The groundwater in Hohu plain is recharged by the seepage from Saba river, creeks and paddy fields. The inflow to and the outflow from the groundwater are balanced in a short period, but for a long period, the level is decreasing by several centimeters a year during the last fifteen years. It brings about gradually the sea-water intrusion to the fresh groundwater.
Flow route of the groundwater can be detected by the head and the temperature distributions, and by 1 m depth ground temperature survey.
The main large wells in the area penetrate the lower aquifer which is separated by an aquiclude from the surface zone, so the vertical flow must be considered to be dominant for the whole groundwater flow system. The analysis of the flow and the balance of the groundwater, using quasi-three dimensional model for underground structure, results that the total recharge is 67.5× 106 m3/year,60% of which,39.9 × 106m3/year, is discharged from the wells, and the rest flows to the sea.
