近30年来长江口典型岸滩动力、沉积及地貌演变特征研究

发布时间：2018-03-10 05:23

本文选题：长江河口　切入点：地貌演变　出处：《华东师范大学》2014年硕士论文　论文类型：学位论文

【摘要】：长江三角洲是长江流域的终端,两千年来随着长江大量下泄泥沙在河口区淤积,三角洲岸滩持续向外推展,直至上世纪80年代仍处于持续快速淤涨状态。但是,随着近30年来上游泥沙补给减少和频繁的圈围工程,长江口岸滩淤涨速率减缓,部分岸段呈现侵蚀趋势,岸滩稳定性势必受到影响,直接关系到近岸工程、航运和人民财产安全。因此,在流域来沙持续减少,围垦、东海和长江大桥及青草沙水库等近岸工程增加,以及全球气候变化等多重原因的驱动下,长江口区自潮间带至水下岸坡发生了何种变化、演变趋势如何等问题亟待深入研究。本文对长江口岸滩水文泥沙、沉积物、地貌进行观测,并分析近30年不同时期的海图资料,在此基础上,探讨长江口岸滩动力沉积地貌演变特征及影响因素,为港口工程和今后岸滩稳定性防护工程建设提供参考依据。主要研究结果如下： 1.北港近岸潮流呈明显往复流特性,落潮优势流明显,岸滩演变主要受到落潮流的控制：自2004年至2012年,北港河槽上段洪季涨、落潮垂线平均流速、含沙量持续减小,含沙量减少约0.2kg/m3；同一时间段,枯季涨、落潮垂线平均流速、含沙量经历了先减后增的变化过程,其中,2007年至2012年枯季涨、落潮垂线平均含沙量均增加1倍以上。南汇南滩地处开敞海域,潮汐潮流作用相对较强,洪、枯季实测水体含沙量均大于1.23kg/m3；2004年至2012年,南汇南滩洪季涨、落潮垂线平均流速增大；涨潮垂线平均含沙量减少；落潮垂线平均含沙量略有增大；枯季涨、落潮垂线平均流速、含沙量均大幅减小。 2.近30年来,长江口岸滩表层沉积物中值粒径Dso与沉积物组分呈“向北变细、向南粗化”的变化特征,横沙东滩北岸、长江和东海大桥下等主要大型工程附近浅地层沉积物柱状样粒序向上显著变粗。 3.目前,除崇明东滩和九段沙外,长江口潮滩普遍较窄、坡度较陡,大部分岸段海塘外潮滩宽度在30-150m,少数岸段无盐沼植被。近30年来,南北边滩0m等深线以浅潮滩无明显淤涨,崇明岛奚家港至东滩南侧沿岸岸滩Om等深线逐年蚀退；南汇嘴0m等深线内潮滩略有淤进,南滩0m等深线变化甚微。 4.近30年来,北港南北岸多段水下岸滩剖面下凹形形态特征明显,坡度变陡,部分岸滩形态演变受岸外沙体变迁影响显著；值得注意的是,2009年青草沙大堤合龙工程后至今,北港岸滩整体恢复淤积格局,青草沙水库北岸冲刷由凸岸前缘有所下移,堡镇港凹岸、东海大桥下方以及横沙岛北沿均发生侵蚀冲刷。南汇南滩水下岸坡坡度近30年来明显增大,滩底发生冲刷,-7～-8m水深处滩底下蚀近1m；-5m水深以浅岸滩以净淤积为主,-5～-6m等深线为水下岸滩冲淤节点；特别是自南汇边滩圈围工程及东海大桥建设以来,南滩及大桥下方岸滩大幅冲刷。总体上,以北港为代表的“江岸型”水下岸坡具有宽度窄、坡度陡、年际变幅大以及岸坡剖面坡折明显的特点；而以南汇南滩为代表的“潮滩型”水下岸滩则具有岸滩宽阔平缓、剖面形态相对稳定等特点。 5.影响近期岸滩演变的因子主要包括流域入海泥沙锐减、水动力条件差异、近岸大型工程建设、河槽沙体变迁以及盐沼植被覆盖。流域入海泥沙锐减是长江口水下岸坡坡度增大、潮滩淤涨速率减缓等侵蚀格局形成的全局性影响因素。鉴于水动力条件的差异性,受落潮流主控的“江岸型”水下岸滩与潮流作用为主的“潮滩型”水下岸滩发育与演变特点迥异；而且,长江口人工岸线新形势下的近岸水动力条件发生显著变化,势必影响岸滩塑造和调整。圈围及近岸大型工程是导致潮滩大面积损失,局部沉积物粗化的主要原因。河槽沙体变迁和盐沼植被覆盖对长江口局部岸滩演变起重要作用。
[Abstract]:The Yangtze River Delta is the terminal of the Yangtze River Basin, two thousand years with lots of sediment in the estuary of Yangtze River water siltation, delta beach continued outward development, until the last century, 80s is still in the rapid siltation state. However, with nearly 30 years of upstream sediment supply reduction and frequent reclamation project, the Yangtze River beach the siltation rate slowed down, part of the coast erosion present trend, bank stability will be affected, directly related to offshore engineering, shipping and people's property safety. Therefore, the reclamation in sediment decreased continuously, and the East China Sea and Yangtze River bridge coastal engineering and Qingcaosha Reservoir increased, driving as well as global climate change and other reasons. The Yangtze River Estuary, from the intertidal zone to the underwater slope the change and evolution trend of such issues should be studied thoroughly. The Yangtze River port beach sediment, sediment, geomorphology observation, Based on the analysis of recent 30 years' chart data, we will discuss the evolution characteristics and influencing factors of beach dynamic sedimentary geomorphology, and provide references for port engineering and future coastal stability protection engineering.
1. North tidal flow showed reciprocating flow characteristics, ebb flow significantly, coastal evolution is mainly controlled by falling trend: from 2004 to 2012, the upper north channel flood season tide rise, the average vertical velocity, sediment concentration decreases continuously, the sediment concentration decreases about 0.2kg/m3; at the same time, the dry season rose, the vertical the average flow velocity, sediment concentration changed, first decrease and then increase the 2007 to 2012 dry season ebb rose, the vertical average concentration increased more than 1 times. Nanhui South Beach at open sea, tidal effect is relatively strong, flood and dry season measured sediment concentration was greater than 1.23kg/m3; from 2004 to 2012. Nanhui South Beach flood season tide rise, the average vertical velocity increases; the vertical average sediment concentration decreases; ebb vertical average concentration increased slightly; the dry season rose, the average vertical velocity and sediment concentration were significantly decreased.
2. in the past 30 years, the Yangtze River beach surface sediment particle size Dso and sediment composition in North thinning, change characteristics of South coarsening, Hengsha East Shoal north of the Yangtze River and the East China Sea Bridge such major project near shallow sediment cores to significantly coarser grain sequence.
3. at present, except the Chongming Dongtan and nine sand, Yangtze Estuary generally narrow, steep slope, most sections outside the beach width in 30-150m, coastal salt marsh vegetation. A few over the past 30 years, South Beach 0m isobath in shallow tidal flat without obvious siltation, Chongming Island Xi to the south coast of Hong Kong Dongtan beach erosion in Nanhui by Om isobath; within 0m isobath tidal mouth slightly siltation, South Beach 0m Isobaths changed little.
4. in the past 30 years, the north shore of North and South segments of the underwater beach profile concave shape characteristics, the steeper slope, part of beach morphology evolution by offshore sand changes significantly; it is worth noting that in 2009 the grass sand levee closure works since the north shore, the overall recovery of sediment pattern. Qingcaosha Reservoir Shore scour by convex front down somewhat, harbour town of Donghai Bridge and below the main erosion occurred along the North Island. Nanhui South Beach underwater slope gradient in recent 30 years significantly increased, beach bottom erosion, -7 ~ -8m deep water erosion under the beach near 1m; -5m water depth in shallow beach. With a net deposition, -5 ~ -6m isobath underwater siltation node; especially since the Nanhui beach reclamation project and the construction of Donghai Bridge, South Beach and coastal erosion. Under the bridge a total, with north as the representative of the "River" water bank under out It has the characteristics of narrow width, steep slope, large interannual variation and obvious slope break, while the tidal flat type underwater beach represented by Nanhui South Beach is characterized by broad and flat shore and stable profile.
The 5. factor impact of recent coastal evolution include reduced sediment basin, different hydrodynamic conditions, the large-scale construction of coastal sand, river channel change and salt marsh vegetation coverage. Watershed sediment is the Yangtze River bank under the sharp slobber slope increases, the global factors affecting the formation of tidal flat deposition rate of slow erosion pattern differences. In view of the hydrodynamic condition, the falling tide master "Jiangan" underwater shoal and tidal action based "tidal" underwater beach development and evolution characteristics of different; and the mouth of the Yangtze River, artificial shoreline under the new situation of coastal hydrodynamic conditions changed significantly, is bound to affect the shape and beach adjust. Circle and offshore engineering is large in the tidal flat area loss, the main reason for local sediment coarsening. Channel sand and salt marsh vegetation changes in the Yangtze River Estuary local beach evolution play an important role Use.

【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV148

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