Page 2193 - Week 06 - Monday, 11 May 2009

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• the impact from bushfires; and

• new modelling techniques including stochastic data simulation.

The Cotter Dam was designed to serve 25,000 people. However, the dam was not constructed to its design height until 1951. The estimated capacity of the dam when work was completed around 1915 was 1.85 GL.

The water supply system including Bendora Dam was designed to serve 97,000 people. The estimated capacity of the dam when completed was 10.7 GL.

The water supply system including Corin Dam was designed to serve 225,000 people. The estimated capacity of the dam when completed was 75.5 GL.

The water supply system including Googong Dam was designed to serve 450,000 people. The capacity of the dam when completed was 124.5 GL.

It should be noted that the design was based on historic inflows up until 1970 (that is without the 1980s and current droughts, the latter of which is the worst on record) to get through the 1940s drought without restrictions. In all cases a worse drought than the 1940s drought (ie, now) would have meant the system would not meet the design criteria. ACTEW now uses a different, national best practice method of choosing when we need a new supply and how many people it will serve.

When Corin Dam was completed in 1968 the average consumption was approximately 600 L/capita/day.

When Googong Dam was completed in 1978 the average consumption was approximately 700 L/capita/day.

(d) The estimated life span of the main structure of a dam is typically 100 years or more.

(5)(a)Bathymetry surveys were conducted using more accurate modern methods at Corin and Bendora Dams in November 2005 to re-calculate the dams’ storage capacities. This resulted in a change to our total storage capacity from 215.4 GL to 211.6 GL. Bathymetry surveys were conducted at Googong and Cotter Dams in October 2006 to re-calculate the dams storage capacities. This resulted in a change to our total storage capacity from 211.6 GL to 207.4 GL.

The capacity of Canberra’s dams is currently estimated as:

Cotter Dam 3.9 GL

Bendora Dam 11.5 GL

Corin Dam 70.9 GL

Googong Dam 121.1 GL

(b) The maximum population these dams would service is dependent on the factors listed above. The existing four dams no longer meet the current service standards and hence ACTEW undertook a substantial body of work culminating in the Future Water Options work of 2005 and following on from that the Water Security program reported in 2007 followed up by the December 2008 report. Under the current climate uncertainty, it is not realistic to assign a maximum population that the Water

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