The Structure of Groundwater Budget around Yoshii Wier (I)

Statistical analysis of observed groundwater level fluctuations around Yoshii Wier

Abstract

Yoshii Wier, which was constructed three hundred years ago, now has fused completely into the natural system surrounding it, and is still continuing to play an important role in forming the subsurface environment there. In this paper, the authors have tried to show that the Yoshii Wier has other functions except the intake of irrigation water from the standpoint of groundwater cycle.
The observed groundwater level fluctua tions in 1982 at representative points around the wier were statistically analyzed, and as a consequence, it seems that the fluctuations generally occur due to the influence of paddy field irrigation and the water level of the Yoshii River. Especially, it has become clear that the groundwater level is mainly affected by the river water level in the upper district of the wier, due to irrigation in the lower district, and by both in the intermediate district. Therefore each fluctuation component is quantitatatively evaluated as multiple regression coefficients.
The time constants in groundwater level discent after irrigation are almost the same everywhere in this district, 9. 5 days.
These conclusions obtained from the statistical analysis give some important input data for simulation using the mathematical model of the regional groundwater flow in the following papers.