Saga Plain belongs to Ariake Sea Coastal region where is known as a lowland area in Japan, consisting of primarily soft ground (Shimoyama, et al. 2010) and much affected by the ocean tide. An environmental monitoring around this area had been established to measure the physical and quality of groundwater under the potential effect of the Ariake Sea Coastal Road construction. Nowadays, the sea level is increasing day by day due to the influence of the global warming (Kyushu University S-8 Research Group et al., 2014). Thus, it is also necessary to consider the physical of groundwater under the tidal fluctuation for further planning in the lowland area. This research will monitor the flow direction and velocity of the groundwater at Saga Lowland under tidal fluctuation within a half of moon cycle.