Page 4031 - Week 12 - Thursday, 20 October 2005

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What is the “water balance method”, see Volume 3, pages 30, 32 and 34, of Think Water Act Water;

(4) What is the “mass balance method”, see Volume 3, page 74, of Think Water Act Water.

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

(1) The gauging stations identified in Think Water Act Water and their locations are detailed in the table below.

Gauging station	Location
410731	Gudgenby River downstream of Naas confluence
410772	Sullivans Creek at Southwell Park
410713	Paddys River at Riverlea property
410743	Jerrabomberra Creek at the Four Mile Creek confluence
410711	Gudgenby River just upstream of the Naas confluence
410736	Orroral River at the Orroral road crossing
410745	Yarralumla Creek at Curtin
410705	Molonglo River at Burbong Bridge
410751	Ginninderra Creek at the Barton Highway
410775	Sullivans Creek at Barry Drive
410781	Queanbeyan River just upstream of Googong Reservoir
410750	Ginninderra Creek at Charnwood
410765	Lake Ginninderra at Dam

(2) One gauging station used in the 1999 Water Resources Management Plan (410774 Burra Creek at Burra Road) was not used in the current Management Plan. At this site the gauging station has silted up making the more recent data unreliable. In addition to the above list, a set of gauging stations in the Cotter catchments and at Googong Reservoir not specifically identified in Think water act water were used to provide data for the water balance model. These stations are detailed in response to the question below.

(3) Yes. Gauging stations in the Corin, Bendora and Lower Cotter subcatchments used in the water balance method are detailed below

410730	Cotter River at Gingera upstream of Corin Reservoir
410742	Corin Reservoir at Dam
410717	Bendora Reservoir at Dam
410704	Cotter Reservoir at Dam
410700	Cotter River below Cotter Dam
410748	Googong Reservoir at Dam

(4) The water balance method is a way of estimating the flow that would have occurred in a river if the dam upstream had not been constructed. With this method all inflows, diversions and losses from a reservoir are taken account of. By mathematically removing diversions and losses, the “pre-dam” flow at a site downstream of an existing reservoir can be calculated.

(5) The mass balance method was used in Think Water Act Water to calculate, in part, the flows for the Parkwood subcatchment. Flows derived from the Parkwood section of the entire Ginninderra Creek catchment were identified by subtracting flows for the part of Ginninderra catchment upstream of Parkwood from the flows at the gauging station in Parkwood itself.

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