Estimating sediment transport capacity for overland flow

Authors: WANG, SHUYUAN - Purdue University; Flanagan, Dennis; ENGEL, BERNARD - Purdue University

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/24/2019
Publication Date: 7/26/2019
Citation: Wang, S., Flanagan, D.C., Engel, B. 2019. Estimating sediment transport capacity for overland flow. Journal of Hydrology. 578:123985. https://doi.org/10.1016/j.jhydrol.2019.123985.
DOI: https://doi.org/10.1016/j.jhydrol.2019.123985

Interpretive Summary: Soil erosion is a process of detachment and transport of sediment particles. Within the United States and throughout the world, accelerated soil erosion is a serious problem that impacts natural resources and agricultural production, and soil conservation efforts are important to maintain those resources and levels of production. Estimation of soil loss is most commonly done using some type of mathematical model, which allows for major input factors of climate, topography, soil, and cropping/management. In many models, one concept is that flowing water has the capacity to transport a limited amount of sediment, which is affected by the flow’s velocity and depth, and the sediment particle characteristics (e.g. size, density). This “sediment transport capacity” concept has been studied by numerous engineers and scientists over the past 75 years, with many experimental studies and equations developed to estimate transport capacity. In this paper, we examined and reviewed many of the previous sediment transport equations and experiments and determined how well the functions predicted transport using available public data. We also developed a new equation, which performed well when utilizing the datasets from the literature. These results impact scientists, engineers, university faculty, students and others working with sediment transport estimation and erosion prediction. New functions may allow for better prediction of sediment transport and soil loss from upland areas. Shortcomings identified in the experiments may also lead to new study designs that expand the hydrological conditions (e.g. soil subsurface seepage or drainage conditions) considered.

Technical Abstract: Reliable estimation of sediment transport capacity is essential for soil erosion modeling. The objective of this study was to evaluate the performance of twelve widely used transport capacity functions with a wide range of hydraulic conditions and soil properties. The comparisons to observed data indicated that none of the selected twelve functions gave satisfactory results for transport capacity prediction over all overland flow datasets in this study, and all of them gave very poor predictions for loess soil. Therefore, a new equation was developed for sediment transport capacity estimation. Among these twelve functions, the Ali equation gave the best fit for the whole dataset, but calibration was necessary when using it for large sediment grains (>2 mm) or loess soil. The Yalin equation and the simplified Yalin equation worked better for soils than sands, and predictions for smaller sands (~0.2 mm) were acceptable. The Govers equation had relatively uniform performance for all datasets. The performance of empirical equations changed dramatically for different datasets. The new function developed in this study was generated based on dimensional analysis and gave good predictions within the range of hydraulic conditions and particle sizes in the datasets considered in this study. The results provide a summary of the transport capacity functions evaluated and suggest an improved function for modeling overland flow sediment transport capacity.