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Daly: Supporting information

  • Above-average annual rainfall contributed to high runoff and aquifer recharge across the region.
  • The wetter conditions resulted in an annual increase in aquifer storage for the first time in four years.
  • 27% of the allocated water was taken in 2020–21, mainly for agricultural purposes.

Schematic representation of the Daly region. In 2020–21, runoff was 18% more than average. Aquifer storage increased during the 2020–21 year for the first time in 4 years. 40% of the total surface water allocation (9 GL) was taken. 26% of the total groundwater allocation (144 GL) was taken.

For further information on the regions water accounting statements scroll down this page or click on the links below:

 

Water assets

 

Groundwater assets

  • Volumes of water stored in the aquifers cannot be quantified due to a lack of available data; however, information on the total annual change in aquifer storage is available.

 

Bar graph of annual change in aquifer storage volume in the Daly region from 2011–12 to 2020–21. In 2020–21, the volume of water in the aquifers increased. The last annual increase in aquifer storage was in 2016–17. The largest annual increase was in 2011–12 during a La Nina period.
Figure S1 Total annual change in aquifer volume in the region at 30 June 2021 compared with the previous 9 years

 

  • Above-average annual rainfall contributed to high groundwater recharge and an annual increase in aquifer storage of 281 GL.
  • This was the first annual increase in aquifer storage for the region in four years.
  • Aquifer recharge was not as high as 2011–12, which was primarily attributed to well above-average rainfall over a 2-year period associated with the 2010–12 La Niña event. The La Niña event in 2010–12 was one of the strongest on record and had a greater influence on northern Australia's climate than the La Niña event in 2020–21.

 

Surface water assets

  • The volume of surface water in the region at 30 June 2021 was 13 GL, all of which is water held in rivers. This volume changes little from year to year.
  • The volume of water in the region's storages (see Region description) could not be quantified; however, this volume is very small compared with the volume of water in rivers.

 

Water liabilities

Katherine River, Daly region (NT Tourism © anonymous)

 

  • Water liabilities in the Daly region refer to the volume of allocation remaining on licence entitlements at the end of the 2020–21 year.

 

Table S1 Volume of surface water allocation remaining at 30 June 2021
Description Individual users (ML) Urban system (ML)
  Opening balance at 1 July 2020 0 0
add Allocation 5,357 3,527
less Allocated diversion 680 2,793
less Adjustment and forfeiture 4,677 734
  Closing balance at 30 June 2021 0 0

 

Table S2 Volume of groundwater allocation remaining at 30 June 2021
Description Individual users (ML) Urban system (ML)
  Opening balance at 1 July 2020 0 0
add Allocation 139,637 4,356
less Allocated diversion 36,891 398
less Adjustment and forfeiture 102,746 3,958
  Closing balance at 30 June 2021 0 0

 

  • 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 and the allocation remaining at the end of the year was 0 ML.
  • A more detailed description of water allocations in the Daly region is given in the Water use section below.

 

Water flows

Katherine River in flood, Daly region (DENR © Sean Lawrie)

 

Figure S2 Water inflows and outflows for the region's water stores during the 2020–21 year

 

  • Total water flows into the region's storages was 12,378 GL. The key item contributing to water inflows was runoff, which made up 86% of the total water inflows for the region.
  • Runoff was above average (based on modelled data from 1971–2021) due to high wet-season rainfall across the region.
  • The key item contributing to water outflows for the region was river outflow, which made up 89% of the total outflows. River outflow was above average due to the relatively wet conditions and high runoff across the region.
  • Water taken for consumptive use was 51 GL, less than 1% of the total outflow (see Water use section below).

 

Water use

Daly River, Northern Territory (Bureau of Meteorology © Bradley Wood)

 

Figure S4 Water taken during the 2020–21 year in the region's key water management areas

 

  • Total surface water diverted in the region was 8,842 ML, mostly from the Katherine River.
  • 61% of the surface water diversions were made under statutory rights; 31% were for the urban system and 8% were supplied to licenced individual users.
  • Total groundwater extracted in the region was 41,749 ML, mostly from the Oolloo Dolostone and the Tindall Limestone water allocation plan areas.
  • 88% of the groundwater extractions were supplied to licenced individual users; 1% were for the urban system and 11% was made under statutory rights.

 


Figure S5 Surface water allocations and diversions in the Daly region for the years ending 30 June, from 2012–2021

 

  • In 2020–21, total surface water allocation was 9 GL, mostly from the Katherine River for town supply; 40% of the allocated surface water was taken.
  • Surface water diversions to the urban system were the same as last year.
  • Surface water allocations for the urban system returned to pre-2018 volumes. In 2018–19, allocations were increased as a precautionary measure in case groundwater supply to Katherine was further limited by the presence of per- and poly-fluoroalkyl substances (PFAS) and more surface water was needed to meet the town's water supply requirements.
  • Surface water allocations and diversions for individual users were similar to the last few years. The relatively large increase in surface water allocation in 2014–15 was due to a number of new licences being granted for the Katherine River, primarily for agricultural purposes.
  • The estimated volume of water diverted under other statutory rights remained unchanged.

 

Bar graph of annual groundwater allocation and extraction for different users in the Daly region from 2011–12 to 2020–21. Most of the groundwater allocations are associated with individual users. In 2020–21, the allocations for individual users were higher than the previous few years. 34% of the allocation for individual users was taken. Allocations for the urban system generally changes little from year to year. In 2020–21, 9% of the allocation for the urban system was taken. Non-allocated groundwater is also taken for individual users under a statutory right.
Figure S6 Groundwater allocations and extractions in the Daly region for the years ending 30 June, from 2012–2021

 

  • In 2020–21, total groundwater allocation was 144 GL, mostly from the Oolloo Dolostone and Tindall Limestone aquifers for agricultural purposes. 26% of the allocated groundwater was taken.
  • Groundwater extractions for individual users were lower than last year; influenced by the above average rainfall condition. There has been an upward trend in extractions in the previous few years which was likely to be influenced by the previously very dry conditions across the region resulting in a high demand from customers.
  • Groundwater extractions for the urban system remained relatively low, similar to last year. Groundwater supply to the town of Katherine has been limited during the last three years due to a requirement for groundwater to be filtered to remove per- and poly-fluoroalkyl substances (PFAS) before transfer to the urban system (see Water restrictions for more detail).
  • The estimated volume of water extracted under other statutory rights remained unchanged.

 

Water restrictions

 

  • A per- and poly-fluoroalkyl substances (PFAS) treatment plant commenced operation in the region in October 2017 to remove higher levels of PFAS identified in the town of Katherine's groundwater supply. Groundwater extracted from the Tindall Limestone Aquifer was filtered to remove PFAS prior to transfer to the urban system.
  • The PFAS removal process has meant that groundwater supply to the town of Katherine has been limited during the last three years. Although most of the town water supply for Katherine comes from surface water, the drop in groundwater contribution meant total water usage in Katherine needed to reduce by 20% to ensure a sustainable water supply.

 

Cultural and environmental water

Kakadu wetland, Northern Territory (istock © Catherine and Simon Gidz)

 

Cultural benefit

  • The water allocation plans for the Daly region recognise Aboriginal rights and interests in water and provide for Aboriginal interests through measures to limit extraction of groundwater (see the Cultural water management section in the 'Region description').
  • The cultural water provisions are strongly linked to the environmental water requirements in the plans (see Environmental benefit below).

 

Environmental benefit

Environmental water provisions

  • Environmental water provisions have been established for the Tindall Limestone and Oolloo Dolostone aquifers based on minimum flow requirements in the Katherine and Daly rivers, respectively.

 

Graph of predicted flow intervals in the Katherine River at the Railway Bridge on 1 November. Predicted flow less than 0.6 cumecs on 1 November is considered very dry and, in this scenario, 87% of annual groundwater discharge from the Tindall Limestone Aquifer is for environmental benefit. Predicted flow between 0.6–1.0 cumecs on 1 November is considered dry and, in this scenario, 80% of annual groundwater discharge is for environmental benefit. Predicted flow between greater than 1.0 cumecs on 1 November is considered normal–wet and, in this scenario, 70% of annual groundwater discharge is for environmental benefit.
Figure S7 Environmental water provisions for the Tindall Limestone Aquifer

 

  • For the Tindall Limestone Aquifer, water provisions are defined based on a model-predicted flow rate at the end of the dry season on 1 November along the Katherine River.
  • The flow on 1 November is equated to an annual groundwater discharge volume from the Tindall Limestone Aquifer into the river. The proportion of discharge reserved for environmental benefit is based on this volume. The remainder of the annual groundwater discharge is allocated for extraction for consumptive use.
  • A more detailed description of the environmental water provisions for the Tindall Limestone Aquifer is provided in the Katherine Tindall Limestone Aquifer Water Allocation Plan.
  • For the Oolloo Dolostone Aquifer, environmental flow targets are defined at key gauging stations along the Daly River. The combined effect of groundwater extractions and surface water diversions in the plan area should not reduce flows beyond these targets for the duration of the dry season (May–October).
  • The environmental flow requirements for the Daly River are provided in Section 4 of the Oolloo Dolostone Aquifer Water Allocation Plan.

 

Environmental water outcomes

Tindall Limestone Aquifer

 

Graph of predicted and observed flow in the Katherine River at Wilden on 1 November 2020. The predicted flow on 1 November 2020 was between 1.8 and 2.1 cumecs, which is considered dry. 80% of the modelled natural flow must be preserved for environmental benefit. The actual observed flow on 1 November 2020 was above 2.1 cumecs, which is considered average and above the modelled preserved flow. Key aspects of the graph are described in the text below the figure.
Figure S8 Environmental water outcomes for the Tindall Limestone Aquifer

 

  • The environmental water provisions for the 2020–21 year for the Tindall Limestone Aquifer were based on a dry year classification.
  • Under this scenario, 80% of the modelled natural flow on 1 November 2020 must be preserved for non-consumptive use. This is the minimum flow requirement.
  • The observed flow on 1 November 2020 exceeded the minimum flow requirement.

 

Oolloo Dolostone Aquifer
  • Total water extracted from the Oolloo Dolostone Aquifer plan area in 2020–21 was 35,000 ML, equivalent to a 1.1 m3/s reduction in natural flow in the Daly River.
  • Flow along the Daly River at Mount Nancar (Station G8140040), which is the most downstream monitoring site and takes into account all extractions from the plan area, was above the environmental flow target of 12 m3/s for the entire 2020 dry season. Above this target, extractions can reduce the natural flow in the Daly River by up to 20%.
  • The 1.1 m3/s reduction in flow from extractions in 2020–21 is less than 20% of the natural flow, which means the non-consumptive water requirements were met in the Daly River.