Abstract
The size distribution of armor layer in mountain rivers is an important factor that affects the stability of the river bed. However, there are relatively few studies on the prediction of armor layer size distribution in the reconstruction process after the previous static armor layer becomes unstable. In response to the above challenges, this study considers the incipient probability of sediment particles as the starting point, and comprehensively considers the coupling relationship between the initial bed materials, bed structure, armor ratio, and flow intensity, using a simple calculation model for predicting the static armor layer size distribution after reconstruction of a gravel-river bed. This paper introduces the concept of critical incipient particle size Dc, and considers that sediment particles smaller than Dc will incipient easily, resulting in a higher probability of being washed out, whereas the incipient probability of sediment particles larger than Dc (this part of the large-particle sediment includes not only the original particles on the bed surface, but also the large sediment particles exposed by the erosion of the bed subsurface) is relatively small. At the same time, this model also uses the armor ratio to reflect the impact of the bed surface structure. This study cites data from five sets of laboratory flume experiments to verify the calculation model, and the experimental results show that the model calculation results are in good agreement with the experimentally measured data, especially in predicting the median diameter D50 of the static armor layer. Our calculation model provides theoretical guidance for the study of mountain riverbed stability, earthquake prevention and disaster reduction.
Highlights
Natural disasters in mountain rivers profoundly affect the healthy development of rivers and, human survival
The results reported by He et al(2002) can be used to accurately calculate the bed surface size distribution when the armor layer is formed under the condition of clear water scour, but this method is not suitable for predicting the bed surface size distribution when it forms after the previous static armor layer is broken
To improve the relatively immature calculation model for the surface layer size distribution of the new static armor layer that forms after the previous static armor layer becomes unstable, this study proposes a new model that is based on the idea of incipient probability and the critical incipient particle size, introduces the armor ratio and other parameters, reconstructs the calculation model of the bed surface bed size distribution when the new static armor layer is formed again after the previous armor layer becomes unstable, and verifies it using laboratory flume experimental data
Summary
Natural disasters in mountain rivers profoundly affect the healthy development of rivers and, human survival. Various scholars have studied the bed size distribution of the static armor layer formation process through flume experiments Little and Mayer, (1972); Shen and Lu, (1983) or field experiments Rovira and Núñez-Gonz); Gessler (1971) first developed a mixed sand and gravel size distribution that considered the coarsening process His method only considered the pulsating effect of flow, and ignored the random distribution of the incipient drag force of sediment particles on the bed surface. Under the constraint of a certain incipient probability, sediment particles larger than this size cannot be moved On this basis, a calculation model is proposed for the static armor layer under the condition of no upstream sediment supply. 1.5). Dietrich et al (1989) obtained a dimensionless sediment transport ratio qp, which is the transport rate for the coarse surface normalized by the transport rate for a surface as fine as the subsurface or load: qp τ − τcs n τ − τct τ
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