Modification of the Ackers-White Procedure to Calculate Sediment Transport by Size Fractions
Abstract
This report documents modifications to the original Ackers-White sediment transport function to calculate sediment transport by grain size classes, to include the new routine in HEC-6, and to increase the number of grain size classes into the cobble-boulder range. The Ackers and White sediment transport procedure gives a total bed material load for a sediment mixture based on the representative particle size of the mixture. The dimensionless transport Ggr is calculated from the mobility factor Fgr according to Ggr = C(Fgr/A - 1)m Ackers and White did not suggest that their procedure could be used to calculate transport by size fractions. This research extended the calculations to particle size classes by modifying the m and C coefficients. The existing subroutine ACKER should continue to be used in HEC-6 with changes made to the equations for m and C as given in Equations 14b and 15d in this report. In the cases tested, this study demonstrates a significantly improved function when the bed distribution is broadly graded. However, it should be tested in HEC-6 using additional, more diverse data sets. This modified function can be applied to particle sizes up through cobbles. It still remains, of course, to find a transport function for boulder size sediments. If HEC-6 is used for the transport of boulders, care should be taken to consider the reasonableness of the results. No matter which version of Ackers-White is used, the argument of the log function in the expression for the mobility factor (Equation 1) must remain greater than zero, i.e., y/ds > 0.1. This should be included in any code involving Ackers-White.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1993
- Accession Number
- ADA274611
Entities
People
- Alan L. Prasuhn
Organizations
- South Dakota State University