Page 2018 - Week 06 - Friday, 6 May 2005

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The new scientific knowledge referred to in Think water act water derives particularly from the active investigation of the effect of flows on the health of the Cotter River. Research and monitoring programs in that catchment have investigated the effects of the environmental releases below dams, the effects of the drought and the influence of the 2003 bushfires on aquatic ecosystems. New knowledge has included the importance of flow variability, especially with low flow releases, and the need for flows of a specific volume to clean sediment out of riffle and pool areas. These findings formed the scientific basis for the review of the environmental flow guidelines prepared by the Cooperative Research Centre for Freshwater Ecology.

The environmental flow guidelines do not provide an assessment of water resources. The need for the guidelines derives from a responsibility under the Water Resources Act 1998 to develop guidelines that specify the flows needed to maintain aquatic ecosystems. As such the guidelines are developed essentially from a scientific understanding of the flow regime needed to protect and maintain those ecosystems.

Flow rates in rivers within the ACT or that contribute to the ACT’s water supply are measured using standard hydrographic techniques. At gauging points, the river height is measured and then converted into a flow rate using a rating table. While rating tables at gauging stations are updated from time to time, the measurement techniques for flow rates have not changed. Subsequent to 1999 two additional gauging stations have been installed upstream of Bendora Dam; one on the Cotter River itself and one on Stockyard Creek. The purpose of these stations is to enable a better assessment of flows in the system as the catchment recovers from the 2003 bushfires.

Since the 2003 bushfires runoff from the Cotter catchment has been assessed to determine the influence of the fires. Normally one would expect an initial increase in runoff with the loss of vegetation, followed by a decrease in runoff as vegetation regenerates. Although we are still in drought, it is possible to assess the effect of the bushfires by comparing runoff from similar rain events prior to the bushfires. No change in runoff from the Cotter catchment attributable to the bushfires could be detected for 2003 or 2004. Should there be a change in runoff in subsequent years, the environmental flow guidelines can respond to such changes by the requirement linking the amount of water released to the amount entering the reservoir. Consequently if inflow drops, environmental releases drop accordingly.

The environmental flow guidelines, currently under review, will be finalised later in 2005.

Water—storage safety margin
(Question No 343)

Mrs Dunne asked the Minister for the Environment, upon notice, on 5 April 2005:

(1) In relation to water requirements for the ACT, what studies, including mass curve studies, have been conducted to determine the minimum safety margin for Canberra’s water storage;

(2) What is the result of these studies.

Mr Stanhope: The answer to the member’s question is as follows:

(1) Mass curve studies are one form of hydrology study that can be used to assess the amount of water that would be needed by the ACT now and in the future.

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