9.2 River inflow to region
This line item refers to the volume of surface water that flowed into the Canberra region from the upstream Murrumbidgee River.
The volume recorded at Murrumbidgee at Angle Crossing (MURWQ09) was 279,763 ML.
The connected surface water flow from the upstream entity was obtained from the gauging station at Angle Crossing. The station is located approximately on the Australian Capital Territory border, downstream of the Canberra region boundary. The location of the gauging station is shown in the following figure.
Assumptions, Limitations, Caveats and Approximations
The level of uncertainty of the Murrumbidgee Angle Crossing is estimated at +/– 20 % during low to medium flows and the uncertainty during high flows is ungraded. This is based on four manual physical flow calibrations performed per year. At these sites the water surface level is measured constantly by on-site equipment. This water level is used to estimate a flow rate, based on a rating curve produced by physical flow gauging in as many flow conditions as possible.
There is some uncertainty in the flow rates, as there is an inherent level of uncertainty in the physical flow gauging process. The river flows have not been gauged under all flow conditions, and the river channel can change from time to time, due to deposition and movement of river sediments and growth and removal of riparian vegetation, which may impact both the cross-sectional area of the channel available for river flow and the velocity of the water.
The gauge used to determine this line item is different to those which were used for the 2010 Account. The Angle Crossing site (gauge ID MURWQ09) was not operational for the entire reporting period of the 2010 Account therefore a re-statement due to a change of methods is not possible. As a comparison, the average flow of the Billilingra site (gauge ID 410050) and the Lobbs Hole site (gauge ID 410761) was 260,085 ML for the 2010–11 year.
The uncertainty estimate was not quantified.
For the 2010 Account a volume of 124,326 ML of connected surface water flow from outside region was reported under the line item 13.2 – Connected surface water flow from upstream entity.