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004 Future Coastal Flood and Erosion Risk Management Schemes at Southsea and North Portsea Island
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004 Future Coastal Flood and Erosion Risk Management Schemes at Southsea and North Portsea Island

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Presentation given by Bret Davies (Havant, Portsmouth & Gosport Coastal Defence Partnership) at UPEN workshop - Climate change and the Solent: Opportunities and Vulnerabilities.

Presentation given by Bret Davies (Havant, Portsmouth & Gosport Coastal Defence Partnership) at UPEN workshop - Climate change and the Solent: Opportunities and Vulnerabilities.

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  • BD
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  • BD CHALLENGES AHEAD – Climate change – sea level rise, increased storminess, wetter winters, shortage of national funding. Need to make difficult decisions. We need to learn to adapt. At all tiers of this process we need data to improve our understanding of the coastline and to inform our decision making. Clive is now going onto explain how we gather some of this information and the types of info we need for design.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • This slide is a general overview of the Risks to Southsea (flood cell 1) If a breach in the defences occurred during a 1 in 200 tidal event today around 2,500 properties would be at risk of flooding In 100 years with sea level rise and increased wave activity the numbers of properties at risk of flooding from the sea increases to 1300. Note that this figure does not include any future development. In order to reduce the flood risk to the Southsea community the strategy estimates that around £57m is spent on new coastal protection schemes to protect over 0.5billion pounds worth of assets. Photo – shows localised wave overtopping at Long Curtain Moat near Clarence Parade
  • If no defences were in place, around 1500 properties are currently at risk of flooding from the sea This number increases to 4700 in 100 years time (not including any future development) This cell is strategically very important to the city because it includes critical access routes on and off the island. The critical infrastructure at risk of flooding from the sea (highlighted on the map) includes two main access roads and the islands only railway line. It is very important that this flood cell is defended.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.
  • The strategy is currently being compiled for submission to the Environment Agency for their technical approval Portsea Island was divided into 7 independent flood cells, the flood cells cover an area modelled as part of the strategy that is at risk of flooding during a 1 in 200 year tidal event. what this means is that a flood (or breach in defences) in any flood cell will not affect its neighbouring flood cells. For example a flood in Flood Cell 1 – Southsea will not flood Flood Cell 2 – Fraser Battery (to the East) or Flood Cell 7 – HM Naval Base (to the West) Hold the Line - The strategy recommends that Portsea Island’s coastline is defended for at least the next 100 years to protect the residential communities and the commercial interests in the city. £1.1 billion assets protected – in the event that no defences were in place, a 1 in 200 year probability flood (which has a 0.5% chance of occurring annually) would flood £1.1 billion pounds worth of assets. Assets include residential, commercial and MOD property and critical infrastructure such as roads, railway links and schools. The strategy has identified that Flood Cells 1 – Southsea and Flood Cell 4 – Portsea Island North are priorities. The flood risk to the communities and the deterioration to the existing defences means that Holding the line in these locations is imperative and schemes should be developed in these locations at the earliest available opportunity. The city councils next step is to seek approval for the strategy to develop business cases for Flood Cells 1 and 4 to release the capital grant to begin scheme design and development.

004 Future Coastal Flood and Erosion Risk Management Schemes at Southsea and North Portsea Island 004 Future Coastal Flood and Erosion Risk Management Schemes at Southsea and North Portsea Island Presentation Transcript

  • Future Coastal Flood and Erosion Risk Management Schemes at Southsea and North Portsea Island 15 th September 2011 Bret Davies Coastal Project Engineer Havant, Portsmouth & Gosport Coastal Defence Partnership
    • Part 1
    • Coastal Responsibilities
    • Coastal Partnership Team
    • Pressures on our Coastline
    • Strategic Coastal Management
    • Part 2
    • Portsea Island: Case Study
    Presentation Overview
    • Defra – Overall policy responsibility for flood and coastal erosion risk management in England
    • Environment Agency – Strategic Overview (all forms of flooding & coastal erosion)
    • Frontagers – responsible for their own frontage.
    • Maritime Authorities have ‘permissive powers’ and will only act in the Public Interest
      • - Technical
      • - Environment
      • - Economic (We can seek 100% Grant in Aid from the Environment Agency)
    Coastal Responsibilities
  • 1) Coastal Protection 2) Flood Defence
    • Water Resources Act - Environment Agency
    • Land Drainage Act - Local Authority
    • Low Lying Areas Susceptible to Flooding
    • Coast Protection Act - Local Authority
    • Land susceptible to erosion
  • HAVANT GOSPORT Coastal Partnership Team PORTSMOUTH PORTSEA ISLAND HAYLING ISLAND
  • “ Aim to reduce risks to people, the developed and natural environment from coastal flooding and erosion by promoting the provision of technical, economical and environmentally sound coastal management measures.”
    • The Coastal Team:
    • Develop strategic plans,
    • Influence the planning process to ensure development does not disrupt coastal processes or adversely effect the environment,
    • Promote sustainable approaches to coastal management
    • Monitor the coastline.
    What Does The Coastal Team Do?
    • Climate change & sea level rise is happening
    • Certainty that it will affect us all,
    • - either threat or opportunity
    • Uncertainty with regard to rates of change
      • uncertainty appears to be increasing as we learn more!
      • larger more sophisticated models does not necessarily reduce uncertainty
    • Relative Rising Sea Levels
      • 4mm/yr till 2025
      • 8.5mm/yr 2025 to 2055
      • 12mm/yr 2055 to 2085
      • 15mm/yr 2085 to 2115
    • Wetter winters and increased frequency of storms
    Pressures on our Coastline: Climate Change
  • Pressures on our Coastline: Climate Change PRESENT DAY YEAR 2115
    • Respond to Climate Change by mitigation and adaptation
    • Promote adaptation techniques in flood and erosion risk management
    • Need to balance the needs of both people & the environment
    • Accept coastal change in some areas & invest in coastal defences in others
  • Pressures on our Coastline: Environmental Designations SSSI SAC Ramsar Site SPA
  • Pressures on our Coastline: Birds & Wildlife Important Network of Bird Roosting Sites
  • Pressures on our Coastline: Coastal Squeeze
    • Foreshore tries to moves landward
    • Sea wall or development stops movement
    • Habitat gets squeezed
      • and there is a risk they be lost altogether
  • <<< Coastal Groups with Local Authorities and Environment Agency >>> Strategic Coastal Management SHORELINE MANAGEMENT PLAN STRATEGY STRATEGY SCHEME SCHEME SCHEME SCHEME SCHEME
  • Photo courtesy of The News Portsea Island Coastal Flood and Erosion Risk Management Schemes
    • Portsea Island Coastal Strategy Study (2010)
    • £1.25billion of property & infrastructure at risk of flooding on Portsea Island
    • 2 Priority Flood Cells:
      • Flood Cell 1: Southsea
      • Flood Cell 4: North Portsea Island
    Flood Cell 1 Flood Cell 4 Introduction: Findings from the Portsea Island Coastal Strategy The Way Forward:
    • Develop 2 schemes to the 2 Priority Flood Cells
  • SHORELINE MANAGEMENT PLAN North Solent SMP (2010) STRATEGY Portsea Island Coastal Strategy Study (2010) SCHEME Portsea Island Coastal Flood & Erosion Risk Management SCHEME OPTION DEVELOPMENT
    • Preferred Option
    • ‘Hold the Line’
    • Present Value Cost = £43m
    • Present Value Benefit = £585m
    • Benefit Cost Ratio = 13.6
    • Flood Risk (Current)
    • 2,311 Residential Properties
    • 202 Commercial Properties
    • Flood Risk (Year 100)
    • 3,932 Residential Properties
    • 377 Commercial Properties
    Photo courtesy of The News Introduction: Flood Cell 1 - Southsea
    • Flood Risk (Current)
    • 1,414 Residential Properties
    • 147 Commercial Properties
    • Flood Risk (Year 100)
    • 4,234 Residential Properties
    • 490 Commercial Properties
    • 2 MoD Properties
    • Critical Infrastructure at Risk
    • Two of three main access roads
    • Railway
    • Preferred Option
    • ‘Hold the Line’
    • PV Cost £37m
    • PV Benefits £569m
    • Benefit Cost Ratio: 15.4
    Introduction: Flood Cell 4 - Portsea Island North Chichester and Langstone Harbours SPA, SAC, SSSI, Ramsar
  • History of Flooding: Southsea Photo’s courtesy of The News
  • History of Flooding: Southsea ‘South Parade’
  • Flood Risk to North Portsea Island, ‘Anchorage Park’ NOTE: 1.8m = High Tide at time of photo, 2.3mAOD = Highest Astronomical High Tide, 2-3mAOD Sea Wall Crest Height, 3.3mAOD 0.5%AEP Extreme Water Level (Year 2009) Front view of Sea Wall Rear view of Sea Wall 1.8mAOD 2.3mAOD 3.3mAOD 2-3mAOD Crest Height
    • Inundation Model (ISIS)
    Priority: Flood Risk to Portsea Island Year 0 Year 10 Year 30 Year 50 Year 10 Year 30 Year 50 Year 100
  • Flood Cell 1: Southsea – Existing ‘Tired’ Coastal Defence Structures
    • Flood Cell 1
    Priority: Coastal Defences COMBINED RISK DOES NOT MEET RECOMMENDED STANDARD OF PROTECTION OR RESIDUAL LIFE LESS THAN 10 YEARS
  • Communities at Flood Risk across Southsea Flat Open Space Key: Assets at Risk of Flooding Residential Properties Non-residential Properties Ferry/Hovercraft Terminal Heritage & Archaeology Main Roads Communities at Flood Risk across Southsea
  • Flood Cell 4: North Portsea Island – Existing ‘Tired’ Coastal Defence Structures
    • Flood Cell 4
    Priority: Coastal Defence COMBINED RISK DOES NOT MEET RECOMMENDED STANDARD OF PROTECTION OR RESIDUAL LIFE LESS THAN 5 YEARS
  • Communities at Flood Risk across North Portsea Island Rear view of Sea Wall Key: Assets at Risk of Flooding Residential Properties Non-residential Properties Railway Station Main Railway Line Main Arterial Roads
  • Useful Web Sites: Havant, Portsmouth & Gosport Coastal Defence Partnership http://www.havant.gov.uk/havant-7221 Partnership for Urban South Hampshire Strategic Flood Risk Assessment http:// maps.hants.gov.uk/havantstrategicfloodriskassessment / North Solent SMP www.northsolentsmp.co.uk Southern Coastal Group www.southerncoastalgroup.org.uk Email: [email_address]