紫色土坡面水流跌坑形态特征及其成因

Configuration Characteristic and Cause of Drop-Pit Development on Purple Slopeland

跌坑的形成是坡面侵蚀过程中的重要一环,是细沟开始出现的临界形态,跌坑的贯穿标志着细沟的形成。本研究采用模拟降雨与微地形测量相结合的方法,调查了不同雨强下紫色土坡面跌坑的发育过程及其形态分布。试验结果表明,降雨初期紫色土坡面水流跌坑边界模糊,横断面上跌坑基本在相同水平线上,与紫色土颗粒组成较粗有关;1.83～2.33 mm/min的雨强下,顺坡跌坑平均间距变化于8.2～9.4 mm之间,跌坑深度顺坡分布呈现较大的波动性,平均深度介于1.4～1.8 cm,总体上随雨强呈增大趋势;横断面上跌坑宽度变化相对较大,平均宽度介于9.4～16.3 cm,随雨强变化趋势不明显;跌坑水平间距除边界外相对稳定,地势低洼处优先形成跌坑,但也并非尽然;基于运动波理论分析认为,紫色土坡面跌坑的连续分布是坡面流运动波的能量周期性波动作用形成。

The investigation on the configuration characteristic of drop-pit is the precondition of rill development mecha- nism research. This study adopted the methods of artificial rainfall and micro-landform measure to investigate the configuration characteristic of drop-pit development on purple soil slope-land. The results displayed that： Firstly, the drop-pit on the sameness horizontal line on transect when the drop-pit were initiated in rainfall. And then, the drop-pit was incised deepen at some point than others, results in overland flow was concentrated at this point. The configuration of micro-morphology evolved when the depth of drop-pit deepen. Although, the drop-pit distributed anywhere, the distance between drop-pit along the slope was similar in different rainfall intensity. The depth of drop-pit were displayed fluctuated along the slope, and had the similar trend with rainfall intensity, reflected the dynamic characteristic of overland flow. On transect, the distance between drop-pit was random, and the point of drop-pit occurred was stochastic too. So it implies that the forming of drop-pit was coupling caused by overland flow and difference erodibility of purple soil.