Introduction to flooding
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Introduction to Flooding. by Environment Agency, Halcrow and Universities of Cardiff, Heriot Watt and Cambridge. General Background to Flooding. Background. Up to 5m people in U.K. are at risk from river and coastal flooding Annual average damage estimated at £0.7 bn

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Introduction to Flooding

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Introduction to Flooding

by

Environment Agency, Halcrow and

Universities of Cardiff, Heriot Watt

and Cambridge


General Backgroundto Flooding


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


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


General Views


Whole towns often affected by flooding


Historic town of York – floods regularly


York Castle does not flood though


Buildings have increasingly been built on flood plain


Commercial properties often badly affected by flooding


Flood water can rise rapidly in steep catchment


Embankment breaches often cause severe damage


Fire service are key providers of emergency support


Army also provides support under severe conditions


Floods bring misery and stress to families


Elderly and disabled often most affected


River TaffSome Typical Challenges


Typical weir built in past for flood control


1979 Flood – defences overtop causing rapid flooding


Flood of 1979 – many properties flooded


Sandbags used to defend against flooding


Typical use of temporary defences


Typical contamination after flooding


Much of Western Cardiff below embankments


Many old bridges throttle flow during floods


Single span modern bridges cause less throttling


Significant changes in resistance either side of river


Hurricane KatrinaAugust 2005


High sea surface temperatures fuel hurricane


Hurricane Katrina from satellite


Hurricane power illustrated by vessel on shore


New Orleans levee protection and bathymetry


Mississippi river pours into New Orleans


Flooding of downtown New Orleans


Flood Defence


Thames Barrier – world’s largest movable flood barrier


Flooding of Thames Estuary


Protection of Property


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


Arch Dam Principle

Mountain

Mountain

Arch Dam

Water Pressure

  • Water pressure transmitted to dam

  • Forces then transmitted to mountain


Flood Guard Principle

House Wall

Door

House Wall

Flood Guards

Water Pressure

  • Water pressure transmitted to flood guard

  • Force then used to increase seal efficiency


Without guards

Protection of Patio Doors

With guards


Air Vent Protection


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


Triangular Mesh


Model Results


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


Environment Agency


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:

    • 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


Environment Agency produce Indicative Flood Maps


Environment Agency provide regular Flood Updates on TV


Environment Agency provide Helpline Services


Historical Flooding in U.K.


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:-

    • 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


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


Catchment Flood Management Plans


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:

    • Land use changes

    • Development planning

    • Flood defence works

    • Flood warning and emergency response

  • Consideration of flood risks and management solutions at catchment wide scale


Summary of Main Steps

  • 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:

    • Land use changes

    • Development planning

    • Flood defence works

    • Flood warning and emergency response

    • Consideration of flood risks and management solutions at catchment wide scale


Summary (Continued)

  • Determine existing and future flood risks and problem areas within catchment

  • Appraise all potential policies and future scenarios for flood risk management - also examine risks upstream and downstream

  • Determine preferred management policies by considering range of alternative scenarios against their relative impact on flood risk

  • Consult on and disseminate preferred CFMP

  • Regularly monitor, review and update CFMP


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

Understand catchment processes

Determine existing and future flood risks and problem areas

Identify opportunities and constraints

Identify future change in catchment processes

Appraise plan policies for each scenario

New or modified plan

Assess effect on catchment responses and flood risks

Define proposals and determine preferred plan (and residual risks)

Feedback Loop

Preferred plan consultation

Plan dissemination


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


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


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


Modelling within a Decision Support Framework


Development Team


Basic Tools

  • MDSF includes flood spreading tools based on ArcView GIS


Hydraulics & Hydrology


Flood Extent & Depth


Economic Assessment


Overseas Challenges


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)


“Water is infinitely more critical to lifeon earth than oil”

HRH The Princess Royal

Bradford University, 1989


Thank You


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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