Horsley Creek is located in the Shellharbour City Council local government area, on the New South Wales coastal plain approximately 100 km to the south of the city of Sydney. It drains an area of approximately 9 square kilometres of mostly urbanised land, discharging into the south-western corner of Lake Illawarra. Flooding in Horsley Creek and its tributaries is adversely affected at many locations by bridges, culverts and intrusions of development onto floodplains. Flooding in the lower reaches of Horsley Creek is in addition affected by the level of flooding in Lake Illawarra and sand build-up in the outfall reach into Lake Illawarra.

The primary objective of the Horsley Creek Flood Study is the development of a reliable, quantified understanding of existing flood behaviour within the catchment. This in turn leads to a number of secondary objectives including:

• The collection and collation of a reliable body of data on the physical characteristics of the catchment and study area
• The collection and collation of a reliable body of data on historic storms and flooding
• The establishment of well calibrated and validated hydrologic and hydraulic models of the catchment and study area
• The determination of flooding characteristics within the study area in terms of flood extents, flood levels, flow depths, velocities and hazard levels for a range of possible future flood events up to and including the Probable Maximum Flood
• The identification of areas within the catchment subject to high hazard or high frequency flooding for specific consideration in the subsequent Floodplain Risk Management Study