31.3 Off-channel water abstraction
The volume reported (6,248 ML) represents the volume of water abstracted from off-channel water stores for use during the 2012–13 year. Note that metered water diversions from on-channel private storages connected to the watercourses in the Barossa Prescribed Water Resources Area area included in the volume of line item 17.11 Entitled diversion of allocated surface water to users.
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). Irrigation, stock and domestic demand literature (Binks 2004; Luke 1987).
The farm dam algorithm written by the Bureau of Meteorology was used to determine the volume of water abstracted from the private water store. Data input to the model included gridded climate datasets, runoff from the AWRA-L version 3.0 (Van Dijk 2010) model, and dam details derived from spatial data (surface area, volume, location and catchment area). Model parameters included irrigation demand factors (Binks 2004) and stock and domestic demand factors (Luke 1987).
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 written by the Bureau of Meteorology 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. The algorithm 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.
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 written by the Bureau and the parameters used.
- The spatial extent of water bodies was subject to the assumptions and methods associated with the spatial data provided by DEWNR.