The Investigation of Gravity Variations Near a Pumped-Storage Reservoir in North Wales
Continuous gravity measurements have been made for several months near the upper reservoir of the pumped-storage hydroelectricity scheme at Dinorwic, N Wales. A Lacoste and Romberg Earth Tide gravimeter, incorporating electrostatic feedback was installed 80 metres on the landward side of the reservoir and at a height of 10 metres above the maximum water level. Water level changes in excess of 30 metres were observed during the experiment involving the redistribution ~7.106 tonnes of water. A data set in excess of one month has been obtained and analysed in terms of the gravitational effects of the Earth’s body and ocean load tides in addition to the gravitational attraction due to the varying water level modelled according to Newtonian gravitational theory. The residual signal was examined in terms of non-Newtonian gravity and possible sources of systematic and random errors considered (e.g. uncertainty in lake geometry, gravimeter calibration and elastic properties of the local rock). The uncertainty in both the permeability and porosity of the rock in the vicinity of the gravimeter is found to be the dominant limiting factor in the overall accuracy of the experiment.
KeywordsOcean Tide Earth Tide Gravitational Attraction Tidal Gravity Landward Side
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