27.1 Off-channel water storages
The volume reported (14,913 ML) represents the total volume of water held in off-channel water storages within the Adelaide region at 30 June 2013.
Bureau of Meteorology: National Climate Centre daily climate grids (rainfall, temperature and solar radiation), Australian Hydrological Geospatial Fabric (AHGF) waterbody feature class; South Australian Department of Environment, Water and Natural Resources (DEWNR): Geographical Information System layers; Geoscience Australia: 9 arc-second digital elevation model (DEM).
The farm dam algorithm written by the Bureau of Meteorology was used to determine the volume of water stored in off-channel water storages. The model was provided inputs from gridded climate datasets, runoff from the AWRA-L v3.0 (Van Dijk 2010) model, and dam details derived from spatial data.
The Adelaide region was split into two subregions for the purpose of estimating the water balance of the off-channel water store. The region was divided using the boundaries of the AHGF contracted catchments between McLaren Vale and the Onkaparinga Valley. The northern region includes the Barossa Valley, the Northern Adelaide Plains, and the River Torrens, Patawalonga and the Onkaparinga catchments. The southern region includes catchments throughout McLaren Vale and the Fleurieu Peninsula.
Only off-channel water storages filled primarily by rainfall-runoff were considered. These were determined from waterbody mapping provided by DEWNR, and excluded waterbodies that were within the Virginia Pipeline Scheme service area and waterbodies that were less than 20 metres away from a channel of second order or higher, or an active bore. 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.
Assumptions, limitations, caveats and approximations
- The gridded climate input data were 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 was subject to the assumptions and methods associated with the spatial data provided by DEWNR.