46-Analysis of Natural Recharge and Groundwater Dynamics in Alluvial Aquifer Systems .

Abstract

Proper knowledge of groundwater recharge is essential for the management and protection of valuable groundwater resources. Natural groundwater recharge is a very complex and dynamic phenomenon, and its determination involves a number of unresolved problems, thereby making direct measurement of natural recharge extremely difficult. Modeling is a very useful tool to analyze groundwater systems and gain new insights. In the present study, an analytical recharge model was used to analyze the spatial and temporal variations of groundwater recharge/discharge. Seven years (1998-2004) daily groundwater level data and other relevant data were obtained from an alluvial aquifer system in Japan. The recharge/discharge rates were estimated at seven sites using the selected model. In order to examine groundwater-surface water dynamics, regression analyses were performed between the rainfall and groundwater levels at the seven sites as well as between the river stage and groundwater levels at these sites. The monthly recharge analysis indicated very limited number of monthly recharge events, which significantly varied from site to site and year to year. At most sites, the groundwater discharge was found to be predominant during the 1998-2004 period. The results of the regression analysis indicated that both the rainfall and the Monobe River stage are major sources of recharge. The aquifer was found to be hydraulically connected with the Monobe River. It is concluded that the analytical recharge model and regression analysis are effective tools for analyzing complex hydrogeologic processes.