National Water Account 2015

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Region overview

Contextual information

Physical information

Administration

Water rights

Climate and water overview

Water Accounting Statements

Water Assets and Water Liabilities

Changes in Water Assets and Water Liabilities

Water Flows

Notes

Accounting policies

Supporting information

Quantification approach

Reconciliations

Water resources & systems

Water access & use

Future outlook

References

Accountability statement

Daly: Supporting information

Introduction

The following set of notes provides consolidated reports for each of the water stores and systems within the Daly region during the 2014–15 year. The water stores and systems included in the region are shown in Figure N1.

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

Figure N1 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 N2. 

Figure N2 Between-store flows that occur within the Daly region

The between-store flows and transfers (Figure N2), which are eliminated from the region's water accounting statements, are shown in italics throughout the following set of notes.

Surface water store

The Daly region's surface water store has three components:

• storages
• unregulated rivers
• lakes and wetlands.

A reconciliation of the surface water Statement of Water Assets and Water Liabilities and Statement of Water Flows is provided in Table N1. Further details on assets, liabilities, and flows are provided in the following sections. 

Methods used to derive reported volumes can be found in the Quantification approach note.

Assets and liabilities

Physical assets

The volume of surface water assets in the region represents the water held in Copperfield Dam (220 ML), the only surface water storage within the region. This volume is very small compared to the volume of water in the region's rivers and lakes and wetlands; however, these volumes could not be quantified due to a lack of available data.

The water volume in Copperfield Dam decreased during the 2014–15 year from 76% to 53% full at 30 June 2015, which reflects the below average wet season rainfall experienced across the region during the year (see Climate and water overview).

Non-physical assets

There are no non-physical surface water assets in the region.

Liabilities

Surface water liabilities in the Daly region refer to the volume of surface water allocation remaining on licence entitlements at the end of the 2014–15 year for:

• individual users—5,771ML
• urban supply—2,902 ML.

The surface water supply licences have a management year that ends on 30 April; allocations for the licence entitlements are announced on 1 May. Therefore, the allocation remaining at the end of the 2014–15 year is the unused component of the annual allocation for these licences. That is, allocation remaining is equal to the volume of allocation announced on 1 May less the portion of that allocation used in May and June of the reporting year.

As there are no carryover provisions for these licences, the portion of surface water allocation that has not been diverted at the end of the water year is forfeited (tables N2–N3).

Further information on all entitlements and allocation arrangements are detailed in the Surface water rights note.

Inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the surface water store in the Daly region is provided in Figure N3.

Figure N3 Water inflows and outflows for the surface water store within the Daly region during the 2014–15 year

Surface water inflows

Total inflows to surface water were 7,540,191 ML and comprised the following:

• Precipitation—89 ML
• Runoff—6,530,000 ML
• Discharge: wastewater—102 ML
• Discharge: groundwater—1,010,000 ML.

The largest water inflow is runoff (6,530,000 ML), which makes up almost 87% of the total surface water inflows. The volume of runoff during the 2014–15 year was approximately 20% less than that of the previous year. This reflects the below average wet season rainfall experienced across the region during the year, particularly during the typically wetter months of February–March (see Climate and water overview).

The remaining surface water inflows reported for the Daly region were 89 ML of precipitation on Copperfield Dam, 102 ML discharged from the Katherine wastewater treatment pond to the Katherine River, and 1,010,000 ML of groundwater discharge.

Surface water outflows

Total outflows from surface water were 4,117,511 ML and comprised the following:

• Evaporation—40,195 ML
• Outflow—4,032,345 ML
• Recharge: groundwater—36,000 ML
• Diversion: statutory rights—5,369 ML
• Allocated diversion: individual users—833 ML
• Allocated diversion: urban system—2,769 ML.

The Daly region's largest water outflow is its river outflow (4,032,345 ML), which refers to the annual volume of flow from the Daly River to the Timor Sea during the 2014–15 year. This outflow was less than half that which occurred during the previous year, which primarily reflects the below average flow conditions in the Daly River compared to the high flow experienced during the 2013–14 year (see Climate and water overview).

Evaporation during the 2014–15 year was 40,195 ML, including 195 ML from Copperfield Dam and 40,000 ML from rivers. Groundwater recharge during the year was 36,000 ML. Diversions made by individual users under statutory rights was 5,369 ML and were all associated with a riparian right.

Allocated diversions

Allocated diversion to individual users during the 2014–15 year was 833 ML, which accounts for 23% of the total allocated diversion in the Daly region. Licences primarily relate to water sourced from Katherine River for agricultural purposes (see Surface water rights note). Some water is also sourced from the Daly, Douglas, and Edith rivers (Figure N4).

Allocated diversion for urban water supply (2,769 ML) made up 77% of the total allocated diversion during the 2014–15 year. Figure N4 shows that this volume includes water diverted from the Katherine River to the town of Katherine (2,719 ML) and from Copperfield Creek to the town of Pine Creek (50 ML).

Figure N4 Water diversions to individual users and the urban water system from each river during the 2014–15 year; percentage of allocation diverted is also shown

Surface water balancing item

The calculation of the surface water balance (Table N4) on the surface water store yielded a balancing item of –3,422,774 ML. This is approximately 45% of the total surface water inflows during the 2014–15 year. The negative balancing item indicates that either the inflows are too high or the outflows are too low.

It is likely that the balancing item is primarily attributed to uncertainties associated with the runoff to surface water (a large source of surface water increase) and river outflow to the sea (a large source of surface water decrease).

Runoff is estimated from a rainfall–runoff model (see Quantification approaches) and it is reasonable to expect a 10–20% uncertainty around the runoff volume (+/– 1,300,000 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 Quantification approaches). As such, outflow to sea is likely to be underestimated by 5–10% (400,000 ML).

Groundwater store

The Daly region's groundwater store has two components:

• water table aquifer
• underlying aquifers.

A reconciliation of the groundwater Statement of Water Assets and Water Liabilities and Statement of Water Flows is provided in Table N5. Further details on assets, liabilities and flows are provided in the following sections.

Methods used to derive reported volumes can be found in the Quantification approach note.

Assets and liabilities

Physical assets

The aquifers in the Daly region are described in the Groundwater section of the 'Contextual information'. While some information exists on water movement to and from the aquifers (see Inflows and outflows below), no value is available for the volume of water stored in the aquifers as indicated by dashes ('–') in the water accounting statements. 

Non-physical assets

There are no non-physical groundwater assets in the region.

Liabilities

Groundwater liabilities in the Daly region refer to the volume of groundwater allocation remaining on licence entitlements at the end of the 2014–15 year for:

• individual users—97,762 ML
• urban water system—3,911 ML.

The groundwater supply licences have a management year that ends on 30 April; allocations for the licence entitlements are announced on 1 May. Therefore, the allocation remaining at the end of the 2014–15 year is the unused component of the annual allocation for these licences. That is, allocation remaining is equal to the volume of allocation announced on 1 May less the portion of that allocation used in May and June of the reporting year.

As there are no carryover provisions for these licences, the portion of groundwater allocation that has not been extracted at the end of the water year is forfeited (tables N6–N7).

Further information on all entitlements and allocation arrangements are detailed in the Groundwater rights note.

Inflows and outflows

A schematic diagram representing all the inflows and outflows associated with the groundwater store in the Daly region is provided in Figure N5.

Figure N5 Water inflows and outflows for the groundwater store within the Daly region during the 2014–15 year

Groundwater inflows

Total inflows to groundwater were 428,000 ML and comprised the following:

• Inter-region inflow—10,000 ML
• Recharge: surface water—36,000 ML
• Recharge: landscape—382,000 ML.

The largest water inflow is recharge from the landscape (382,000 ML), which makes up almost 90% of the total groundwater inflows. The volume of recharge during the 2014–15 year is more than 20% greater than that during the previous year, which doesn't reflect the below average wet season rainfall conditions experienced across the region (see Climate and water overview). There is often a lag in groundwater recharge, so the increased recharge in the 2014–15 year may actually be attributed to the well above average rainfall that occurred during the 2013–14 year.

The remaining groundwater inflows reported in the Daly region were 10,000 ML of inter-region flow into the region and 36,000 ML recharge from surface water.

The volume of inter-region flow into the region from the coast (– ML) and leakage from the urban system (– ML) could not be quantified due to a lack of available data.

Groundwater outflows

Total outflows from groundwater were 1,035,450 ML and comprised the following:

• Inter-region outflow—0 ML
• Discharge: surface water—1,010,000 ML
• Extraction: statutory rights—4,280 ML
• Non-allocated extraction: individual users—180 ML
• Allocated extraction: individual users—20,075 ML
• Allocated extraction: urban system—915 ML.

The largest water outflow, discharge to surface water (1,010,000 ML), makes up almost 98% of the total groundwater outflows.

Non-allocated extraction of groundwater by individual users (180 ML) and extractions under statutory rights (4,280 ML) are associated with groundwater extractions for non-intensive stock and domestic purposes. These extractions are made by small volume groundwater users within the Daly Roper Water Control District. Because the extractions associated with each user is less than 5 ML/year/property they are not required to be licensed (under the Northern Territory Water Act 1992).

The volume of inter-region flow out of the region from the coast (– ML) and discharge to landscape (– ML) could not be quantified due to a lack of available data.

Allocated extractions

Allocated extraction to individual users during the 2014–15 year was 20,075 ML, which accounts for more than 95% of the total allocated extraction. Licences primarily relate to water sourced from the Jinduckin, Oolloo, and Tindall aquifers (Figure N6). The majority of the water is used for agricultural purposes (see Groundwater rights note).

Allocated extraction for urban water supply (915 ML) accounts for less than 5% of the total allocated extraction and relates to groundwater extraction from the Tindall aquifer for Katherine town supply (Figure N6).

Figure N6 Water extractions to individual users and the urban water system from each aquifer during the 2014–15 year; percentage of allocation extracted is also shown

Groundwater balancing item

The calculation of the groundwater balance (Table N8) on the groundwater store yielded a balancing item of 607,450 ML. Given that the volume in the groundwater stores within the Daly region could not be quantified, the positive balancing item indicates that the outflows from the region's aquifers were much higher than the inflows.

The Department of Land Resource Management was able to estimate the change in groundwater store during the 2014–15 year based on groundwater model outputs. The department estimated a decrease in groundwater store of 592,000 ML during the year, which is almost equivalent to the balancing item for the groundwater store (Table N8).

Therefore, it is considered that the volume disclosed as the balancing item (607,450 ML) represents a net decrease in the groundwater store during the 2014–15 year.

Unaccounted-for difference

In the Daly region, the unaccounted–for difference of (2,815,324) ML represents 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 N9.

The unaccounted–for difference can also be calculated by summing 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 N10.

Tables N9 and N10 show that most of the unaccounted–for difference volume is observed in the surface water store.  Details regarding the balancing item's calculation are given in the Surface water store and Groundwater store notes.

The unaccounted-for difference is largely attributed to the uncertainty which is expected when modelling both groundwater and surface water flows, and exclusion of groundwater store volumes in the account. The majority of uncertainty is associated with the estimation of runoff to surface water, river flow out of the region, groundwater recharge from landscape, and groundwater discharge to surface water.

The volume of water in the groundwater stores within the Daly region could not be quantified due to lack of data. This is another contributing factor to the unaccounted-for difference.