www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1

Emerging Issues in Managing River Sediments, Flood Risks and Habitats

Colin ThorneNottingham University

www.floodrisk.org.uk EPSRC Grant: EP/FP202511/1

AcknowledgementThe research reported in this presentation was conducted as part of the Flood Risk Management Research Consortium with support from the:

• Engineering and Physical Sciences Research Council • Department of Environment, Food and Rural

Affairs/Environment Agency Joint Research Programme • United Kingdom Water Industry Research• Office of Public Works Dublin• Northern Ireland Rivers Agency

Data were provided by the EA and the Ordnance Survey.Additional information was kindly supplied by Mervyn Bramley.

Overview1. The Policy Backdrop:

• EU Directives and UK Legislation 2. The Science Base:

• Flood Risk Management Research Consortium• EA-Defra River Sediments and Habitats Project3. Future Flooding:• GO-Science Foresight Project on Future Flooding

4. Science into Policy into Practice:• Risks to be Managed • Speech to CIWEM by Richard Benyon MP• Delivering Sustainable Sediment & Debris Management

5. Take Home Messages

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1. The Policy Backdrop

DEFRA Policy and WFDWorking with natural processes• Defra policy requires “understanding

of natural processes to ensure that the impacts of different options are properly appraised and opportunities to work with nature to reduce risk are identified”

• Water Framework Directive requires “practicable steps that can be taken to mitigate adverse impact from physical modifications to our watercourses, coasts and estuaries”

http://publications.environment-agency.gov.uk/pdf/GEHO0310BSFI-e-e.pdf

Biodiversity 2020 - A Strategy for England's wildlife and ecosystem services

• Caroline Spelman launched this strategy in August 2011. • Hence, it is the current Government’s strategy not the last

one’s. • Summary of priorities and key actions (Annex A, Theme 4,

p.39) includes a priority water management action (3.7) to:

“promote approaches to flood and erosion management which conserve the natural environment and improve biodiversity”

http://www.defra.gov.uk/publications/files/pb13583-biodiversity-strategy-2020-110817.pdf

Environment Agency Initiatives

• Removing or altering the position of a weir is a potential way of improving longitudinal connectivity to help meet EU WFD targets.

• Our findings suggest that weir removal, lowering or modification can generate a range of hydromorphological and ecological benefits.

• Fisheries professionals and even some of the Rivers Trusts (who are now important player in delivering ‘Programmes of Measures’) are planning to remove hundreds, perhaps thousands of weirs.

Weir removal, lowering and modification: a review of best practice – EA Report – SC070024

WFD Programmes of Measures

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River Menasgin – Impact of weir removal?

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People’s Perceptions

Wood in Rivers• Another topical issue related to River Restoration,

Habitats Directive, BAPs and WFD.• The benefits of wood and natural/engineered log jams

to morphological diversity, ecohydraulics, habitats, and ecosystem services are being promulgated by academics – especially in the UK, Europe and USA.

• e.g. it is no longer acceptable to refer to wood as ‘debris’ – it is now a legitimate and valuable component of the fluvial system.

Academic Research Findings

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River Ennig, Talgarth – Impact of woody debris

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Woody debris and fallen trees have been positively encouraged in the channel upstream

Extreme flows transport this debris into the town downstream - blocking bridges and causing flooding

Linking wood to local flood risk

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Woody debris management measures

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Main channel is now maintained relatively clear of large size woody debris.

Major tree debris screen upstream of Talgarth. Steel joists - 2m high x 750mm clear opening.

Local Solutions

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2. The Science Base (i)

FRMRC - Sediments Morphology and Habitats

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

UK 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

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

Risks of Blockage at Structures

Belfast Case StudyAnalysis of records – Causes of Blockage

Blockage prediction - Catchment Properties

Pb = constant + (T x b1) + (A x b2) + (MDM x b3)

Impact of sediment management for FRM on ecological statusNational trends in ecological indices in managed reaches:

• Reduced in-stream 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.

Impacts on River Habitats

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2. The Science Base (ii)

EA-Defra Project SC040015 River Sediments and Habitats:

1. There is a presumption against removing sediment

from rivers1. The justification to manage

or remove sediments must be evidence-based

2. When sediment actions are justified best practice must be employed in performing the necessary work with the aim of maximizing benefits to habitats and ecosystems while avoiding or at least minimising damage to the environment.

Sediment Management: Policy-related premises

Project Structure

Guiding Principles

Typology e-Learning Module

Guidebook of Applied

Geomorphology

Channel Management Guidebook

EU - UK Policies (HD,

WFD etc.)

FRM Ops Delivery Actions

EA/SEPA R&De.g. Bank Erosion manual

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3. Future Flooding

Government Office for Science:Foresight on Flooding Project 2004

(updated 2008)

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

4. Science into Policy into Practice:-

closing the gap between current practice amongst asset managers and the

underpinning science

Richard Benyon MP (Defra)Parliamentary Under-Secretary for Natural Environment and Fisheries

• Natural environment• Ecosystem services• Biodiversity• National parks and areas of outstanding

natural beauty• Wildlife• Joint Nature Conservation Committee:

statutory adviser to the UK Government on national and international nature conservation, maintaining and enriching biological diversity, conserving geological features and sustaining natural systems.

• Flooding and water (including Nitrates)

• Inland waterways• Land management (including

commons and contaminated land) and soil

Speech to CIWEM – April 7th 2011

Defra CATCHMENT MANAGEMENT APPROACH• based approach on implementing the WFD.• focuses on delivering environmental benefits. • enhance the environment for people, businesses &

wildlife. • organisations will integrate water and land management:

– water company schemes like SCAMP, – Local Authority led initiatives like that in the Parrett catchment, – National Trust and NGO initiatives.

• aim is finding the right solutions in the right places.

Speech to CIWEM – April 7th 2011

Sediment & Debris-related Risks• SCOUR:

– Local scour endangering FRM or LD structures– Reach-scale degradation

• DEPOSITION:– Vegetation and sediment reducing channel conveyance– Blockage at culverts, screens, and bridges– Local shoaling and/or high points in channel bed – Reach scale aggradation

• FALLING FOUL OF ENVIRONMENTAL LEGISLATION:– Need to reduce adverse environmental impacts (particularly for WFD)

Ordinary watercourse

Main river

Adaptive management cycle for the channel asset • Asset management enshrines an on-going

process of building up ‘evidence’ on the particular channel assetand system

• Adaptive management (as distinct from ‘project-based’ work) is now a meeting point for engineers and natural scientists!

• 3 types of ‘evidence’ can be used, as appropriate: peer-reviewed scientific knowledge and tools site specific information (e.g. from monitoring) practical knowledge of experienced practitioners

Building on Best Practice

Bringing modellers and practitioners together • Better collaboration is needed between engineers

and scientists modelling floods and those modelling sediment, debris and ecohydraulics.

• They must exchange knowledge with practitioners to better understand the impact and effects of management actions and measures on other river functions.

• There are multiple functions for each channel asset, but there is only one river.

Joining up our Thinking

Closure:

Take Home Messages

TAKE HOME MESSAGES1. Sediment and debris-related flood risks and damages

are significant and flood victims recognise this.

2. Flood Risk and environmental management actions can substantially increase or decrease sediment and debris-related flood risks.

3. Unless we act, future sediment and debris impacts are likely to increase.

4. Sediment and debris management must be properly aligned with environmental legislation.