An automatic seepage meter using a heat pulse method was developed to obtain a continuous measurement of ground‐water seepage rates. According to calibrations of the automatic seepage meter fitted with a 50 cm diameter collection funnel, seepage rates from 2 X 10‐5 to 5 X 10‐4 cm/sec can be obtained by measuring the time when the temperature as measured by a thermistor peaks after applying a heat pulse. The automatic seepage meter was used to measure continuous seepage rates into Lake Biwa, Japan. The ground‐water seepage rate measured by the automatic seepage meter in Lake Biwa changed by six times within 12 hours. The automatic seepage meter is useful for surface‐/ground‐water studies, because a continuous seepage rate can be obtained without errors caused by the resistance of a collection bag to water flow.

Numerical analyses of seiche and continuous measurements of water level and groundwater seepage rates into Lake Biwa, Japan, were made to evaluate interactions between surface and subsurface waters. An automatic seepage meter was used to obtain continuous groundwater seepage rates. Analyses of the fluctuations of seepage rate and water level in the lake were done using the fast Fourier transform method. The finite element method was used for analysis of the seiche in the lake. Dominant periods of fluctuations of the groundwater seepage rate into Lake Biwa agree well with those of fluctuations of water levels in the lake. The dominant fluctuations of the groundwater seepage rate are caused by the seiche in Lake Biwa.

Recently, in Japan, a new interest has been shown to the specific discharge of groundwater from the lake bottom in order to elucidate its influence on the quality and quantity of lake water. Using conformal mapping techniques, the authors describe analytically the steady two‐dimensional groundwater flow in an idealized confined aquifer, which extends infinitely with uniform thickness and constant inclination and is exposed to the lake bottom surface with a gentle slope. The techniques enable analytical calculation of the head and stream functions of groundwater in the aquifer and also the distribution of specific discharge at lake bottom surface. From the results of calculation, it is found that most of the aquifer water flows into the lake through the upper part of the surface of contact between lake and aquifer. This analysis may be useful in the evaluation of the role of groundwater seepage in the water balance of large lakes.

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