Ground water reservoir response to earth tides

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Virginia Polytechnic Institute and State University

Existing models for the response of artesian aquifers to earth tides have been examined anda new model developed. A formula for the computation of poresity from tidal water level measurement is presented. Tidal water level fluctuations in three artesian wells of southwest Virginia were recorded, digitized and harmonically analysed. Corrections for non tidal water level fluctuations and barometric pressure effects were made. Porosities of .22 near Blacksburg, Virginia, and .098 and .05 near Cripple Creek, Virginia, at depths of 156, 300, and 425 meters respectively were computed. An analysis of variability yields errors of about five per cent. Deviations of observed response from expected values is explained in terms of leakage and decoupling.

It is concluded that values of porosity computed from tidal water level fluctuations must be considered as upper limits on true porosity.