本文關鍵詞： 潮流 懸沙濃度 懸沙粒徑 時空變化 懸沙通量 輸運機制 長江口北槽　出處：《華東師范大學》2014年碩士論文　論文類型：學位論文

【摘要】：北槽是長江水沙入海的重要通道,它處于長江口最大渾濁帶區(qū)域的核心區(qū)域,同時還是深水航道所在河段。在長江流域來沙銳減和強烈人類活動的雙重影響下,北槽內的泥沙運動強烈,泥沙運動過程和懸沙輸運機理復雜多樣。 本文根據(jù)2012年4月14日至23日在長江口北槽中段河道獲得的小潮至大潮連續(xù)的水文泥沙資料,研究了北槽中段河道小潮至大潮期間流速、懸沙濃度和懸沙粒度的時空分布特征,運用通量機制分解法對北槽中段的水沙輸運機制進行了分析,并對全粒級懸沙和不同粒級懸沙的輸移特征進行了較為深入的探討。 研究結果表明：北槽中段的潮汐為非正規(guī)半日潮；潮流為非正規(guī)半日淺海潮流,水流運動形式以往復流為主。在單個潮周期內,漲、落潮流不對稱現(xiàn)象非常顯著,落潮流速和歷時均明顯大于漲潮流速和歷時；受潮差變化所影響,流速的大小潮變化十分明顯,大潮平均流速約為小潮時的2倍；垂向上流速變化明顯,從表層向底層逐漸遞減。 在北槽中段,懸沙濃度的漲落潮和大小潮變化非常明顯,從小潮到大潮隨著潮流作用的增強,懸沙濃度不斷增加,大潮時的平均懸沙濃度約為小潮的3-4倍；在多數(shù)潮周期內漲潮階段的懸沙濃度明顯大于落潮階段。垂向上,懸沙濃度從表層向底層逐漸增加,濃度梯度在0.6H(H為水深)處通常出現(xiàn)明顯變化。 粒度分析結果顯示,在北槽中段懸沙顆粒較細,粒徑介于4-62.5um的泥沙是懸沙的主要成分。觀測期間懸沙粒徑具有明顯的時空分布特征,主要表現(xiàn)為：落潮粗于漲潮,大潮粗于小潮,下部水層粗于上部水層。在北槽內表層沉積物總體較細,以砂質粉砂和粉砂為主,平均粒徑的均值僅為19μm。粒徑趨勢分析結果顯示,在北槽內深槽南、北兩側的泥沙向海輸運。懸沙與底質的泥沙交換作用與潮汐強度密切相關,小潮時動力和再懸浮作用較弱,懸沙與底質的泥沙交換作用很小,懸沙與底質在粒徑組成上差異很大；中潮時動力和再懸浮,較強,底層懸沙與沉積物存在明顯的交換作用,交換的主體粒徑為20～90μm的顆粒；在大潮漲、落急時刻底層懸沙與底質的泥沙交換強度最大,此時的底層懸沙主要來自于懸浮起來的底床泥沙,二者在粒徑組成上非常接近。 從小潮到大潮,北槽中段的余流流速、單寬凈輸水量和單寬凈輸沙量的上升趨勢不明顯。觀測期間,歐拉余流的方向向海,流速較強,斯托克斯余流的方向向陸,流速較弱,后者的平均流速僅為前者的1/4；各潮周期的單寬凈輸水方向皆指向口外。全粒級懸沙的輸運結果表明：在各輸沙項中,平流輸沙占主導地位,其方向向海,輸沙量從小潮到大潮逐漸增加；潮泵輸沙占次要地位,但其輸沙量和輸沙方向具有隨潮周期變化頻繁的特點；垂向凈環(huán)流向陸輸沙,其量值最小,對潮周期凈輸沙的影響也最小。此外,全粒級懸沙的輸運結果還進一步表明,一些重要懸沙輸運項(比如平均流輸沙項、斯托克斯輸沙項、潮汐捕集項和重力環(huán)流輸沙項等)對凈輸沙的貢獻率存在顯著的潮周期變化,這意味著懸沙輸運結構在不同的潮周期里有時會存在較大差異。 不同粒級懸沙的輸運結果顯示,粘土類和細粉砂類懸沙具有相同的輸運特點；在中、大潮期間,粗粉砂類懸沙的潮泵輸沙與其他粒級存在明顯差異；細砂類懸沙在平流輸沙、潮泵輸沙、垂向環(huán)流輸沙方面與其他粒級都存在明顯差異,這意味著細砂類懸沙的輸運特點與其他粒級存在明顯差異。該研究結果表明今后在開展懸沙輸運機制研究時,需要對不同粒級懸沙分別進行處理,以便深入探討、分析不同粒級懸沙的輸運特征和機理。
[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 .

【學位授予單位】：華東師范大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TV148

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