Study On Hydraulic Properties Of Shallow Flow On Slope Surface

Overland flow is produced by the movement of the slope and along with the slope after the loss of rainfall. Because the water depth is very thin and the influence factors are very complicated, it is very difficult to ascertain the mechanism of soil erosion on the slope. And it is clear that the evolution law of soil erosion is based on the dynamic characteristics and the evolution law of the thin layer flow on the surface of the slope. In recent years, domestic and foreign scholars have made a lot of research on the dynamic characteristics of thin layer water flow, but it is not enough to study the evolution law of the rolling wave. The main reason is that the accuracy of the existing measurement methods is not high and the workload is huge. In this paper, the water level measurement method is used to simulate the thin layer flow simulation test. The results show that the method is as follows:(1) Put forward the new method of rolling wave ultrasonic measurementAccording to the measurement of the ultrasonic water level gauge, the relative error and variation coefficient of the system are in reasonable range, and the system has good accuracy and stability. The measured parameters of the two methods are analyzed, and the water depth is the highest in the two methods, The correlation coefficient is 0.938. And ultrasonic water level measurement is not limited by the space position, high automation and simple operation, can be directly calculated on the basis of the water depth data to calculate the wave velocity, frequency and slope length. Therefore, compared with the traditional method, the measurement system greatly reduces the test time and workload, and improves the efficiency of the test.(2) Studied the effect mechanism of different roughness of hydraulic characteristics of overland flowAccording to the critical flow area, the thin layer flow can be divided into the stable zone, the transition zone and the transition region. The flow pattern index of the steady zone with the increase of roughness decreases and then increases, while the flow pattern index of the other two zones is negatively correlated with the degree of roughness. The flow Froude number and single wide flow, slope, roughness is power function relationship, and decreases with the increase of roughness, and discharge per unit width, and there is a positive correlation between the slope, the water flow test to rapids as slow as a supplement. The coefficient of flow resistance is a power function with the single wide flow, the energy slope and the roughness. The resistance coefficient increases with the increase of the roughness, and with the increase of the single wide flow rate, the slope has little effect on the drag coefficient. Compared with the open channel flow at the same Reynolds number when the overland flow resistance is greater than the channel flow resistance, the effect of increasing resistance.(3) Explored the laminar flow of rolling wave evolutionAt the same slope and the flow rate, the wave velocity and wave height decrease with the increase of roughness, and the wave frequency is opposite. Roll waves with the water along the way gradually mature, but velocity vary along the little change in the process, because the adjacent rolling wave polymerization, roll wave height and wavelength along the path is increased, rolling wave frequency attenuation along the way. With the same roughness, the roll wave velocity increases with the increase of the flow rate of the single width, and then decreases with the increase of the slope. The rolling wave frequency has a positive correlation with the slope of the single wide flow. Roll wave height increases with the single wide flow increased first and then decreased, at q=0.3 Lï¹’m-1ï¹’s-1, the maximum wave height. Roll wave height shows a single hump type change trend with the slope, and reaches the maximum value at about 10 degrees.(4) obtained the critical hydraulic condition of rolling wave instabilityUnder certain conditions of the slope, the critical flow rate of the laminar rolling wave decreases with the increase of the roughness. When the roughness is constant, the critical flow rate decreases with the increase of slope gradient. The critical law of the transition region is different, the transition loss of stable critical flow increases with the increase of roughness, so the increase of bed surface roughness in the transition flow region can restrain the generation of the rolling wave. In the case of the same roughness, the transition loss of the stability of the critical slope increases with the increase of the slope decreases, which indicates that the gradient will lead to the transition of the flow of water to reach the stable region.