【摘要】：河口最大渾濁帶作為河口區(qū)中的一個特殊區(qū)段,是河口徑流、潮汐等相互作用的產(chǎn)物,其實質(zhì)是泥沙的沉積動力過程。最大渾濁帶具有高含沙量、高濁度的特性,它直接影響著沉積過程中細顆粒泥沙的聚集和輸移,進而對河口灘槽的發(fā)育與演變起到顯著的影響。長江口橫沙淺灘、九段沙以及北槽深水航道都位于最大渾濁帶,研究最大渾濁帶水沙運動,探索河口淺灘和攔門沙的形成、發(fā)育及演變規(guī)律,對該地區(qū)的工程整治及建設(shè)有著十分重大的意義。 本文基于1982年洪枯季、2011年枯季與2013年洪季長江口渾濁帶水域多測點實測水文泥沙資料,對渾濁帶水沙時空特性進行了系統(tǒng)分析。根據(jù)多點連續(xù)實測數(shù)據(jù),闡述長江口最大渾濁帶水域水動力的時空特征；并在此基礎(chǔ)上對最大渾濁帶懸沙濃度及粒度特征進行分析,包括平面分布、垂向分布以及周期性特征；對比1982年與2011年枯季、2013年洪季長江口最大渾濁帶的水沙特性,分析30年來最大渾濁帶的水沙特征變化；通過計算各測點單寬懸沙通量以及分解通量機制,了解渾濁帶泥沙輸運規(guī)律和動力控制因子。 主要結(jié)論如下： (1)從最大渾濁帶外緣向內(nèi)到核心區(qū)域,潮流從旋轉(zhuǎn)流過渡為往復(fù)流。洪枯季流速大小比較接近,但是洪季流速方向角度普遍要大于枯季,這是因為徑流通過長江口在科氏力的作用下向南偏,使得漲潮時,流速偏向西北,落潮時流速偏向東南。大潮漲落潮流速大于小潮漲落潮流速,最大可達到相差2倍以上。在北港和北槽縱向上,從內(nèi)向外,流速大體上逐漸減小,在南匯淺灘外,從內(nèi)向外,流速逐漸增加。橫向上比較,位于渾濁帶核心區(qū)的點流速從北向南逐漸減小,而在渾濁帶外緣,從北向南,流速逐漸增大,但是最大流速仍然出現(xiàn)在最大渾濁帶核心區(qū)域。 (2)渾濁帶核心區(qū)流速梯度最大,在最大渾濁帶核心區(qū),三個汊道對比：北港北槽南槽,而在渾濁帶外緣,北港北槽南槽；在南匯外,水動力情況比較類似,三者的流速梯度基本都在0.04s-1左右,所以整體上北港內(nèi)流速梯度最大,北港外流速梯度最小。在潮周期內(nèi)最大垂向流速梯度一般出現(xiàn)在漲急或落急時刻前后,且一般落急流速梯度更大。 (3)從最大渾濁帶核心區(qū)到外緣,懸沙濃度逐漸降低,且最大渾濁帶核心區(qū)濃度遠高于其他區(qū)域,在大潮時,核心區(qū)懸沙濃度與外緣的比值在2.8～13倍之間；大潮水動力條件強于小潮,使得大潮懸沙濃度較小潮高,最高可為小潮懸沙濃度的14倍；在開闊水域,研究區(qū)域受到風(fēng)浪掀沙,枯季泥沙起動強度大,懸沙濃度較洪季大。各點懸沙濃度受到水流動力強弱影響會隨時間會出現(xiàn)周期性的變化,由于泥沙再懸浮的滯后性,最大懸沙濃度一般出現(xiàn)在急流時刻后1-2h,北港枯季大潮和南槽洪季大潮水體再懸浮能力強,在低潮位時,整體水體深度上懸沙濃度都很大。最大渾濁帶3個主槽懸沙濃度一般北槽懸沙濃度最大,南槽次之,北港最小。 (4)渾濁帶核心區(qū)懸沙中值粒徑較外緣大,在大潮時,差距超過50%,而在小潮時核心區(qū)懸沙中值粒徑略小于外緣。對比渾濁帶核心區(qū)三個汊道的懸沙中值粒徑,北槽最大,其次為南槽,北港最小。一般在大潮時,水體動力強,懸沙中值粒徑較小潮時大,而且只有在大潮時懸沙中才會出現(xiàn)砂的成分,且在北槽中懸沙三組分中砂的含量最多。 (5)近30年來長江口年徑流量基本無變化,年輸沙量減少了近60%,長江口渾濁帶整體流速大小變化不大,只有在渾濁帶核心區(qū)流速出現(xiàn)相對較大的差別,2011、2013年大潮時流速較1982年同期增大20%左右,小潮流速減小了15%左右,外緣流速相差很小,增減幅度不超過10%。近30年來懸沙濃度有明顯減小,2011、2013年懸沙濃度較1982年同期減少了50%左右。 (6)通過計算渾濁帶水域懸沙通量,發(fā)現(xiàn)整體上北港懸沙通量向東輸送,北槽向東南輸送,南匯外靠內(nèi)測點主要在南北方向上來回輸送,渾濁帶外緣懸沙向東南方向輸運。懸沙通量受懸沙濃度和流速大小的影響,一般大潮大于小潮；最大渾濁帶外邊緣洪枯季懸沙通量對比特征不明顯,而在核心區(qū)洪季懸沙通量要大于枯季。最大渾濁帶核心區(qū)的懸沙通量較外緣要大,3個漢道北槽懸沙通量最大。通過機制分解法進行分析,發(fā)現(xiàn)平流輸移項和潮泵效應(yīng)項是長江口最大渾濁帶的主要輸沙機制,在最大渾濁帶核心區(qū)以平流輸移項為主,主要向海輸沙,在渾濁帶外緣以潮泵效應(yīng)項向陸輸沙為主,阻礙懸沙向海輸移,這也是造成渾濁帶核心區(qū)泥沙淤積的原因之一。 通過對長江口最大渾濁帶水沙特性的分析,發(fā)現(xiàn)在最大渾濁帶核心區(qū)水動力最強,流速梯度最大,強水動力和強底層流速梯度能造成底部泥沙劇烈起動,造成水體懸沙的高中值粒徑,整個水體的強流速梯度能使水體維持高懸浮泥沙濃度狀態(tài)；在最大渾濁帶核心區(qū),向海輸沙的平流輸移項占主導(dǎo),在渾濁帶外緣,則以向陸輸沙的潮泵效應(yīng)為主,阻礙懸沙向海輸移,使得最大渾濁帶區(qū)域泥沙聚集,形成了最大渾濁帶；而最強的水動力和高懸沙濃度,使得最大渾濁帶核心區(qū)的懸沙單寬通量最大。
[Abstract]:The largest turbidity zone in the estuary, as a special section in the river mouth area, is the product of the interaction of the river mouth runoff, the tide and the like, the essence of which is the sediment dynamic process of the sediment. The maximum turbidity zone has the characteristics of high sediment concentration and high turbidity, which directly influences the accumulation and transport of fine-grain sand in the deposition process, and further has a remarkable effect on the development and evolution of the river-mouth beach. It is of great significance to study the formation, development and evolution of the river-mouth shoal and the sand-retaining sand, and to explore the formation, development and evolution of the river-mouth shoal and the sand-retaining sand in the cross-sand shoal, the nine-section sand and the deep-water channel of the north trough, and to explore the formation, development and evolution of the river-mouth shoal and the sand-retaining sand. The time-and-space characteristics of the muddy water and sand are systematically divided based on the measured hydrological and sediment data of the multi-measuring points in the turbid zone of the Yangtze River estuary in the dry season of 1982, the dry season of 2011 and the flood season in the Changjiang Estuary in 2013. In this paper, the temporal and spatial characteristics of the water power in the maximum turbidity zone in the Yangtze River estuary are described based on the multi-point continuous measured data, and the suspended sediment concentration and the particle size characteristics of the maximum turbidity zone are analyzed on the basis of the data, including the plane distribution, the vertical distribution and the periodicity. The characteristics of the water and sediment of the largest turbid zone in the Yangtze River estuary in the Yangtze River Estuary in the first quarter of 2013 and the dry season of 2011 are compared. The change of the water and sediment characteristics of the largest turbid zone in the past 30 years is analyzed. By means of the calculation of the single-width suspended sediment flux and the decomposition flux mechanism of each measuring point, the sediment transport law and the power control of the turbidity belt are known. Primary junction The theory is as follows: (1) from the outer edge of the largest turbid zone to the core area, the tide flows from the rotation The flow velocity of the flood season is close to that of the flood season, but the flow direction of the flood season is generally greater than the dry season, because the runoff is shifted to the south by the influence of the Coriolis force by the Yangtze River estuary, so that the flow velocity is biased to the northwest and the tide is in the ebb tide. The speed of the spring tide is greater than the tidal current speed of the small tide, and the maximum can reach the phase. 2 times the difference. In the longitudinal direction of the north and the north, the flow rate is gradually reduced from inside to outside, outside the Bank of Nanhui, from inside to outside, flow The velocity is gradually increased. In the transverse direction, the point flow rate in the core area of the turbid zone gradually decreases from the north to the south, and at the outer edge of the turbid zone, the flow rate gradually increases from the north to the south, but the maximum flow rate is still at the maximum turbidity. With the core area, (2) the maximum velocity gradient of the core area of the turbid zone is the largest in the core area of the largest turbid zone, and in the core area of the largest turbid zone, the three main channels are compared: the south trough of the north trough of the north port, and the south trough of the north trough of the north port on the outer edge of the turbid zone; and the water power situation is similar in the south of the south sink, and the flow rate gradient of the three is basically zero. It is about 04s-1, so the velocity gradient in the whole north port is the largest, and the north port The gradient of the external flow velocity is the least. The maximum vertical velocity gradient in the tidal cycle generally occurs before and after the rising or falling time, and generally falls (3) The concentration of suspended sand is gradually reduced from the core area of the largest turbid zone to the outer edge, and the concentration of the core area of the largest turbid zone is much higher than that of the other regions. In the spring tide, the ratio of the concentration of suspended sand to the outer edge of the core area is between 2.8 and 13 times, and the spring tide The water dynamic condition is stronger than that of the small tide, so that the suspended sediment concentration of the spring tide is high, and the maximum can be 14 times of the suspended sediment concentration of the small tide; in the open water area, the research area is affected by the wind wave and the sand, and the starting strength of the dry season sediment is large The concentration of suspended sand is larger than that of the flood season. The concentration of suspended sand at each point is affected by the dynamic strength of the water flow, which can change with the time. Due to the lag of the re-suspension of the sediment, the maximum suspended sediment concentration is generally 1-2h after the time of the jet, and the spring tide of the northern port and the water body re-suspension in the spring of the flood season in the south trough. The ability is strong, at low tide level, the whole body of water is deep The suspended sediment concentration in the maximum turbidity zone is the largest, and the concentration of suspended sand in the north trough is the largest. The south channel is the second and the north port is the smallest. (4) The median particle size of the suspended sand in the core area of the turbid zone is larger than that of the outer edge. In the spring tide, the gap is more than 50%, while in the core area of the small tide The median particle size of the suspended sand is slightly smaller than the outer edge. The median particle size of the suspended sand in the three main channels in the core area of the turbid zone is compared with that of the north trough. The second is the south trough and the north port is the smallest. Generally, in the spring tide, the water body power is strong, the median particle size of the suspended sand is small, and only the sand is present in the suspended sand during the spring tide, and the sand is suspended in the north groove The content of sand in the three-component sand is the most. (5) The annual runoff of the Yangtze River estuary has not changed basically in the past 30 years, the annual sediment concentration is reduced by nearly 60%, and the change of the whole flow velocity of the turbid zone in the Yangtze River estuary is not large, and only in the area of the core area of the turbid zone, the flow velocity is less than 1 in the spring tide of 2011 and 2013. In the same period of the same period in the year of 982, about 20%, the small flow rate was reduced by about 15%, and the flow rate of the outer edge was different. In recent 30 years, the suspended sediment concentration has been significantly reduced, and the suspended sediment concentration in 2011 and 2013 is 19. In the same period, about 50% was reduced in the same period in the same period. (6) Through the calculation of the suspended sediment flux in the water area of the turbid zone, it is found that the floating sand flux in the north port of the whole is transported to the east, and the north groove is transported to the southeast, and the inner measuring point of the south sink is mainly transported back and forth in the north-south direction. The flux of suspended sand is affected by the concentration of suspended sand and the flow velocity, and the general spring tide is larger than that of the small tide; the contrast of the suspended sediment flux in the maximum turbid out-of-band edge is not obvious. The suspended sediment flux in the core area of the core area is greater than the dry season, and the suspended sediment flux in the core area of the largest turbid zone is lower than the outer edge The maximum suspended sediment flux in the north trough of the three Han channels is the largest. Through the analysis of the mechanism decomposition method, it is found that the advection transfer term and the tidal pump effect term are the main sediment transport mechanism of the largest turbid zone in the Yangtze River estuary. It is also caused by the fact that the outer edge of the belt is dominated by the tidal pump effect and is mainly used for transporting sand to the sea, and the suspended sand is prevented from being transported to the sea, which is also caused The cause of sediment deposition in the core area of the turbid zone is one of the causes of silting in the core area of the turbid zone. Through the analysis of the characteristics of the water and sediment in the largest turbidity zone in the Yangtze River Estuary, it is found that the maximum hydrodynamic force, the maximum velocity gradient, the strong water power and the strong bottom layer flow velocity gradient in the core area of the largest turbidity zone can cause the bottom sediment the high-school value particle size of the suspended sediment in the water body is caused by severe starting, the strong flow velocity gradient of the whole water body can enable the water body to maintain a high suspended sediment concentration state, The tidal pump effect of the sand is the main reason, and the suspended sand is prevented from being transported to the sea, so that the sediment in the maximum turbid zone is collected, the largest turbid zone is formed, and the strongest water power and the high suspended sediment concentration are made,
【學(xué)位授予單位】：華東師范大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TV148

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