Change of Agricultural Water Management and Its Evaluation of Influence on Hydrological and/or Water Quality Environment in the Area of Lake Shinji and Nakaumi

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The basic purpose of this study is to develop a technique offering the hydrological and water quality information needed for agricultural water management of Hii River. It also provides an useful information for future way of water environment in this district. The results are as follows : 1. (1) Availability of a proposed method for indentification of runoff model was examined , in which was improved with respect to evaluate a set of runoff model parameter in the any significant digit designated for each parameter. (2)A runoff analysis system was developed by UNIX workstation. (3)But, it was recognized that the further improvement of runoff model and investigation of identification method was necessary for the analysis considered inundation phenomena and condition of agricultural water management. 2. (1) The pollutant fluxes of pollutants were elucidated in a paddy field watershed where a circular irrigation system was implemented. The contribution of pollutant flux in return flow to theater environment was evaluated. (2)The pollutant runoff from upland fields in the mountainous area was evaluated, The nitrogen outflows including the pollutants on rainy days were monitored in experimental lysimeters. It was concluded that saving fertilizer application using resin-coated fertilizer can contribute to the reduction of nitrogen outflows from upland fields. 3. (1) Drainage from undisturbed paddy soils, upland field soils and forest soils were analyzed using soft X-ray radiography. Drainage proceeded from macropore first then to matrix in paddy and upland field soils. On the other hand for forest soils, drainage has occurred in matrix only. Unsaturated hydraulic conductivity obtained from inverse problem showed discontinuity between saturation and near-saturation, which indicated flow region was different. Macropore was considered to channel the drainage at early stage, then matrix conducted the water flow.