This report details the flood gauging operation undertaken on 5th and 6th August, 1986 and presents the data collected for the Georges River catchment in Sydney.

The Georges River catchment area is approximately 960 square kilometres and is shown in Figure 2.1. The main arm of the river begins its course near the Cataract Dam, and exits into Botany Bay. The main channel is joined throughout its course by minor streams and creeks, and also by the Woronora River; which exits into the Georges River.

The catchment area comprises a large part of the south western urban area of the city of Sydney, and the floods that have occurred in the catchment have at times caused significant damage to property.

To rationalise future development of the area in the face of potential flood threats, various numerical and physical models have been developed by both the University of N.S.W. Water Research Laboratory, and the Public Works Department's Manly Hydraulics Laboratory. The success of the models in predicting the flooding characteristics of various flood events depend upon collecting specific flood data over a series of floods· for model calibration and verification. To this end, all known information regarding previous floods has been documented (Ref. 1), but there is a need for more comprehensive flood data, especially for major floods.

Manly Hydraulics Laboratory's Data Collection Section was requested by the Department's Rivers and Ports Branch to co-ordinate and undertake flood monitoring at various sites over the area which is being modelled. These monitoring sites appear in Figure 1.1. A previous report (Ref. 1) details the results of gauging of minor floods undertaken in 1978 and 1983.

Flood gauging on the 5th and 6th August, 1986 was carried out by personnel from Manly Hydraulics Laboratory, Rivers and ports Branch and the Water Research Laboratory.

The general extent of the flooding can be seen in Plates 1.1 - 1.3.

The current metering lines, flood gauge locations and automatic recorder locations from which data was collected are as follows:

i) Current metering/gauge observations at:

1. East Hills Footbridge
2. Milperra Road Bridge
3. Mountbatten Bridge
4. Lansdowne Bridge

ii) Automatic recorders located at:

1. Milperra Bridge
2. Cutler Road, Lansvale
3. Liverpool. Weir.

Data collection from the Irelands Bridge current metering station and the Scrivener Street auto recorder is also specified under the Georges river flood data collection program, but inaccessibility to the bridge and equipment malfunction respectively, precluded data collection from these sites on this occasion.