Warragamba Dam - Overview

Overview

The Warragamba River flows through a gorge that varies in width from 300 metres (980 ft) to 600 metres (2,000 ft), and is 100 metres (330 ft) in depth. This gorge opens out, at the upper end, into a large valley, the Burragorang Valley. This river configuration allows a relatively short but high dam wall in the gorge to impound a vast quantity of water.

In 1845, Paweł Edmund Strzelecki drew attention to Warragamba River as a water supply catchment. In 1867, supporters proposed a dam. Between 1867 and 1946, supporters proposed various schemes before the site and design of the current dam received approval. In 1940, a weir and pumping station known as the Warragamba Emergency Scheme reached completion, just downstream of the main dam site.

In 1943 the Metropolitan Water, Sewerage and Drainage Board invited the geologist William Rowan Browne to investigate a proposed site. Browne found a more suitable site and continued as geological adviser until completion. The site was reviewed and approved by Dr John L. Savage (considered the pre-eminent expert in this field) and formally accepted by the Board on 2 October 1946. The engineer was Thomas Haynes Upton. Dam construction began in 1948 and completed in 1960. The resulting dam of the Warragamba River formed Lake Burragorang, which is one of the largest reservoirs for urban water supply in the world. There is also a hydroelectric power station at the dam that can generate 50 Mega-Watts.

The dam wall comprises 1,612,000 cubic yards (1,232,000 m3) of concrete. It was laid as interlocking blocks roughly 17 metres (56 ft) on a side, which were later grouted together to form a continuous monolithic wall. It is so large that the engineers had to use two techniques to stop the temperature becoming too hot as the concrete set. One was to add ice to the wet concrete, which was the first application of this technique in Australia. The other was to embed cooling pipes into the concrete and circulate chilled water through the pipes. As a result, the dam wall was cooled in a few months instead of the estimated 100 years to cool naturally.

The main spillway has five crest gates: A central drum gate with a 27 metres (89 ft) clear span with a pair of radial gates on each side. Each radial gate has a 12 metres (39 ft) clear span. The drum gate is hinged along the upstream edge to the upstream crest and lowers into the dam wall to allow water to flow over it. When fully open, it forms a continuation of the crest profile. All gates will open automatically as the dam passes full water level, or can be manually opened. The secondary spillway is normally closed by a series of fuse plugs. These will be washed away in the event of an extreme flood event.

As originally designed, the dam could safely withstand a peak inflow of 500,000 cusec (approximately 14Ml/sec), leading to a peak discharge of 354,000 cusec or 10,000 tonnes/sec down the spillway. Following a 1987 and 1989 re-evaluation of the potential rainfall and flood risks, the government raised the dam wall by 5 metres (16 ft) and constructed an auxiliary spillway on the east bank of the dam.

In 2006, the Warragamba Deep Water Storage Recovery Project, part of the NSW Government’s Metropolitan Water Plan, penetrated the base of the dam wall to allow the previously inaccessible lowest water in the reservoir to be available. This new outlet was below the minimum level required for gravity flow, which delivered water from the existing outlets. So, the project constructed a new pumping station downstream of the dam. The new pumping station is within the Emergency Scheme pumping station chamber. This project provided access to 8% more water or approximately six months of extra supply. On 15 April 2006, the project reached a major milestone when it increased the available storage from 1,857,000 Megalitres to 2,027,000 Megalitres. A similar scheme is currently underway at Nepean Dam.

Other recent major work includes a complete upgrade of the three passenger lifts within the dam wall, an upgrade of the traveling crest crane and a complete upgrade of the four water supply outlets in the valve house, which includes the replacement of the major valves. A full electrical upgrade is currently in advanced planning stage, as is a mechanical upgrade that will address the drum gate and four radial gates.

Although the engineers did not design Warragamba Dam as a flood control measure, it can mitigate flooding by holding floodwaters back while the reservoir fills.

Warragamba Dam was also a popular picnic spot for Sydneysiders but access to the public had been restricted since 1999 due to $240 million of upgrades in that time. It reopened to the public on November 8, 2009.