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Flood Risk Assessment for Emergency Preparedness and Response .

Flood Risk Assessment for Emergency Preparedness and Response. Paolo Reggiani & Nathalie Asselman WL | Delft Hydraulics Symposium on Multihazard Early Warning Systems for Integrated Disaster Risk Management WMO- Geneva 23-24 May 2006. Definition of Flood Risk:. Risk = damage x probability.

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Flood Risk Assessment for Emergency Preparedness and Response .

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  1. Flood Risk Assessment for Emergency Preparedness and Response. Paolo Reggiani & Nathalie Asselman WL | Delft Hydraulics Symposium on Multihazard Early Warning Systems for Integrated Disaster Risk Management WMO- Geneva 23-24 May 2006

  2. Definition of Flood Risk: Risk = damage x probability

  3. Damage Damage is function of: • type and number of buildings • land use • infrastructure • flooding characteristics….

  4. Flooding characteristics Important flooding characteristics: • time of inundation (winter / summer) • rate of rise • duration of inundation • water depths • flow velocities

  5. Damage andcasualties model developed at Delft Hydraulics for the Dutch situation

  6. General • Development of a standard method to compute costs and casualties caused by flooding. • Implemented in a Hydrological Information System (HIS). • Initiated by Road and Hydraulic Engineering Division, Directorate-General of Public Works and Water Managementm, The Netherlands. • The method is applicable for situations world-wide.

  7. Aim and applicability • Modelling system to estimate/predict damage caused by low-frequency floods. • Floods and inundations originating from “larger” water bodies. YES: dike breaks. NO: local inundation from sewage systems. • No difference between salt and fresh water.

  8. What is modelled? • Casualties • Damage • loss of capital goods (houses, infrastructure, etc.) • reduced productivity • loss of income (businesses, shops, restaurants, etc.)

  9. Data • land use type • nr of inhabitants • etc. land use Procedure damage damage function water depth • Model • damage functions Flooding scenario

  10. Total damage estimation: with: i = damage-factor for category i (e.g. houses, roads, etc.) ni = number of units in category i Di = max. damage per unit in category i

  11. Damage factor i Varies from 0 to 1 Function of: • depth of inundation • (critical) flow velocity • storm(waves) • rate of rise (important for number of casualties)

  12. Problems: • Number of casualties depends on water depth and flow velocities after dike break, but also on possible warning and evacuation beforehand • Damage relations for other categories mainly based on theory as little ‘experimental’ data are available form previous flood experience • Use of experimental data still poses problems

  13. North Sea Amsterdam Den Haag Utrecht Rotterdam Rhine Meuse

  14. December 1993 - January 1995

  15. Damage claims

  16. Damage data private properties: houses

  17. Damage data private properties: furniture

  18. Why are the costs for the second flood lower ? • People take measures to reduce the damage: • tiled floor instead of parquet floor • put furniture on first floor when probability for flooding increases --> difficult to include in damage model !!

  19. Improvement of the damage models: current research • adjust damage functions • economic – loss of income (TU Twente) • houses and roads (TNO) • environmental risks (Alterra, TNO, GeoDelft, CSO, WL) • casualties / victims (WL, DWW)

  20. Case study area ‘Zuid-Holland’

  21. Flooding characteristics: water depth

  22. Flooding characteristics: flow velocities

  23. Isochrones of inundation (in hours after dike break)

  24. Is it possible to escape ? • based on evacuation model for different area empirical relationships established for different areas

  25. Percentage of inhabitants that are able to escape (based on data on road network)

  26. Estimated number of casualties (based on 1953 flood data, Zeeland province)

  27. The Problem – time to escape

  28. First estimate

  29. Second estimate

  30. Main lesson learned? • A traffic / transport model is needed to obtain the most realistic estimate of potential number of casualties • Good instructions beforehand may reduce the risk of wrong decisions with respect to choice of route

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