长江三峡库区现代坡地剥蚀速率研究

Study on the Modern Slope Denudation Rate in the Three Gorges Reservoir Area of the Yangtze River

三峡库区以山地为主 ,人口密度较大 ,三峡工程引起的移民搬迁以及经济建设的需要 ,造成坡地上人类活动强度越来越大 ,从而造成现代坡地剥蚀作用的加剧。采用简便、实用且操作方便的地貌测量方法 ,对三峡库区草堂河流域三个坡段进行了现代坡地剥蚀速率研究。结果表明 ,<15°的缓坡、15°～ 4 5°的斜坡和 >4 5°的陡坡的现代剥蚀速率分别为 4 .0、4 .9和 7.1mm/a。当地平均现代坡地剥蚀速率已达 4 .9mm/a (790 2t/km2 ·a) ,即达到强度剥蚀标准 ,未来三峡库区坡地退耕还林 (草 )以及水土保持等生态建设任务十分艰巨。

In the Three Gorges Reservoir area of the Yangtze River, the main geomorphology unit is mountain, its area accounts for 78%. The uprightness altitude difference is about 2 000 m. Because there are very high mountains, very steep sloping field, human kinds' cultivation, transmigrant because of Three Gorges Project and the demand of economic development, the slope fields are exposed to very strong man-made disturbance. So the modern slope denudation process is very violent. Geomorphic measure means is a way of calculating sloping field's substance denudation mass by means of measuring the geomorphic deformation. Because of saving a great lot of middle taches, this means is very simple, practical and expediently manipulative. And its results can reflect the difference of denudation rates between slope fields which have different slope gradient. Adopting geomorphic measure means, this paper studies the modern slope denudation rates of slope fields in the Caotang River watershed. First, all slope fields can be classfied to three species according to their slope gradients. There are gentle solpe which slope gradient is less than 15°, moderate slope which slope gradient is between 15°and 45°, and steep slope which slope gradient is greater than 45°. Adopting the means of measuring root can confirm the denudation rate of gentle slope. Its principle is dividing the root's bare height by tree ages. And through measuring eroded channel length, width and depth on the moderate and steep slope, so their volume can be obtained. Its volume is representation of denudation mass of moderate and steep slope. To the moderate slope, we select three plots which slope gradient is 20°, 30° and 40° respectively but their vegetation coverage are similar. To the steep slope, we select two plots which are man-made through opening road and their gradient are 50° and 60° respectively. By the measuring and deducing, the results is as follows. The modern slope denudation rates of gentle slope are 3.0 mm/a and 5.0 mm/a respectively to 7°-8° and 15° slopes. The ones of moderate slope are 4.1mm/a, 5.5mm/a and 5.0mm/a respectively to 20°, 30°and 40° slopes. The ones of steep slope are 5.7mm/a and 8.5mm/a respectively to 50° and 60° slopes. So the modern denudation rates of three species of slope field are 4.0 mm/a, 4.9mm/a and 7.1mm/a respectively. The mean modern slope denudation rate of the Caotang River basin is 4.9 mm/a (i.e. 7902 t/km^2·a), which is agree with intensely denudation degree according to national erosion standard. This result is larger than others' data. It is mainly induced by human activities in last few years. Because ecological environment is becoming worsening, so water and soil conservation is a very tough task in long time of future in the Three Gorges Reservoir Area.