Canberra
31.3 Off-channel water abstraction

This line item refers to the water used from off–channel water storages. The volume reported for 2013 was 4,552 ML.

Bureau of Meteorology (The Bureau), National Climate Centre daily climate grids (rainfall, temperature and solar radiation); Geoscience Australia, mapping of human-made waterbodies spatial dataset, built up areas spatial dataset and 9 arc-second digital elevation model (DEM).

The farm dam algorithm written by the Bureau was used to determine the volume of water abstracted from the private water store. The model was provided inputs in the form of climate from gridded climate datasets, runoff from the AWRA-L v3.0 (Van Dijk 2010) model, and dam details derived from spatial data.

The Canberra region was divided up into five subregions for the purpose of estimating the water balance of the off-channel water store. Four of the subregions were the catchments of the major storages and the fifth was the remaining land.

The off-channel water store consisted of off–channel storages filled primarily by rainfall-runoff. These were determined from waterbody mapping provided by Geoscience Australia and were waterbodies that were greater than 50 m from built-up areas in the Canberra region.

The farm dam algorithm written by the Bureau determines the water stored in each off-channel water store at each time point and determines the volume required for use from the off-channel water store. FORTRAN code tool assumes that water will be abstracted from the off-channel water store at the rate required unless off-channel water store empties, at which time, abstraction will cease.

• The gridded climate input data are subject to approximations associated with interpolating observation point data to a national grid detailed in Jones et al. (2007).
• The estimated volume available in storage for evaporation is subject to the assumptions associated with the farm dam algorithm written by the Bureau and the parameters used.
• The spatial extent of waterbodies subject to the assumptions and methods associated with the data provided by the Geoscience Australia.

The uncertainty estimate was not quantified.