Transport and deposition of nonuniform sediment
Abstract
A field study was conducted to determine the effects of rainfall on the sediment transport and deposition processes in shallow rill channel flows. Simulated rainfall at intensities of 72, 142, and 254 mm/h was applied to pre-formed ridge-furrows having average bed slopes of 0.5, 1, 2, and 4%. Soils examined were a fine sand, a silt loam, and a silty clay. Rainfall intensity had a significant effect on the sediment transport capacity of the shallow rill flows on the silt loam soil. Average sediment transport from the rills on the silt loam soil subjected to a 254 mm/h intensity rainfall was over three times the transport resulting from the 72 mm/h rainfall, and about twice the transport resulting from the 142 mm/h rainfall, at the same level of hydraulic shear stress. Transport of the majority of the sediment was more correlated with rainfall intensity than with flow shear stress, and this may have been due to the ease of suspension of this fine sediment (2 to 50 $\mu$m in size). The silt loam data were also used to determine a relationship between the rainfall turbulence factor in a widely used deposition equation and the average flow depth and rainfall intensity. The silty clay soil was more cohesive, and was thus more difficult to detach and transport. However, the transport of the individual sediment particle size classes was significantly affected by both the level of flow shear stress and by the rainfall intensity level. A scheme was developed by which the transport rates of several different particle types could be predicted based on a reference size class. Results on the sandy soil were inconclusive as to the effects of rainfall due to extremely high soil infiltration rates which normally limited runoff on the plots to the highest rainfall intensity. Sediment transport capacity of the sand was well related to hydraulic shear stress, indicating that the sand particles moved largely as bedload.
Degree
Ph.D.
Advisors
Laflen, Purdue University.
Subject Area
Agricultural engineering
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