Physical Modelling

Warragamba Dam

Warragamba Dam is located about 70 km south west of Sydney and is the largest of Sydney's dams, holding 80 percent of Sydney's water supply. The present dam was completed in 1960 at which time it was designed for a peak outflow of 12,700 cu m/s. Since then the Probable Maximum Flood (PMF) has been reassessed a number of times with the peak outflow now estimated at 38,000 cu m/s. Interim works were performed on the dam in 1987-89 by adding post tensioned anchors and raising the crest 5.1m. However, in its current form it has been estimated that there is a 1 in 1,500 chance per year that Warragamba Dam could be overtopped by a flood event which could cause the dam wall to collapse, releasing almost 2 million megalitres of water.

A general view of the model looking up stream.

Manly Hydraulics Laboratory operates a 1:100 scale physical model of Warragamba Dam. The model, which was originally constructed by Sydney Water has been used to investigate ways of ensuring that the dam can safely withstand flood events up to the PMF. The model occupies an area of approximately 10 m x 30 m and can simulate prototype outflows up to 40,000 cu m/s.


View of the main dam wall.	Headwaters of the dam showing flow diffusers which stabilise inflow and a water level sensor used to record water levels.

The model has been adapted to test a number of options and in recent years investigations have focused on the performance of a second, or auxiliary spillway which would enable extreme flood events to be diverted around the dam, preventing dam failure. A number of auxiliary spillway options have been investigated, with the most recent being a chute spillway in the righthand abutment of the dam, referred to as the Waratah Ridge scheme.

Looking up the Waratah Ridge Auxiliary Spillway, shown painted yellow.