采用人工模拟降雨试验,研究不同雨强(40,66,80 mm/h)和坡度(5°,10°,15°)条件下,湖北省武汉市蔡甸区红壤坡面流速、产流产沙时空变化及水动力学过程。使用长2.5 m,宽0.5 m,高0.3 m的可调坡度径流土槽,每场降雨试验在槽子底端出口开始产流后持续60 min,每3 min收集一次径流泥沙样品。结果 表明:相同坡度下,坡面平均产流率和产沙率均随雨强增加而增大; 产流率在降雨初期波动增长,随降雨时间延长而逐渐稳定; 产沙率在降雨初期急剧上升,随后稍有下降并逐渐趋于平稳。坡度从5°增加到15°,雨强为40,66,80 mm/h下的平均产流率依次增加24%,22%和15%,平均产沙率依次增加89%,60%和84%。随雨强或坡度增加,流速均增大,且雨强对流速的影响较坡度更大; 流速沿坡长方向呈增大趋势,且细沟流速是细沟间的1.33～2.10倍。66 mm/h,10°条件下,坡面形成细沟并发生明显下切和溯源侵蚀。相同雨强下,径流剪切力随坡度增加而增大、达西—韦斯巴赫阻力系数随坡度增加而减小。坡面径流属于层流且为急流,水动力学参数和侵蚀产沙率的拟合方程表明,弗劳德数和流速可以较好地模拟坡面产沙率。研究结果可为南方红壤区水土流失治理提供参考。
The overland flow velocity, temporal and spatial variations of runoff and sediment yield, and hydrodynamic processes on the red soil slope in Caidian, Wuhan, Hubei Province were studied under different simulated rainfall intensities(40 mm/h, 66 mm/h, 80 mm/h)and slope gradients(5°, 10° and 15°). The soil sample was filled in a steel trough(2.5 m in length, 0.5 m in width, and 0.3 m in height)with adjustable slope gradient. Each rainfall simulation lasted for 60 minutes after the generation of runoff at the outlet of the trough, and runoff and sediment samples were collected every 3 minutes. The results showed that under the same slope gradient, the average runoff and sediment yield increased with the increase of rainfall intensity; the runoff increased with fluctuation in the early stage of the rainfall, and gradually became stable, while the sediment yield rate increased sharply at the beginning of the rainfall, then decreased slightly, and gradually stabilized; with the slope gradient increasing from 5° to 15°, the average runoff rates at rainfall intensities of 40 mm/h, 66 mm/h and 80 mm/h increased by 24%, 22% and 15%, and the mean sediment yields increased by 89%, 60% and 84%, respectively; with the increase of rainfall intensity or slope, runoff velocity increased, and the effect of rainfall intensity on velocity was greater than that of slope gradient; mean flow velocity increased along the downslope direction, and the velocity in rills was 1.33～2.10 times of that in the interrill; under the condition of 66 mm/h and 10°, rills formed on the slope surface and obvious downcutting erosion and headward erosion occurred; under the same rainfall intensity, the runoff shear force increased and the Darcy-Weisbach resistance coefficient decreased with increase of slope gradient. Under the experimental conditions, the overland flow belonged to laminar flow and supercritical flow. The fitting equation of hydrodynamic parameters and sediment yield rate indicates that Froude number and flow velocity can well simulate the sediment production rate. The results of this study can provide the reference for the control of soil erosion in the red soil area of southern China.
