This report documents the Burrill Lake Catchment Flood Study which defines existing flood behaviour and establishes the basis for floodplain management activities in the future.

This report documents the Burrill Lake Floodplain Risk Management Study and Plan which investigates and presents a flood risk management strategy for the catchment. The study identifies the existing flooding characteristics and canvasses various measures to mitigate the effects of flooding. The end product is the Floodplain Management Plan, which describes how flood liable lands within the Burrill Lake catchment are to be managed in the future.

Tabourie Lake Floodplain Risk Management Study- to be read in conjunction with the Floodplain Risk Management Plan

The Raymond Terrace Flood Study has been prepared for Port Stephens Council (Council) to define the existing flood behaviour in the western Raymond Terrace catchments and establish the basis for subsequent floodplain management activities. The study will also assist Council in considering future upgrades to the drainage network and flood relief pump capacity to the Hunter River. This project has been conducted under the State Assisted Floodplain Management Program and received State financial support.

Introduction A Floodplain Risk Management Study (FRMS) and Floodplain Risk Management Plan (FRMP) for the Broughton Creek catchment has been prepared by Cardno for Shoalhaven City Council. The Study identifies and examines options for the management of flooding within the Broughton Creek catchment floodplain. This Plan takes the recommendations from the Study and incorporates them into a plan of implementation. Both studies have been prepared in accordance with the NSW Government Floodplain Development Manual (2005).

1.3 Overview of Report This Report (Volume 1) summarises the investigations and presents plans showing water surface profiles and the indicative extents of flooding. The Report is supported by three Appendices, which provide additional details on flooding patterns and are bound in Volume 2. Section 2 of the Report contains background information including a description of the catchments, a review of the data base available for the study and a discussion on the history of flooding in the two catchments. This led to the selection of the historic floods for calibration and testing of the RORB hydrologic model of Currambene Creek. Streamflows recorded at The Falls gauging station, together with pluviographic data recorded at the RAN Air Station at HMAS Albatross and daily rainfall data were used for this purpose. Appendix A provides further details of the calibration process. Section 3 deals with the derivation of design runoff hydrographs from the study catchments. The RORB runoff-routing program was adopted for this study. Models of the catchments of Currambene and Moona Moona Creeks were developed. This step involved the determination of design storm rainfall depths over the catchments for a range of storm durations, and conversion of the rainfall hyetographs to discharge hydrographs. Further details of this phase of the investigation are presented in Appendix B. Section 4 deals with the development of the hydraulic models of the main streams and their estuarine surrounds. The unsteady flow version of the HEC-RAS software was used for this purpose. There were no historic flood level data available for calibration of the hydraulic models. Accordingly, selection of model parameters required a detailed review of the engineering literature and previous studies of a similar nature undertaken by the Study Team, supplemented by sensitivity analysis. The results of model testing are presented in the first part of Appendix C. Section 5 details the results of the hydraulic modelling of the design floods using HEC-RAS. Results are presented as water surface profiles and plans showing indicative extents of inundation. Appendix C presents further details on the derivation of design flood information and contains diagrams showing zones of provisional high and low hazard on the floodplain for selected design floods events, categorisation of the floodplain into floodway and flood storage areas and tabulations of peak levels and flow velocities at each cross section in the hydraulic models. Section 6 summarises the flood study investigations and identifies several flood related issues on the tributaries of Currambene Creek which will require further study during the Floodplain Risk Management Study and Plan. Section 7 contains a list of References.

Floodplain RIsk Management Plan to be read in conjunction with 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).

The Flood Study, Floodplain Risk Management Study and Floodplain Risk Management Plan documents

Chapter 2 contains background information including a brief description of the study catchment and its drainage system, details of previous flooding investigations, a summary of community consultation undertaken as part of this present study (refer Appendix A for details), and a brief history of flooding within the catchment. Chapter 3 deals with the hydrology of the Lane Cove River and Swaines Creek catchments, and describes the development of the RORB and DRAINS hydrologic models which were used to generate discharge hydrographs for input to the hydraulic model. Chapter 4 deals with the development of the TUFLOW hydraulic model which was used to analyse flood behaviour in the study area. Chapter 5 deals with the derivation of design discharge hydrographs, which involved the determination of design storm rainfall depths over the catchments for a range of storm durations and conversion of the rainfalls to discharge hydrographs. Chapter 6 details the results of the hydraulic modelling of the design floods. Results are presented as water surface profiles and plans showing indicative extents of inundation for a range of design flood events up to and including the PMF. A provisional assessment of flood hazard and hydraulic categorisation is also presented. (The assessment of flood hazard according to velocity and depth of floodwaters is necessarily “provisional”, pending a more detailed assessment which includes other flood related criteria, to be undertaken during the future FRMS.) The results of various sensitivity studies undertaken using the TUFLOW model are also presented, including the effects of changes in hydraulic roughness, partial blockage of the piped stormwater system, and potential increases in rainfall intensities and sea levels due to future climate change. This chapter also deals with the selection of Interim FPL’s for the study area. Chapter 7 contains a list of references. Chapter 8 contains a list of flood-related terminology that is relevant to the scope of the study. Appendix A provides details of the collection of historic flood data and describes the testing of the hydrologic and hydraulic models. Figures referred to in both the main report and the appendices are bound in a separate volume of the report (refer Volume 2).