Water balance

Surface water and groundwater balances include a number of components such as rainfall, runoff, evaporation, aquifer recharge, storage, discharge, leakage and water extraction. An estimation of annual groundwater and surface water extraction is outlined in companion product 1.5 for the Galilee subregion (Evans et al., 2015).

Mean annual potential evaporation far exceeds rainfall, particularly in the summer months (companion product 1.1 for the Galilee subregion (Evans et al., 2014)) and rainfall, for the most part, is highly variable across the subregion. These major components of the water balance assert a significant control on the availability of surface water in the Galilee subregion. These factors are likely to dominate the water balance for small closed lake basins such as Lake Galilee and Lake Buchanan (Figure 18). Potential evaporation may also influence availability of surface water in spring pools that are associated with some spring vents. Further detail on variations in hydrology of spring pools is outline in Section 3.5 in companion product 3-4 (Lewis et al., 2018).

As outlined in Section, the Galilee subregion is situated in the headwaters of seven major river basins, all of which flow out from the Galilee subregion. While limited, available streamflow data suggest that surface water flows are extremely variable in all river basins and that most streams in the Galilee subregion have prolonged no-flow periods. Hence, surface water in rivers is only available for limited periods in a given year. The lack of continuous surface water flow throughout the year in most river basins suggests that groundwater discharge is not sufficient to keep most streams continuously flowing during prolonged low rainfall periods. Exceptions may be along tracts of the Carmichael River and Warrego River.

Due to variability in the availability of surface water resources, there is a strong dependence by agriculture and town water supplies on groundwater resources, particularly in the area encompassed by the Eromanga Basin (Figure 18). Most groundwater in the Galilee subregion is extracted from GAB aquifer systems, the Hutton-Precipice and the Wyandra-Hooray aquifers. The most utilised aquifer system of the Galilee Basin sequence is the Clematis Group aquifer. The main uses for groundwater were either agricultural purposes or town water supplies. Groundwater is also extracted from Cenozoic sediments and can be the source of some town water supplies (e.g. Alpha township).

Last updated:
17 December 2018