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Reducing life threatening conditions during extreme flood events: Benefits from implementing spillways to dykes
 

Reducing life threatening conditions during extreme flood events: Benefits from implementing spillways to dykes

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Reducing life threatening conditions during extreme flood events: Benefits from implementing spillways to dykes

Reducing life threatening conditions during extreme flood events: Benefits from implementing spillways to dykes

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    Reducing life threatening conditions during extreme flood events: Benefits from implementing spillways to dykes Reducing life threatening conditions during extreme flood events: Benefits from implementing spillways to dykes Presentation Transcript

    • Reducing life threatening conditions during extreme flood events: Benefits from implementing spillways to dykes Neuhold, C. & Nachtnebel, H.P. University of Natural Resources and Applied Life Sciences Department of Water, Atmosphere and Environment Institute of Water Management, Hydrology and Hydraulic Engineering
    • Content
      • Introduction
      • Objectives
      • Methodology
        • Case study area
        • Considered alternatives and scenarios
        • Flood risk assessment
      • Results
        • People exposed
        • Implementation of a spillway
        • Overall flood risk
      • Conclusions
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • Introduction
      • Substantial amounts were
      • invested in flood protection measures
      • Reported damages increase
      • tremendously and continuously
      • Period of 1900-2008
      • floods affected highest
      • number of people
      • compared to other
      • natural disasters (www.em-dat.com)
      • One of main causes – change in land use
      31 05 2010 Reducing life threatening conditions during extreme flood events source: Munich RE
    • Introduction
      • Change in land use within flood plains mainly from agricultural utilisation to industrial and residential areas
      • Modifications lead to remarkable increase of damage potential and people exposed
      • Implemented flood protection measures induce a feeling of safety and trigger improved land use
      • Need for integrated flood risk management strategies considering
        • recent flood experience
        • unexpected dyke failures
        • residual risk
        • non achievable total safety
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • Objectives
      • Implementation of a spillway to existing flood mitigation schemes
      • Analyses of hydrodynamic consequences
      • Assessment of overall flood risk on a micro scale level under special consideration of the number of people exposed , residential buildings and industrial sites
      • Discussion of benefits for flood risk management and resulting increase of flood protection reliability - compared to reported catastrophic consequences of dyke failures due to
        • Overtopping and subsequent breach formation
        • Insufficient maintenance and reduced stability
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • Methodological approach 31 05 2010 Reducing life threatening conditions during extreme flood events
      • Analyses focuses on an Austrian municipality
      • Numerous utilisations were exposed to floods
      • Implementation of a flood mitigation scheme in 1999 (safety up to a 100-years flood)
      • Development of several industrial firms accompanied by increasing residential areas in the former flood plain.
      • Substantial increase of vulnerability
    • Methodological approach
      • Considered flood mitigation alternatives for the case study area:
      • existing flood protection scheme
        • dykes
        • flood walls
        • flood retention basin
      • implementation of a spillway
      • restricted development in the flood plain area by imposing a building ban
      • Considered scenarios:
      • 30-years up to 5000-years flood event, including dyke breach
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • Methodological approach
      • Hazard assessment
        • hydrologic modelling (scenarios)
        • hydrodynamic modelling (alternatives and scenarios)
      • Vulnerability assessment
        • socio-economic consequences
        • people exposed (census data)
        • residential buildings (mapping)
        • industrial sites (interviews with chief operating officers)
      • Flood risk assessment
        • interaction of hazard and vulnerability
        • micro scale procedure (single object based)
        • economic criteria and intangible aspects
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • Results 31 05 2010 Reducing life threatening conditions during extreme flood events
      • First count: number of affected building
      • (Second count): people exposed
      • No count: no (reliable) data was available
      • In case of dyke overtopping people are exposed to floods regardless of the implementation of a spillway – outlines high development pressure within the municipality
      • Flood risk management strategies (spillway, building ban) demonstrate a considerable potential in increasing the effectiveness of the flood protection scheme
      Scenario alternative 1 alternative 2 alternative 3 dyke breach no protection HQ 30 170 HQ 100 1 1 196 HQ 300 80 (254) 41 (53) 71 276 437 (1072) HQ 1000 218 (635) 235 (647) 187 277 HQ 5000 330 (645) 291 331 (840)
    • Results 31 05 2010 Reducing life threatening conditions during extreme flood events
      • Effectiveness of spillway for flood events above the design level
      • Tremendous decrease of people exposed for 300-years flood (from 254 to 53)
      • Effect of spillway decreases by increasing flood discharge up to a 1000-years flood
      • For even higher floods no more positive effects are to be expected
      Scenario alternative 1 alternative 2 HQ 300 80 (254) 41 (53) HQ 1000 218 (635) 235 (647)
    • Results
      • Alt 1: existing mitigation scheme
      • remarkable increase of losses due to hinterland development
      • exceedingly high losses for scenario without measures
      • Alt 2: spillway
      • reduction of losses 10-15%
      • Alt 3: building ban
      • remarkable reduction of
      • overall losses
      • Dyke breach scenarios
      • increase of calculated losses
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • Conclusions
      • Implementation of spillways leads to an increase of reliability, because dyke failure and uncontrollable overtopping would be very unlikely
      • Further, there is a large potential to reduce the overall number of people exposed due to implementing spillways to existing dyke structures
      • The positive effect decreases with increasing return periods of flooding and will be compensated by a 1000-years flood within this case study area
      • The implementation of spillways is effective and efficient in terms of reducing the number of people exposed to extreme floods and provides sufficient time for emergency measures
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • Conclusions
      • The increase in vulnerability is clearly indicated by remarkably higher annual expected losses due to land use change and increasing development pressure
      • This increase of vulnerability would have been easily avoided by imposing a building ban after the implementation of the protection scheme
      • Risk assessment showed that a combination of all considered alternatives
        • flood mitigation measures
        • Spillway
        • building ban
      • would be the most effective flood risk management strategy
      31 05 2010 Reducing life threatening conditions during extreme flood events
    • 25 11 2009 A qualititative approach to assess flood risk associated with landfills Thank you for your attention! [email_address] +43 1 47654 5507 University of Natural Resources and Applied Life Sciences Department of Water, Atmosphere and Environment Institute of Water Management, Hydrology and Hydraulic Engineering