The lower Georges River Valley is subject to widespread flooding from time to time. The Moorebank-Milperra area, which is centred around Milperra Bridge, has been identified as a major floodway hazard zone due to substantial residential development on floodprone land.

Any restriction to the passage of floodwaters placed downstream of Milperra Bridge is likely to create an afflux (i.e. an increase in flood levels) in the Moorebank-Milperra area. The Department of Main Roads was therefore concerned as to the effects of its proposed South-Western Freeway crossing of the Georges River 3 km downstream of Milperra Bridge.

The Public Works Department's Manly Hydraulics Laboratory was engaged to construct and test a physical hydraulic flood model of the area in order to determine the afflux caused by the bridge structure during a 1 in 100 year flood.

This report provides details of the investigation and gives model test results and conclusions.