Evaluation of Regional Ecosystem for the Patterns of Agricultural Water Balance

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Purpose of this research is the evaluation of influences on the regional ecosystem for water management at paddy fields. Researches and investigations had been carried for two years at the different agricultural watersheds. The results may be summarized as follows :(1) Kasegawa river system ; The operation and management of the irrigation system is characterized by reuse of return flow and drainage condition in low lying paddy area. A complex tank model was proposed to explain the water reuse mechanism and evaluated with actual water balance measurements. The conceptual definition of cyclic use of returning flow was presented for evaluating the water use efficiency in irrigation system. The water reuse mechanism is very effective for conserving irrigation water resources but it has very severe impact on water quality.(2) Nakagawa river system ; The water balance in Nakagawa river basin could be substantially clarified by computing tank model method. And the concept of the pattern index … More for water use being induced, this index was explained clearly by the factors of weather and land use conditions. And the runoff water quality cleared that water quality of irrigation water affected greatly on the water quality of runoff water from the watershed. It cleared that water quality of rainfall also affected very much on water quality of runoff water.(3) Shinanogawa river system ; Some analysis of water budget in two irrigation districts located in Niigata Plain showed that the upstream flow taken into a long open channel is not necessarily fitted to the demand water in down parts of the channel, resulting waste water to drainage canals, and that the water reuse system is a reasonable one from the view of efficient irrigation, simple management and water quality conservation.(4) Ishikarigawa river system ; It is unrestricted of water use at the paddy field that irrigation water source is the diversion dam in this river basin. Therefore, the reuse ratio of irrigation water is small relatively. But that ratio increases for recent years, it is expected that water quality become worse. Less