Study on the Quantitative Evaluation about the Factor of Turbid Water in the Up er Basin of Resirvor

近年来，在许多水库中发现了由强降雨引起的长时间的水浑浊，并且由于浑浊水的排放而对下游区域的环境影响已经成为严重的问题。据认为，浊水的滞留是由于上游流域产生的悬浮固体的存在，并被河流带入水库。然而，在浊流的研究中，还没有研究浊流与研究区地形、地质和土地覆盖因素之间的关系，以澄清浊流的来源。本研究利用地理资讯系统，撷取可能影响水体浊度的因子，并进行定量分析。此外，在位于宫崎县的一津濑大坝上游流域测量了水位和浊度。利用收集到的数据，通过修改水文水槽模型，开发了一个评估悬浮固体流出量的模型。该模型还进行了基于四个典型的降雨条件分类的总降雨量的数据。在运用简单线性分析和多元回归分析等统计方法对水库上游流域悬浮物出流进行预测的同时，建立了悬浮物出流预测模型，结果表明，在所有潜在的影响因素中，发现影响悬浮固体流出的因素，并考虑了流出特性与各机械参数空间分布之间的相关性。因子定量评价了水库上游流域相应降雨条件下悬浮物出流的潜在风险。

Recently, prolonged water turbidity induced by heavy rainfall has been identified at many reservoirs, and the environmental impact in downstream regions due to discharge of the turbid water have been a serious problem. The retention of turbid water is believed to be due to the existence of suspended solids generated in the upper river basin and carried into the reservoir by rivers. However, none of the research on turbidity has investigated the relationship between turbidity currents and topographical, geological and land-cover factors of the research area to clarify the source of turbidity currents. In this research, possible factors of water turbidity are extracted and analyzed quantitatively using a geographical information system. Additionally, the water level and turbidity were measured in upper river basins of Hitotsuse dam located in Miyazaki prefecture. Using the collected data, a model that evaluates the amount of suspended-solid outflow was developed by modifying the hydrological tank model. The model was conducted also based on four typical rainfall conditions categorized by total amount of rainfall data. Then the prediction model of suspended-solid outflow is constructed while the suspended-solid outflow in the upper basin of the reservoir is forecast by using a statistical method such as simple linear analysis and multiple-regression analysis.As a result, among all potentially influential factors were found to affect the outflow of suspended solids with consideration of the correlations between efflux characteristics and spatial distribution of each mechanical factor. Furthermore, the potential risk of suspended-solid outflow under corresponding rainfall condition in the upper river basin of the reservoir was quantitatively evaluated.