Daly: Statement details
A single storm event in late December that caused major flooding in the region was the primary reason annual runoff increased compared with the previous year. During January–March, the typically wettest months of the year, rainfall across the region was below average, which resulted in a decrease in aquifer recharge during the 2015–16 year. The annual drop in aquifer storage, however, was not as high as the previous three years.
Water assets
The surface water and groundwater storages in the Daly region are described in the Water resources section of the 'Region description'. While information exists on water movement to and from the rivers and aquifers (see Water store note), volumes of water stored in the rivers and aquifers cannot be quantified.
The only water asset able to be quantified represents the water held in Copperfield Dam (220 ML), which is the only surface water storage within the region; however, this volume is very small compared to the volume of water in the region's rivers, lakes and wetlands, and aquifers. Therefore, the total volume of water assets in the region is represented by dashes ('–') in the water accounting statements to indicate total water assets could not be quantified.
Information on the total annual change in aquifer storage volume is available, which provides an indication of whether groundwater levels in the region's aquifers are increasing or decreasing. Below average rainfall during the typically wettest months of the year contributed to a decrease in aquifer storage (Figure S1). This is the fourth consecutive annual drop in aquifer storage for the region.
Figure S1 Total annual change in aquifer volume in the region at 30 June 2016 compared with the previous 4 years
Water liabilities
Water liabilities in the Daly region refer to the volume of allocation remaining on licence entitlements at the end of the 2015–16 year.
As there are no carry-over provisions for water supply licences in the Daly region, the portion of water allocation that has not been abstracted at the end of a water year is forfeited. The allocation remaining at the end of the 2015–16 year was 0 ML. The allocation (water liability increases), allocated abstraction (water outflow), and the adjustment and forfeiture (water liability decreases) for each licence entitlement is provided in tables S1–S2.
A more detailed description of water allocations and associated water rights in the Daly region is given in the Water rights note.
| Individual users (ML) | Urban system (ML) | |
| Opening balance at 1 July 2015 | 0 | 0 |
| Allocation | 5,855 | 3,417 |
| Allocated diversion | (971) | (2,728) |
| Adjustment and forfeiture | (4,884) | (689) |
| Closing balance at 30 June 2016 | 0 | 0 |
| Individual users (ML) | Urban system (ML) | |
| Opening balance at 1 July 2015 | 0 | 0 |
| Allocated | 100,924 | 2,359 |
| Allocated extraction | (25,599) | (965) |
| Adjustment and forfeiture | (75,325) | (1,394) |
| Closing balance at 30 June 2016 | 0 | 0 |
Water asset increases
Total water asset increases for the region (9,048,219 ML) comprised:
- surface water increases—8,668,219 ML
- groundwater increases—380,000 ML.
The key water asset increases for the region were runoff and recharge: landscape, which made up more than 95% of the surface water and groundwater increases, respectively.
During the 2015–16 year, runoff was more than 30% greater than the previous year. This increase in runoff is largely attributed to a single storm event in late December that caused major flooding in the region (see Climate and water). Recharge from the landscape was similar to last year. Most of the aquifer recharge occurs during the typically wettest months of the year (January–March), and rainfall during this period was relatively poor, similar to the previous year.
Water asset decreases
Total water asset decreases for the region (9,640,642 ML) comprised:
- surface water decreases—9,636,182 ML
- groundwater decreases—4,460 ML.
The key water asset decrease for the region was outflow from surface water, which made up more than 95% of the total water asset decreases. The outflow was more than 100% greater than the previous year, which is primarily attributed to the single storm event in late December that caused major flooding in the Daly River (see Climate and water). More than 50% of the total annual outflow occurred during that 2-week flood event.
Groundwater decreases represents non-allocated water extractions from the region's aquifers. These extractions change little from year to year.
Water flows
Total water inflows to the region (9,048,219 ML) is equal to the volume of Water asset increases above. Total water outflows from the region (9,670,905 ML) is marginally higher than the volume of Water asset decreases (9,640,642 ML) because the volume of water outflows also includes the flows corresponding to the accrual transactions, that is, the allocated diversions and extractions of water (see the Water liabilities section above).
A detailed description on all the water flows associated with the surface water and groundwater stores is provided in the Water stores note.
Unaccounted-for difference
The volume recognised in the water accounting statements, 286,686 ML, represents the total unaccounted-for difference for the Daly region for the 2015–16 year.
The unaccounted–for difference is the volume necessary to reconcile the opening water storage and closing water storage with the total water inflows and total water outflows reported in the water accounting statements. It is calculated according to Table S3.
| Volume ML | |
| Opening water storage balance at 1 July 2015 | – |
| Total inflows | 9,048,219 |
| Total outflows | (9,670,905) |
| Change in water storage | 336,000 |
| Closing water storage balance at 30 June 2016 | – |
| Unaccounted-for difference | 286,686 |
The unaccounted–for difference can also be calculated by adding the volumes necessary to reconcile (balance) the opening and closing storage with the water inflows and outflows of each of the separate water stores of the region, as shown in Table S4.
| Volume ML | |
| Surface water store | 248,662 |
| Groundwater store | 38,024 |
| Unaccounted-for difference | 286,686 |
The unaccounted-for difference is largely attributed to the uncertainty which is expected when modelling both groundwater and surface water flows in the account. The majority of uncertainty is associated with the estimation of runoff to surface water. The unaccounted-for difference for the 2015–16 year is much lower than that for the previous year (see the Statement of Changes in Water Assets and Water Liabilities), which likely reflects a more accurate estimation of runoff relative to last year's estimate.