| Summary: | 碩士 === 逢甲大學 === 土木及水利工程所 === 98 === For many rivers in Taiwan, bedload transport contributes most for river-bed aggadation/degradation. Some people use empirical formulas to predict bedload transport or adopt a fixed ratio between suspended-load and bedload may both result into high error in high flow situation if no any field data can be used for calibration. In this study, a newly invented device was employed for field measurement of bedload transport in a cobble/gravel bed river named Fazih in Taichung area, Taiwan.
Based on eight measurements in two location, one location has significant deposition, and the other has mild degradation during a single flood event. When the surface velocity of river was less than 2.0 m/s, the gradation of transported bedload was much finer than the bed surface material. When the surface velocity was more than 3.8 m/s, the gradation of transported bedload approached that of bed surface material. Compared among seven bedload formulas, only Ho(1987) and MPM(1948) predicted near the measured amounts. In terms of accuracy, the bed-slope of a larger scale is better than the local scale or calculated local energy-slope for using in the Ho’s formula. Compared between the Ho and MPM formulas, the input parameters are much simpler in Ho’s formula, because only bed slope S, median diameter of bed surface material D50, and unit width discharge q are needed. By sensitivity analysis, based on the data of Fazih river, the bed slope S and median diameter of bed surface material D50, are the most sensitive parameters in the Ho’s formula, nevertheless, the discharge q has only a linear effect on the predicted amount. This gives a clear guide on how to emphasize the data collection for predicting better bedload transport rates in high flow situations in the Fazih river.
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