不同雨强和坡度下侵蚀性风化花岗岩母质坡地产流产沙特征

为研究解决南方侵蚀性风化花岗岩地区的水土流失问题,该文采用室内人工模拟降雨方法研究了不同降雨强度(30,60,90,120,150 mm/h)和不同坡度(5°,8°,15°,25°)条件下的风化花岗岩残积坡地的土壤侵蚀过程。结果表明:1)坡面径流的初始产流产沙时间都随着坡度和雨强的增大而提前;2)坡面径流量与坡度之间不呈简单的正相关关系,径流系数随雨强的变化呈现指数相关关系,入渗率在雨强为30~120 mm/h之间在坡度8°左右出现极大值;3)侵蚀产沙量随坡度和雨强的增大而增大,其与坡度之间的关系可以用幂函数表示,决定系数均达到0.815,与雨强之间为指数函数关系,决定系数均达到0.889以上;4)水力侵蚀对泥沙具有分选性,径流侵蚀挟带泥沙中的粉粒、黏粒以及细砂粒含量较多;5)坡度和雨强对于侵蚀产沙量的综合影响可以用线性相关方程来比较准确地描述,对产沙量的影响权重排序为:含沙量雨强径流系数坡度。

Characteristics of runoff and sediment yield under different rainfall intensities and slope gradients in erosive weathered granite area

Slope gradient is not only one of the major factors affecting soil particle detachment and transport but also an important factor in universal soil loss equation. There is no unanimous conclusion about the influence of slope gradient and rainfall intensity on soil erosion at present. Soil erosion in the rainy and thin-soil area of southeast China, however, is serious and thus can not be overlooked. In order to study and solve the problem of water-soil erosion loss on the weathered granite sloping land, in this study, we investigated the erosion process of the soil developed from weathered granite parent materials under different rainfall intensities (30, 60, 90, 120 and 150 mm/h) and slope gradients (5°, 8°, 15° and 25°) with the method of indoor artificial rainfall simulation. Stratified soil samples from different profiles including 0-60 cm were collected and then put into the soil tanks (2.0 m length ×1.0 m breadth × 0.6 m height) every 5 cm respectively for controlling the original bulk density. The simulated rainfall had uniformity of above 80%, similar to natural rainfall in raindrop distribution and size. Two experiments were carried out for each treatment to ensure the test precision. Soil on the top 5 cm was replaced after each rainfall simulation and the soil moisture was monitored before the next experiment to ensure the same initial soil moisture. The total time for runoff and sediment collection on the slope was 90 min after the appearance of runoff and the mixed samples were collected every 3 min and measured for volume and then used for subsequent analysis. The rest of the sample was dried to measure the sediment yield. The erosive sediment yield equations under different cross treatment conditions were established. The critical rainfall intensity of soil erosion and the critical slope gradient where soil and water conservation should be strengthened were clarified in the study area. The results indicated that the starting time of runoff and erosive sediment occurrence on the sloping land advanced with the increasing slope gradient and rainfall intensity. There was no simple positive correlation between runoff and slope gradient, and the relationship between runoff coefficient and rainfall intensity could be expressed as a potential function. The maximum infiltration rate under 30-120 mm/h appeared at the slope gradient of about 8°.The erosive sediment yield increased with the increasing slope gradient and rainfall intensity, and the relationship between slope gradient and sediment yield could be expressed by a power function with determining coefficient reaching 0.815, while the determining coefficient of the exponential relationship between rainfall intensity and sediment yield reached 0.889. Water erosion was selective for sediment as the content of silt, clay and fine sand entrained by runoff was relatively rich, and there was a boundary of erosive rainfall intensity between 60-90 mm/h in the study area. The combined effect of slope gradient and rainfall intensity on erosive sediment yield could be more accurately described by a linear correlation equation and the weighting order of sediment yield was listed as follows: sediment concentration > rainfall intensity > runoff coefficient > slope gradient. Research on the impact of slope gradient and rainfall intensity on sloping land erosion would contribute to soil and water conservation in the erosive weathered granite area.