Introduction to Flooding
by
Environment Agency, Halcrow and
Universities of Cardiff, Heriot Watt
and Cambridge
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General Background
to Flooding
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Background
• Up to 5m people in U.K. are at risk from river and
coastal flooding
• Annual average damage estimated at £0.7 bn
• Recent floods have been more frequent
• Damage extent exacerbated by:
 Extensive building on flood plains
 Alterations to riverine channels
 Changes in recorded rainfall patterns
 Changes in land management use
• Climate change expected to increase flooding
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Background
• River flooding essentially a natural process that helps
shape landscape
• Flooding generally caused by high rainfall and inability
of land to drain water effectively - aggravated further
when ground saturated
• Flooding frequently leads to serious water pollution and
epidemiological problems
• Flood damage extent often exacerbated by:
 Inadequate flood warning systems
 Use of crude hydroinformatics tools
 Inadequately trained model users
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General Views
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Whole towns often affected by flooding
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Historic town of York – floods regularly
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York Castle does not flood though
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Buildings have increasingly been built on flood plain
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Commercial properties often badly affected by flooding
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Flood water can rise rapidly in steep catchment
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Embankment breaches often cause severe damage
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Fire service are key providers of emergency support
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Army also provides support under severe conditions
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Floods bring misery and stress to families
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Elderly and disabled often most affected
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River Taff
Some Typical Challenges
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Typical weir built in past for flood control
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1979 Flood – defences overtop causing rapid flooding
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Flood of 1979 – many properties flooded
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Sandbags used to defend against flooding
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Typical use of temporary defences
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Typical contamination after flooding
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Much of Western Cardiff below embankments
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Many old bridges throttle flow during floods
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Single span modern bridges cause less throttling
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Significant changes in resistance either side of river
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Hurricane Katrina
August 2005
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High sea surface temperatures fuel hurricane
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Hurricane Katrina from satellite
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Hurricane power illustrated by vessel on shore
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New Orleans levee protection and bathymetry
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Mississippi river pours into New Orleans
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Flooding of downtown New Orleans
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Flood Defence
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Thames Barrier – world’s largest movable flood barrier
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Flooding of Thames Estuary
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Protection of Property
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Floodguards International
 State-of-art flood guards designed to protect homes and
properties from flooding
 Accessories designed to complement guards e.g. brick
sealant and one-way toilet valves
 Based on principle of arch dam design with pressure force
used to enhance seal
 Simple glass reinforced plastic (GRP) guards:
 Permanent and unobtrusive narrow frame fixed around
doors and air vents
 Removable curved lightweight guards readily clipped in
place before flooding
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Arch Dam Principle
Mountain
Mountain
Arch Dam
Water Pressure
• Water pressure transmitted to dam
• Forces then transmitted to mountain
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Flood Guard Principle
House Wall
Door
Flood Guards
Water Pressure
• Water pressure transmitted to flood guard
• Force then used to increase seal efficiency
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House Wall
Without guards
Protection of
Patio Doors
With guards
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Air Vent Protection
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Model of Seepage through Brickwork
Aim:- Predict protection times and seepage for
extended flooding
• Research Centre’s model HEMAT used to predict
seepage rates through brickwork and under wall
foundations
 Finite volume method solves flow equations
 Irregular triangular mesh used to fit domain
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Triangular Mesh
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Model Results
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Summary of Floodguards
Benefits
• Based on state-of-the-art technology
• Relatively inexpensive and lightweight
• Frame can be fitted easily and concealed
• Prevents flooding of properties through doors, windows,
air vents etc
• Prevents silt and sewage contamination
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Environment Agency
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Who Are They?
• Have over 10,000 staff - mainly scientists, engineers,
planners - responsible for environmental protection
• Have an annual operating budget of over £0.5 billion
• Work in following areas:
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Air Quality – regulate release of pollutants
Conservation – important role, especially along rivers
Fish – monitor and study fish habits and ecology
Flood – warn public about flood risk and build defences etc
Land Quality – seek to prevent land from becoming polluted
Navigation – responsible for rivers, estuaries and harbours
Recreation – managing use of inland and coastal waters
Waste – regulate waste management through licencing
Water Quality – ensure quality of surface and ground water
Water Resources – monitor and issue abstraction licences
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Environment Agency produce Indicative Flood Maps
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Environment Agency provide regular Flood Updates on TV
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Environment Agency provide Helpline Services
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Historical Flooding in U.K.
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Flood Details
• Spring 1998: Floods lasted 6 days and affected large parts of central and
eastern England
 More than 1,500 people were evacuated and 5 people died
(questionably from floods)
 Damage caused was approximately £0.75 billion
• Autumn 2000:
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Floods were wettest in U.K. since records began
Rainfall in October was four times mean for month
More than 10,000 properties were flooded
Insurance claims totalled some £0.7 billion damage
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Lessons from Floods
• Flooding impact and damage to property etc was often
much worse where defences were breached
• Flooding in parts of catchments often made much worse
by construction on floodplain or elsewhere along river,
e.g. flood defences or realignment etc
• Flooding impact exacerbated by responsibility being
unclear between local and national authorities
• Government reviews through various bodies have
particularly highlighted need for a more strategic and
catchment wide approach to flood risk management
• Catchment Flood Management Plans (CFMPs) being
prepared for all 80 catchments in England and Wales
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Catchment Flood Management
Plans
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What Are They?
• Three year programme introduced by DEFRA and
Environment Agency to develop Flood Management
Plans for all catchments in England and Wales
• Aim is to identify long-term sustainable policies to
manage flood risk throughout catchment
• Wide range of issues affect flood risk management:
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Land use changes
Development planning
Flood defence works
Flood warning and emergency response
• Consideration of flood risks and management solutions
at catchment wide scale
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Summary of Main Steps
1. Three year programme introduced by DEFRA and
Environment Agency to develop Flood Management
Plans for all catchments in England and Wales
2. Aim is to identify long-term sustainable policies to
manage flood risk throughout catchment
3. Wide range of issues affect flood risk management:
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Land use changes
Development planning
Flood defence works
Flood warning and emergency response
Consideration of flood risks and management solutions at
catchment wide scale
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Summary (Continued)
4. Determine existing and future flood risks and problem
areas within catchment
5. Appraise all potential policies and future scenarios for
flood risk management - also examine risks upstream
and downstream
6. Determine preferred management policies by
considering range of alternative scenarios against their
relative impact on flood risk
7. Consult on and disseminate preferred CFMP
8. Regularly monitor, review and update CFMP
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Catchment Flood Management Plan
Process as Defined in Guidelines
Define catchment
Periodic review
of plan
Scoping study
Collect catchment data and consult with stakeholders
Identify future scenarios
climate change / land use
change
Identify future change
in catchment
processes
New or modified plan
Understand catchment processes
Determine existing and future flood risks
and problem areas
Appraise plan policies for each scenario
Identify
opportunities
and
constraints
Assess effect on catchment responses and
flood risks
Define proposals and determine preferred plan (and residual risks)
Preferred plan consultation
Plan dissemination
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Feedback Loop
Catchment Data Types
• Flood management, e.g. flood defences, flood warning,
existing flood maps, historical data
• Catchment processes, e.g. climate, hydrology,
hydraulics, hydro-geology, morphology
• Economics, e.g. flood damage estimates, capital
investment, maintenance of defences
• Environment, e.g. nature conservation, landscape,
recreation, archaeology, habitat
• Land use and planning, e.g. national and municipal
plans, and local plans (e.g. farmland changes)
• Social aspects, e.g. population profiles at risk, sites of
high risk facilities such as hospitals
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Broad Scale Modelling
• DEFRA and Environment Agency have introduced Broad
Scale Modelling (BSM) initiative which includes following
models:
 Distributed rainfall-runoff processes
 River flow routing throughout river basin
 Effect of all potential flood risk management options on flood
flows
 Hydro-geological processes where applicable
 Probability distribution predictions for different drivers of
flooding risk
 Effects of new developments and land use change
 Effects of climate change and sea level rise
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Outputs from CFMPs
• Assessment of current position across catchment
• Clear statement of flood risk management objectives
• Preferred long-term and sustainable policies for
catchment wide flood management
• Assessment of risks and uncertainties associated with
preferred catchment flood management plan
• Timetable for reviews of and revisions to CFMPs
• Up to date list of references and related studies
• Prioritised programme for future monitoring and
modelling, and production of strategic plans
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Modelling within a Decision
Support Framework
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Development Team
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Basic Tools
 MDSF includes flood
spreading tools based on
ArcView GIS
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Hydraulics & Hydrology
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Flood Extent & Depth
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Economic Assessment
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Overseas Challenges
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Water – Some Challenges
• 1.2 b people on this earth have no access to safe
drinking water > 3 mpa die of diarrhoea
• 2.4 b people on this earth do not have basic water
sanitation > 1 mpa die from hepatitis A
• A child dies in Africa every 30s due to Malaria  a
disease related to stagnant water
• Flooding often causes many deaths world- wide  over
250,000 in Indonesia tsunami
• More than half hospital beds in world filled by people
with water related diseases (BMJ 04)
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“Water is infinitely more
critical to life
on earth than oil”
HRH The Princess Royal
Bradford University, 1989
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Thank You
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Presentation Produced by
Professor Roger Falconer (Cardiff University)
Professor Garry Pender (Heriot Watt University)
Professor Binliang Lin (Cardiff University)
Dr Dongfang Liang (University of Cambridge)
Dr Jon Wicks (Halcrow)
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