长江源辫状河道群体沙洲的切割特征及机制  

Characteristics and Mechanism of Water Flow Eroding Group Bars in Braided Channel of the Yangtze River Source

作　　者：李志威[1,2] 冉韶华 蒋昌波 LI Zhiwei;RAN Shaohua;JIANG Changbo(School of Hydraulic Engineering,Changsha University of Science&Technology,Changsha 410114,China;Key Laboratory of Water-Sediment Sciences and Water Disaster prevention of Hunan Province,Changsha 410114,China)

机构地区：[1]长沙理工大学水利工程学院,湖南长沙410114 [2]水沙科学与水灾害防治湖南省重点实验室,湖南长沙410114

出　　处：《应用基础与工程科学学报》2020年第5期1057-1067,共11页Journal of Basic Science and Engineering

基　　金：国家自然科学基金项目(91647118,51709020);湖南省自然科学基金项目(2020JJ3036);湖南省教育厅重点项目(19A017)。

摘　　要：长江源区呈现扇形水系分布,广泛发育辫状河道,其河道内沙洲林立,形态各异,其数量众多和形态不规则是主要由水流的切割作用产生.基于近10年的Landsat遥感影像,选取长江源通天河的局部辫状河段为研究对象,分析辫状河道内群体沙洲的水流切割角度、切割后整体沙洲形态变化和水流切割机制.群体沙洲的水流切割形式以斜向切割为主,约占94%,其余为横向切割,约占6%,主要原因是洪水期水流发生漫滩冲刷,其冲刷及切割过程的发生具有不确定性,但是趋向于沿河道纵向方向的斜向切割更普遍.群体沙洲发生水流切割的主要机制在于相邻汊道之间存在水位差,致使水流漫滩后易于发生表面斜向冲刷和切割形成新汊道;局部河床存在横向坡降,导致水流加速运动冲刷一侧汊道,增加两侧汊道的水位差,致使漫滩水流易横向切割沙洲.The fan-shaped river network in the Yangtze River source widely develops braided channels,where large quantities of unstable group bars have time-varied morphology and irregular shapes mainly produced by water flow eroding.Using the Landsat remote sensing imagery,the Tongtian River reach in the Yangtze River source was selected to study eroding angles of water flow within the braided channel,change of group bar morphology,and the mechanism of water flow eroding.Results show that the direction of water flow eroding group bars is mainly the oblique erosion,accounting for 94%,and the rest is the transverse erosion.Although the occurrence of eroding and cutting processes is uncertainty,the oblique erosion tends to be more common along the longitudinal direction of the river.The main mechanism of water flow eroding group bars is that water level difference among adjacent branches leads to easily scour bar surface to produce a new branch after forming overbank flow,and the local riverbed in braided channel has the lateral channel slope,which causes water flow accelerating to scour one of adjacent branches.Thus,increasing water level difference between two adjacent branches,results in overbank flow laterally eroding bar surface.

关 键 词：辫状河道 群体沙洲 漫滩冲刷 横向坡降 推移质运动 遥感影像 长江源 

分 类 号：TV147[水利工程—水力学及河流动力学]