Groundwater flow

The hydrostratigraphic framework for the Cooper subregion has been developed based on the work of Cresswell et al. (2012), Dubsky and McPhail (2001), Golder Associates (2011), Kellett et al. (2012), Keppel et al. (2013)and Toupin et al. (1997) and shown in Figure 23. This classification recognises the heterogeneous lithological nature of units within the Eromanga Basin, discussed in more detail in Kellett et al. (2012) and the potential interconnectedness between the Nappamerri Group of the Cooper Basin and the Jurassic units of the Eromanga Basin, described further by Kellett et al. (2012) and Keppel et al. (2013).

The main aquifers are the upper part of the Cadna-owie Formation, the Algebuckina Sandstone, Adori Sandstone and Hutton Sandstone, within the Jurassic to Early Cretaceous system.

Partial aquifers include the Winton and Mackunda formations, Coorikiana Sandstone, Murta Formation, Birkhead Formation and Poolawanna Formation.

Leaky aquitards include the Wallumbilla Formation, the Westbourne Formation and the lower part of the Cadna-owie Formation.

Tight aquitards are the Allaru Mudstone and Toolebuc Formation of the Rolling Downs Group, as well as the basal siltstone of the Murta Formation where it is present.

On a regional scale, groundwater in the Eromanga Basin flows from recharge areas along the Great Dividing Range west toward the discharge zones of the Western Eromanga Basin. Discharge areas include mound springs to the west of Lake Eyre and an arcuate band containing lakes Frome, Callabonna, Blanche and Gregory (Kellett et al., 2012). Watertable and potentiometric surfaces

The watertable throughout the Cooper subregion lies in the Early to Late Cretaceous Winton Formation, and less commonly, in the underlying Early Cretaceous Mackunda Formation. The Winton and Mackunda formations form a hydraulically continuous unit, and thus water levels in the Mackunda Formation can also be regarded as equivalent to the regional watertable. The watertable also lies in Cenozoic sediments overlying the Eromanga Basin sequence, such as the Eyre Formation. The water levels in Quaternary floodplain sediments generally form a continuum with the pressure surface and the underlying rock aquifer, however following periods of high river stage temporary head differences of up to 10 to 15 m have been observed in perched alluvial systems (Kellett et al., 2012). A density (salinity) corrected watertable map is provided in Figure 24.

Watertable mapping shows a watertable mound which coincides with the Innamincka Dome. This geological feature is a broad anticline in the vicinity of Innamincka, and exposes Winton Formation material along its axis. The mound is likely to be a local recharge mound, whereby extension fractures formed as a result of unloading and folding provide enhanced infiltration capacity, where they have remained open (Kellett et al., 2012). Groundwater flow bifurcates around this mound, but the regional flow direction to the south-west is generally maintained across the subregion.

The south-westerly flow direction is mirrored in potentiometric surfaces for deeper hydrostratigraphic units, such as for the Cadna-owie – Algebuckina aquifer mapped by Love et al. (2013). This same general flow direction is evident from potentiometric surfaces presented by Dubsky and McPhail (2001) for the Cooper Basin hydrostratigraphic units. Love et al. (2013) note a depression in the Cadna-owie – Algebuckina aquifer potentiometric surface around Moomba of approximately 20 m, stating that it is related to groundwater extraction associated with petroleum and gas industries over several decades. Figure 25 shows an example of the density (temperature) corrected potentiometric surface for the Cadna‑owie – Algebuckina aquifer in the Cooper subregion.

Figure 24

Figure 24 Density (salinity) corrected regional watertable level for the Cooper subregion

Source: after Figure 5.13 from Kellett et al. (2012)

Groundwater flows diminish into areas in the centre of the subregion where the Eromanga Basin aquifers are deeply buried. Within the Central Eromanga Depocentre, flow is hard to quantify, as there are few bores and hydrochemical tracer methods are complicated. Flow rates are inferred to be lower than 0.3 m/year (Cresswell et al., 2012).

Figure 25

Figure 25 Density (temperature) corrected potentiometric surface of the Cadna-owie - Algebuckina aquifer in the Cooper subregion

Data: Geoscience Australia (Dataset 2) Inter-aquifer connectivity

Vertical leakage or cross-formational flow takes place in the Cooper subregion from the lower, higher pressure aquifers in the Nappamerri Group and deeper Jurassic aquifers through the overlying leaky aquitards and aquifers of the Birkhead Formation, Adori Sandstone and Westbourne Formation and subsequent overlying aquifers in the Algebuckina Sandstone and the Cadna-owie Formation, and through the leaky aquitards of the Rolling Downs Group and Bulldog Shale into the Cretaceous aquifers of the Mackunda Formation and Winton Formation, or the regional watertable (Kellett et al., 2012; Keppel et al., 2013; Love et al., 2013; Toupin et al., 1997). Measured pressure differences between aquifers are an indication of the vertical leakage or flow, which is supported by hydrochemical indicators (Cresswell et al., 2012; Dubsky and McPhail, 2001; Love et al., 2013; Toupin et al., 1997).

Based on a regional hydrostratigraphic classification of Eromanga Basin units, potential for connectivity with underlying basins is provided by the overlap of adjacent aquifers and leaky aquitards above and below the basal unconformity of the Eromanga Basin. In Figure 26, the basal hydrostratigraphic units of the Eromanga Basin are shown by patterns and the uppermost stratigraphic units of the Cooper Basin are depicted by colours. This highlights that the upper units of the Cooper Basin are in hydraulic connection with the basal units of the Eromanga Basin. Recharge and discharge

The only source of potential rainfall recharge to the Eromanga Basin is via the Innamincka Dome. No other Eromanga Basin units crop out in the Cooper subregion. Some limited recharge via diffuse infiltration of sporadic rain water, flood waters or streamflow through Quaternary and Cenozoic cover sequences may occur, although this is likely to be effectively zero, as a result of extremely low rainfall and high evaporation (Cresswell et al., 2012; Love et al., 2013). The most significant source of groundwater to the Eromanga Basin sequence in the Cooper subregion is inflow from areas outside the subregion.

Recharge to the Cooper Basin can only occur through vertical leakage from underlying or overlying aquifers or cross-formation flow.

Natural leakage or natural discharge to surface takes place at springs and areas of seepage, as well as in lakes, which are abundant around the margins of the Central Eromanga Basin (Love et al., 2013; Radke et al., 2000). Discharge springs in the subregion are discussed in Section 1.1.6.

Figure 26

Figure 26 Areas of potential hydraulic interconnection in the Cooper subregion between the Eromanga Basin and underlying Cooper Basin

Data: Kellett et al. (2012)

Last updated:
9 January 2019
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