Analyses of Tidal Fluctuations of Groundwater Discharge.

Abstract

Groundwater discharge, temperature and electrical conductivity of an artesian well were measured at Nishiawakura, Okayama Prefecture, southwest, Japan. The groundwater discharge showed tidal fluctuations of about 50 cm3/s induced by the tidal strain. Although the groundwater temperature also reflected the same tidal fluctuations as the discharge, the electrical conductivity did not manifest any tidal fluctuations. The discharge response to , the tidal strain for the diurnal frequency constituents is different from that for the semi-diurnal frequency constituents. The response theory of a partially confined aquifer to the tidal strain, which has been used for explanation of the well water level fluctuations, can quantitatively explain these fluctuations of the discharge. It seems important that the theory could also be applied to the real groundwater flow fluctuations induced by the crustal strain because the strain-induced groundwater movement is considered to have close relation to geothermal and geochemical precursors to earthquakes.