北方风沙区砾石对堆积体坡面径流及侵蚀特征的影响

为了研究砾石对工程堆积体降雨侵蚀规律的影响,采用室内人工模拟试验,以土质堆积体(砾石质量分数为0)为对照,研究了10%、20%和30%砾石质量分数堆积体边坡在模拟降雨条件下的径流水力特征、产沙过程及侵蚀动力机制。结果表明:1)产流0~6 min,砾石促进堆积体坡面细沟间径流流动;产流12~30 min后,砾石阻碍堆积体坡面细沟径流流动;2)含砾石堆积体坡面粗糙度增大,水流流态变缓,水流速度降低,且均以层流为主。较土质堆积体而言,30%砾石质量分数堆积体坡面阻力系数增大88.8%~288.4%,弗汝德数降低28.9%~41.8%,水流速度降低0~45.8%;3)径流含沙量随产流历时经历快速降低-平稳过渡-波动上升3个阶段,土质及10%砾石质量分数堆积体高含沙水流现象频发,且随雨强增大,重力坍塌次数增加,重力侵蚀程度增强。20%、30%砾石质量分数堆积体发生高含沙水流的几率约为0。相对土壤流失比与砾石质量分数呈极显著负指数函数关系;4)土壤剥蚀率与各侵蚀动力参数均可用简单线性函数关系描述,单位径流功率是描述风沙区土质和10%砾石质量分数工程堆积体侵蚀产沙的最优因子,径流功率是刻画20%、30%砾石质量分数工程堆积体土壤侵蚀参数更为合理的因子。结果可为全国范围工程堆积体土壤侵蚀模型的建立提供科学依据。

Effect of gravel on runoff and erosion characteristics on engineering accumulation slope in windy and sandy area, northern China

Different from abandoned field and cropland and natural landscape, engineering accumulation is a special man-made geomorphic unit and has been found much more serious soil erosion. The anthropogenic accelerating erosion poses great threat to ecological environment of construction sites with surrounding regions and seriously hinders local economic growth and improvement of people’s living standard. Gravel is always an important composition of depositions and it causes particular erosion characteristics. An indoor artificially simulated rainfall experiment was carried out in the State Key Laboratory of Soil Erosion and Dryland Agriculture on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, China to investigate runoff hydraulic character and sediment yield process and erosion dynamic mechanism on slope of engineering deposition with different content of gravel. Soil sample, collected from Jingbian, Shanxi (N37°26′08″, E108°54′53″), was evenly mixed with gravel to be used as the main test material. According to preliminary field investigations, the grain diameter≤50mm of gravel was chosen as the gravel for the test and divided into 3 classes with different ranges of diameter: 2-14 mm (small) and 14-25 mm (medium) and 25-50 mm (large). Gravel sample for each test was consisted of 30% small, 50% medium, 20% large gravel. Mass content of gravel designed varied from 0 to 30%. Mobile hydraulic steel tank with the size of 5m×1m×0.6m (length×width×height) was applied for holding test material. Test slope was adjusted to 25° according to construction requirement of standard experimental plot. The results showed that: 1) Flow velocity on soil-rock deposition slope was higher with a maximum amplification of 52.8% during 0-6 min due to the positive effect of gravel on confluence compared to the bare. Whereas it was lower with a maximum damping of 408.5% when rill erosion dominated on the slope because of inhabitation from gravel which was exposed in the rill; 2) In terms of average level in an event, surface roughness increased and runoff, acted as laminar flow, flowed more slowly with smaller velocity on the slope of deposition with gravel. For the accumulation with 30% gravel content, resistance coefficient increased by 88.8%-288.4% and Froude number and flow velocity decreased by 28.9%-41.8% and 0-45.8% respectively compared to the homogeneous; 3)Sediment yield process could fall into 3 stages: quick reduce - smooth transition - fluctuate increase, in the third period, hyper-concentrated flow was easily found on the slope of the bare and the deposition with 10% of gravel, and frequency and degree of gravitational collapse increased with rainfall intensity increasing. The chance of hyper-concentrated flow approximately equaled to 0 for deposition with 20% and 30% of gravel. Relative soil loss ratio decreased exponentially with increasing gravel content; 4) The relationship between soil detachment rate and hydrodynamic parameters could be described with linear function. Unit stream power was the best one of all the hydrodynamic parameters to describe the hydrodynamic process of soil erosion on accumulation with 0 and 10% of gravel contents, whereas stream power tended to be more scientific to study the erosion process on deposition with 20% and 30% gravel contents. The results provide valuble information for the establishment of empirical and process-based model of soil and water loss on engineering accumulation on a national scale.