Sediment transport in shallow flow through a parabolic flume
Abstract
A series of indoor laboratory experiments were conducted by using a 4 m long flume, with a parabolic cross-section and adjustable slope, to investigate the sediment transport capacity of shallow concentrated flow under the influence of simulated rainfall. Sediment inflow and outflow samples along with the flow parameters and bed slope were used to develop sediment transport relationships. Variation in the particle size distribution of sediment yield with time was also studied. The equilibrium slope of the deposited sediment decreased with an increase in rainfall whereas the sediment leaving the flume bed from the depositional area increased with increasing rainfall. Sediment transport relations were developed by using regression analysis for cohesive and non-cohesive sediment. In the case of non-cohesive sediment, the dimensionless sediment transport capacity was well related to a power function of excessive shear stress. Sediment transport did increase with an increase in rainfall on the flume bed as a function of stream power or shear stress. The rainfall effect was small when the ratio of flow depth to drop diameter was greater than approximately two. For non-cohesive sediment, the observed sediment transport capacity could be adequately predicted as a power function of the dimensionless shear stress with an exponent of 1.5. Rainfall on the flume bed did not significantly change the exponents or coefficients of the dimensionless sediment transport relationship. The particle size distribution of the eroded sediment was bimodal, due to the significant amount of large aggregates greater than 1 mm. Dimensionless transport capacity was found to be a function of excessive shear stress based on particle mean weighted diameter. In general, there was a unique relationship between the dimensionless transport capacity and shear stress based on particle mean weighted diameter for the 10 and 20-min experimental runs. When sediment transport capacity was related to a stream power, the sediment transport capacity increased with increasing rainfall on the flume bed as a result of the decreased mean flow velocity. The raindrops induced turbulence and decreased the mean flow velocity. The increase in turbulence, as a result of raindrop impact on the flow surface, increased the mobility of the sediment. The results indicated that the degree of coarseness of the eroded material was well related to the degree of equilibrium of the flow condition for a given sediment supply rate and rainfall intensity on the flume bed. At a given time, the median size of the deposited sediment on the flume bed increased in the downslope direction due to selective sorting.
Degree
Ph.D.
Advisors
Monke, Purdue University.
Subject Area
Agricultural engineering
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