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

近年来，日本的林业由于经营成本的增加而木材价格的下降、林业工人的减少和老龄化等原因，其利润福尔斯急剧下降，从而导致了日本林业的衰退。因此，森林在砍伐后经常被遗弃，造成山坡和山洪的严重破坏。本研究以三重县的宫川水坝为例，通过对该水坝的泥沙淤积、森林砍伐和造林的时间变化进行研究，明确了森林措施对泥沙淤积的影响。在此基础上，建立了考虑年降水量和森林生产条件的产沙预测模型。并将该模型应用于宫川坝流域。模拟结果表明，该模型能够较好地预测宫川坝流域的产沙量，并能较好地反映森林根系的影响（活根和腐根）是造成土壤层结构不均匀的主要因素之一，它们对水文过程，即土壤层中的水分运动，在位于Shigenobu-Liver上游的Kamiyadono流域的山坡上进行了田间喷洒试验。这些田间试验证实了以下事项。雨水集中在树根周围。随着雨强的增大，其趋势也增大。林木根系周围的等效导水率是土壤基质部分的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.