三峡水库下游弯曲河型演变规律调整及其驱动机制

doi:10.11821/dlxb201703005

摘要/Abstract

摘要：

大型水库的兴建深刻改变了下游水沙输移特点,进而导致河床演变规律显著调整,水库下游弯曲河型对水沙过程改变响应敏感,是水库下游河床演变、航道整治、河势控制等方面研究的关键区域。本文基于1996-2016年的实测水文、地形资料,对长江三峡水库下游弯曲河型的演变规律及其驱动机制开展研究,结果表明：① 三峡水库蓄水前,下荆江存在“凸淤凹冲”、“凸冲凹淤”两类弯曲河型,而三峡水库蓄水后均表现为“凸冲凹淤”的一致性规律;② 在水库拦沙作用的影响下,下荆江河段平滩河槽存在累积性冲刷现象,冲刷部位集中于枯水河槽与基本河槽之间的低滩,冲淤部位调整主要由变化的流量过程所驱动,上游河势、河道边界以及支流入汇等因素均有一定驱动作用;③ 在三峡水库蓄水后缺乏大洪水的情况下,凸岸水流挟沙力随流量增加逐渐增强,水流对凸岸冲蚀力度在平滩流量级附近（20000~25000 m3/s）达到最强,平滩流量附近流量级的持续时间超过20天时,弯曲河道发生凸冲凹淤现象。而悬沙中造床粗沙的减少,增强了水流冲刷强度,加剧了凸岸的冲蚀程度。

关键词: 水库下游, 弯曲河型, 冲淤调整, 驱动机制, 下荆江

Abstract:

The impoundment of huge reservoirs deeply changes the water and sediment process in the downstream reaches and then influences the evolution of the downstream rivers. The meandering rivers sensitively responded to the variation of water and sediment process. That is why the meandering rivers are the important survey regions of river evolution, channels regulation and flood control projects. Based on the measured hydrological and morphological data from 1996 to 2016, the evolution law and its driving mechanism of the typical meandering river in the downstream reaches of Three Gorges Reservoir (TGR) are studied. By building the relationship between the cross-sections variation and the influencing factors, the mechanism is well examined. The results show that (1) before the establishment of the Three Gorges Reservoir, the meandering rivers have two types of evolution laws named "Convex banks deposition and concave banks erosion" and "Convex banks erosion and concave banks deposition". After the impoundment of the great project, the meandering rivers are featured only by the latter type. (2) After the retaining of water and sediment of TGR since 2003, the low flow channel and bankfull channel in Lower Jingjiang River have been continually eroded and the erosed areas are found in the low shoal of convex banks. The phenomenon is mainly resulted from the variation of water flow and sediment transportation and also influenced by the upstream river region, riverbed boundaries and branches. (3) The growing process of flow discharge from low water to bankfull discharge can lead to the increase of sediment transport capacity. When no big flood of discharge over 35000 m3/s is observed after the impoundment of TGR, the duration of bankfull discharge (22000-25000 m3/s) decides the erosion or deposition of convex banks after the impoundment. When the number of lasting days of bankfull discharge (22000-25000 m3/s) exceeds 20, the convex banks will be eroded. The concentration of coarse sand decrease contributes to the improvement of strength of water.

Key words: downstream reaches of reservoirs, meandering river, evolution adjustment, driving mechanism, Lower Jingjiang River

樊咏阳, 张为, 韩剑桥, 余梦清. 三峡水库下游弯曲河型演变规律调整及其驱动机制[J]. 地理学报, 2017, 72(3): 420-431.

Yongyang FAN, Wei ZHANG, Jianqiao HAN, Mengqing YU. The typical meandering river evolution adjustment and its driving mechanism in the downstream reach of TGR[J]. Acta Geographica Sinica, 2017, 72(3): 420-431.

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数据类型	测站名称	测量时间	测量间隔	数据来源
水文数据	沙市水文站监利水文站	2003-2013年 1996-2015年	24 h	长江委水文局
水文数据	城陵矶水文站	1996-2015年	24 h	长江委水文局
断面流速	荆江固定断面	2014年8月, 2015年1月	-	长江航道局测量中心
断面数据	莱家铺弯道	2003-2016年^a	1年	长江航道局测量中心
断面数据	荆江固定断面	1996年, 2003年, 2016年10月	-	长江委水文局
河床组成	莱家铺弯道	2009年9月, 12月	3个月	长江航道局测量中心
河床组成	七弓岭弯道	2009年9月, 12月	3个月	长江航道局测量中心

流量级(m3/s)	均值	2003年	2004年	2005年	2006年	2007年	2008年
平滩流量(20000~25000)	32	43	36	40	5	27	33
洪水流量(>35000)	1	0	5	1	0	6	0
流量级(m3/s)	2009年	2010年	2011年	2012年	2013年	2014年	2015年
平滩流量(20000~25000)	41	46	17	29	38	67	15
洪水流量(>35000)	0	0	0	3	0	2	0