Burdekin: Water stores
These notes provide a water balance for each of the region's water stores for the 2015–16 year. Increased rainfall during the wet season, compared to last year contributed to increased runoff particularly in the northern part of the region. The improved rainfall conditions resulted in a 20% decrease in irrigation water use during the year.
Surface water store
The volume of water in the Burdekin region's surface water store increased during the 2015–16 year from 1,479,551 ML at 1 July 2015 to 1,871,324 ML at 30 June 2016 (Table S5).
| 2016 ML | 2015 ML | |
| Opening surface water store | 1,479,551 | 2,003,189 |
| Inflows | 2,594,670 | 1,730,603 |
| Outflows | (2,846,619) | (2,446,226) |
| Balancing item | 643,722 | 191,985 |
| Closing surface water store | 1,871,324 | 1,479,551 |
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
Surface water inflows
Total inflows to surface water (2,594,670 ML) increased by approximately 50% compared with the previous year, reflecting improved rainfall conditions (see Climate and water).
The largest natural water inflow in the region is runoff. The total volume of runoff increased by 53% (from the previous year) to 2,509,517 ML during the 2015–16 year. Precipitation on surface water storages decreased slightly, as the higher rainfall occurred away from these locations. More than 85% of the total volume of precipitation on surface water in the region occurs at Lake Dalrymple.
Surface water outflows
Total outflows from surface water (2,846,619 ML) increased by approximately 16% compared with the previous year. This is primarily attributed to the 65% increase in river outflow during the year.
Evaporation during the 2015–16 year was 30% lower than that which occurred during the previous year (see Climate and water). Approximately 90% of the total volume of evaporation from surface water in the region occurs at Lake Dalrymple. River and floodplain losses could not be quantified accurately due to a lack of available data; however, the river losses are considered to be relatively large and its omission may have a material impact on the water balance of the surface water store.
Total surface water diverted, including transfers made under inter-region commitments in the region was 841,961 ML. Allocated diversions make up 80% of this volume and comprise allocated diversion: irrigation scheme (533,681 ML), see Figure S4. Allocated diversion: individual users (134,177 ML) and allocated diversion: urban system (2,263 ML).
Two inter-region transfers (Figure S4) with a total volume of 13,096 ML (9,126 ML from Bowen–Broken WSS and 3,970 ML from Paluma dam) occurred during the 2015–16.
Non-allocated diversion: individual users accounts for the remaining 20% of diversions and was estimated to be 158,744 ML during the 2015–16 year, which assumes 100% of the licenced entitlement was taken.
Figure S4 Allocated water diversions and inter-region transfers during the 2015–16 year; percentage of allocation diverted is also shown
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 calculation of the surface water balance (Table S5) yielded a balance volume of 643,722 ML, which is approximately 34% of the total surface water store volume at the end of the 2015–16 year. The positive number indicates that inflows are either too low or the outflows are too high.
It is likely that the balancing item volume is primarily attributed to uncertainties associated with the runoff to surface water (a large source of surface water increase), river outflow from the region (a large source of surface water decrease), and the lack of reliable estimates of river and floodplain losses and surface water discharge to groundwater.
Runoff is estimated using a combination of observed streamflow data and rainfall–runoff model outputs (see Methods) and it is reasonable to expect a 10–20% uncertainty around this estimated runoff volume (+/– 375,000 ML). The river outflow to sea is based on measured flow data collected at the most downstream station along a river. There is no adjustment made for the contributing area below the gauging station (see Methods). As such, outflow to sea could be underestimated by up to 10% (150,000 ML).
Groundwater store
The water balance indicates that the licence entitlement asset volume of water in the Burdekin region's groundwater store increased marginally during the 2015–16 year from 93,451 ML at 1 July 2015 to 107,714 ML at 30 June 2016 (Table S6).
| 2016 ML | 2015 ML | |
| Opening groundwater store | 93,451 | 93,451 |
| Inflows | 112,483 | 81,673 |
| Outflows | (80,433) | (54,860) |
| Balancing item | (17,787) | (26,813) |
| Closing groundwater store | 107,714 | 93,451 |
A schematic diagram representing all groundwater inflows and outflows during the 2015–16 year is provided in Figure S5.
Figure S5 Water inflows and outflows for the groundwater store during the 2015-16 year
Groundwater Inflows
The only physical water movement to aquifers in the Burdekin region that can be quantified is managed aquifer recharge (98,220 ML). In addition a non-physical inflow "other" groundwater increases (14,263 ML) represents the difference in total groundwater licence entitlements from the previous 2014–15 year.
Inter-region inflow across the region boundary, recharge: landscape, recharge: surface water and leakage: irrigation are considered to be applicable to the region; however, these flows cannot be quantified.
Groundwater Outflows
Total outflows from groundwater was 80,433 ML. Allocated extraction: individual users was 28,434 ML representing 35% of the total extraction. Non-allocated extraction: individual users was estimated to be 51,999 ML during the 2015–16 year, see the Groundwater rights note for more information on groundwater extractions and associated allocations.
Inter-region groundwater outflow across the region boundary, discharge: landscape and discharge: surface water could not be quantified
Groundwater balancing item
The calculation of the groundwater balance; (Table S6) represents the difference between the measured opening and closing balances of the groundwater store, after physical / non-physical inflows and outflows have been applied. The balance is the difference between the managed aquifer recharge from individual users (98,220 ML), the difference in total groundwater licence entitlements from the previous year (14,263 ML) with the total volume of groundwater extraction (80,433 ML), as shown in Table S6.