REC324-4303

Risk-based approach to calculating flood planning: That, to take account of greater knowledge of climate change, Government reinforce its adoption of a risk-based approach to calculating the flood planning level for planning purposes and, through the NSWRA, immediately start a process of revising all flood planning level calculations in the state’s high-risk catchments. Flood planning level re-determinations for all high-risk catchments should be completed within 3 years. These revised flood planning levels will need to be factored into all development applications (in-progress and new) in those high-risk catchments. The risk profile of high-risk catchments should be revisited at appropriate time intervals to check that levels are current. A review should take place if there has been a significant trigger event (i.e. changed rainfall, development) or at least every 5 years. As well as reviewing the flood planning level, this 5-yearly review should include reviewing any floodplain lease conditions and adjusting them as necessary in the light of better knowledge of climate change impacts. In working out a tolerable, risk-based flood planning level, consideration should be given to the PMF, 1% AEP, 0.02% AEP, existing development, approved but not yet constructed developments, and existing and approved but not yet constructed evacuation routes.
In coordinating this flood planning level re-determination process, NSWRA should work closely with local councils, DPE, communities, state water authorities and state and national engineering and research organisations. In doing so, the NSWRA should also:
• extend and then maintain the DPE state-wide flood database and associated visualisation interface. This database, which should link to LandiQ, would support:
— monitoring of the flood warning and sensing environment
— monitoring of trends in rainfall activity and impacts, including timing, cause, extent and intensity
— tracking trends and identifying patterns in associated weather and climate signals that contribute to severe floods
— evaluation of the cost and effectiveness of risk mitigation efforts, including land preparation, planning use and management, to enable a better understanding of what works
— simulation of extreme rainfall events and resultant flooding
— identification of ‘at risk’ river and catchment systems for flash flooding
— rapid and effective deployment of resources during a flash flood event
• act as the main coordination point for all NSW hydrological modelling, working with local government, other state agencies, universities, professional bodies (e.g. Engineers Australia) and the Australian Government (especially the Bureau of Meteorology and CSIRO) to improve future NSW flood risk assessment (and hence accuracy and timeliness of flood prediction) by building more formal connections between the extensive existing physical hydrological modelling (done by various NSW agencies) with the Bureau’s meteorological and climatological research and riverine flood models
• support local councils to improve modelling of and ensure adequate and appropriate alarm systems for flash flooding.