The groundwater flow system in an upland area which faces a lake is analyzed to investigate thefollowing aspects: (1) the role of dissected valley on a groundwater drainage system; (2) interaction betweenupland groundwater and lake water; and (3) the regional groundwater flow patterns. Threedimensionalanalyses are used to represent the actual phenomenon of the groundwater flow system bymeans of tracer method. Environmental tritium and water quality are used as groundwater tracer, andwater samples arc obtained in a regional scale. For the interpretation of tritium data, groundwater agesare estimated using the convolution integral method with consideration of infiltration rates as theweighting function.
The results, which are of a preliminary stage, indicate that: (1) two main rivers and dissected valleysare playing important role as the groundwater drainage system of the upland; (2) groundwater isrecharged in the upland area and is primarily discharged to the river or valley as a whole; (3) thegroundwater flow interactions between upland and lake are not occurred actively; and (4) groundwater,deeper than about 20 meter below sea level, flows very slowly as a different flow systm from thosein the upper layers.