Evaluating Shallow Overland Flow Sediment Transport Capacity Model

摘要

Previous works have demonstrated the poor performance of fluvial sediment transport equations when applied to overland flow. An empirical sediment transport capacity model specifically designed for overland flow has been developed, calibrated, and validated. The model separates the portion of the transport capacity due to flowing water from the portion due to rainfall-impact. Model development has been described by Guy (1990). This paper outlines model calibration results, and model interpretation. Tests of the calibrated model are presented in Guy (1990). Model calibration data were obtained in a 1.50 m long by 0.253 m wide flume, with rainfall supplied by a single-nozzle rainfall simulator, and flow provided by a constant head tank. Sediment was injected into steady flow over an impermeable, roughened bed, at a rate which balanced the outflow rate. Transport capacity and hydraulic measurements were obtained at five slopes between 1 and 12%, with four test materials covering a range of size and density, four simulated rainfall intensities, and a range of baseflow rates. Hydraulic measurements obtained in the laminar Reynolds number flows indicate that the level of zero velocity is raised into the moving sediment layer, such that depths exceed predictions of the velocity profile model. Surface velocities match model predictions, such that flow resistance does not need explicit consideration in developing a transport model. The transport component due to flow processes depends on discharge, slope,and material properties, and is similar to the Schoklitsch (1962) equation. Hie relative significance of bed slope and discharge is intermediate between the relative significance required by stream power per unit bed area and shear stress concepts. Thecomponent due to rainfall-impact depends on rainfall intensity, discharge, slope, and relative particle density. A finding of statistical insignificance of particle size may be due to the relatively small size range examined. The portion of the transportcapacity due to rainfall-impact varies from 100% at the lower limit of the study data (at flows less than the fluvial transport thresholds) to approximately 50% at the upper limit. Results suggest that sediment transport can be classified into three typ