Transcript Slide 1

Emerging Issues in Managing River
Sediments, Flood Risks and Habitats
Colin Thorne
Nottingham University
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
Acknowledgement
The 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.
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
Overview
1. The Policy Backdrop:
• EU Directives and UK Legislation
2. The Science Base:
• Flood Risk Management Research Consortium
• EA-Defra River Sediments and Habitats Project
3. 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
1. The Policy Backdrop
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
DEFRA Policy and WFD
Working 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
Environment Agency Initiatives
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
WFD Programmes of Measures
Weir removal, lowering and modification: a review
of best practice – EA Report – SC070024
• 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.
People’s Perceptions
River Menasgin – Impact of weir removal?
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
Academic Research Findings
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.
Linking wood to local flood risk
River Ennig, Talgarth – Impact of woody debris
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
www.floodrisk.org.uk
flooding
hhhhh
EPSRC Grant: EP/FP202511/1
Local Solutions
Woody debris management measures
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.
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
2. The Science Base (i)
FRMRC - Sediments Morphology and
Habitats
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
UPLAND CATCHMENTS
Catchment Sediment Yields: natural vs intensive pasture
Coarse sediment yield
12x greater
Melin-y-grug
Fine sediment yield
5x greater
Pen-y-cwm
Pontbren
Experimental
Catchments
Most excess sediment
generated from within
channel network
Henshaw, A.J. (2009) Impacts of land use changes and land management practices on upland catchment sediment dynamics: Pontbren, midWales. Unpublished PhD thesis. University of Nottingham. Available online at http://riverscience.wikidot.com/alex-henshaw
TRAGIC EVIDENCE
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.
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 Study
Analysis of records – Causes of Blockage
Blockage prediction - Catchment Properties
Pb = constant + (T x b1) + (A x b2) + (MDM x b3)
Impacts on River Habitats
Impact of sediment
management for FRM on
ecological status
National 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.
2. The Science Base (ii)
EA-Defra Project SC040015
River Sediments and Habitats:
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
Sediment Management:
Policy-related premises
1. There is a presumption
against removing sediment
from rivers
1. 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.
Project Structure
Guiding Principles
Typology
FRM Ops
Delivery
Actions
e-Learning Module
Guidebook of
Applied
Geomorphology
EA/SEPA R&D
e.g. Bank Erosion manual
Channel
Management
Guidebook
EU - UK Policies
(HD, WFD etc.)
3. Future Flooding
Government Office for Science:
Foresight on Flooding Project 2004
(updated 2008)
www.floodrisk.org.uk
EPSRC Grant: EP/FP202511/1
Environmental Regulation and Flood Risk Management
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
4fold 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.”
4. Science into Policy into Practice:closing the gap between current practice
amongst asset managers and the
underpinning science
Speech to CIWEM – April 7th 2011
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.
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)
Main river
Ordinary watercourse
Building on Best Practice
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
Joining up our Thinking
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.
Closure:
Take Home Messages
TAKE HOME MESSAGES
1. 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.