Study on influence of natural and social environment on sediment yield in the mountainous area

近年来，在日本，由于木材价格在森林经营成本增加的情况下变得便宜，林业工人减少和老龄化的原因，其利润急剧下降，林业正在衰落。因此，森林砍伐后往往会留下森林，造成山坡和洪水的严重破坏。本研究通过对位于米耶县的宫川大坝的泥沙淤积以及森林采伐和造林随时间的变化情况进行分析，以明确森林采伐对产沙量的影响。在此基础上，建立了考虑年降水量和林业实际条件的产沙量预测模型。并将该沉积模型应用于宫川坝址盆地。模拟的结果表明，该模拟模型能够较好地预测宫川坝区的产沙量。此外，为了了解林木根系(活根和腐根)对土壤水分运动的影响，在神谷湖上游神谷多诺流域的一个山坡上进行了田间喷洒试验。通过田间试验，证实了以下几点。雨水集中在森林根部周围。其趋势随雨强的增大而增大。林木根部周围的等效导水率是土壤基质的1.1~3.2倍。

Recently, in Japan forestry is decline because its profit falls down drastically for reasons that price of timbers get cheap in spite of increase of forest management cost, forestry workers decrease and get aged. Therefore, forests become to be left frequently after deforestation, resulting in serious devastation of hill slopes and torrents. In this study, sedimentation of Miyakawa-dam where located in Mie prefecture, and changes of deforestation and forestation with time was grasped to clean influence of forest practice on sediment yield. Using these results, sediment yield predicting model considering annual precipitation and forest practice conditions was constructed. And this sedimentation model was applied to Miyakawa-dam basin. As the result of this simulation, comparison of the observed and calculated sedimentation showed that this simulation model was adequate for the predicting the sediment yield in Miyakawa-dam basin.Furthermore, in order to understand effects of forest roots (living - root and decayed - root), which are a portion in primary factor to make soil layer structure heterogeneous, on hydrologic processes, that is, water movement in soil layer, field sprinkling experiments were carried out on a hillslope in the Kamiyadono basin where located in upper stream of Shigenobu-Liver. The following matters were confirmed by these field experiments. Rainwater concentrates on the surroundings of forest roots. And, its tendency is enlarged in proportion to an increase of rainfall intensity. Equivalent hydraulic conductivity at surrounding of forest roots is 1.1〜3.2 timeses as large as one of the part of soil matrix.