Warragamba Dam

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Warragamba Dam Wall

Warragamba Dam is the structure that provides the major water supply for Sydney, Australia, situated approximately 65 km to the west of Sydney in the Burragorang Valley.

1 Overview
2 See also
3 External links
4 References

[edit] Overview

Warragamba River flows through a 300-600 m wide gorge, about 100 m deep before opening out into a large valley. This allows a relatively short and high dam to impound a vast quantity of water. In 1845, Paweł Edmund Strzelecki first drew attention to Warragamba River as a water supply catchment. A dam was first proposed in 1867, with various schemes proposed and investigated between then and 1946 when the site and design of the current dam was approved. In 1940, a weir and pumping station known as the Warragamba Emergency Scheme were completed, just downstream of the main dam site.

Construction began in 1948 and was completed by 1960. It dams the Warragamba River to form 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 which can generate 50 MW.

The dam wall comprises 3,000,000 tonnes (1 200 000 m³) of concrete. In order to control the temperature rise as the concrete set, ice was added to the mix (the first time this had been done in Australia) and chilled water was circulated through cooling pipes embedded in the concrete.

Between 1987 and 1989, the dam wall was raised by 5 m. Between 1998 and 2002, an auxiliary spillway was constructed on the east bank of the dam. Both these measures were undertaken following a re-evaluation of the potential rainfall and flood risks.

As of late-May 2006, the Warragamba Deep Water Storage Recovery Project, part of the NSW Government’s Metropolitan Water Plan, was well under way. This involves penetration of the base of the dam wall to allow the previously inaccessible lowest water in the reservoir to be drawn on. As this new outlet is below the minimum level required for the gravity flow, which currently delivers water from the existing outlets, a new pumping station is being constructed downstream of the dam as part of the project. The pumping station is being built within the Emergency Scheme pumping station chamber.

The Deep Water Recovery scheme is scheduled for late 2006 completion and will provide approximately six months extra supply from the Dam. A major project milestone was reached on 15 April 2006 as the available storage was officially increased from 1,857,000 Megalitres to 2,027,000 Megalitres. A similar scheme is currently underway at Nepean Dam.

Other recent major works include a complete upgrade of the three passenger lifts within the dam wall, an upgrade of the travelling 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 stages, as is a mechanical upgrade that will address the drum gate and four radial gates.

Although it was not designed as a flood control measure, Warragamba Dam can mitigate flooding downstream by holding floodwaters back while the reservoir fills. Its limitations, however, become apparent when the reservoir reaches capacity and water must be released through the floodgates.

Warragamba Dam is also a popular picnic spot for Sydneysiders, with up to 3000 people visiting the area on Father's Day.

[edit] Catchment

The catchment area is 9050 square kilometres. The areas closest to the lake, making up around 30% of the total catchment, are restricted access special areas. Most of the rest of the catchment consists of cleared farming land, and contains many large and small towns which discharge treated sewage into the catchment.

[edit] Dam statistics

Height: 142 m
Length: 351 m
Thickness at top: 8.5 m
Thickness at base: 105 m
Width of central spillway: 90 m
Width of auxiliary spillway (at mouth): 190 m
Length of auxiliary spillway: 700 m
Hydro-electric plant capacity: 50 MW

[edit] Lake Burragorang statistics

Available storage (when full): 2,027,000 ML (note: the lowest depths have recently become available for supply)
Total capacity (when full): 2,031,000 ML
Surface area: 75 km²
Length of lake: 52 km
Length of foreshores: 354 km
Deepest point: 105 m
Catchment area: 9051 km²
Average annual rainfall: 840 mm