Recharge processes at the St George Irrigation Area

Recharge processes at the St George Irrigation Area

Since the 1950s, irrigated cropping has taken place in the St George Irrigation Area (SGIA), following clearance of the native vegetation and construction of water canals, carrying river water to the agricultural lands. The change from open-forest to arable lands mostly irrigated involved changes to the groundwater balance and in turn, groundwater quality. Deep-drainage and leaks from the water canals and dams, to name two possible water sources, which carry different amounts of salts into the sub-surface, may affect the groundwater salinity.
The groundwater under the SGIA ranges in quality from fresh water, with about 50 mgCl/L, to salty water, with ~10,000 mgCl/L. We analysed all of the available bore water samples, to detect any on-going salinity trends (rising/stable/falling) and identify potential sources. Results indicate the existence of four end-members, namely, saline formation water, brackish deep-drainage, slightly brackish flood-recharge water, and fresh imported river-water. Each of these has a typical geochemical composition, which allows reconstructing the past and the current recharge processes in the SGIA. The groundwater composition at many bores varied over time, to reflect the changes in the dominant end-member.
This study demonstrates that effective changes in groundwater quality can occur in a relatively short time-frame.

Abstract only published in Proceedings.
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