Adelaide

The volume reported in the water accounting statement (382,060 ML) comprises both rainfall and irrigation recharge. The groundwater recharge for 2009–10 is presented in the table below.

Data source

Rainfall recharge

Bureau of Meteorology: National Climate Centre (NCC) raster climate data.

Australian Soil Resources Information System (ASRIS): soil information.

Bureau of Rural Sciences: Water2010 and land use mapping.

South Australian Department for Water bore locations and groundwater-level data from water regulations.

Irrigation recharge

Irrigation efficiency literature (Binks 2004)

Irrigation application: Line Items 14.6.5.6, 16.4.2, 16.5.3.2, 20.3.1 and 20.3.2

Bureau of Meteorology: Australian Hydrological Geospatial Fabric (AHGF) 9 arc-second directional flow grid and waterbodies

South Australian Department for Water: farm dams, drillholes and stream order spatial data

Bureau of Meteorology: National Climate Centre (NCC) raster climate data

Data provider

Bureau of Meteorology.

Method

Rainfall recharge

Groundwater recharge was estimated using the Water Atmosphere Vegetation Energy and Solutes (WAVES ) model (Dawes et al. 1998; Zhang and Dawes 1998). WAVES is a one-dimensional soil–vegetation–atmosphere transfer model that integrates water, carbon and energy balances. Climate, depth to the water table (only for the sedimentary areas), soil and vegetation data were used as inputs to the model. The climate data include rainfall, rainfall duration, maximum and minimum temperatures, vapour pressure deficit and solar radiation.

The WAVES model has been used by CSIRO in its Sustainable Yields projects (Crosbie et al. 2008) and the Bureau of Meteorology has built on this methodology. WAVES was run at selected points across the Adelaide region for all combinations of soil type, vegetation type and depth to the water table. The point estimates of the groundwater recharge fraction for 2009–10 were interpolated to a 5 km grid based on soil type, vegetation type and depth to the water table, and multiplied by a grid of annual rainfall for 2009–10. The net recharge (recharge less evapotranspiration from shallow groundwater) within the Adelaide region was determined by summing the spatially interpolated recharge estimates.

Irrigation recharge

The estimate of recharge to groundwater from irrigated areas was based on the findings of a study that evaluated irrigation practices within the Mount Lofty Ranges (Binks 2004). The study found that recharge from irrigated areas averaged approximately 5% of the total irrigation water use between 2000 and 2003. Therefore, recharge from irrigation was estimated to be 5% of all irrigation application.

Total irrigation application was calculated as the sum of all irrigation application line items in the Adelaide water accounting report plus irrigation from farm dams (refer to table below).

The STEDI model (SKM 2010) was used to determine the volume of water taken from the off-channel private water store (farm dams) for irrigation. Farm dams with a capacity greater than 5 ML were assumed to be used primarily for irrigation (based on Jordan and Wiesenfeld 2007; Lowe et al. 2005; Ritson 2007). The volume of water applied for irrigation was calculated as a function of water demand and availability. The maximum water available for was set as the maximum capacity of farm dams used for irrigation and the STEDI model estimated the actual water available by performing a water balance at each timestep. The annual demand factor was set at 0.2 based on McMurray (2003) and monthly demand patterns for individual crops were taken from Binks (2004).

Uncertainty

Ungraded.

Assumptions, approximations and caveats/limitations

Rainfall recharge

• The assumptions made in developing the WAVES model as described in Dawes et al. (1998) were all applicable to the recharge estimations for the Adelaide region.
• The national land use grid (ABARES 2010) was reclassified to three vegetation classes that include annuals, perennials and trees. The major vegetation classes modelled were C3 annual pasture, C3 perennial pasture and eucalypt trees with a grass understorey.
• Net recharge was estimated for the whole Adelaide region, including both sedimentary and fractured rock areas. Recharge to the sedimentary areas was modelled given the effects of a shallow water table, while free drainage conditions were assumed at the base of the soil profile within the fractured rock areas.

Irrigation recharge

This approach assumes that irrigation recharge was directly related to the total irrigation applied, independent of soil type, crop type, topography and irrigation practices. It also assumes that the irrigation recharge for the period 2000–03 was representative of recharge occurring during 2009–10.