Canberra
27.1 Off-channel water storages

This line item refers to the volume of water stored in off-channel water storages within the Canberra region. That was 7,214 ML.

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

A water-balance based farm dam algorithm written by the bureau was used to determine the volume of water stored in off-channel water storages. The code was provided inputs in the form of climate from gridded climate datasets, runoff from the AWRA-L model version 3.0 (Van Dijk 2010) 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 private 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 catchment of each individual storage was determined via analysis of the 9 arc-second DEM.

The farm dam algorithm performs a water balance on each individual storage at each time step using runoff and precipitation as inflows and spills, evaporation and usage as outflows. The volume of water held in storage is an output of this water balance.

• 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 and the parameters used.
• The spatial extent of waterbodies are subject to the assumptions and methods associated with the data provided by the Geoscience Australia.

The uncertainty estimate was not quantified.