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.