Risks in the current groundwater regulation approach in the Beetaloo region, Northern Territory, Australia

Figures & data

Figure 1. Location of the study area showing extent of the Cambrian Limestone aquifer (CLA) and underlying Beetaloo basin, the boundary between Top End and Arid zones as defined in the NT water allocation framework, and relevant water allocation plan areas. SREBA = Strategic Regional environmental and Baseline Assessment area, as defined in Northern Territory Government (2020).

Table 1. Estimates of groundwater recharge rate to the CLA.

Basin/Unit(s)	Point-based recharge rate estimates (mm/year)	Volumetric recharge rate (CLA)	Method(s) used	Reference
Daly Basin (Tindall Limestone).	8.7 to 28.5 mm/yr (diffuse recharge in areas of shallow/exposed CLA)	Approx. 330 GL/yr (range from 286 to 722 GL/yr).	Water table fluctuations, Chloride mass balance, water balance, model	Bruwer and Tickell (2015)
		177 GL/yr	Coupled ground-surface water modelling	Knapton (2020).
	49 to 156 mm/yr (5^th to 95^th percentiles)		Chloride mass balance, probabilistic, constrained using baseflow separation & remote sensing data	Crosbie and Rachakonda (2021)
Georgina Basin (Gum Ridge/Anthony Lagoon Formation)	0.9 to 12.2 mm/yr (diffuse recharge in areas of shallow/exposed CLA)	20 to 179 GL/yr (Gum Ridge Fm) 51 GL/yr (Anthony Lagoon Fm)	Chloride mass balance	Tickell and Bruwer (2017)
	5 to 18 mm/yr (diffuse recharge, 5^th to 95^th percentile)		Chloride mass balance, probabilistic, constrained using baseflow separation & remote sensing data	Crosbie and Rachakonda (2021)
		315 GL/yr (Georgina);	Coupled ground-surface water modelling	Knapton (2020)
		585 GL/yr	Coupled ground-surface water modelling	Northern Territory Government, 2023a.
Wiso Basin (Montejinni Limestone)		46 GL/yr	Coupled ground-surface water modelling	Northern Territory Government, 2023a.
	9 to 31 mm/yr (5^th to 95^th percentile)		Chloride mass balance, constrained using baseflow separation and remote sensing data	Crosbie and Rachakonda (2021)
Beetaloo region (including northern Georgina and Wiso basins, and southern Daly basin)	1 to 25 mm/yr (diffuse, increasing from south to north); 140 to 190 mm/yr (preferential recharge through sinkholes)		Tritium, Chloride mass balance (recharge rate); CFCs, SF6 and noble gases (qualitative insights)	Deslandes et al., (2019)

Table 2. Current status of knowledge regarding groundwater resources of the CLA.

Question/issue	Daly Basin	Georgina Basin	Wiso Basin	Beetaloo sub-Basin	Reference(s)
Groundwater monitoring network	Moderate to good	Moderate to good	Poor to moderate	Poor	Northern Territory Government, 2021; Amery and Tickell (2022); Currell and Ndehedehe (2023)
Inter-aquifer connectivity	Moderate	Poor – moderate	Poor	Poor	Lamontagne et al., (2021); Frery et al., (2022); Northern Territory Government 2021; Tickell (2022); Currell and Ndehedehe (2023).
Aquifer extent and thickness	Good	Moderate – good	Moderate	Poor – moderate	Evans et al., (2020); Northern Territory Government, 2021; DEPWS (2022)
Aquifer hydraulic parameters	Moderate – good	Moderate	Moderate	Poor	Northern Territory Government, 2021; Tickell and Bruwer (2017); Knapton (2020); T (2022)
Groundwater recharge and discharge processes, locations and rates	Moderate – good	Moderate – poor	Poor	Poor	Northern Territory Government, 2021; Currell and Ndehedehe (2022); Table 1 (this paper).
Dependence of ecosystems on groundwater	Moderate	Poor-moderate	Poor-moderate	Poor	Karp (2008); Knapton (2009); Lamontagne et al., (2021); Oberprieler et al., (2021); Gautam et al., (2022).
Tolerance of GDEs to changes in water level & quality	Poor	Poor	Poor	Poor	Currell and Ndehedehe (2022); Currell and Ndehedehe (2023)
Indigenous cultural values associated with groundwater	Moderate – good	Poor	Poor	Poor	Barber and Jackson (2012); (2014); (2015); Cooper and Jackson (2008); Northern Territory Government (2023a)

Figure 2. Conceptual representation of the risk/impact of increasing rates of extraction from Cambrian Limestone aquifer sub-regions (modified from Currell and Ndehedehe 2022). Note that water level surfaces are approximate representations, for visualisation purposes only.

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