一、水土流失的状况与特征 1.水土流失的环境条件 孙家岔流域位于黄土丘陵沟壑区第五副区边缘地带,地势由东南倾向西北,山多沟深,梁峁起伏,流域全长11.21km,平均宽度3.75km,主沟道比降2.5—7.1％。按地貌类型分,流域内梁峁地(坡度<5°)占流域面积的11.0％,缓坡地(5°—15°)占26.0％,中坡地(15°—25°)占30.0％,25°以上的陡坡地占21.3％,沟壑面积占11.7％,沟壑密度为1.88km/km~2,村庄、道路面积占2.7％。 I. Conditions and Characteristics of Soil and Water Loss 1. Environmental Conditions of Soil and Water Loss Sunjiacha Basin is located in the marginal zone of the fifth sub-district in the loess hill and gully area. The terrain changes from southeast to northwest, km, the average width of 3.75km, the main channel down 2.5-7.1%. According to the types of geomorphology, the area of ​​the valley (slope <5 °) accounts for 11.0% of the drainage area, gentle slope (5 ° -15 °) accounts for 26.0%, medium slope (30 ° -25 °) accounts for 30.0% The steep slope above 21.3%, the gully area 11.7%, the gully density 1.88km / km ~ 2, the village, the road area accounts for 2.7%.