基于^137Cs示踪法的小流域系统坡长要素坡面侵蚀机制

Mechanism of grade element slop erosion in small watersheds based on ^137Cs trace method

基于^137Cs示踪法研究了小流域不同坡度、坡面植被类型下的系统坡长侵蚀作用规律．结果表明：在系统坡长尺度上坡面侵蚀强度存在峰值，且该峰值的位置位于系统坡长的中、下游．系统坡长侵蚀作用过程呈溅蚀一片蚀一近坡纹沟发育一细沟发育一切沟、冲沟侵蚀排泄一坡面侵蚀稳定（至基准面）的动态演化过程．各过程对应的坡面分布区域，上段坡面以溅蚀、片蚀为主，中上段以纹沟侵蚀为主，中下段以细沟侵蚀为主并发生侵蚀泥沙径流经由切沟、冲沟排泄现象，下段以溅蚀为主并辅以一定的下泄面蚀．在系统坡长要素侵蚀作用过程中，坡度仅对峰值出现位置起控制作用，而对坡长侵蚀作用规律无影响．地表植被对坡长侵蚀作用干扰较强，主要是通过对地表径流的拦蓄作用实现的．

The mechanism of grade erosion effect law with different slopes and ground vegetations in small watersheds was investigated, which showed that there is peak value in the slope erosion intensity on the system length of the slope size scale and that the peak value appeares in the middle or lower course of the system length of the slope. The process of dynamical evolution falled into six steps： slaps erosion, sheet erosion, near-slope riIl development, rill development, slipping and gully erosion excretion, system erosion stability （to the datum plane）. Every step had its own zone of scatter： the slope in the upper course was of mainly slaps erosion and sheet erosion, the slope in the upper middle course was of mainly rill erosion and the slope in the middle lower course was of mainly rill erosion. At the same time, erosion sediment run-off occurred, and the slope in the lower course was of mainly slash erasion and secondly some letdown surface erasion. In the process of system element erosion, the slope played a leading role in the place where the peak value occurred and had no effect on tile law of erosion effect. The ground vegetation presented a stronger interference in the effect of slope erosion mainly by the way of impoundment for direct runoff.