27.1 Off–channel water storages
Off–channel storages–for surface water
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 FORTRAN code 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 2.0.0 (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 private 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 FORTRAN code 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.
Assumptions, limitations, caveats and approximations
- 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 FORTRAN code 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.