Journal of the Japan Society of Erosion Control Engineering, Vol.61,No.3,2008

Comparative analysis of sediment discharge estimated by indirect methods and yearly reservoir sedimentation in Hokuriku region

Hiroaki NAKAYA


the first place, which resulted in various experimental bed load equations. Field sediment transport observation such as direct sediment sampling in mountain streams has been circumvented by many obstacles such as the inherent brevity of its observation. Since direct sampling is indispensable in the calibration of bed load equations, however, it has been undertaken by various means. The sampling and observation efforts led to the development of more indirect but stable sediment transport monitoring methods (hereafter gindirect method") in recent years. One of the indirect methods, a hydrophone sediment discharge measuring system (hereafter ghydrophone system"), has been intensely studied for the development of practical sediment transport monitoring. Hydrophone systems have been tested quantitatively in relation to bed load equations as well as to directly sampled sediment discharge in 100 and 200 km2]scale river basins. The reliability of sediment discharge estimation made by hydrophone systems has been quantitatively assessed in comparison to direct sampling results obtained by sediment traps. The tests were carried out on a unit width basis and have not been expanded to full]scale river width thus far. The results of the tests were also limited by the brevity of sample observations, which lasted not more than a few days.
In this study, the scope of reliability analysis concerning hydrophone systems was expanded both in space and in time. Unit width sediment discharge was observed and analyzed in 2 river basins in Hokuriku region, and then converted to full scale by multiplying their discharge ratios. Observation periods in the basins were extended to more than a year. Combined, the observation results constituted sets of basin]wide sediment discharge estimated on a yearly basis. Basin]wide sediment discharge has long been studied as a subject of reservoir sedimentation. Quality observation data of reservoir sedimentation are available in Hokuriku region. Estimated sediment discharge in observed basins was converted to total load quantity over unit area, so that it became comparable to corresponding reservoir sedimentation, which consisted of a wider range of sediment particles.
Reservoir sedimentation was statistically analyzed in terms of regional and geological characteristics. Sample frequency distributions of yearly unit area sedimentation used for comparative analysis were formed from sedimentation samples with similar basin]wide geologic properties. The spread of the frequency distributions were analyzed by classifying reservoir service periods. Unit area total load sediment discharge estimation fell in large part within a normal range of yearly unit area reservoir sedimentation at 5% statistical significance. The results of the verification were thought to become more rigorous by further examining the ratio between bed load and total load discharge based on simultaneous total load observation and analysis in the basins.

Key wordsFsediment discharge, hydrophone, reservoir sedimentation

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