通过实地观察,分析三峡工程坝区河谷深槽的地貌特征,并在此基础上,对三峡深槽的成因及其发育年代进行探讨。结果表明：(1) 三峡坝区河谷深槽是在三峡地区构造抬升过程中,水流顺构造裂隙强烈侵蚀下切而形成的;对深槽堆积物中朽木进行的14C测年表明,三峡深槽的深切侵蚀大约发生在30~40ka BP;(2) 三峡深槽的向下深切主要是急流 (特别是漩流) 携带岩砾对槽底进行研磨、掏蚀作用形成的;三峡坝区坝上深槽中的岩礁和左壁以及坝下深槽的右壁还受到急流携带岩砾的撞击、冲蚀、磨蚀和下沉流的垂向磨蚀作用;坝下深槽的左壁则是发育了深槽之后,由槽壁岩石的减压张裂及其水下的坍塌而拓展形成的;(3) 深槽的平面延伸受到纵向裂隙构造的控制,最容易发生强烈深切的位置,则受到横向裂隙与纵向裂隙的受切部位控制;深槽中的深潭向下深切所能达到的深度,主要与局部水势的变化及床底岩石抗蚀强度的差异有关,其深度不受海面高度的限制。

This paper describes valley bottom troughs of the Changjiang River and infers the geomorphological development of troughs. Based on the morphology of the troughs, the following conclusions are drawn. (1) The deep troughs on the Three Gorges valley bottom are formed by river downcutting along the structurally zones on the background of regional tectonic uplift. The data of 14C dating indicate that the downcutting of the troughs occurred at about 40-30 ka BP. (2) When river downcutting occurred in the river bed of Changjiang, the jets current with a large number of pebbles, ground and eroded the valley bottom, resulting in trough formation and deepening. Meanwhile, water currents with gravels and pebbles eroded the bank and the left wall of No.76 trough as well as the right wall of No.77 trough by striking, scouring, horizontal and vertical grinding. The left wall of No.77 trough was developed after trough deepening, when the pressure-released fracture formed on trough bank and hence induced collapse of the wall under the water. (3) The trend of the troughs is controlled by longitudinal structural fissures. The deepest points of the troughs are normally located at the intersection of the longitudinal fissures with the transverse ones. The depth of the trough is mainly determined by the intensity of the water current and the consistency of bedrock against erosion, of which the trough is composed, and is not controlled by the altitude of the sea level as the base level.