2.7.3 'Springs' landscape group

Summary

The ‘Springs’ landscape group contains springs of two types: recharge (also referred to as ‘outcrop’) springs and discharge springs. Recharge springs typically occur in topographically elevated areas. The source aquifers are unconfined, with groundwater draining under gravity or where the saturated aquifer intersects the ground surface. In contrast, discharge springs originate from aquifers under confined pressure, or form where the confining bed (aquitard) is weakened or thin, or where the aquifer is disrupted by faults, folds or basement rocks. Water is brought to the surface under artesian pressure. At the surface, the discharge spring is commonly mounded and there is moisture accumulation around the vent. Discharge springs are located remote from their recharge zones.

The Lake Eyre Basin Springs Assessment Project recognised three geographical clusters of springs that occur within the zone of potential hydrological change of the Galilee subregion, and these may potentially be impacted by the additional coal resource development. From north to south these are: (i) the Doongmabulla Springs complex, (ii) a series of springs that overlie the Colinlea Sandstone or Joe Joe Group, which are geological units of Permian age (hereafter referred to as the ‘Permian springs cluster’), and (iii) a series of springs associated with Triassic geological units (hereafter referred to as the ‘Triassic springs cluster’). The physical environment of these three spring clusters is described in this section, focusing on the geographic location of springs/spring clusters, vegetation assemblages, flora and fauna at the species level (with a focus on endemicity and threatened species), and hydrological regimes and connectivity.

A qualitative mathematical model is presented for the ‘Springs’ landscape group. This includes two signed digraphs showing key components of the spring ecosystems. In these models, experts considered that the critical factor in preserving the aquatic communities associated with springs is the rate of groundwater flow that maintains a damp or submerged state in the spring. An increase in water depth above this threshold supports a wetted-area regime around the perimeter and downstream of the spring that is beneficial to emergent vegetation, the building of peat mounds, tail vegetation (i.e. vegetation at the outfall or tail end of a spring) and groundwater-dependent vegetation. Within the free-water area of a spring, an increase in surface water depth supports an increase in primary production (i.e. phytoplankton, macrophytes and benthic algae), and increases habitat for aquatic grazers.