小流域岩土侵蚀规律研究——以子洲县周家圪崂乡桥沟小流域为例

桥沟小流域位于子洲县周家圪崂乡东部，系黄河四级支流，面积19km^2。桥沟主沟长5．75km，坡降12．8％，沟谷切深100m左右。流域内地貌为黄土梁峁及沟壑，出露地层主要有侏罗系砂泥岩、新近系（原为第三系）红土和第四系黄土。黄土层中下部含地下水，在黄土与基岩接触带，多有下降泉溢出。从地层岩性上看，第四系黄土分布广，厚度大，结构松散，遇水易解体。岩土侵蚀环境地质类型有三：一是降雨对谷坡面的面状冲刷一坡面侵蚀；二是地表径流对谷底的侧蚀一沟谷侵蚀，三是滑塌对谷坡坡体的破坏一重力侵蚀。三种侵重力蚀的防治措施各有侧重点，对于坡面侵蚀的防治措施主要是退耕还林种草，改造微地貌；对于沟谷及重力侵蚀的防治措施主要是沟道坝系建设，即在重力侵蚀及沟谷侵蚀发育区下游，修建淤地坝，从而抬高侵蚀基准，减少重力侵蚀的发生。

GEOTECHNICAL EROSION IN SMALL WATERSHED——a sample in Zishou county

Situated in the east part of the Shoujiakelao Village of Zizhou County, the Qiaogou small watershed is one of the four-grade branches of the Yellow River. It covers an area of 19km^2. The major Qiaogou valley has a length of 5.76 km with a slope gradient 12.8% and dissected depth about 100m. Landform in the watershed appears in loess ridges and valleys and outcrops of strata include the Jurassic sandy mudstone, Neogene laterite and Quaternary loess. Underground water occurs in the lower part of the loess beds. It is common that gravity spring occurs in the contact between the loess and basement rocks. According to the stratigraphy and the lithology, the Quaternary loess spreads extensively, which is considerably thick, loose in textures and easily broken by water. There are three types of geotechnical erosion in environmental geology. They are： （1） planer scouring by precipitation ——slope erosion; （2） lateral erosion by surface runoff to ravine ——ravinement; （3） slope broken by landslide—— gravity erosion. Prevention measures for the three types of erosion will be considered according to their characteristics. For slope erosion, returning land from farming to forestry will be used and for ravine and gravity erosion, dam system will be built for uplifting the erosion base level.