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Natural Disasters: Impact Assessment for Sustainable Recovery STRATEGIC PLANNING AND ASSESSMENT

Natural Disasters: Impact Assessment for Sustainable Recovery STRATEGIC PLANNING AND ASSESSMENT Professor Bryan Jenkins Waterways Centre for Freshwater Management. ASSESSMENT APPROACHES. Resilience assessment for natural disasters - flood management for Waimakariri River

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Natural Disasters: Impact Assessment for Sustainable Recovery STRATEGIC PLANNING AND ASSESSMENT

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  1. Natural Disasters: Impact Assessment for Sustainable Recovery STRATEGICPLANNING AND ASSESSMENT Professor Bryan Jenkins Waterways Centre for Freshwater Management

  2. ASSESSMENT APPROACHES • Resilience assessment for natural disasters • - flood management for Waimakariri River • Strategic assessment for development strategy • - Greater Christchurch Urban Development Strategy • Natural hazard assessment • - Liquefaction risk in Christchurch • Recovery strategy • - Avon Otakaro River Park

  3. MANAGING NATURAL HAZARDS • Traditional Approach • - design for protection for a specified return event • 2004 Manawatu Floods • - Palmerston North protected • - rural areas flooded when stopbank failed • - flooded areas remain flooded: flood waters unable to get back to river

  4. Manawatu - Fitzroy Bend

  5. Oroua - Kaimatarau Rd

  6. Waimakariri in Christchurch, 1868

  7. CHRISTCHURCH FLOOD RISK

  8. RISK MANAGEMENT APPROACH TO FLOODING • Design flow for stopbank capacity • 1 in 500 year flood flow: 4,730 cumecs • Risk for flood flows greater than design flow • 1 in 10,000 year flood: 6,500 cumecs • Risk of breakouts from stopbank failure below design flow • 70% design flow: 3,300 cumecs • Risk in 30 year period • 50% chance of stopbank threatened • 10% chance of urban area flooding

  9. RESILIENCE APPROACH • Secondary stopbank designed for 1 in 10,000 year flood: 6,500 cumecs • Primary stopbankfailure: floodwaters retained between primary and secondary banks and returned to the river • Secondary stopbank failure: only excess volume released and time available for emergency response

  10. SECONDARY STOPBANK

  11. CONTAINMENT AND RETURN OF BREAKOUT FLOW

  12. STRATEGIC ASSESSMENT FOR GREATER CHRISTCHURCH URBAN DEVELOPMENT STRATEGY • Non Statutory Collaborative Approach • Development Opportunities and Constraints • Consideration of Development Options • Assessed against Four Well-Beings • Key Indicators for Comparison • Community Feedback • Final Strategy • Statutory Backing through Regional Policy Statement

  13. Limits on Development Airport Noise and Aquifer Protection Zones • Other environmental “layers” taken into account, e.g.: • Port Hills • Floodplains • Ecological systems • Strategic Infrastructure

  14. Canterbury Regional Policy Statement Plan Change 1

  15. RPS ENDORSED UNDER SPECIAL LEGISLATION • Planning framework has to provide for relocation and rebuild following red zoning • RPS process needs to be sped up and modified to accommodate earthquake events • More intensive use of land within existing urban areas and greenfields development • RPS covers: areas for urban development; residential densities; provisions for business; sequencing of developments; enabling integrated management

  16. Canterbury Regional Policy Statement Approved Map

  17. NATURE OF LIQUEFACTION RISK • Ground shaking of unconsolidated silts and sands • Soil mass compacts and decreases in volume • This causes water to be ejected: sand boils • Ground surface may subside: differential settlement puts foundations at risk • Lateral spread on sloping surfaces near rivers streams and coastal areas

  18. FACTORS USED TO ASSESS LIQUEFACTION POTENTIAL • Strength of ground shaking • Duration of shaking • Soil properties (grain size and density) • Depth to water table • Confining pressures

  19. ASSESSMENT OF LIQUEFACTION GROUND DAMAGE • Ground subsidence • Slope failure of sloping ground • Lateral spread of natural banks and embankments

  20. HOUSE CRACKING DUE TO LATERAL SPREAD FROM LIQUEFACTIONSept 4 2010earthquake

  21. MITIGATION OF LIQUEFACTION RISK • Avoidance of areas with liquefaction potential • Methods of mitigation - stabilising ground - foundation design - strengthening structures • Examples of mitigation - vibro compaction of soil: W/W treatment plant, • Pegasus subdivision - piles through liquefiable layers: Opawa road bridge - stone columns: Paul Kelly stand

  22. LAND DAMAGE IN SUBURBS ALONG AVON RIVER (as at 5 Nov 2010)

  23. PHYSICAL IMPACTS OF EARTHQUAKES • Building damage • Liquefaction • Ground settlement • Sewage discharge • Hydrology changes

  24. ELEVATION CHANGE IN ESTUARY

  25. EFFLUENT EFFECTS ON ESTUARY Water nitrogen (blue) Sea lettuce chlorophyll (green) Diversion Quake I Quake II

  26. LAND ZONED RED

  27. AVON OTAKARO RIVER PARK • Ecological and recreational reserve • Memorial to those who lost lives • Retention of garden elements of demolished homes • Pedestrian and cycle paths • Land and water based recreational facilities • Tangatawhenua cultural enhancement • Stormwater wetland treatment and sewage overflow temporary storage

  28. CONCLUDINGCOMMENTS • Use of Resilience Assessment - design to prevent failure not a frequency standard • Use of Strategic Assessment - valuable in guiding expected development; invaluable in unexpected events • Use of natural hazard assessment - avoidance or mitigation of risk • Recovery Strategy - opportunity to address old as well as new issues

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