中文摘要：

针对三峡工程坝下游不同类型分汊河段在三峡蓄水后的演变特点及规律,依据原观资料,对宜昌～虎牙滩河段、宜都河段、关洲河段及芦家河河段进行河床演变分析,并按照水流动力轴线年内交替与否将以上河段分为水流动力轴线年内交替型分汊河道和水流动力轴线年内不交替型分汊河道。研究表明：三峡蓄水后,各典型河段具有各自的演变特点,其主要冲淤规律的不同在于冲刷主要部位的不同,但均为洪水水流动力轴线的所经之地,对于水流动力轴线年内交替型分汊河道而言,表现为其洪水主汊冲刷幅度大于枯水主汊,这一变化显然不利于该类型分汊河段分流格局的稳定,应当引起防洪及航运部门的重视。

英文摘要：

Riverbed evolution features and trends of different braided types downstream the Three Gorges project（TGP） including the reaches of Yichang-Huyatan,Yidu,Guanzhou and Lujiahe,are analyzed using the prototype observation data.The braided streams in these reaches are divided into non-alternant and alternant types according to whether or not their dynamic axes of flow alternate annually.This analysis shows that since the operation of TGP,these reaches has evolved into a variety of different features,but the major difference in their bed features is reflected by erosion position.In different reaches,the erosion positions are quite different,while they are all on the dynamic axis of flood-season flow.For the alternant-braided streams,the erosion extent of flood-season main branch is larger than the dry-season main branch.This trend is obviously unfavorable to the stability of diversion pattern and it should call a great attention of the flood control and shipping departments.