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 2013–14 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 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. 

Figure 2 Between-store flows that occur within the Daly region

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.

Surface water store

Surface water assets

The volume of the surface water assets includes water that is held in Copperfield Dam. Copperfield Dam is the only surface water storage within the Daly region that is used for public water supply and supplies water to the town of Pine Creek. The volume of water in unregulated rivers and lakes and wetlands could not be quantified due to a lack of available data.

The volume of water held in Copperfield Dam was reported as 314 ML at the end of the reporting year based on a level reading taken on the 2 July 2013. This is a reported decrease from the previous year of 99 ML, however the volume quantified for the 2013 National Water Account was an assumed full supply volume of 413 ML.

Surface water liabilities

Water liabilities in the Daly region refer to the volume of surface water allocation remaining on licence entitlements at the end of the 2013–14 year for:

• individual users
• urban supply.

The Department of Land Resource Management administers a number of surface water licences held by individual licensees for the purposes of agriculture, stock and domestic, industry and public water supply. Licences primarily relate to water sourced from the main Daly River channel; Copperfield Dam; Bamboo Creek; and the Douglas, Edith and Katherine rivers for the agricultural and mining sectors. The urban water supply licences relate to town supply for Pine Creek and Katherine.

The surface water supply licences have a management year that ends on 30 April. Therefore, the allocation remaining at 30 June is the volume of allocation announced at 1 May less the portion of that allocation used in May and June of the reporting year.

Surface water 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 3.

Figure 3 Water inflows and outflows for the surface water store within the Daly region during the 2013–14 year

Surface water inflows

The tropical climate prevailing in the Daly River region usually results in a large volume of rainfall and consequently large volumes of surface water inflow during the wet season of November–April (see Climate overview). Surface water runoff volume reported for the 2013–14 year was 8,013,000 ML, which is approximately 12% more than the volume reported for the 2012–13 year of 7,131,000 ML but less than one third of the runoff reported for the 2011–12 year (30,590,000 ML). Runoff volumes are highly influenced by both rainfall, its distribution and intensity.

Other surface water inflows reported in the Daly region are 103 ML of precipitation on Copperfield Dam and 130 ML discharged from the Katherine wastewater treatment pond to the Katherine River. Groundwater discharge to surface water was reported as 967,000 ML for the 2013–14 year.

The volume of overbank flood return to the river channel could not be quantified due to a lack of available data; however, even during periods of major flooding this volume is expected to be relatively small.

Surface water outflows

The largest water outflow from the Daly region was the river outflow from the region (9,373,000 ML) which correlates with the large amount of runoff reported for the year. This volume represents the total volume of water outflow from the Daly River to the Timor Sea during the reporting period. This is approximately 45% larger than the volume reported in the 2012–13 year (6,146,000 ML).

Evaporation reported from surface water was 36,119 ML, including 119 ML from Copperfield Dam and 36,000 ML reported from rivers; 25,000 ML was reported as groundwater recharge from surface water.

The volume of overbank flood spilling from the river channels cannot be quantified due to a lack of available data; however, even during periods of major flooding this volume is expected to be relatively small.

Diversions made by individual users under statutory rights was estimated at 5,369 ML. These diversions were all associated with a riparian right. Entitled water abstractions from the surface water store are described in Surface water allocation diversions below.

Surface water allocation diversions

As the surface water management licences in the Daly region run from 1 May-30 April each year, in order to align with the National Water Account reporting year the diversions quantified in the Daly region account represent volumes that were diverted from surface water from July 2013–April 2014 (under the 2013–14 allocation announcement) plus the diversions made from May–June 2014 (under the 2014–15 allocation announcement).

Entitled diversion of surface water in the Daly region for the 2013–14 year is 2,287 ML, made up of 263 ML for individual users, and 2,024 ML diverted to the urban water supply system. Surface water diversions by individual users decreased from 745 ML, a reported decline in use of 482 ML. Diversions under this entitlement were from Copperfield Dam, the Daly River, Edith River, Katherine River, and Stray Creek. The majority of these diversions were for agricultural purposes, with a smaller amount for industry.

Total urban water supply diversions for the reporting year was 2,024 ML, 430 ML less than what was diverted in the previous year. All water reported as urban diversion was from Katherine River for supply to the town of Katherine. No volume was reported as being diverted from Copperfield Creek for the 2013–14 year.

Entitled diversion of allocated surface water for urban water supply in the Daly region during the 2013–14 year is shown in Figure 4.

Figure 4 Water allocations and diversions for the Daly and Katherine Rivers during the 2013–14 year

Surface water forfeitures

As the surface water supply licences of the Daly region have a water management year that ends on 30 April, and there are no rules for carryover, forfeiture reported for individual user licences is calculated as the total allocation remaining on 1 July 2013 less the total allocation diversion between 1 July 2013–30 April 2014.

Water forfeitures in the Daly region were 3,167 ML for individual users, and 1,430 ML for the urban water system for the 2013–14 year.

Surface water allocation announcements

 Water allocation announcements in the Daly region during the 2013–14 year refer to surface water supply to:

• individual users
• urban water system.

There are 23 separate licences for individual users in the Daly region which cover water for agricultural, stock and domestic, or industry purposes. The total volume of allocation announced for individual users on 1 May 2014 in the region was 5,361 ML. Around 92 % of this allocation announcement was for agriculture, approximately 7% for industry, and the remainder for licensed stock and domestic use. Figure 5 shows the annual allocation announcement for each licence purpose for the 2013–14 year.

Figure 5 Surface water allocation announcement for individual users during the 2013–14 year

Total urban water allocation volume for the 2013–14 reporting period was 3,417 ML. Urban water supply licences in the Daly region refer to 150 ML allocated for water supply to the town of Pine Creek from Copperfield Creek and 3,267 ML allocated to the town of Katherine which is supplied from the Katherine River. These volumes are not included in Figure 5. 

A more detailed description of surface water allocations and associated water rights in the Daly region is given in the Surface water rights note.

Surface water balancing item

The balancing item volume represents the difference between the measured opening and closing balances of the surface water store, after physical 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 balance.

The balancing item is calculated according to Table 3.

The calculation of the water balance on the surface water store yielded a balancing item of (461,443) ML. This is approximately 5% of the total surface water inflows during the 2013–14 year.

The balancing item is primarily attributed to uncertainties related to the inflows and outflows modelled for the region. A large source of surface water increase is the volume of runoff, and there is a level of uncertainty associated with the modelled volumes which can affect the balancing item. 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). 

Groundwater store

Groundwater 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 Water 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. 

Given that the volume of groundwater within the region is unknown, the Department of Land Resource Management derives 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 configured for the region to ensure groundwater is not over-allocated.

Groundwater liabilities

Water liabilities in the Daly region refer to the volume of groundwater allocation remaining on licence entitlements at the end of the 2013–14 year for:

• individual users
• urban water system.

The Department of Land Resource Management administers a number of groundwater licences held by individual licensees for the purposes of agriculture, stock and domestic, industry and public water supply. Most of the water held under licences refers to water from the Jinduckin, Oolloo and Tindall (Katherine) aquifers with some smaller entitlements for the Tindall (other) and smaller local aquifers. A small volume is held for public water supply from the Tindall (Katherine) water source.

The groundwater supply licences have a management year that ends on the 30 April. Therefore the allocation remaining at 30 June is the volume of allocation announced at 1 May less the portion of that allocation used in May and June of the reporting year.The allocation remaining for each licence entitlement is provided in the following tables.

Groundwater 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 6.

 
Figure 6 Water inflows and outflows for the groundwater store within the Daly region during the 2013–14 year

The Department of Land Resource Management (The Department) uses the Finite Element Subsurface Flow system (FEFLOW) to estimate the natural water movement to and from the groundwater store within the Daly region. FEFLOW estimates groundwater movement for the entire extent of the Oolloo aquifer and the Tindall aquifer, which extends beyond the Daly region boundary. The volumes reported in this account refer to the natural water movement that occurs within these aquifers within the Daly region boundary.

The Oolloo and Tindall aquifers are karstic and were modelled as an equivalent porous media with relatively limited storage. The groundwater model was calibrated using regional aquifer parameters to reproduce the observed groundwater levels and discharge to the rivers, as outlined in NRETAS 2010.

 The Department of Land Resource Management provides a combination of metered data and estimates to quantify extractions from groundwater.

Groundwater inflows

As a result of similar climatic conditions between the two years, all groundwater inflows were very similar to the volumes reported in the 2012–13 year. The total recharge from landscape was 315,000 ML in the 2013–14 year compared to 335,000 ML in the 2012-13 year, and recharge from surface water in 2013–14 was 25,000 ML compared to 23,000 ML in the 2012–13 year. There was no difference in the volume reported for groundwater inflow into the region from the coast at 10,000 ML.

Groundwater outflows

Similar to water inflows, the groundwater outflows reported for the Daly region are comparable to the previous year.  The only natural outflow that was able to be quantified for the region was discharge to surface water at 967,000 ML.

Extraction of groundwater by users that was not associated with an allocation was estimated at 4,280 ML, almost the same as the previous two years. This volume is associated with individual users extracting groundwater for non-intensive stock and domestic purposes under the Water Act 1992. Approximately 180 ML was extracted for entitled non-allocated individual use, also for 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 Water Act).

Groundwater allocation extractions

As the groundwater management licences in the Daly region run from 1 May–30 April each year, in order to align with the National Water Account reporting year the extractions quantified in the Daly region account represent volumes that were extracted from groundwater from July 2013–April 2014 (under the 2013–14 allocation announcement) plus the extractions made from May-June 2014 (under the 2014–15 allocation announcement).

Most of the 19,062 ML reported as licensed use for individual users from the groundwater store was for agriculture. These extractions were made from the Jinduckin, Oolloo, Tindall (Katherine), Tindall (other), and local aquifers. Extractions made for agricultural purposes was 18,003 ML, 961 ML was obtained for industry, and the remaining volume was for stock and domestic use. 

Urban extractions for public water supply to the town of Katherine from the Tindall aquifer was 509 ML.

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.

Groundwater forfeitures

As the groundwater supply licences of the Daly region have a water management year that ends on 30 April, and there are no rules for carryover, forfeiture reported for urban and individual user licences is calculated as the total allocation remaining on 1 July 2013 less the total allocation extraction between 1 July–30 April.

Allocation forfeitures in the Daly region were 36,458 ML for individual users, and 3,432 ML for the urban water system for the 2013–14 year.

Groundwater allocation announcements

Groundwater allocation announcements in the Daly region during 2013–14 refer to the groundwater supply to:

• individual users
• urban supply.

Given that the volume of the groundwater asset within the region is relatively unknown, the Department of Land Resource Management derives allocations for groundwater extraction based on the predicted volume of flow in the Katherine and Daly rivers at the end of the dry season (1 November). The predicted flow is estimated using models configured for the region to ensure groundwater is not over-allocated.

A total of 101,186 ML is allocated in the Daly region for individual licensed users. These licences are separated into agricultural, industry, or stock and domestic use. Around 98% of the total allocated volume for the 2013–14 year was held for agricultural purposes and this amount was mostly from the Oolloo aquifer. Figure 5 below shows the breakdown of use types for the total allocation for individual users.

Figure 7 Groundwater allocation announcement for each licence purpose for the 2013–14 year

Groundwater was used to supply public water to the town of Katherine during the reporting year. A volume of 4,076 ML was allocated for this purpose from the Tindall (Katherine) water resource. This volume was not included in Figure 7.

Groundwater balancing item

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 represent a complete groundwater store balance.

The balancing item is calculated according to the following table.

The calculation of the water balance on the groundwater store yielded a balancing item of (641,031) ML.

Although the volume in the groundwater stores within the Daly region could not be quantified, the Department of Land Resource Management was able to estimate the change in groundwater store during the 2013–14 year based on groundwater model outputs. The estimated change in groundwater store of (627,000) ML is almost 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 2013–14 year.

Unaccounted-for difference

In the Daly region, the unaccounted–for difference of (1,102,474) 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 7.

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 8.

Tables 7 and 8 show that most of the unaccounted–for difference volume is observed in the groundwater store.  Further details of the balancing item calculations is given in the Water Access and Use note.

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.