National Water Account 2016

Murray–Darling Basin: Water stores

This note provides a water balance for each of the region's water stores for the 2015–16 year. Relatively poor rainfall over most of the year contributed to low streamflows across the region and a drop in storage volumes. As a result, water availability decreased compared with the previous year, which led to a decrease in water use.

 




 

Surface water store

Cawndilla and Menindee lakes. Source: Bureau of Meteorology © Paul Sheahan

The volume of water in the Murray–Darling Basin region's surface water store marginally increased during the 2015–16 year from 12,458,729 ML at 1 July 2015 to 12,913,129 ML at 30 June 2016 (Table S6). While storage volumes decreased, river channel volumes increased due to several heavy rainfall events that occurred near the end of the reporting period (May–June 2016).

 

Table S6 Water balance for the surface water store
 2016
ML
2015
ML
Opening surface water store12,458,72916,187,404
Inflows23,777,88817,814,473
Outflows(23,323,488)(21,543,148)
Balancing item(0)(0)
Closing surface water store12,913,12912,458,729

 

A schematic diagram representing all surface water inflows and outflows during the 2015–16 year is provided in Figure S3.

 

Figure S3 Water inflows and outflows for the surface water store during the 2015–16 year

Figure S3 Water inflows and outflows for the surface water store during the 2015–16 year

 

Surface water inflows

The largest surface water inflow in the region was runoff. The volume, 19,091,888 ML, was an increase of more than 30% than the previous year. The increase in runoff is largely attributed to several high rainfall events that occurred during the year (see Climate and water). Despite the increased runoff, it was still relatively low compared to earlier years (see 2011 Account) and consequently, surface water storage still dropped during the year (see Surface water assets). Precipitation also increased by approximately 10% from last year. The remaining natural surface water inflow, discharge: groundwater, decreased by 80% from the previous year.

The largest surface water transfer in the region (delivery: inter-region agreement) comprised 2,389,860 ML of water delivered from Snowy Hydro Limited and 2,449 ML from Glenelg River. Water delivered from Snowy Hydro Limited was 90% more than the previous year. Point return: irrigation and discharge: wastewater were similar to the previous year, while the reported volume of return flow: environmental purposes increased by approximately 90%.

 

Surface water outflows

One of the larger natural water outflows in the region was evaporation, and this was approximately 25% less than the previous year. The decrease in evaporation reflects the increase in rainfall compared to last year and changes made in the calculation method (see Climate and water and Methods).

Overflow: landscape increased from the previous year, which reflects the increased streamflow primarily associated with several high rainfall events that occurred during the year (see Climate and water). Outflow and recharge: groundwater both decreased compared with the previous year.

The volume of gross surface water diverted in the region totalled 8,549,056 ML (including the gross volume of held environmental water delivered), a decrease of more than 10% from the previous year that reflects the decreased availability of surface water in the region compared to last year. Allocated diversion: individual users accounted for 60% of the total diversion in the region. The volume of water diverted from each water resource plan area for individual users is shown in Figure S4. The volume diverted is compared against the water available, which was calculated as carryover from the previous year plus the allocation announcement made during the year.

 

Figure S4 Surface water diversion to individual users by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water diverted are also shown
Figure S4 Surface water diversion to individual users by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water diverted are also shown

 

Allocated diversion: urban system accounted for 5% of the total diversion in the region. The volume of water diverted from each water resource plan area to the urban water system is shown in Figure S5.

 

Figure S5 Surface water diversion to the urban water system by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water diverted is also shown
Figure S5 Surface water diversion to the urban water system by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water diverted are also shown

 

Allocated diversion: environmental purposes accounted for 22% of the total diversion in the region. Diversions: statutory rights and non-allocated diversions accounted for less than 1% and almost 10% of the total diversions in the region, respectively. For a more detailed description of the water usage in the region, and the associated entitlements, see the Surface water rights note.

 

Surface water balancing item

The surface water balance (Table S6) yielded a balance of 0 ML. Uncertainties associated with the measurements and estimations of item volumes result in a balancing volume; however, the balancing volume of 0 ML (Table S6) does not imply that there were no uncertainties associated with the surface water store.

For the Murray–Darling Basin region, the volume of uncertainties is incorporated within the river and floodplain losses and is estimated using a water balance approach. Work is underway to more reliably estimate the river and floodplain losses in the region. A more reliable estimate of the river and floodplain losses will allow uncertainties to be quantified separately in the surface water balancing item.

 

Groundwater store

Bore channel near Walgett. Source: Murray–Darling Basin Authority © Arthur Mostead

The volume of water in the Murray–Darling Basin region's groundwater store in 2015–16 remained the same as the previous year at 3,333,740 ML because sustainable diversion limits are recognised as groundwater assets (Table S7).

 

Table S7 Water balance for the groundwater store
 2016
ML
2015
ML
Opening groundwater store3,333,7403,262,640
Inflows671,1452,716,986
Outflows(1,685,068)(4,008,866)
Balancing item1,013,9231,362,980
Closing groundwater store3,333,7403,333,740

 

A schematic diagram representing all groundwater inflows and outflows during the 2015–16 year is provided in Figure S6.

 

Figure S6 Water inflows and outflows for the groundwater store during the 2015–16 year

Figure S6 Water inflows and outflows for the groundwater store during the 2015–16 year

 

Groundwater inflows

The largest natural water inflows in the region were recharge: landscape and recharge: surface water, which combined made up approximately 99% of the total groundwater inflows. Both of these recharge volumes were less than the previous year, primarily due to the lack of data available for several of the region's aquifers. The remaining natural groundwater inflows, inter-region inflow and inter-region coastal inflow, are less climate-dependent and change little from year to year.

Managed aquifer recharge: individual users increased from the previous year.

 

Groundwater outflows

The largest natural water outflows in the region were discharge: landscape and discharge: surface water, which combined made up 99% of the total natural flows from the region's aquifers. Both of these discharges were less than the previous year, however, this is primarily due to the lack of data available for several of the region's aquifers. The remaining natural outflows, inter-region outflow and inter-region coastal outflow, are less climate-dependent and change little from year to year.

The volume of groundwater extracted in the region totalled 1,528,993 ML, which was similar to the previous year. Allocated extraction: individual users accounted for 83% of the total extraction in the region. The volume of water extracted from each water resource plan area for individual users is shown in Figure S7.

 

 

Figure S7 Groundwater extractions to individual users by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water extracted is also shown
Figure S7 Groundwater extractions to individual users by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water extracted are also shown

 

Allocated extraction: urban system accounted for 1% of the total extraction. The volume of water extracted from each water resource plan area to the urban system is shown in Figure S8. It should be noted that these volumes are likely to be an underestimate of the actual volumes extracted for urban supply. For many sustainable diversion limit resource units, town supply volumes have been incorporated under the individual user category; however, information is not available to separate between them.

 

Figure S8 Groundwater extractions for urban system by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water extracted is also shown
Figure S8 Groundwater extractions for urban system by water resource plan area against water availability during the 2015–16 year; volume and percentage of available water extracted are also shown

 

Extractions: statutory rights accounted for approximately 15% of the total extraction in the region. There were no groundwater extractions for environmental purposes during the year. Non-allocated extractions could not be quantified due to a lack of available data. For a more detailed description of the water usage in the region, and the associated water rights see the Groundwater rights note.

 

Groundwater balancing item

The calculation of the groundwater balance (Table S7) yielded a balance of 1,013,923 ML, which was 150% of the total groundwater inflow over the year.

It is likely that the balancing item is primarily attributed to uncertainties associated with the groundwater recharge from landscape (a large source of groundwater increase) and groundwater discharge to landscape (a large source of groundwater decrease). Both of these flows are estimated from a groundwater model (see Methods), and it is reasonable to expect a relatively high uncertainty around these volumes.