The Nonuniformity Aspect Of Gransizes To Bedload

Abstract

Rivers are the best sites to observe the natural effects of sediment transport. To consider the effect of nonuniformity of bed material on sediment transport rates, various representative of bed material sizes have been proposed. In this paper, the effect of nonuniformity on the transport of sediment mixtures is studied using Engelund and Hansen (1967) and Brownlie (1981) formulas. The bed materials used in this study are collected from Krasak river with three samples which have median diameters (d50) 10,2 mm, 0,9 mm, and 0,7 mm respectively. The nonuniformity of sediment was tested using five nonuniformity coefficients defined as SG,T, SI, SF&W, G, and σ in the calculation using equivalent representative diameter (de), variable representative diameter (dev) and a size gradation correction factor (Kd). The accuracy of the results are determined using discrepancy ratio (r), which is a ratio of the calculated values to the measured values. The results are analyzed using a number of percent data as a criteria in the range of 0,25 – 1,75 of r values for each calculations. The results from Engelund and Hansen’s formula based on de parameter indicated that the best accurate prediction is on G coefficient with 48,28% of data; whereas on Kd factor, G and SG,T coefficient give highest percentage with 51,28% of data respectively. The best performance for dev parameter is on SF&W coefficient with 62,07% of data, however σg coefficient gives poor prediction with 48,28% of data. In general, Brownlie’s formula gives more accurate prediction compared with the earlier for G nonuniformity coefficient with 82,76% of data.