This report describes the hydraulic modelling for the first stage of a flood study of the Hawkesbury-Nepean Valley commissioned by the Water Board in 1987. The study is required in order to "determine the effects that various arrangements of major or future works for Warragamba Dam have on flooding in the valley" (Revised Brief for the Preparation of an E.I.S., Water Boards August 1987). Stage 1 required a simplified model to be developed, calibrated and used to provide a measure of the relative effects on flooding of options for such works.

The model used is described in Section 2. Section 3 describes the calibration phase, in which three historical floods were used to adjust model parameters in order to match historical and modelled flood heights. The various options for Warragamba Dam flood protection works have an impact on the outflow hydrographs from the dam. Outflow hydrographs were determined for each option for five "design" floods and run through the calibrated hydraulic model. Peak flood heights were then tabulated and compared at three key locations In the valley. Section 4 describes the options while Section 5 discusses the modelling methods used to run these cases. The results are presented as a series of tables and graphs.