Adelaide
10.3 Recharge from landscape

Supporting information

The volume reported (373,428 ML) represents recharge to groundwater from both rainfall and irrigation in the Adelaide region during the 2012–13 year. The volume reported is itemised in the following table by groundwater management and fractured rocks areas.


Recharged from landscape for each management area and for irrigation recharge in the 2012–13 year

Process

Region

Recharge from landscape (ML) 

Rainfall recharge

Adelaide Plains

94,255

McLaren Vale

22,801

Western Mount Lofty Ranges (fractured rocks1)

251,849

Subtotal

368,905

Irrigation recharge

Adelaide region

4,523

Total

373,428


1 Recharge to the fractured rocks of the Myponga River catchment and Fleurieu Peninsula is not included in the 2013 Account as described in the 'Quantification approach' section.

The recharge from landscape is calculated using the Water Atmosphere Vegetation Energy and Solutes (WAVES) model. The output from WAVES is best considered to be potential diffuse groundwater recharge that potentially could reach the water table under the conditions of rainfall, land use and soil type in the region. The recharge volume estimate does not take into consideration the time lag that occurs between the rainfall infiltrating into the soil and water actually reaching the water table. In addition, the groundwater discharge from the water table through evapotranspiration from the water table could be underestimated which will have the effect of increasing the net groundwater recharge value presented in the 2013 Account. In the WAVES model application used in the 2013 Account, the evapotranspiration from the water table and the unsaturated zone cannot occur at depths greater than four metres, although it is known that deep-rooted vegetation can access groundwater at greater depths.

For more information on additional estimates of annual recharge for the Western Mount Lofty Ranges see the Western Mount Lofty Ranges Prescribed Water Resources Area Water Allocation Plan and for the Adelaide Plains, Aquaterra (2011).

Quantification approach

Irrigation recharge

Data source

Irrigation efficiency literature (Binks 2004).

Provided by

Bureau of Meteorology.

Method

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). This study found that recharge from irrigated areas averaged approximately 5% of the total irrigation water use between 2000 and 2003. Therefore, recharge from irrigation and other activities that apply water to the landscape was estimated to be 5% of all water applied to the landscape as itemised in the following table.

Irrigation recharge in the Adelaide region during the 2012–13 year

Line Item

Location

Assumptions

Volume applied to the landscape (ML)

Recharge estimate (ML)

17.6 Surface water diversions – other statutory rights

Western Mount Lofty Ranges

Assumes 100% diversions used for irrigation

2,006

100

17.11 Entitled diversion of allocated surface water2

Barossa PWRA 

90% diversions used for irrigation

1,010

46

18.7 Groundwater extractions – other statutory rights

Western Mount Lofty Ranges PWRA

100% extractions used for irrigation

25,456

1,273

18.11 Entitled extraction of allocated groundwater

Barossa PWRA

93% extractions used for irrigation

4,851

225

McLaren Vale PWRA

95% extractions used for irrigation

5,499

261

Northern Adelaide Plains PWA

74% extractions used for irrigation

17,177

633

All areas

11% of extractions used for industrial purposes

27,527

145

19.4 Delivery to urban water system users

Potable water consumption

Potable water and recycled water supplied for Agricultural / individual irrigation use

4,240

212

Recycled wastewater

Recycled water used for on-site irrigation/outdoor use

208

10

20.4 Delivery to irrigation scheme users

All irrigation schemes

Assumes 100% water delivered used for irrigation

26,170

1,309

31.3 Off-channel water abstraction

Adelaide region

Assumes 100% farm dams abstractions used for irrigation

6,178

309

Total

120,328

4,523


PWA = Prescribed Wells Area, PWRA = Prescribed Water Resources Area

1 Groundwater extractions reported at line item 18.11 are not all used for irrigation purposes. The proportion of the volume allocated for irrigation purposes, detailed at line item 22.1 Groundwater allocation announcements, was used to estimate the proportion of the volume of groundwater extracted for irrigation purposes.

2 Surface water diversions reported at line item 17.11 are not all used for irrigation purposes. The proportion of the volume allocated for irrigation purposes, detailed at line item 21.1 Surface water allocation announcements, was used to estimate the proportion of the volume of water diverted for irrigation purposes.

Assumptions, limitations, caveats and approximations

This approach assumes that irrigation recharge was directly related to the total irrigation volume applied independent of soil type, crop type, topography and irrigation practices. It also assumes that the irrigation recharge for the period 2000 to 2003 was representative of recharge occurring during the 2012–13 year.

Uncertainty information

The uncertainty estimate was not quantified.

Rainfall recharge

Data source

Bureau of Meteorology: National Climate Centre (NCC) daily climate grids (rainfall, temperature, solar radiation and vapour pressure deficit); CSIRO: Australian Soil Resources Information System (ASRIS) soil information; Australian Bureau of Agricultural and Resource Economics – Bureau of Rural Sciences 2010: land use mapping; South Australian Department of Environment, Water and Natural Resources (DEWNR): Drillhole Enquiry System, bore locations and groundwater level data from online groundwater database; Aquaterra 2011.

Provided by

Bureau of Meteorology.

Method

Groundwater recharge was estimated using the Water Atmosphere Vegetation Energy and Solutes (WAVES) model described in Zhang and Dawes (1998) and Dawes et al. (1998). WAVES is a one dimensional soil-vegetation-atmosphere-transfer model that integrates water, carbon and energy balances. Climate, depth to 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 the 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 from across the Adelaide region for all combinations of soil type, vegetation type and depth to water table. The point estimates of the groundwater recharge fraction were interpolated to a 1 km grid based on soil type, vegetation type, annual rainfall for the 2012–13 year and depth to water table.

The recharge within the Adelaide region was determined by summing the spatially interpolated positive recharge estimates.

The following figure illustrates the net groundwater discharge (in red) and recharge (in grey) across the Adelaide region during the 2012–13 year using the WAVES model.

Map showing net groundwater recharge and discharge in the Adelaide region during the 2012–13 year
Map showing net groundwater recharge and discharge in the Adelaide region during the 2012–13 year

Assumptions, limitations, caveats and approximations

  • The assumptions of the WAVES model as described in Dawes et al. (1998) were all applicable to the recharge estimates for the Adelaide region.
  • The national land-use grid (Australian Bureau of Agricultural and Resource Economics – Bureau of Rural Sciences 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.
  • Annual recharge was estimated for the whole of Adelaide region including both sedimentary and fractured rock areas. Recharge was modelled using a shallow water table surface area estimated by interpolating measured groundwater levels. The water table depth was interpolated using the methodology presented in Peterson et al. (2011). This method uses groundwater elevation and the 9" digital elevation model to improve groundwater levels interpolation in data poor areas within this area of high relief.
  • Rainfall recharge was estimated for the fractured rock area contributing to the flow in the confined sediments only (see fractured rock boundaries in the figure above for diffuse rainfall recharge). Recharge to the fractured rocks of the Fleurieu Peninsula and Myponga River catchment is not included in the balance.

Uncertainty information

The uncertainty estimate was not quantified.

Comparative year

The comparative year volume for line item '10.3 Recharge from landscape' was restated in the water accounting statements from the 2012 Account due to an error identified in the method used to calculate this volume. Please refer to Restatement of comparative year information in the 'Water accounting policies' for more information.