Development of Cost-effective Geothermal Probes for Use in Shallow Seas and Lakes: Measurements in Lake Travis, Central Texas

Abstract

Instruments for acquiring geothermal data underwater have been available for a few decades. But, most of them are designed for measurements in very deep (>1,000m) water. They are not particularly cost-effective for operations in shallow seas and lakes. The equipment is quite heavy, weighing one ton or more. A large ship with a high-powered winch is required for its deployment. It cannot be used in small inland lakes where there is no access to such a ship. In this study, we develop a new type of geothermal instrumentation that is specifically designed for shallow-water operations and has significant advantages over the previous ones in terms of cost and logistics. The new instrument is of much simpler mechanical and electrical designs. It weighs only ∼30kg and can be deployed from a small boat. It free-falls through the water column and penetrates to the bottom sediments by its momentum and transmits the data back through an electrical cable. We have tested this instrument successfully in Lake Travis in central Texas and obtained 3 sets of geothermal measurements over a one-year period. Analyzing these data with additional information on the bottom water temperature history, we obtain constraints to the background geothermal heat flow of the lake and the heat budget of the bottom sediments.

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