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Thesis - University Access Only
Master of Science (MS)
Alan L. Prasuhn
The sediment transport is computed by different procedures and results may differ from one another by an order of magnitude or more. Therefore, engineers must exercise their judgement when choosing a suitable sediment transport procedure in which they have confidence. Many sediment transport procedures rely on one representative sediment size, whether it is d50, d35, or d65. The notation d50, d35, and d65 refers to the diameter of the sediment particle, in millimeters at which 50%, 35%, and 65% are finer by weight respectively. The size fractions are represented by the geometrical mean size, ie. the square root of the product of the upper and lower limits of the size interval. The sediment transport by size fractions becomes more and more important as computer modeling of fluvial processes improves and advances. A computer model, such as HEC-6 requires sediment transport procedures that are capable of predicting sediment transport by size fractions. The breakdown into size fractions enables the HEC-6 model to take into account the selective aggradation and degradation of the riverbed. A single representative size can sometimes describe the bed distribution in a sand-bed river. Consequently, some of the transport procedures for sand use a single representative size while others use a breakdown into size fractions. On the other hand, a gravel-bed river usually consists of a very broad nonuniform bed distribution. Therefore, a single representative size sediment transport procedure cannot be used. Einstein, Proffitt and Sutherland, White and Day, Misri et al., Samaga et al., Lewandowski, and Bagherzadeh have all investigated the phenomenon of sediment transport of nonuniform bed distributions. Alonso studied the accuracy of eight sediment transport procedures, including the Ackers and White procedure. The Ackers and White procedure is considered as one of the best procedures. The percentage of tests falling within a factor of two of the measured data, ranges from 73% to 89.6%. White et al. investigated eight types of sediment transport procedures by using 1040 sets of flume data and 260 sets of river data. They concluded that the Ackers and White procedure was one of the best procedures. The Ackers and White procedure is a bed material load model with no provision for predicting sediment transport by size fractions. Instead, a representative size, d35, is used to represent the bed distribution. This inability of the Ackers and White procedure to predict sediment transport by size fractions limits its application in computer modeling of fluvial processes. White and Day, Proffitt and Sutherland, Lewandowski, and Bagherzadeh undertook independent studies to modify the Ackers and White procedure in order to permit prediction by size fractions. The objective of this study are: 1. To further evaluate the Lewandowski and Bagherzadeh procedures with more extensive laboratory and field data. 2. To improve the Lewandowski and Bagherzadeh procedures so that they are capable of predicting sediment transport of large sediment with increased confidence. 3. To recommend, if possible, additional modifications of the Ackers and White procedure in order to better predict nonuniform sediment by size fractions.
Library of Congress Subject Headings
Bed load -- Measurement
Number of Pages
South Dakota State University
Heng, Hock Hwee, "Sediment Transport Procedure for Nonuniform Bed Sediment by Modification of the Ackers and White Procedure" (1989). Electronic Theses and Dissertations. 4582.