The focus of this paper is on studying novel approaches to estimate sediment exchange between suspended-load and bed material in an unsteady sediment-laden flow with fine-grained sand. The erosion-deposition characteristics of the channel have close relation with the variation of size compositions of both suspended-load and bed material. These aims are addressed by deducing the sediment exchange equations from the mass conservation perspective and establishing a river-sediment mathematical model based on the theory. The model is applied in the middle and lower Yellow River, China, and calibrated and verified under both deposition and erosion conditions using a generalized channel and a large quantity of measured data in the Yellow River basin. The results indicate that the grading curves of suspended-load and bed material calculated by the mathematical model are close to those of the measured data. The temporal and spatial variations in the mean sizes of suspended-load and bed material, flow rate, sediment concentration and erosion or deposition volume estimates during the entire flood process can be accurately predicted. The model performance is considered acceptable for determining the sediment exchange process and the change in channel morphology for unsteady sediment-laden flow.
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