The role of bedrock groundwater on runoff and landslide initiation

为了检查在相对未风化的花岗岩和页岩下的非常陡峭的地形上的径流生成过程，对几个小流域进行了监测；两个在页岩中，两个在伊娜岛的花岗岩中，两个在日本中部卡沼的页岩中。页岩集水区对同一暴雨事件的径流响应差异明显，而花岗岩集水区对同一暴雨事件的径流响应相似；高峰径流与降雨高峰重合。大部分暴雨径流水被定义为“老水”，在页岩盆地中，一半以上在花岗岩盆地中。在页岩流域，即使在暴雨期间，土壤水分也垂直向下渗透到基岩中，而在花岗岩流域，地下暴雨流与斜坡平行。这些数据表明，即使在非常陡峭的山区，地下风暴流也占主导地位，花岗岩盆地以地下地幔流为主，而页岩盆地以基岩流为主。

To examine runoff generation processes in very steep terrain underlain by relatively unweathered granite and shale, several small watersheds were monitored ; two are in shale and two are in granite in Ina, two are in Shale in Kanuma, central Japan. The shale catchments had distinctly different runoff responses to the same storm event, whereas the two granite catchments had similar runoff response ; high peak runoff coincides with rainfall peak. Most of the storm runoff water is defined as 'old water', in shale basins, and more than half in the granite basin. Soil water percolated vertically downward into bedrock even during storm event in shale watershed, whereas subsurface storm flow parallel to slope is observed in granite watersheds. These data suggest that subsurface storm flow is dominant even in very steep mountains, and subsurface flow through soil mantle is dominant in granite basins, whereas bedrock flow is dominant in shale basins.