Introduction
Study area
Region | Reference | Summary |
---|---|---|
Daly catchment | (Jolly 1984) | Using baseflow analysis of Douglas River (northern Daly catchment), the study found regional average recharge of 100 mm/year. Using bore hydrographs, recharge of 190 mm/year was found where there is no Cretaceous cover |
Sturt Plateau | (Yin Foo and Matthews 2001) | Recharge estimated as 1–3% of rainfall (6–18 mm/year) using the CMB in the northern and southern Sturt Plateau (roughly Elliot to Mataranka on Fig. 1). Recharge not estimated in the central Sturt Plateau where sinkholes are assumed to dominate the recharge |
Daly River catchment | (Jolly 2002) | Using bore hydrographs, in the north (Douglas-Claravale), the study found recharge of 40 mm/year with Cretaceous cover and 150 mm/year without; in the south (Katherine area), recharge of 50 mm/year under Cretaceous cover, 100 mm/year without. Using differential gauging found an areal average of 90 mm/year |
Daly River catchment | (Tickell 2002) | Using CMB average, recharge was found to be 40 mm/year to the Oolloo Dolostone (but thought to be a low estimate) |
SE Georgina Basin | (Read 2003) | Most of the area studied is in the Georgina catchment but the groundwater flows to the Gregory River and Lawn Hill Creek. Using CMB, recharge was estimated at 2–6 mm/year. Using baseflow in the Gregory River and Lawn Hill Creek recharge was estimated at 3–4 mm/year |
Daly River catchment | (Wilson et al. 2006) | The study looked at land-use change using a water balance and chloride. Native vegetation. 50–200 mm/year recharge using water balance and 60 mm/year using CMB. Annual pasture recharge of 300–540 mm/year was found using water balance and 40–200 mm/year using CMB |
Daly Basin, Roper catchment | (Jolly et al. 2004) | Recharge estimated from baseflow in the Roper River of 16 mm/year (ET from groundwater was accounted for). Recharge from CMB further south in the Georgina Basin of 2.8, 5.2 or 13.2 mm/year. Recharge in Wiso Basin from bore hydrographs at Elliot of 5–20 mm/year and nearby in wet years of 30–70 mm/year |
Daly, Roper and SW Gulf catchments | (Crosbie et al. 2009) | Used chloride mass balance over the entire catchments (not just CLA): Daly 65 mm/year with a range of 14–276 mm/year; Roper 72 (7–168) mm/year; and, SW Gulf catchments 72 (6–170) mm/year. Numerically modelled recharge using WAVES (Zhang and Dawes 1998): Daly 153 mm/year; Roper 95 mm/year; and, SW Gulf catchments 54 mm/year |
GW to the Daly and Roper rivers | Recharge estimated for all the subcatchments (SW & GW) of the Roper and Daly rivers using a surface-water balance model that fed into a FEFLOW groundwater model | |
Southern Daly Basin | (Bruwer and Tickell 2015) | Used bore hydrographs to estimate recharge as 44 mm/year around Mataranka and 8 mm/year around Larrimah |
Central and Northern Georgina Basin | (Tickell and Bruwer 2017) | Study used CMB on an area between Daly Waters and Tennant Creek. Areas with Cretaceous cover >25 m thickness were assumed to have negligible recharge. Where Anthony Lagoon Fm outcrops recharge was estimated as 1.9 mm/year. The major recharge areas are assumed to be where the Gum Ridge Fm outcrops or subcrops: recharge estimated to be 1.9–8.0 mm/year in the west, 0.9–8.0 mm/year in the south and 1.2–12.2 mm/year in the north-east |
Beetaloo region | (Deslandes et al. 2019) | Using CMB, average recharge was found to be 1.7 mm/year in the south, 5.0 mm/year in the centre and 7.4 mm/year in the north. The northern part was further split into east and west with 2.0 and 12.8 mm/year respectively. Using tritium analysis, the recharge was found to be 66, 140 or 190 mm/year depending on the method used in the NW of the Beetaloo region. This was the recharge rate in sinkholes not an areal estimate |
Entire CLA | This study | Used probabilistic estimates of recharge from CMB upscaled to the entire CLA on a 2,500-m grid. The uncertainty in the recharge estimates was constrained using observations of baseflow and remotely sensed evapotranspiration. This is the first study to estimate recharge over the entirety of the CLA and to thoroughly consider the uncertainty in the recharge estimates |
Methods
Chloride mass balance
Point-scale estimates of recharge
-
Bores that had a chloride concentration below 2 mg/L or above 2,000 mg/L were either unrepresentative or had their values mistranscribed and so were excluded
-
Bores with a drilled depth greater than 150 m were considered unlikely to be in the water-table aquifer and so were excluded
-
Bores located within surface-water flowlines were excluded. Flowlines are usually where the water table is shallowest and potentially subject to evapoconcentration of the groundwater.
Upscaling using regression kriging
Baseflow separation
Water balance using remotely sensed evapotranspiration
Constraining the CMB recharge
Results
Chloride mass balance
Point-scale estimates of recharge
Coefficient | Significance | |||
---|---|---|---|---|
Estimate | SE | t value | p > |t|) | |
Intercept (β0) | −5.60E-01 | 6.76E-02 | −8.284 | 2.00E−16 |
Rain (β1) | 3.96E-03 | 2.18E-04 | 18.133 | 2.00E-16 |
Rain2 (β2) | -1.00E-06 | 1.43E-07 | −6.99 | 3.28E-12 |
Clay (β3) | −6.01E-03 | 1.06E-03 | −5.676 | 1.49E-08 |
NDVI (β4) | −1.96E+00 | 3.61E-01 | −5.418 | 6.42E-08 |
Upscaling using regression kriging
Baseflow separation
Gauge | Gauge No. | SW catchment area (km2) | GW catchment area (km2) | Mean baseflow (m3/s) | Baseflow (mm/year) |
---|---|---|---|---|---|
Gregory River at Riversleigh No. 2 | 912105A | 11,343 | 71,679 | 11.4 | 5.0 (3.5–6.5) |
Lawn Hill Creek at Lawn Hill No. 2 | 912103A | 3710 | 3069 | 1.4 | 14.4 (10.1–18.7) |
Flora River at U/S Stoney Creek | G8140205 | 6417 | 69,208 | 8.6 | 3.9 (2.8–5.1) |
Roper River at Elsey Homestead | G9030013 | 13,787 | 120,186 | 21.2 | 5.6 (3.9–7.3) |
Water balance using remotely sensed evapotranspiration
Catchment | Rainfall (mm/year) | AET (mm/year) | Excess Water (mm/year) |
---|---|---|---|
Internal Catchment E | 799 | 670 | 130 (−71–331) |
Upper Western Creek | 863 | 726 | 137 (−80–355) |
Lake Woods | 690 | 561 | 129 (−39–298) |
Internal Catchment W | 760 | 688 | 72 (−134–279) |
Roper River | 666 | 536 | 129 (−31–290) |
Gregory River | 409 | 326 | 83 (−15–181) |
Lawn Hill Creek | 510 | 400 | 110 (−10–230) |
Flora River | 748 | 618 | 131 (−55–316) |
Constraining the CMB estimates of recharge
Constrained recharge (mm/year) | Unconstrained recharge (mm/year) | |||||
---|---|---|---|---|---|---|
5th | 50th | 95th | 5th | 50th | 95th | |
Geological regions | ||||||
Daly Basin | 49 | 82 | 156 | 26 | 63 | 178 |
Wiso Basin | 9 | 17 | 31 | 5 | 13 | 37 |
Georgina Basin | 5 | 9 | 18 | 3 | 7 | 21 |
Beetaloo Sub-basin East | 7 | 12 | 23 | 4 | 9 | 26 |
Beetaloo Sub-basin West | 27 | 48 | 92 | 14 | 37 | 106 |
Surface-water catchments | ||||||
Roper River | 27 | 49 | 93 | 15 | 38 | 112 |
Daly River | 61 | 101 | 192 | 31 | 77 | 218 |
Victoria River | 29 | 50 | 94 | 15 | 38 | 107 |
Limmen Bight River | 9 | 15 | 30 | 4 | 12 | 34 |
McArthur River | 19 | 35 | 67 | 10 | 26 | 78 |
Robinson River | 11 | 20 | 39 | 5 | 15 | 45 |
Calvert River | 7 | 15 | 39 | 4 | 12 | 44 |
Wiso region | 6 | 10 | 19 | 3 | 8 | 22 |
Barkly region | 5 | 9 | 17 | 3 | 7 | 19 |
Nicholson River | 13 | 28 | 58 | 7 | 20 | 67 |
Georgina River | 4 | 6 | 12 | 2 | 5 | 13 |