【作者】 于欣；

【导师】 高建华；

【作者基本信息】 南京大学 ， 海洋地质学， 2012， 硕士

【摘要】 河口最大浑浊带受潮汐动力、河口环流、径流等影响,动力条件复杂。了解最大浑浊带内的水动力与悬沙输运,对沉积物输运过程、沉积动力学研究有着重要的科学意义,可为当地自然资源开发利用、海岸工程建设等提供数据支撑。2009年8月及2010年7月和8月在鸭绿江中水道进行了定点长周期观测,上下游同步全潮观测,及断面走航观测,获取水体的流速、悬沙浓度、温度、盐度数据。基于观测数据,本文分析了鸭绿江河口的流速、温盐度及悬沙浓度的时空分布特征,并对河口悬沙进行通量分解,研究其输运机制,以探讨不同动力机制及径流变化对悬沙输运的影响,在此基础上分析最大浑浊带的成因机制。实测结果显示,鸭绿江河口受往复流控制,落潮时间大于涨潮时间,潮差最大可达6.0m,属于强潮型河口。最大垂线平均流速出现在涨潮、落潮中后期,最大可达1.2ms-1,涨潮和落潮的垂线平均最大流速相差不大,一般在0.9-1.2mS-1。底部三角架测量结果显示,涨潮底部最大流速大于落潮,最大流速差可达0.5ms-1。这与垂线平均流速落潮期间大于涨潮的现象截然不同,主要与径流的存在有重要关系。计算结果显示,拉格朗日余流除Y02站(最大浑浊带上游)小潮向陆外,其余站点方向均向海,欧拉余流均为向海,斯托克斯漂流则全为向陆。大潮期间各项余流较小潮明显增大。Y01作为长时间序列观测站,余流计算结果比较有代表性。Y01站拉格朗日余流为5.5cms-1方向向海,欧拉余流为15.2cms-1,方向向海,斯托克斯漂流为9.7cms-1,方向向陆。Y01站涨落潮期间悬沙浓度垂向分布有明显差异,涨急时刻垂向混合强烈,水体上下悬沙差异不大,平均可达1000mgL-1,落急时底部出现高值中心,最高可达1600mgL-1以上,水体中上部悬沙浓度则较低,往往低于400mgL-1。Y01站涨落潮悬沙垂向分布的差异主要与径流有关。在盐淡水锋面存在的重力环流对悬沙在水体中的扩散有着重要影响,涨潮期间盐淡水锋面往往可到达Y01站,因此而产生的重力环流加快了底部悬沙向上扩散的速度,悬沙垂向分布均匀；相反,落潮期间,锋面下移,底部悬沙向上扩散缓慢,因而只在底部出现高值中心。悬沙输运机制分解结果显示,向海的欧拉余流项,向陆的斯托克斯漂流项和潮汐捕捉项对鸭绿江河口的悬沙输运起着重要作用。Y01站平流输运占泥沙输运的很大比例,但潮泵贡献项与泥沙输运相关系数显著,R2达到0.82。可以说平流输运是泥沙输运的主导机制,但潮泵效应对悬沙输运的影响十分强烈,其贡献大小变化决定了泥沙输运的变化趋势。底部边界层观测表明,同一个潮周期内100cm处悬沙浓度落潮远大于涨潮,悬沙浓度最大值在涨潮期间往往小于1000mgL-1,落潮期间则常常大于2000mgL-1。底部悬沙涨落潮差异主要与涨落潮底部再悬浮时间差异有关,落潮期间底部再悬浮时间为涨潮期间底部再悬浮时间两倍以上。观测期间水库放水,径流增大,底部再悬浮并未受到显著影响,但悬沙在水体中的扩散受到抑制,特别是涨潮,因而导致放水期间水体整体悬沙浓度降低,通量分解各项瞬间量变化幅度也相应降低,同时向海的悬沙输运增多。强烈的底部再悬浮作用是鸭绿江河口最大浑浊带形成的主要因素。最大浑浊带内的底部再悬浮一方面提高了水体的悬沙浓度,另一方面也可为上下游分别向陆和向海的泥沙输运提供充足的物源。更多还原

【Abstract】 Turbidity maximum(TM) zone of estuaries is suffered from complex dynamic conditions, and affected by many processes, such as tide, estuarine circulation, runoff et al.. Well understanding the sediment dynamics are not only beneficial to study the hydrodynamic and suspended sediment transport in the TM, but also helpful to the coastal engineering and management of local resources exploitation. In this study, several observations in different position of the Estuary of Yalu River were carried out. During the August,2009, synchronization data including current, salinity, temperature and suspended sediment concentration (SSC) at both upstream and downstream of TM zone (Y02, Y03) were collected during both spring and neap tides. A mooring observation within long-term period (Y01) was observed from19th Jun. to2nd Aug,2010, and the same haydrodynamic parameters were obtained in station Y02and Y03. In addition, a cross-section observation from the upstream to the entrance of Yalu River was explored on2nd Aug,2010. Subsequently, the distribution of velocity, SSC, salinity and temperature were analyzed. Using method of flux decomposition of suspended sediment transportation, the mechanism of sediment transport was discussed. Finally, the TM forming mechanisms of the Yalu River Estuary were discussed.The analysis results of these observations showed that the Yalu River estuary, with a maximum tidal range of6m, was characterized by reversing current, and the ebb duration was longer than the flood duration. The maximum depth-averaged velocity were observed3-4hours before and2-3hours after the flood slack, with a range from0.9m s-1to1.2m s-1. Contrasting to the depth-averaged velocity, the flood current which was much greater than that the ebb current were recorded in the near sea bed current. The max difference between the bottom velocity between ebb and flood reach0.5m s-1, which was quite different with the depth-averaged velocity induced by the runoff.Lagrangian, ulerian and stokes residual current were caculted. The results showed that, lagrangian residual current was seaward, except during the neap tide of Y02. Ulerian residual current was seaward and Stokes residual current was landward for all the stations. All the three kinds of residual current were much larger during the spring tides rather than that during the neap tides. Y01was a long-term observation station. The lagrangian residual current, ulerian residual current and the stokes residual current was5.5cm s-1(seaward),15.2cm s-1(seaward), and9.7cm s-1(landward), respectively.The SSC distribution during the flood was different from that during the ebb. The maximum flood velocity were always connected with the uniformly vertical distribution of suspended sediment concentration, and the corresponding maximum SSC was up to1000mg L-1. Contrastly, high SSC were only observed in the bottom layer, in terms of high quantity of1600mg L-1, when maximum ebb velocity occurred; however, The SSC of upper water body was quite small, which was always smaller than400mg L-1. This phenomenon may be caused by the bottom suspended sediment diffusion blocked by stratification. During the flood phase, the saltwater wedge could reach station Y01, which accelerate the diffusion of bottom suspended sediment. In contrast, during the ebbs, there was no saltwater wedge, and the diffusion was slow down, causing a high value of SSC only in the bottom water body.The result of flux decomposition of sediment transport showed that, the items of Eulerian Residual current (seaward), stokes residual current (landward) and tidal trapping played important roles on the suspended sediment transport in the Yalu River Estuary. In the Y01, the suspended sediment transport was dominated by Advection transport. However, tidal pumping show a high linear correlation with the suspended sediment transportation (R2=0.82), implying that the variation of suspended transport was determined by that of tidal pumping.The bottom boundary observation showed that, SSC of100cm was much bigger during ebb than that during flood. The maximum SSC was always smaller than1000mg L-1during the flood phase, and larger than2000mg L-l during the ebb phase, which may be related with the difference of the resuspension time between the ebb and flood phase. Calculation result showed that resuspension time during the ebb was more than two times of resuspension time during the flood.During the observation of Y01, flood discharge of upstream reservoir increased the quantity of runoff. Although the resuspension of bottom sediment was not significantly influenced, the bottom suspended sediment diffusion was strongly restained, especially during the flood phase. Therefore, the decreased diffusion resulted to the lowerening of the total SSC. Furthermore, the variation ranges of instantaneous item of flux decomposition was also reduced, and the landward sediment transport was correspondly decreased..Strong resuspension of bottom sediment is the most important factor that maintain TM of Yalu River. The resuspension in TM not only increases the SSC of water body, but also supply rich sediment source which transported landwards and seawards, respectively.更多还原