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A geophysical survey was undertaken at Wiri area of the Andong in southeastern Korea to delineate subsurface structure and to detect the fault zone, which affected the 1997 mountain-hill subsidence and subsequent road heaving initiated by the intense rainfall. Electrical resistivity methods of dipole-dipole array profiling and Schlumberger array sounding and seismic methods of refraction and reflection profiling were used to map a clay zone, which was regarded as the major factor for the landslide. The clay zone was identified in electrical resistivity and seismic sections as having low electrical resistivity (\100 Xm) and low seismic velocity (\400 m/s), respectively. The clay zone detected by using geophysical methods is well correlated with its distribution from the trench and drill-core data. The results of the electrical and seismic surveys showed that slope subsidence was associated with the sliding of saturated clay along a fault plane trending NNW-SSE and dipping 10°-20°S W. However, the road heaving was caused by the slope movement of the saturated clay along a sub-vertical NNEtrending fault.

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The objectives of this study are to analyze the relationship between the long-term stream discharge and the change of groundwater use and to estimate the potential usable water resources due to the change of groundwater use. The watershed model SWMM−GE, which considers the aquifer-stream interaction, is used to calculate the long-term stream discharge of the Gapcheon watershed in Korea according to the increasing groundwater use. In the results, the annual runoff discharge is absolutely affected by the annual rainfall, but the annual baseflow is less affected than the annual runoff discharge. The annual baseflow is decreased by increasing the groundwater use, but the potential usable water resources are increased by increasing the groundwater use. In case groundwater use is doubled, the potential usable water resources are increased by about 44% of pumping case. Excessive groundwater use, however, could dry up some streams or make instream flow insufficient. Thus, those results should be considered to determine suitable amount of ground water use.