Abstract
To increase the available land area, a large-scale land remediation campaign was carried out in the loess hilly and gully area. A large number of high and steep slopes have been produced in the construction of road engineering and water conservancy engineering, and these slopes will cause serious soil erosion under rainfall conditions. Because rainfall runoff is simultaneously affected by slope, bed surface and rainfall, the runoff movement characteristics are complex. It is difficult to consider all influencing factors in the existing models, especially for steep slopes. In this study, artificial rainfall experiments were conducted to study the rainfall-runoff hydraulic processes under different rainfall intensities and slope gradients, and a modified method was proposed to model the key hydraulic parameters (i.e., equilibrium time, water surface line, and runoff processes) on steep slopes. The results showed that (1) For steep slopes (a 70° slope compared to a 5° slope), the runoff generation time, confluence time and equilibrium time of the slope decreased significantly. At the same time, the single width runoff of the steep slope had a power function relationship with the rainfall intensity and gradient. (2) The runoff patterns of steep slopes were different from those on gentle slopes and runoff patterns were more likely to change. The Reynolds number and Froude number for slope flow changed slowly when the slope was less than the critical gradient and increased significantly when the slope exceeded the critical gradient. (3) Based on the analysis of the “double turbulent model theory of thin-layer flow on a high-steep slope”, combined with the dispersed motion wave model, a modified method for calculating the hydrodynamic factors of rainfall runoff was proposed. Then, this method was verified with indoor and outdoor experiments. The research results not only have theoretical significance, but also provide a more accurate calculation method for the design of high and steep slopes involved in land treatment engineering, road engineering and water conservancy engineering.
Highlights
A large number of high and steep loess slopes were formed in the project, and their safety has attracted wide attention[5,6]
In terms of runoff generation processes and runoff velocity distribution, the effect of discharge on the mean flow velocity was determined by flume tests on slopes ranging from 3°~10°, and the results showed the vertical velocity profile with the changes in bed morphology[8]
Drainage scouring and rainfall experiments were carried out to explore the effects of rainfall intensity and roughness on the hydrodynamic characteristics of slope flow, and the results showed that the thin layer of water flow was in the laminar flow and the flow area of the transition flow, as the slope increased, the shallow flow had a shifting trend from laminar flow to transition flow[16]
Summary
A large number of high and steep loess slopes were formed in the project, and their safety has attracted wide attention[5,6]. The process of runoff generation on a loess slope was studied by an artificial rainfall simulation experiment, and the comprehensive effects of rainfall intensity, slope gradient and slope length on the thin-layer runoff depth on a loess slope could be expressed as a three-dimensional linear empirical equation[11,12]. Drainage scouring and rainfall experiments were carried out to explore the effects of rainfall intensity and roughness on the hydrodynamic characteristics of slope flow, and the results showed that the thin layer of water flow was in the laminar flow and the flow area of the transition flow, as the slope increased, the shallow flow had a shifting trend from laminar flow to transition flow[16]. Gao first proposed a double-turbulent sheet flow model for high and steep slopes in the study of “a simulation study on the variation characteristics of a rainfall-runoff erosion flow on a complex underlying surface”.
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