Synthetic evaluation of efficiency in hydrological cycle in large watershed

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The investigation was conducted aim at the evaluation of Efficiency for water use in large watershed(Chikuma-Shinano river basin). The results are summarized as follow. (1) For the evaluation of discharge fluctuation of flowing water, the pattern index by which characteristics of river basin being explained was induced. (2) The concept of "Water Cycle Efficiency" should involve the socio-economic view-point of "What and how much does a water cycle bring to the society ?" as well as the physical one. The general factors which decide the efficiency are fluctuation in flow rate, water quality and intensity of water recycling, though it include intangible effects on a society.(3) We investigated the reality of sediment transport and low water temperature which are minus factors of water use in paddy fields. As a result of the analysis, it is clarified that the distribution of unstable sediment in river bed is the most important factor for sediment transport, and that the solar radiation directly or indirectly plays an important role for the formation of water temperature. (4) As a result of analyzing hydrology data observed over the 3 years, the author obtained that the runoff ratio is 38%, the recession constant 0.043 (d^<-1>) and the peak runoff coefficient 0.1-0.2. The results indicate that the infiltration is high and the water holding capacity poor. From this fact, if considering from the standpoint of rain storage, can be interpreted that the hydrology efficiency for the given study area is low. (5) The efficiency of return flow using ratio were measured in the area of sloping paddy fields. These paddy fields used for the production of paddy rice and upland crops in 1990, the percentage of paddy ricle was 100% but it decreased to 66% in 1992, and the efficiency of return flow also decreased from 290% to 80%. The temperature of irrigation water rose up much higher in 1990 than in 1992.