Bedrock groundwater (BGW) has a contribution area that differs from that of the surface watershed. To date, there has been no analysis using BGW observations to determine to what extent the BGW catchment area influences surface runoff characteristics. This study determined the BGW catchment area from the water table, using densely nested boring wells (61 in bedrock and three in the soil layer) drilled in the granitic basin (2.3 ha). Streamflow runoff was also measured concurrently across the entire watershed (F0) and the subwatersheds (F1 to F6). The BGW catchment area of F3 accounted for 191% of the watershed area derived from surface topography, reducing the area of adjacent watersheds through cross-watershed flow. The annual precipitation input to the BGW catchment area and baseflow volume was highly correlated, indicating that the BGW catchment area reflected the actual catchment effect in the bedrock layer more accurately than the surface watershed area. The degree of bedrock weathering showed that the BGW table was distributed along the boundary of the C_L–C_M classes. The estimated actual permeability of the C_M class bedrock based on the deep percolation rate suggests that the depth near the C_L–C_M boundary is the hydrological basement surface; this defines the BGW catchment area. This study demonstrates that the BGW catchment area concept provides an accurate prediction of streamflow runoff in mountainous headwater basins that are heavily governed by hydrological processes in bedrock.

中文翻译：

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基岩地下水集水区揭示了源头盆地的降雨-径流过程

基岩地下水 (BGW) 的贡献面积不同于地表流域的贡献面积。迄今为止，还没有使用 BGW 观测来确定 BGW 集水区在多大程度上影响地表径流特征的分析。本研究使用在花岗岩盆地（2.3 公顷）中钻探的密集嵌套钻孔（61 口在基岩中，3 口在土层中）从地下水位确定 BGW 集水区。还同时测量了整个流域 (F0) 和子流域 (F1 到 F6) 的径流径流。F3 的 BGW 流域面积占地表地形衍生的流域面积的 191%，通过跨流域流减少了相邻流域的面积。BGW集水区的年降水量输入与基流量高度相关，表明 BGW 流域面积比地表流域面积更准确地反映了基岩层中的实际流域效果。基岩风化程度表明 BGW 表沿边界分布C _L – C _M类。根据深部渗流率估算的C _M级基岩实际渗透率表明C _L – C _M边界附近的深度为水文基底面；这定义了 BGW 集水区。这项研究表明，BGW 集水区概念可以准确预测山区源头流域的径流，这些流域主要受基岩中的水文过程控制。