30.1 Precipitation on off-channel water store
The volume reported (9,063 ML) represents the volume of water that precipitated on off-channel water storages during the 2012–13 year.
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).
Monthly precipitation data were produced by the Bureau of Meteorology. It was based on daily data from approximately 6,500 rain gauge stations and interpolated to a 0.05 degree (approximately 5 km) national grid (Jones et al. 2007).
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 average precipitation depth across the Adelaide subregions was determined as the weighted mean of precipitation occurring from the relevant grid points within the region boundary. Points were weighted upon the area they represented within the Adelaide landscape to remove edge effects (where the area represented is not wholly within the reporting region) and the effect of changing area represented with changing latitude. The average precipitation depth was used as an input into the farm dam algorithm written by the Bureau and converted the depth of precipitation to a volume using the surface area of off-channel water stores within a region.
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 spatial extent of waterbodies was subject to the assumptions and methods associated with the spatial data provided by DEWNR.