金沙江下游元谋盆地冲沟发育特征和过程分析

Analysis on Development Characteristics and Process of Gully in Yuanmon Basin on Lower Reaches of Jinsha River

金沙江下游元谋盆地广泛分布的下更新统元谋组地层为粘土层与砂土层互层 ,冲沟发育。冲沟侵蚀蚕食耕地、造成土地劣化 ,对土地资源危害很大。论述了元谋组地层冲沟具有沟壁直立、溯源侵蚀速度快、沟头组合形态多样等特征 。

The Low Pleistocene Series Yuanmon Group alternate sand and mud beds are widely distributed and the gullies are developed in yuanmon Basin. It lies on the south bank of Jinsha River, the upper reaches of Changjiang River(Yangtze R.). Some distribution regions of Pliocene-Pleistocene strata were scoured by running water, and formed thousand of gullies and ravines and some stretches of earth columns in the basin. This landscape is the result of gulling. The gullies erode the farmland, forme the erosion bad land (the earth forsest) and breake the landresources. The gully erosion, as a special erosion shape, received attention only recently. The gully erosion in the Yuanmou Basin is formed under the synthetical influence of local varied conditions, such as stratigraphy, tectonism, climate, soil, vegetation, water dynamic condition, etc. The Yuanmou Basin located in subtropical climate beit is controlled by the south west monsoon of the Indian Ocean in rainy seasons and by the continental air mass of the tyopics in dry seasons. Its foehn effect was obvious. The climate of the basin is dry and hot, ecpecially in dry seasons with in November April. The annval average temperature in the basin is 21.8℃, with the maximum of 42℃ and minimum of -1℃. The annual averag rainfall is 615mm, 90 per cent of which is concentrated in the rainy seasons within May October. The annual vaporization capacity is 3-6 times of precipitation. In rainy seasons the running water carried sand gravel in the gully to make its scouring capacity enhanced and to speed up its incision and headward erosion. The lateral erosion of running water was further enhanced to make some loose sand beds below the gully wall and gully head wall become eroded, and the walls of the gully and gully head became convex-shaped on the top of it, and concav-shaped at the bottom of it, and then the walls of gully and gully head could cause eboulement after a rainstorm, some isolated earth shield and pillars remained. The gully continually stretches to platform at the same time. This article discusses following gully characteristics: (1) the gnlly bank is vertical; (2) the headward erosion is fast; (3) the combination form of gully head is varied. Then the development process and influence factors of gully are analysed. The important influence factors of gully development are folowing: (1) the strata is alternation of sand and mud beds; (2) the vertical joint is development in earth body; (3) the clay particle capacity is larger and the crevice is development in surface soil; (4) the climate is dry and hot and distinct dry season and moist season.