The Hawkesbury-Nepean River catchment is one of the largest coastal basins in NSW with an area of 21,400 square kilometres. The catchment at Penrith is 52% of the total area and of this portion, 80% is under the control of Warragamba Dam. This study culminates several stages in the progressive evolution of a two dimensional numerical flood model of the Nepean River through the Penrith Local Government Area. The initial flood model development commenced in 2005 by revising an earlier version with LiDAR terrain data that had been captured in 2002. The flood model then progressed in stages as more historic data was uncovered, enabling a more detailed and rigorously calibrated model to be developed. The final model awaited the completion of the lakes’ terrain landscape and the hydraulic control structures within the Penrith Lakes Scheme. A new LiDAR data set was captured for the Lakes Scheme and the surrounding area in 2016, enabling completion of the study.

The flood modelling was undertaken using the RMA-2 hydrodynamic modelling package and covers the floodplain between Glenbrook Creek and Yarramundi Bridge. The calibration was greatly facilitated by a set of vertical air photos taken 3 hours after the peak of the 1978 flood, the largest flood with suitable recorded data (the others being 1986 and 1990). Upstream flow hydrograph and downstream stage discharge boundary condition data was sourced from the one dimensional Hawkesbury-Nepean model that had been developed for Sydney Water’s Warragamba Dam studies in the mid 1990s. Eight design flood hydrographs were run through the model, including the 20yr ARI, 50yr ARI, 100yr ARI, 200yr ARI, 500yr ARI, 1000yr ARI, 2000yr ARI and the probable maximum flood.