Broughton Creek Floodplain Risk Management Study

Introduction

Cardno were commissioned by Shoalhaven City Council to undertake the Floodplain Risk Management Study and Plan for the Broughton Creek catchment. The catchment is approximately 518 km2 in size and surrounds the township of Berry on the NSW south coast. The study has been undertaken to define the existing flooding behaviour and associated hazards, and to investigate possible mitigation options to reduce flood damage and risk. The tasks were undertaken alongside community consultations to ensure that community concerns were addressed. In the past, flooding in the catchment has caused property damage and posed a hazard to residents. Significant flood events occurred in 2011, 2005, 2002, 1988 and 1974. A flood study was previously prepared that identified the flood behaviour in the study area (SMEC, 2008). An update has subsequently been undertaken in this study to improve the definition of the flood behaviour in the Berry Township, and in the areas immediately adjacent to the township. Details on the update and outcomes of the study are provided in Appendix B through Appendix E. Flooding was assessed for the 50% AEP, 20% AEP, 10% AEP, 5% AEP, 2% AEP and 1% AEP events, as well as the Probable Maximum Flood (PMF). Flood levels, depths and velocities were determined, as well as provisional hazard categories, and hydraulic categories. From the base case results, a number of flood mitigation options were examined to manage flooding within the Broughton Creek catchment. The identification and examination of these options was done in accordance with the NSW Government Floodplain Development Manual (NSW Government, 2005).