KWRRI Research Reports


The movement of sediment in non-submerged flow through a rigid grass media was studied experimentally by simulating the media with cylindrical nails. Models of sediment movement were developed from probablistic reasoning and from the use of existing parameters describing total bed material in open channel flow. In the probability analysis, the percent sediment trapped was found to be a power function of the number of potential fall paths, Nf,a particle could make from the surface to the bed while traveling through the filter media. The percent trapped was also found to be an inverse power function of the Reynolds number ReT. The characteristic length used in the Reynolds number was a hydraulic radius calculated assuming rectangular open channel flow with a width equal to the spacing between elements and a depth equal to the depth of flow. This is defined as the spacing hydraulic radius, Rs. The percent trapped was finally related exponentially to a combined power function of Nf and ReT.

Total bed material transport functions of Graf and Einstein were modified and evaluated as predictors of suspended and bed load. Bed shear was assumed to be equal to γRsS where γ is the weight density of water and S is channel slope. Both Graf's and Einstein's parameters were found to be good predictors of suspended and bed load.

Based on the results of the study, procedures are proposed for analyzing the trapping capability of sediment by grass filters.

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The work on which this report is based was supported in part by funds provided by the Office of Water Research and Technology, United States Department of the Interior, as authorized under the Water Resources Research Act of 1964.