modelling landscape opportunities, multiple benefits and … landscape... · modelling landscape...

Modelling landscape opportunities,

multiple benefits and impacts

Iain Craigen and Charlotte Beattie

In partnership with:

Natural Flood Management and Working With Natural Processes

Modelling Landscape Opportunities | JBA Consulting

• There is a growing evidence base

for applying Natural Flood

Management (NFM) measures to

manage flood risk

• http://naturalprocesses.jbahosting.com

• NFM and Working With Natural

Processes (WWNP) include storing

water, increasing soil infiltration,

slowing water and reducing flow

connectivity to reduce flooding

impacts

• Measures include:

– Upland mire restoration, built water

storage, river restoration, revised land

management, woodland creation,

sediment management and more… qgis2web © OpenStreetMap contributors,CC-BY-SA

http://naturalprocesses.jbahosting.com/

Overview

• Strategic catchment (rainfall-runoff) flood modelling across SW Peak District

– Based on the updated Flood Map for Surface Water (uFMfSW)

• Identifying Working With Natural Processes (WWNP) opportunities

– JBA Runoff Attenuation Feature Finder (JRAFF)

• Simulating opportunities and analysing impact on the flood hydrograph

– Monitor peak flow attenuation throughout catchment

• Interactive mapping

– Colour theming by potential for storage and attenuation

– Highlighting other constraints to identified opportunities

• Weighing up opportunities against potential downstream impacts / benefits


Introduction


• Project aim to investigate strategic

potential for Working With Natural

Processes (WWNP) at catchment scale

• Development of catchment rainfall-runoff

model across South West Peak District

comprising drainage from 17 catchments

across an area of 350km2

• Simulation of runoff attenuation features

and Woodlands for Water opportunities

• Simulations monitored across over 70

sub-catchments within study area with

primary focus on headwater sub-

catchments

Methodology

• Based around the uFMfSW national surface water flood risk methodology

• JRAFF tool to data-mine model outputs to identify natural depressions or Woodlands for Water opportunities

• Classify these as an opportunity for enhancement

• Evaluate potential to ‘slow the flow’ or attenuate

• Visualise the benefits interactive maps

Prepare 2m Digital Terrain Model ensuring downstream connectivity

Apply rainfall design storm profiles for 10 & 30 year Return Periods, use ReFH losses model

Run JFLOW – 2D overland flow model and record peak depths and hydrographs

Use JRAFF to identify locations of stored water or Woodlands for Water and enhance the

storage before re-running

Analyse changes in peak flows – assuming uptake of all storage or tree planting

Visualise using interactive maps allowing user to change layers / view constraints


Whole catchment JFLOW + ReFH losses modelFully distributed 2m resolution


MethodologyIdentification and application of runoff attenuation features

• Natural depressions (100-5,000m2) identified from surface water flood risk map (shallow depths filtered out)

• Opportunities filtered out by a number of constraints (urban areas, buildings and roads)

• Runoff attenuation features excavated or bunded into existing Digital Terrain Model (DTM) by up to 1m additional depth


MethodologyApplication of Woodlands for Water features

• Woodlands for Water comprises a range of target areas (riparian and floodplain zones)

• Dataset filtered by a range of constraints (urban areas, inland water, deep peat and existing forestry)

• Applied to model through increases in surface roughness coefficients


Floodplain Woodlands for Water opportunities

Riparian Woodlands for Water opportunities

Contains Ordnance Survey data © Crown copyright and database right 2016

© Crown Copyright. All rights reserved. Environment Agency, 100024198 2016

Model results, impact on hydrograph:Monitoring catchments - peak flow reduction from adding additional storage


Model results, impact on hydrograph:Monitoring catchments – hydrograph attenuation from Woodlands for Water



30-year return period

predicted percentage peak flow reduction

within headwater sub-catchments


30-year return period

predicted catchment opportunity storage (m3)


• Runoff attenuation features/storage opportunities or woodlands for

water opportunities toggled within each sub-catchment

• Overlaid with additional toggled constraints including environmental

designations and ancient woodland

Opportunities for upstream storage

considering potential downstream

communities impacted

SUMMARY & RECOMMENDATIONS

Summary and recommendations

• Strategic analysis of NFM/WWNP opportunities and impacts on catchment hydrographs across South West Peak District.

• Demonstrates an approach to complement other risk management measures, currently assumes a ‘complete’ adoption of all features

• Need detailed examination and engagement with local stakeholders to provide additional constraints prior to design stage

• Need combining with ecosystem services to complete analysis of best sustainable opportunities and understand additional environmental benefit

• Refined opportunities recommended to be simulated within calibrated rainfall-runoff model to improve understanding of confluence interactions and investigate flood risk impacts and potential benefits


modelling landscape opportunities, multiple benefits and … landscape... · modelling landscape...

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