American Society of Civil Engineers

Gamma Distribution and Transport of Suspended Sediments

by Nazeer Ahmed, M.ASCE, (Engineering Manager, All Star Inspections, Inc. 4480 West Hacienda Avenue, Suite 109, Las Vegas, Nevada 89118; E-mail:
Section: Statistical Distributions of the Components of the Hydrological Cycle: I, pp. 1-6, (doi:

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Document type: Conference Proceeding Paper
Part of: World Environmental and Water Resources Congress 2008: Ahupua’A
Abstract: For design projects in the water resources area such as sediment control structures, a sedimentgraph is commonly used for the determination of weight of sediments generated by a given drainage basin. The division of total weight of sediments as attributed to direct runoff and baseflow in a natural channel is generally carried out based on engineering judgment. A large sample of sedimentgraphs from different geographical areas of the 48 contiguous states is considered in this investigation. A two-parameter Gamma Distribution is fitted to each one of the sample sedimentgraphs. The two parameters of the distribution are related to the dimensionless shape parameter and storage time constant for the same designated drainage basin, respectively. Both parameters are determined through the analysis of the measured sediment data at a given stream gaging station. The calibrated form of the Gamma Distribution describes the natural sedimentgraph well and furnishes accurate estimates of the sediment load carried by the direct runoff and the baseflow, respectively, for the same given drainage basin.

ASCE Subject Headings:
Suspended sediment
Sediment transport
Open channel flow