长江口北槽中段河道悬沙时空变化和输运机制研究

发布时间：2018-01-29 16:50

本文关键词： 潮流悬沙浓度悬沙粒径时空变化悬沙通量输运机制长江口北槽　出处：《华东师范大学》2014年硕士论文　论文类型：学位论文

【摘要】：北槽是长江水沙入海的重要通道,它处于长江口最大浑浊带区域的核心区域,同时还是深水航道所在河段。在长江流域来沙锐减和强烈人类活动的双重影响下,北槽内的泥沙运动强烈,泥沙运动过程和悬沙输运机理复杂多样。本文根据2012年4月14日至23日在长江口北槽中段河道获得的小潮至大潮连续的水文泥沙资料,研究了北槽中段河道小潮至大潮期间流速、悬沙浓度和悬沙粒度的时空分布特征,运用通量机制分解法对北槽中段的水沙输运机制进行了分析,并对全粒级悬沙和不同粒级悬沙的输移特征进行了较为深入的探讨。研究结果表明：北槽中段的潮汐为非正规半日潮；潮流为非正规半日浅海潮流,水流运动形式以往复流为主。在单个潮周期内,涨、落潮流不对称现象非常显著,落潮流速和历时均明显大于涨潮流速和历时；受潮差变化所影响,流速的大小潮变化十分明显,大潮平均流速约为小潮时的2倍；垂向上流速变化明显,从表层向底层逐渐递减。在北槽中段,悬沙浓度的涨落潮和大小潮变化非常明显,从小潮到大潮随着潮流作用的增强,悬沙浓度不断增加,大潮时的平均悬沙浓度约为小潮的3-4倍；在多数潮周期内涨潮阶段的悬沙浓度明显大于落潮阶段。垂向上,悬沙浓度从表层向底层逐渐增加,浓度梯度在0.6H(H为水深)处通常出现明显变化。粒度分析结果显示,在北槽中段悬沙颗粒较细,粒径介于4-62.5um的泥沙是悬沙的主要成分。观测期间悬沙粒径具有明显的时空分布特征,主要表现为：落潮粗于涨潮,大潮粗于小潮,下部水层粗于上部水层。在北槽内表层沉积物总体较细,以砂质粉砂和粉砂为主,平均粒径的均值仅为19μm。粒径趋势分析结果显示,在北槽内深槽南、北两侧的泥沙向海输运。悬沙与底质的泥沙交换作用与潮汐强度密切相关,小潮时动力和再悬浮作用较弱,悬沙与底质的泥沙交换作用很小,悬沙与底质在粒径组成上差异很大；中潮时动力和再悬浮,较强,底层悬沙与沉积物存在明显的交换作用,交换的主体粒径为20～90μm的颗粒；在大潮涨、落急时刻底层悬沙与底质的泥沙交换强度最大,此时的底层悬沙主要来自于悬浮起来的底床泥沙,二者在粒径组成上非常接近。从小潮到大潮,北槽中段的余流流速、单宽净输水量和单宽净输沙量的上升趋势不明显。观测期间,欧拉余流的方向向海,流速较强,斯托克斯余流的方向向陆,流速较弱,后者的平均流速仅为前者的1/4；各潮周期的单宽净输水方向皆指向口外。全粒级悬沙的输运结果表明：在各输沙项中,平流输沙占主导地位,其方向向海,输沙量从小潮到大潮逐渐增加；潮泵输沙占次要地位,但其输沙量和输沙方向具有随潮周期变化频繁的特点；垂向净环流向陆输沙,其量值最小,对潮周期净输沙的影响也最小。此外,全粒级悬沙的输运结果还进一步表明,一些重要悬沙输运项(比如平均流输沙项、斯托克斯输沙项、潮汐捕集项和重力环流输沙项等)对净输沙的贡献率存在显著的潮周期变化,这意味着悬沙输运结构在不同的潮周期里有时会存在较大差异。不同粒级悬沙的输运结果显示,粘土类和细粉砂类悬沙具有相同的输运特点；在中、大潮期间,粗粉砂类悬沙的潮泵输沙与其他粒级存在明显差异；细砂类悬沙在平流输沙、潮泵输沙、垂向环流输沙方面与其他粒级都存在明显差异,这意味着细砂类悬沙的输运特点与其他粒级存在明显差异。该研究结果表明今后在开展悬沙输运机制研究时,需要对不同粒级悬沙分别进行处理,以便深入探讨、分析不同粒级悬沙的输运特征和机理。
[Abstract]:The north trough is an important channel for the Yangtze River to enter the sea . It is located in the core area of the largest turbidity zone in the Yangtze River Estuary and is located in the river section of the deep water channel . In the Yangtze River valley , the sediment movement is strong , the sediment movement process and the sediment transport mechanism are complex . In this paper , the spatial and temporal distribution characteristics of the flow velocity , suspended sediment concentration and suspended grain size in the middle section of the North Channel during the period from 14 to 23 April 2012 in the middle section of the North Channel of the Yangtze River Estuary were studied . The sediment transport mechanism in the middle section of the north trough was analyzed by using the flux mechanism decomposition method . The results show that the tide in the middle section of the north trough is the irregular semi - diurnal tide ; the tidal current is the shallow sea tidal current of the irregular half day , and the flow movement takes the form of reciprocating flow . In the single tidal cycle , the flow velocity and duration of the ebb tide are obviously higher than that of the flood tide ; the flow velocity and duration of the ebb tide are obviously larger than that of the flood tide ; the average flow velocity of the tide is about 2 times of the tide ; the vertical velocity change is obviously , gradually decreasing from the surface layer to the bottom layer . In the middle section of the north trough , the fluctuation of the concentration of suspended sediment is very obvious , the concentration of suspended sediment increases with the increasing trend of the tide , the concentration of suspended sediment is about 3 - 4 times of the tide , and the concentration of suspended sediment at the tide stage is obviously higher than that of the ebb tide . The results of the particle size analysis show that the suspended sediment in the middle of the north trough is finer and the sediment with the grain size of 4 - 62.5 um is the main component of the suspended sediment . The sediment exchange between the suspended sediment and the sediment is very small . The sediment exchange between the suspended sediment and the sediment is very small . The sediment exchange between the suspended sediment and the sediment is very small . In addition , the transport results of full - grain suspended sediment indicate that the sediment transport structure has a significant influence on the net sediment transport rate in different tidal cycles , which means that the sediment transport structure can sometimes have a large difference in different tidal cycles . The results show that the transport characteristics of fine sand suspended sediment are different from those of other particles . The results show that the transport characteristics of fine sand suspended sediment are different from those of other particles .

【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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