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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #215429

Title: Formulas for sediment porosity and settling velocity

item WANG, S.S.Y.

Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2005
Publication Date: 8/1/2006
Citation: Wu, W., Wang, S. 2006. Formulas for sediment porosity and settling velocity. Journal of Hydraulic Engineering, ASCE, 132(8):858-862.

Interpretive Summary: Several formulae are available to determine the initial porosity and settling velocity of particles in sediment transport calculations. These formulae were obtained from specific studies involving a limited selection of materials. In this study existing formulae were tested by many additional data sets obtained from other countries and regions. The existing relationships were modified to be more generally applicable and to have better reliability and convenience of use.

Technical Abstract: The formulas of Komura (1963) and Han et al. (1981) for the initial porosity of sediment deposits were tested using data sets collected in different countries and regions. It was found that Komura’s formula slightly underestimates the dry density for sand and gravel deposits and overestimates those of silt and coarse clay deposits. Han et al.’s semi-empirical formula, which was developed for uniform-size sediment mixtures, exhibits more errors than the collected data. The coefficients in Komura’s formula have been recalibrated by using the additional data set. The relationship between the settling velocity with particle size and shape recommended by the Subcommittee on Sedimentation of the U. S. Interagency Committee on Water Resources (1957) has been reanalyzed. The original curves and tables are replaced by an explicit mathematical expression for the settling velocity that can be used more conveniently. The proposed formula has been tested by using not only the data used by the Interagency Committee, but also data from other sources. For sediment particles coarser than 0.2 mm, the proposed formula has almost the same accuracy as the original relationships recommended by the Interagency Committee. For sediment smaller than 0.2 mm, the proposed formula should yield better accuracy than the original relationships because it was calibrated by using measured data rather than assumed values based on Stokes’ law of spheres. The proposed formula also yielded better results than other similar formulas in the literature.