Groundwater Seepage into Lake Biwa (I): Distribution of Groundwater Quality as Indicators of Seepage Patterns

The spatial distributions of groundwater quality were investigated at the western shore of Lake Biwa where shallow groundwater near shore contains high CaCl2 concentrations. Seepage groundwater having high CaCl2 concentrations occurs mainly within an approximate 20m distance from shore. Confined groundwater flows through a low permeable layer and then seeps into the lake offshore. Contour lines of Cl-concentration of interstitial water veer almost vertically upward on the shore side near the inflexion point of the lake bed. The spatial patterns of water quality distribution along the transect are consistent with those of seepage flux observed by seepage meter. These results indicate that in shallow groundwater seepage into the lake in a narrow zone near shore, groundwater flow is controlled by geometric configuration of the lake bed. Seepage measurements confirm the validity of the direct method of using a seepage meter for observing groundwater flow into the lake.