Water ploblem analysis for water management of river area

河流地区的许多水问题，如水资源短缺、水污染等，除了农业用水外，城市化和用水需求的增加也引起了这些问题。为了解决这些水问题，需要在流域内进行水质和水量的综合管理。本研究的目的是开发Onga和Chikugo地区的水管理系统。水问题分析是分析水政策和水管理体系的第一个重要步骤。首先，根据近20年的昂加河和奇库戈河水质观测资料，分析了该河的水质问题。本研究利用地理信息系统（GIS）探讨了两河流域污染物负荷分析的框架。利用GIS数据显示了这些地区非点源的污染物密度和/或分布。结果表明，河口水库富营养化主要发生在夏季，尤其是低流量期。其次，研究了昂嘎河水质对营养物的影响机制。利用营养物浓度与流速的关系，探讨了水质形成的机理以及营养物负荷与流速的关系。结果表明，包括农用地硝酸盐氮淋溶在内的降水径流过程影响了河水中硝酸盐氮的浓度。非点源如城市污水是氨氮和磷的主要污染源。最后，通过对现有水质和水量管理的比较，指出了建立综合水管理替代理念的必要性。

Many water problems in a river area, such as the shortage of water, water pollution etc., are occasioned by the urbanization and the increase of water demand in addition to agricultural water use. To solve these water problems, an integrated water management in the watershed both in terms of water quality and quantity is needed. The objective of this study is to develop the water management system for Onga and Chikugo areas. Water problem analysis is a first important step for analyzing water policy and the management system.First of all, the water problems of Onga and Chikugo River were analysed based on the observed data of the water quality of the river for the last twenty years.In this study, geographic information system, GIS, was used to discuss the framework for pollutant load analysis in both river areas. The pollutants density and/or distribution of non-point sources in these areas were demonstrated by using GIS data. It was clearly shown that eutrophication in the estuary reservoir takes place in summer season, especially in the low flow rate period.Secondary, the mechanism of water quality formation on nutrients in Onga River was studied.The relationship between the nutrients concentrations and the flow rate was used to discuss the mechanism of the water quality formation as well as the relationship between the nutrients load and flow rate. It was shown that the runoff process of precipitation that includes the eluviation of nitrate nitrogen in agricultural land affected the concentrations of nitrate nitrogen contained in the river water. Non-point source such as municipal wastewater seems to be a main pollutant source of ammonia nitrogen and phosphorus.Finally, the necessity of establishing the alternative concepts for the integrated water management was pointed out through comparing the existing water management in terms of water quality and quantity.