10.3 Recharge from landscape
The volume reported (685,221 ML) includes recharge to groundwater from both rainfall and irrigation. The volume reported is itemised in the following table by groundwater management area.
|Process||Region||Recharge from landscape (ML)|
|Rainfall recharge||Adelaide Plains||136,164|
|Western Mount Lofty Ranges (fractured rocks*)||527,613|
|Irrigation recharge||Adelaide region||5,392
* Recharge to the fractured rocks of the Myponga River catchment and Fleurieu Peninsula is not included in the 2011 Account as described in the Quantification approach section.
The volume reported for recharge from landscape is significantly greater than the average annual recharge estimated for the Western Mount Lofty Ranges (142,802 ML) and the Adelaide Plains (Aquaterra 2011).
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: this is the 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 watertable. In addition, groundwater discharge from the water table through evapotranspiration from the water table is possibly largely underestimated – this will have the effect of increasing the net groundwater recharge value presented in the 2011 Account. In the WAVES model application used in the 2011 Account evapotranspiration from the water table and the unsaturated zone can not 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 estimates of annual recharge for the Western Mount Lofty Ranges (WMLR) see the Draft WMLR Water Allocation Plan; and for the Adelaide Plains (Aquaterra 2011).
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 was estimated to be 5% of all irrigation application. The volume estimated for recharge from landscape, from water for irrigation and other activities that apply water to the landscape, is itemised in the following table.
|Line Item||Location||Notes||Volume applied to the landscape (ML)||Leakage estimate – 5% of applied volume (ML)|
|Central Adelaide PWA (stock and domestic portion)||Assumes all extraction is used for irrigation||2,386||119|
|Western Mount Lofty Ranges PWRA & Central Adelaide PWA||Assumes all extraction is used for irrigation||19,641||982|
|Kangaroo Flat portion of the Northern Adelaide Plains PWA||Irrigation extraction only||1,010||51|
|Barossa PWRA||Irrigation extraction only||1,320||66|
|McLaren Vale PWA||Assumes all extraction is used for irrigation||2,529||126|
|Northern Adelaide Plains PWA||Irrigation extraction only||10,392||520|
|Western Mount Lofty Ranges
||Assumes all extraction is used for irrigation||2,728||136|
|Barossa PWRA||Assumes all extraction is used for irrigation||1,098||55
|All irrigation schemes||Assumed all water is used for irrigation||14,789||739|
|Adelaide region||STEDI model output||7,970||399|
|Potable water consumption||Outdoor water use based on SA Water land use codes (see tables below)||43,615||2181|
PWA = Prescribed Wells Area, PWRA = Prescribed Water Resources Area
* 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.
**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.
According to this approach:
- In the Barossaa PWRA 95% of groundwater is allocated for irrigation purposes and 90% of surface water is diverted for irrigation purposes.
- In the Northern Adelaide Plains PWA 94% of groundwater is allocated for irrigation purposes.
- In the McLaren Vale PWA information on the proportion of groundwater allocated for irrigation purposes was not available; therefore it was assumed that 100% was used for irrigation purposes.
|SA Water land use code||National Water Account land use code||Potable water consumption (ML)
||Percentage used for irrigation and other outdoor activities||Volume applied to the landscape (ML)|
|Country lands||Other – agriculture||2,147||100%||2,147|
|Primary production||Other – agriculture||995||100%||995|
|Vacant land||Remaining other||1,518||40%||607|
|Wastewater treatment plant||Application||Recycled water consumption (ML)
|Victor Harbor||Municipal and agricultural irrigation||96|
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 2010–11 year.
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 were interpolated to a 1 km grid based on soil type, vegetation type and depth to water table and multiplied by a grid of annual rainfall for the 2010–11 year.
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 2010–11 year using the WAVES model.
Map showing net groundwater recharge and discharge in the Adelaide region during the 2010–11 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 to the sedimentary areas was modelled using a shallow water table surface area estimated by interpolating measured groundwater levels. For fractured rocks the shallow water table 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.
This line item corresponds to 15.2.1 Diffuse groundwater recharge from landscape water reported in the 2010 Account. Following publication of the 2010 Account, an error was identified in the volumes reported. The scope of this line item also changed. Restatement of the volume published in the 2010 Account was made as the difference was material and increased the accuracy of the information provided to the users of the National Water Account. The following summarises the changes that were made that caused the 2009–10 year value to be restated:
- An error was identified in the volumes reported in the 2010 Account. In the 2010 Account a bias correction applied to the satellite-derived solar radiation dataset was incorrect resulting in an overestimation of incoming solar radiation. When the bias correction was updated recharge from landscape was re-estimated and the comparative year volume increased.
- In the 2010 Account, the scope of this item included recharge to the fractured rocks of the Myponga River catchment and Fleurieu Peninsula. However, in the 2011 Account these fractured rock areas were not included in recharge from landscape calculations (see Quantification approach).
It was not possible to separate the change in volume due to error corrections and scope changes. The changes and their respective volumes are detailed in the following table. The restated comparative year volume is 373,888 ML.
|2010 Account line item name||Process||Groundwater area||Volume at 30 June 2010 reported in 2010 Account (ML)||Value difference to volume reported due to changes (ML)||Volume at 30 June 2010 reported in 2011 Account (ML)|
|15.2.1 Diffuse groundwater recharge from landscape water||Rainfall recharge||Adelaide Plains||377,709||(8,672)||64,171|
|Rainfall recharge||McLaren Vale||16,306|
|Rainfall recharge||Western Mount Lofty Ranges (fractured rocks)||288,560|