A TEMPERATURE ANALYSIS OF GROUNDWATER FLOW SYSTEM IN THE UPPER PART OF THE ASHIGARA PLAIN

The groundwater flow system of the upper part of the Ashigara plain was studied in order to demonstrating the feasibility of the groundwater temperature for the natural tracer. The changes in groundwater temperature were observed from November, 1983 to February, 1987. The surface water in the recharge area greatly influenced to the temperature of groundwater. According to the flow-nets of the study area, two main flow systems were understood to be a basin-wide system and a local one. The stratified distribution of temperature recognized in three thermal profiles of A-A', B-B' and C-C were considered to have reasonable relations to these two-flow systems. Analyzing changes in the monthly water temperature in the profile along the river, the warm and cool groundwater afflux were traced. The velocity of groundwater was calculated at 2.5 m day1 and the estimated permeability of the aquifer was 2.9 x 10 1 cm s1. Tracing the changes in the annual temperature depth profiles at two places of X at Miyanodai and Y at Kawaramachi, the cool and warm surface-water intrusion into the ground were clarified. The river water intrusion by the Sakawa river was traced in more than 30 m deep and the irrigation water intrusion in the paddy field was traced in 18 m deep. These observations will be useful for future investigations using a thermal groundwater model.