The Macquarie Rivulet catchment drains an area of 110 square kilometres extending from the shores of Lake Illawarra upstream for a distance of approximately 23 km to the Illawarra escarpment. The upper parts of the catchment (up to 770 mAHD) are characterised by steep gradients moving to flatter terrain in the lower reaches of Macquarie Rivulet dropping to approximately mean sea level. The catchment is made up of a number of tributaries including the main Macquarie Rivulet, as well as Frazers Creek, Marshall Mount Creek and Yellow Rock Creek. There have been several recorded instances of flood-producing storms in the catchment, including February 1984, June 1991, February 1992 and most recently March 2011. The largest recent historical floods within the catchment are believed to have occurred in 1959, 1961 and 1975, however there is limited information regarding these earlier floods.

The key objective of the Macquarie Rivulet Flood Study is the development of computational hydrologic and hydraulic models that define design flood behaviour for the 20%, 10%, 5%, 2%, 1%, 0.5% and the Probable Maximum Flood (PMF) design storms in the study area. The key sequential reporting stages include:

• Stage 1: Data Collection plus Assessment and Community Consultation;
• Stage 2: Model Calibration and Validation;
• Stage 3: Modelling and Mapping of Design Flood Events.