Abstract

In the Great Artesian Basin (GAB) of Australia the combination of high temperatures and deep wells makes the calculation of groundwater heads challenging. Regulatory requirements set small drawdown conditions that require improved accuracy in the determination of head. The objectives of this study are to calculate temperature-inclusive groundwater heads to a sub-metre precision and analyse the implications of including temperatures in head calculations on groundwater management in the GAB. If groundwater is discharged from an ordinary well containing cold and fresh water, both the wellhead pressure and head decline; once the well is shut-in both the wellhead pressure and head recover. Observations in several deep and hot wells in the GAB confirm that if a well is allowed to flow, the wellhead pressure measured at the surface increases. Wellhead pressure has also been observed to decrease in several wells in the GAB after shut-in with corresponding cooling of the wellhead. A method has been developed to calculate temperature-inclusive head. The head may be calculated from well depth, elevation, wellhead pressure and near-surface and bottom-hole temperatures. Hydraulic gradients and therefore groundwater inflow to South Australia, calculated using current practices of temperature-exclusive heads or assuming constant temperatures in wells, may be incorrect.

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