芦生演習林内トヒノ谷におけるパイプ流が洪水流出機構に及ぼす影響

Abstract

京都大学芦生演習林内トヒノ谷流域において、パイプ流が山地源流域の洪水流出機構に影響を及ぼす機構を明らかにするために、物理水文観測、水温観測、水質観測を行った。その結果、山地源流域の洪水流出機構はパイプ流の発生を契機に大きく変化することが明らかにされた。パイプ流が発生する以前は流出水の起源は流域末端に限られ、土壌コアサンプラーを用いて求めた飽和透水係数とダルシー則によって説明できる流れであることが分かった。一方、パイプ流発生後は流出水の寄与域は斜面上方へ移動し、大量の水が上流から、流域末端における地下水との混合の影響を受けずに流域末端の湧水点にもたらされたことが示された。その結果、土層の有効透水係数計算値は土壌コアサンプラーを用いて求めた土壌の飽和透水係数に比べて1から2オーダー大きくなった。

In order to clarify effects of pipe flow on storm runoff process at a forested headwater catchment, hydromertic and hydrochemical observations were carried out in Toinotani, Kyoto University forest in Ashiu. These observation results showed that the change of runoff generation process is mainly controlled by the occurrence of pipeflow. When the rainfall amount was small, the pipe flow did not occur. In this case, the main source of streamflow was limited to the end of the catchment. The water runoff phenomenon could be explained by Darcy's law with the saturated hydraulic conductivity measured by using soil core samples. Under a heavy rainfall condition, the water run off from a soil pipe and the spring water was mainly delivered from the upper hillslope through soil macopores, short cutting the normal mixing process through the soil matrix. In this case, the source of spring water accorded with the source of pipe flow and the effective hydraulic conductivity of the slope is larger than the saturated hydraulic conductivity of the soil core samples by one to two orders of magnitude.