Research on the monitoring of groundwater level movement in alluvial fan

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The Rokugo alluvial fan lies 39^o 25' north latitude and 140^o 34' east longitude in northern Japan. It covers an area of neary 14 square kilometers. The distance between the head, 90 meters above sea level, and outer fringe, 45 meters above sea level, of the fan is about four kilometers. The center of Rokugo town which is situated on the fringe numbers 7,000 inhabitants. They privately bore wells and pump unconfined ground water for domestic uses. Ground water is recharged in the fan's area, which is utilized mainly for rice cultivation.The author performed a study of the monitoring of ground water level movement in this alluvial fan in the three years from 1991 to 1993. Piezometers, of which depths are 20, 50 and 100 meters, were constructed at the center and the outer fringe, respectively. Hydraulic heads were measured by the piezometers.Some results are obtained : (1) Hydraulic heads clearly differ in each depth.Some results are obtained : (1) Hydraulic heads clearly differ in each depth. (2) Hydraulic head decreases from shallow point to deep point from the ground surface. (3) Difference of the hydraulic heads appears in every seasons, such as irrigated period and non-irrigated period as well snow-covered period and snow melting period. (4) Ground water level changes as follows : It is high during the season of melting snow and the period of irrigation activities from May to August. The highest level appears at the end of the melting of the snow and the beginning of irrigation, and the lowest one occurs around the time when snow cover reaches a maximum, which is usually about 130-150 centimeters in depthj.The results of the study will lead a next research project, "Forcasting Ground Water Lever in Alluvial Fan."