Establishment of earth tides effect on water level fluctuations in an unconfined hard rock aquifer using spectral analysis

TL;DR

This study demonstrates that earth tides significantly influence water level fluctuations in an unconfined hard rock aquifer, with spectral analysis revealing a strong correlation, unlike groundwater withdrawal effects.

Contribution

The paper introduces spectral analysis as a method to identify earth tide effects on water levels in unconfined aquifers, highlighting a previously unobserved cyclic fluctuation.

Findings

Water level fluctuations strongly correlate with earth tides.

Groundwater pumping shows no significant correlation.

Unconfined aquifer characterized by low porosity.

Abstract

Short-interval water level measurements using automatic water level recorder in a deep well in an unconfined crystalline rock aquifer at the campus of NGRI, near Hyderabad shows a cyclic fluctuation in the water levels. The observed values clearly show the principal trend due to rainfall recharge. Spectral analysis was carried out to evaluate correlation of the cyclic fluctuation to the synthetic earth tides as well as groundwater withdrawal time series in the surrounding. It was found that these fluctuations have considerably high correlation with earth tides whereas groundwater pumping does not show any significant correlation with water table fluctuations. It is concluded that earth tides cause the fluctuation in the water table. These fluctuations were hitherto unobserved during manual observations made over larger time intervals. It indicates that the unconfined aquifer is characterised by a low porosity.