Daly
Water resources and systems

The following set of notes provides consolidated reports for each of the water stores and systems within the Daly region during the 2012–13 year. The water stores and systems included in the region are shown in Figure 1.

For more information about the region, please refer to the General description section of the 'Contextual information'.

Figure 1  Schematic diagram of the water stores and systems within the Daly region

Information on all water flows to and from each water store and system are presented in this note, including between-store flows and transfers that are not presented in the water accounting statements. The between-store flows and transfers that occur in the region are presented in Figure 2.

The numbers on the diagram refer to the line item numbers in the water store notes. For each between-store flow, there are two line item numbers: one refers to flow out of a water store and the other refers to flow into a water store.

Figure 2  Schematic diagram of between-store flows that occur within the Daly region. Line item numbers are provided next to the flows.

The between-store flows and transfers (Figure 2), which are eliminated from the region's water accounting statements, are shown in italics throughout the following set of notes.

A description of the Daly region's surface water resources is provided in the Surface water section of the 'Contextual information'.

While good information exists on water movement to and from the surface water store (see following section on 'Changes in water store'), only limited data are available for the volume of water in the store. No value could be estimated for the volume in 1.2 Unregulated river, indicated by a dash ('–') for  in Table 1, which is the largest component of the surface water asset. The volume of water in lakes and wetlands (1.4 Lakes and wetlands) also could not be quantified due to a lack of available data.

The Statement of Water Assets and Water Liabilities for the surface water store (Table 1) shows that total surface water liabilities decreased marginally during the 2012–13 year in the Daly region. 

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the surface water store are provided in Table 2 and Table 3 respectively.

A schematic diagram representing all the inflows and outflows associated with the surface water store in the Daly region is provided in Figure 3. The numbers in brackets on the diagram refer to the line item numbers in Table 3.

Figure 3 Schematic diagram of water inflows and outflows for the surface water store within the Daly region during the 2012–13 year; line item numbers are provided in brackets

Allocations and diversions

Diversions from surface water are to individual users under statutory rights (17.6 Surface water diversions – other statutory rights), which accounts for approximately 60% of the total diversion (Figure 4). Just over 32% of the diversion from surface water is for Katherine town water supply (17.12 Entitled diversion of allocated surface water to urban water system).

Figure 4 Graph of diversions from surface water within the Daly region during the 2012–13 year; line item numbers are given in brackets

The allocated diversions (line items 17.11 Entitled diversion of allocated surface water to users and 17.12 Entitled diversion of allocated surface water to urban water system ) are associated with a water access entitlement. When an allocation is announced, a present obligation (water liability) is created on the surface water to deliver water to the users. As there is no carry-over provision in the region, the portion of the announced allocations that were not diverted by the end of the year was forfeited.

The entitlement, allocation announcement and forfeiture for each of these water rights during the 2012–13 year are provided in the Surface water rights section of the 'Water access and use' note.

The balancing item volume represents the difference between the measured opening and closing balances of the surface water store, after water inflows and outflows have been applied. This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete surface water store balance. The closing balance of 413 ML differs from the opening balance of 500 ML because of updated survey information on Copperfield Dam. It is not due to a loss of water. 

The balancing item is calculated according to Table 4.

The calculation of the water balance on the surface water store yielded a balancing item of 1,867,654 ML. This is approximately 23% of the total surface water inflows during the 2012–13 year.

The balancing item is primarily attributed to river and floodplain losses (including evaporation and seepage) that are not included in the account. It is likely that these losses are a relatively large source of surface water decrease throughout the region. In addition, the balancing item will also be attributed to uncertainty associated with the runoff (a large source of surface water increase, 9.4 Runoff to surface water). The runoff volume is derived from a rainfall–runoff model and it is reasonable to expect a 20% uncertainty around the estimated runoff volume (+/– 1,400,000 ML).

A description of the Daly region's groundwater resources are provided in the Groundwater section of the 'Contextual information'.

While good information exists on water movement to and from the groundwater store (see following section on 'Changes in water store'), no value is available for the volume of water in the aquifers. No value could be estimated for the volume of the groundwater asset either, indicated by dashes ('–') in Table 5. Given that the volume of groundwater within the region is unknown, the Department of Land Resource Management derive allocations for groundwater extraction based on the predicted volume of flow in the Katherine River at the end of the dry season (1 November). The predicted flow is made using models fitted for the region to ensure groundwater is not over-allocated.

The Statement of Water Assets and Water Liabilities for the groundwater store is shown in Table 5.

The Statement of Changes in Water Assets and Water Liabilities and the Statement of Water Flows for the groundwater store are provided in Table 6 and Table 7, respectively.

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Daly region is provided in Figure 5. The numbers in brackets on the diagram refer to the line item numbers in Table 7.

Figure 5 Schematic diagram of water inflows and outflows for the groundwater store within the Daly region during the 2012–13 year; line item numbers are provided in brackets

Some line items show a substantial decrease in volumes between the 2011–12 year and the 2012–13 year such as 10.3 Recharge from landscape and 18.4 Discharge to surface water. This can be attributed to the difference in weather patterns experienced between the wet seasons. The 2011–12 year rainfall was average to above average (see Climate overview from the 2012 Account). The rainfall patterns of this season was characterised by monsoonal rainfall thorughout much of the season. These heavy periods of rain caused rapid movement of water through the catchment. The 2012–13 wet season exhibited a very different pattern. The wet season as a whole recorded an average rainfall, but this was characterised by long dry periods interspersed with short, wet bursts. These rainfall patterns limited the amount of water movement and resulted in much less recharge and discharge.

Allocation and extractions

Most of the extractions from the groundwater store are for licensed private use (18.11 Entitled extraction of allocated groundwater to users), which accounts for 70% of the total extraction (Figure 6). The majority of the allocated private water extractions are for agricultural use. Approximately 4% of the extraction from aquifers is for Katherine town water supply (18.12 Entitled extraction of allocated groundwater to urban water system).

Figure 6 Graph of extractions from aquifers within the Daly region during the 2012–13 year; line item numbers are given in brackets

The allocated diversions (line items 18.11 Entitled extraction of allocated groundwater to users and 18.12 Entitled extraction of allocated groundwater to urban water system) are associated with water access entitlements. When an allocation is announced, a present obligation (water liability) is created on the surface water to deliver water to the users. As there is no carry-over provision in the region, the portion of the announced allocations that were not diverted by the end of the year was forfeited. Current allocations and extractions represent a very small proportion of the recharge and discharge of the groundwater asset and therefore it is unlikely that they will be a cause of concern in relation to a decline in the net water asset.

The entitlement, allocation announcement and forfeiture for each of these water rights during the 2012–13 year are provided in the Groundwater rights section of the 'Water access and use' note.

The balancing item volume represents the difference between the measured opening and closing balances of the groundwater store, after water inflows and outflows have been applied. This item is an indication of both the accuracy of the volumes reported and the degree to which the reported water flows represents a complete groundwater store balance.

The balancing item is calculated according to Table 8.

The calculation of the water balance on the groundwater store yielded a balancing item of (599,978) ML.

Although the volume in the groundwater stores within the Daly region could not be quantified (2.1 Water table aquifer and 2.2 Underlying aquifers), the Department of Land Resource Management were able to estimate the change in groundwater store during the 2012–13 year based on groundwater model outputs. The estimated change in groundwater store of (599,978) ML is the same as the balancing item for the groundwater store.

Therefore, it is considered that the volume disclosed as the balancing item represents the net change in groundwater store throughout the 2012–13 year. See 25.1 Unaccounted-for difference for a further explanation on this volume and the uncertainty associated with modelling techniques.