On the Estimation of Phreatic Aquifer Parameters by the Tidal Response Technique

This paper focuses on the effects of tidal fluctuations on groundwater in the Konan groundwater basin of Japan and the methodology for estimating aquifer parameters by the tidal response technique. The field investigation revealed that the twowells (H-5 and I-2) near the coastline are significantly affectedby seawater intrusion, and the water quality is not suitable for most beneficial uses. The tidal cycle further aggravates the groundwater contamination by seawater intrusion into the basin. Using the tidal response model, the aquifer hydraulic conductivity(K) at these two sites is estimated to be 4.5 × 10-3 and 5.1 × 10-3 m s-1, respectively. It was also indicated by the inverse modeling that the tidal fluctuations affect the study area up to about 1 km from the coastline. Further, the tidal efficiency was determined in the range of 20 to 21% at Site I-2 and 38 to 41% at Site H-5. The estimates of the storage coefficient (S) based on the time lag equation were not found reliable for the phreatic aquifer. However, the tidal efficiency-factor equation yielded reliable S estimates in this study. Finally, it is concluded that the tidal response techniqueis effective and reliable for estimating aquifer parameters in the coastal region, and that the Konan basin must be managed judiciously to ensure sustainable utilization of its vital groundwater resources.