FLOW THROUGH FAULTED SHALE: INSIGHTS FROM THE GREAT ARTESIAN BASIN

The Western Margin of the Great Artesian Basin of South Australia has been known for spring flow since the indigenous peoples of Australia began to use them thousands of years prior to European settlement. These springs emanate from the sandstones of the Cadna Owie and Algebuckna formations though the Bulldog shale. The shale thickness varies from 0-800 meters in the spring area. As a statistically significant number of springs exist, numbering in the thousands, the site makes an ideal study facility for the potential for fluid discharge through faulted shales. An analysis of the potentiometric surface, spring discharge and confining unit thickness of 74 spring complexes in the Western Margin of the Great Artesian Basin indicates that pressure head needs to be 33% higher than hydrostatic to generate spring discharge for most springs. Deeper springs require less pressure head as a percentage of confining unit thickness. Discharge from springs appears to be higher in regions with thicker confining units although the relationship is less clear.