Climate change: Meeting the challenge of flood risk

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Climate changeMeeting the challenge of flood
risk

• James Sharp - Pellings LLP
• Planning Flood Risk
• Alan Fogarty - Cundall
• Flood Risk Assessments
• Peter Wade - Pellings LLP
• Flooding Why we should care and what we can do

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James Sharp

• Planning Flood Risk

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Planning and flood risk

• 2007 The Year of the Flood
• 13 killed in Northern and Western England
• 48,000 homes and 7,000 businesses inundated
• Massive disruption and financial losses

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Assessment of flood risk
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Types of flooding

• Flooding from rivers
• Flooding from the sea
• Flooding from land
• Flooding from ground water
• Flooding from sewers
• Flooding from reservoirs, canals, and other
  artificial sources

66 of homes flooded in summer 2007 occurred from
surface water drains, culverts and sewers
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PPS25 Development and flood risk

• Key Objectives
• Appraising Risk
• Managing Risk
• Reducing Risk

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Key features of PPS25 are as follows

• A strategic, plan led focus with more front
  loading of flood risk
• More attention to flooding from sources other
  than rivers and the sea
• Formalisation of regional flood risk appraisals
  and strategic flood risk assessments,
  contributing to sustainability appraisals and
  soundness tests
• A stronger sequential approach to allocating land
  and granting permission in areas at risk of
  flooding

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Key features of PPS25 are as follows

• Introduction of vulnerability classes for
  different types of development
• Climate change allowances based on the UK climate
  impact programme 2002 projections to provide a
  quantifiable measure for developers and planners
• A new Exception Test where development in flood
  zones is needed for wider sustainability reasons
• A focus on the consequences as well as the
  probability of flooding, because the schemes have
  to be safe over their life time taking climate
  change into account

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Flood zones

• Zone 1 Low probability
• Less than in 1,000 annual probability of river or
  sea flooding in any year
• Zone 2 Medium probability
• Between a 1 in 100 and 1 in 1,000 annual
  probability of river flooding or a 1 in 200 and
  1 in 1,000 annual probability of sea flooding in
  any year
• Zone 3a High probability
• 1 in 100 or greater annual probability of river
  flooding or 1 in 200 or greater annual
  probability of flooding from the sea in any year
• Zone 3b The functional flood plain
• Land where water has to flow or be stored at
  times of flood

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The Exception Test

• For the Exception Test to be passed
• It must be demonstrated that the development
  provides wider sustainability benefits to the
  community that outweigh flood risk
• The development should be on developable
  previously developed land
• A FRA must demonstrate that the development will
  be safe, without increasing flood risk elsewhere,
  and, where possible, will reduce flood risk
  overall

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Alan Fogarty

• Flood Risk Assessments

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Flood Risk Assessments
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Introduction

• Introduction
• Flood Risk Assessment
• BREEAM
• SUDS

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PPS 25 Development Flood Risk

• Securing the Future preparing for the climate
• change that cannot now be avoided
• Rising sea levels
• High intensity rainfall
• River flooding
• Flash flooding

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Climate Change

• Rising Sea Level
• Land rising in the North
• Dropping in the South East

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Climate Change UK 2000
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Swiss Alps
200?
1875
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Climate Change Ireland 2000
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Climate Change

• Deeper water increased wave height
• Increased wind speed
• Greater potential for storm surges

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Flooding

• A natural phenomena types
• River
• Sea
• Land
• Rising Groundwater
• Sewers

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Planning Authorities

• Regional and Local authorities should

• Appraise Risk Regional flood risk assessment
• Manage Risk Identify low risk sites and
  restrict development in higher risk sites
• Reduce Risk Storage, SUDS, Defences

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Testing

• Sequential Test Direct development to sites of
  lower risk
• Exception Test Where Sequential Test cannot
  deliver acceptable sites, but development is
  necessary to avoid social or economic blight and
  the need for essential civil infrastructure to
  remain operation during floods

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Environmental Agency

• The Environment Agency has statutory
  responsibility for flood management and defence
  in England
• Will support the planning system
• Providing timely information and advice on
  flooding issues that is fit for purpose

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Environmental Agency Flood Maps
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Planning Flood Risk Assessment

• FRA are required in almost all cases
• Large developments and high risk areas require
  direct discussions with EA
• Otherwise directly with the LPA

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EA Flood Zones
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Purpose of Flood Risk Assessment

• Identify whether site at risk from current or
  future flooding
• Demonstrate that the site is safe and reduces
  overall flood risk
• Identify any flood risk elsewhere
• Mitigation

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Methodology of Flood Risk Assessment

• Conduct a background search including
  consultation with EA Local Authority or other
  potential sources of data.
• Review topographic survey of the site and
  proposed site layouts in relation to the
  potential flood risks and procure additional
  survey as required.
• For surface water drainage, assess the existing
  and proposed surface water runoff from the site
  based on proposed layouts.
• For fluvial flood risk build a mathematical
  hydraulic model of to confirm the extent of the
  flood risk.
• Attend project meetings to discuss the
  development of an outline drainage scheme.
• Assess all other potential sources of flood
  risk-such as overland flow and groundwater
  flooding.
• Advise the design team on issues that may affect
  the acceptability of the scheme to the
  Environment Agency and Local Authority.
• Agree mitigation measures through
  discussions/meetings with the Environment Agency.
• Prepare a flood risk assessment report to submit
  with the planning application to the Local
  Authority. A discussion of mitigation measures to
  minimise the flood risks will be included in the
  report.

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EA Flood Zones

• Zone 1 Low Probability site not at risk from
  flooding from adjacent watercourses or marine
  tides. Suitable for all development types.
• Zone 2 Medium Probability site lies within
  the floodplain of the extreme flood event. Not
  suitable for police/fire stations, basement
  dwellings, permanent caravan parks.
• Zone 3 High Probability A site lies within
  the floodplain of the 1 probability event.
  Water compatible and essential infrastructure.

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EA Flood Zones

• Zone 1 the primary flood risk is to others by
  surface water runoff
• Mitigation EA
• Encourages SUDS
• On-site attenuation of the 100 year event
• Run off rate green field site

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EA Flood Zones

• Zone 2 3 on and off site risk
• Mitigation EA
• No habitable spaces below 1 flood level
• Occupants must be able to evacuate safely
• Developments should not obstruct flood waters or
  reduce flood plane storage

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EA Flood Zones
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BREEAM

• 2 Credits in a zone with low annual probability
  of flooding or
• 1 Credit in a zone of medium annual probability
  of flooding and the ground level, car parking and
  access is above the design flood level

1.5 .75
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BREEAM

• 1 Credit Sustainable Urban Drainage attenuate
  50 of the peak flow rate to natural watercourses
  or municipal drainage systems, in Zone 1 or
• 1 Credit Sustainable Urban Drainage attenuate
  75 of the peak flow rate to natural watercourses
  or municipal drainage systems, in Zone 2 or
• 1 Credit Sustainable Urban Drainage attenuate
  100 of the peak flow rate to natural
  watercourses or municipal drainage systems, in
  Zone 3

1.5
No credit awarded if development has proceeded
against the recommendation of the relevant flood
defence agency
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Mitigation Traditional Drainage Problems

• Designed to move rainwater rapidly to either a
  watercourse or soak away
• Hard surface run-off increase the risk of
  flooding downstream, as well as speed
• Surface water run-off can contain contaminants
  such as oil, affecting biodiversity and potential
  use
• Diverting rainfall to piped systems, depletes
  ground water in dry weather

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Mitigation SUDS

• Sustainable Urban Drainage Systems
• Reduce the potential of flooding on new and
  existing developments
• Helps to protect and enhance ground water quality

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Mitigation SUDS
Permeable Pavement
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Mitigation SUDS
Surface Water retention filtration
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Mitigation SUDS
Attenuation Tanks
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Summary

• Increased Planning complexity
• Early consultation with EA
• Early consultation with Local Planners

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Peter Wade

• Flooding Why we should care and what we can do

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Facts and Figures

• 1 in 3 new homes will be built on floodplains
• Two million homes are at risk 1 in 10
• 200,000 homes are at very high risk
• 160,000 businesses are at risk
• The average annual damage from flooding is
  currently 1 billion. This could increase to 20
  billion if we take no effective action
• Risks from weather are increasing by 2.4 per
  year on ABI evidence

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Facts and Figures

• Sea levels are rising by 3.1mm per year
• High water in London has risen by 0.8 metre per
  century
• Global mean sea level has risen about 0.22 metre
  per century. With global warming this could
  become 0.33 metre
• Last years floods led to 55,000 homes being
  flooded and the damage costing 3 billion.
  Average claims were 20,000 per property

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What can be done?

• A new Thames Barrier is planned along with
  improvements to flood defences
• The new Thames Tideway Tunnel is planned to
  assist with sewer surcharge
• Owners of properties should carry out audits to
  establish which ones are at risk
• Owners should undertake physical measures where
  possible such as moving equipment out of basement
  areas, installing electronic warning devices and
  having temporary barriers, airbrick covers etc
  ready in the event of imminent flooding

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What can be done?

• New buildings should be designed to cope with
  flooding
• Elements of both existing and new buildings can
  be designed to be more resilient to flood waters
  such as use of render plaster, keeping electrics
  above flood levels and making basement and ground
  storeys watertight where possible
• In the event of imminent flooding, valuable or
  essential items should be moved away from the
  flood risk areas
• Take a photographic record of the existing
  condition of the property particularly where
  historic buildings are involved

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What can be done?

• Prepare a flood plan and ensure all occupiers
  know what to do and agree evacuation routes
• If flooding is likely, turn off electrical power
  and gas supplies
• Avoid moving in flood water as it is nearly
  always contaminated. Following a flood,
  sterilisation of internal areas is important and
  power supplies should be checked before being
  re-connected
• Check with the Environmental Health Department
  whether contaminants are likely to be present
• Soil beneath timber floors may need to be
  completely removed if contaminated

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What can be done?

• With historic buildings special care is needed
  and consent may be required to replace damaged
  timber and plaster finishes
• Dry out buildings slowly or else historic
  features could be damaged. Where possible use low
  background heating, natural ventilation and
  dehumidifiers
• With new buildings, minimise the use of hard
  landscaping to avoid excessive run-off and
  surcharging of drains
• With new drainage installations in vulnerable
  areas, install one-way valves and ensure drainage
  connections can be turned-off if surcharging is
  likely

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What can be done?

• Check all drains following a flood as silt and
  debris can cause blockages
• Monitor timber for evidence of fungi and rot for
  at least six months after a flood
• Some defects will only become apparent many
  months after the building has dried out

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The Thames Barrier

• It was 1922 when central London last flooded
  killing 14 people and causing widespread damage
• 1953 was a major wake-up call. A storm surge
  caused 300 deaths and this largely affected the
  lower parts of the Thames
• The barrier was designed in the 1970s when sea
  levels were rising by 1.8mm per year. Levels are
  now rising by 3.1mm per year
• The barrier opened in 1984 at a cost of around
  500 million
• The barrier is designed to cope with 8mm of sea
  rise per year and should cope with a 1 in 1,000
  year storm surge up to 2030

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The Thames Barrier

• A new barrier is currently being planned as the
  predictions are worsening
• Current climate predictions are optimistic and it
  is thought that by 2030 the current barrier may
  not be able to cope
• Much depends on the rate of melting of the
  Greenland and Antarctic ice sheets. Latest
  evidence shows these to be melting at an alarming
  rate
• It could take 20 years to design and construct a
  new barrier and associated flood defences

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Thames Tideway Tunnel

• In 2006 the Minister of State for Climate Change
  and the Environment approached Thames Water to
  look at ways of tackling Londons sewer
  overflows. This was following recent discharges
  of raw sewage directly into the River Thames.
  This is a regular occurrence
• Thames Water produced two options, the most
  likely one being the construction of a 30km long
  tunnel beneath the Thames
• This tunnel will be 7 metres in diameter and the
  work will also include improvements to the
  Beckton Sewage Works and other major sewers
• The latest estimated cost is 1.7 billion

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Thames Tideway Tunnel

• The work will be subject to a Public Enquiry and
  the purchasing of land
• It is likely that the work will take up to 13
  years to complete and there is a need to complete
  some of the work in time for the Olympics
• At the present rate, the work could add up to 50
  to each of Thames Waters customers annual bills
• In addition to reducing raw sewage discharge into
  the Thames, it is hoped that surcharging of
  secondary sewers throughout London will be
  alleviated. This risk increases with increased
  development
• Remember that last year 66 of homes flooded was
  due to drain and sewer surcharges

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Sources of Information

• The following websites are useful sources
• Environment Agency www.environment-agency.gov.uk
  
• Environment Agency postcode search facility
  www.environment-agency.gov.uk/subjects/flood
• Thames Water www.thames-water.com
• English Heritage www.english-heritage.org.uk
  (use search box for the Technical Advice Notes)
• Association of British Insurers www.abi.org.uk
• In addition the internet is an excellent source
  of flood prevention productswww.aquatitesystems.
  com, www.floodark.co.uk, www.floodguards.com,
  www.floodgate.ltd.com

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