2 5.2
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Control Run results Berm 1m High CSF Targetting Blanket Changes Arable Blanket Changes Improved Grazing Blanket Changes Coniferous Blanket Changes Rough Grazing Blanket Changes Deciduous Watercourse Buffers Improved Grazing Watercourse Buffers Coniferous Watercourse Buffers Rough Grazing Watercourse Buffers Deciduous Arable 3m3s-1 Arable 4m3s-1 Arable 5m3s-1 Floodplain 4m3s-1
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Buffer Scenarios Blanket & targeted change
Scenarios
Flow Restriction Scenarios
SuD/Attenuation
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Positives/Negatives of Features
• Vegetation
+ Easily Managed - Cost to buy vegetation
+ Secondary Harvest - Cost of land take
+ Ecology Benefits - Requires spatial targeting
• Large wood debris
+ Slow Flow deposition - Construction costs
+ Easily Maintained - Cost of land take
+ Ecology Benefits - Maintenance/Replacement
• Attenuation
+ Water Quality Improvements - Construction costs
+ Provide secondary income - Cost of land take
+ Habitat creation - Maintenance
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Summary
� CRUM3 has evidenced that effective use of SuDS and
NFM features can lead to simulated reductions in peak
flow
� CSF simulation shows targeted landcover change could
be more effective than generic changes
� Targeting techniques using SCIMAP-Flood can yield
effective reductions
� Interrelationships of catchment characteristics heavily
influence most effective mechanism for flood
management
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Thank you for your time
� Thanks to Nick Fraser, Heritage Lottery Fund, staff at Tees Rivers Trust, Northumberland
County Council and Durham County Council
� Alex Fraser – [email protected] /
� Sim Reaney, [email protected]