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一、流域概况常家沟小流域在永定河上游重点治理县—怀安县境内白云山脚下,属石质山区范围。地质条件以石灰岩为主,並有部分风化的花岗片麻岩。植被稀疏,有小叶杨、洋槐、榆树、油松、侧柏、柳树及灌木沙棘、紫穗槐、锦鸡儿、黄芦等生长。土壤为黄土,仅保存于阴坡半阴坡。属干旱寒冷气候区域。无霜期在100—140天,年平均气温7℃。年降雨量在400毫米以上。整个流域地形由南向北倾斜,南北长约4公里,东西宽约1.5公里。总面积约15平方公里。有较大干沙河二条,大小支沟50余条,汇流入第九屯沙河后,注入永定河的主要支流—洋河。
First, the basin profile Changjiagou watershed in the upper reaches of the Yongding River key counties - Huai’an County at the foot of Baiyun Mountain, is a rocky mountain range. Geological conditions mainly limestone, and some weathered granite gneiss. Sparsely populated, poplar, acacia, elm, Pinus tabulaeformis, Platycladus orientalis, willow and shrubs seabuckthorn, Amorpha fruticosa, Caragana, Huanglu and other growth. Loess soil, only preserved in the shady half-shady slope. Arid and cold climate area. Frost-free period of 100-140 days, the annual average temperature of 7 ℃. Annual rainfall above 400 mm. The basin from the north to the topography of the terrain, north and south about 4 km, 1.5 km east-west width. The total area of about 15 square kilometers. There are two large dry Shahe, the size of more than 50 branch ditches, confluence into the ninth Tun Shahe, Yongding into the main tributaries of the river - Yang.