长江口底沙再悬浮及其影响

【作者】 蒋智勇；

【导师】 程和琴；

【作者基本信息】 华东师范大学 ， 自然地理学， 2004， 硕士

【摘要】 本文以河口中段的沙波分布区为研究区域，选取具有较强代表性的1998年洪季、2000年枯季、2002年枯季末期洪季初期三个年份，覆盖南、北港及南、北槽四个站点的流速、悬沙浓度、盐度、水深、粒度、床面形态、颗粒态及溶解态重金属浓度等特征数据，采用水文学、泥沙运动力学和数理统计学相结合的方法，运用SPSS和Matlab等软件技术手段，着重分析了底沙再悬浮的动力机制、扬动流速、周期特征及其影响等，获得以下结果： 1．野外观测获取的长江口连续时间序列的可视化紊动“猝发”ACP图像数据表明，用水流紊动“猝发”作用解释泥沙再悬浮的动力过程具有合理性，而且水流的紊动“猝发”特征(时间间隔和历时、频率和强度等)与底沙的起扬运动、各种尺度沙波的形成、悬浮泥沙浓度等直接相关。 2．基于扬动流速一般公式，对长江口区流向稳定时期同步观测的垂线平均流速、底部悬沙粒径、水深和泥沙沉速等数据进行回归分析，拟合获得长江口区非均匀细颗粒粘性泥沙扬动流速公式，相关系数达0.85以上。经该公式计算的长江口非均匀细颗粒粘性泥沙扬动流速值大于已有公式计算值，这主要是由于长江口区泥沙为细颗粒粘性泥沙，颗粒的稳定性主要受制于粘结力所致。 3．在长江口沙波分布区，底沙再悬浮的周期性特征是多种不同尺度周期叠加耦合的结果，有4.2h、35min和2min三个显著的周期。其中4.2h的周期是第一峰值周期，可能与径潮流及盐水楔的作用有关；35min的周期是第二峰值周期，可能与该区域发育的中等及大型沙波的运动有关；2min的周期是第三峰值周期，可能与该区域水流的紊动猝发有关。 4．底沙再悬浮泥沙浓度的主要影响因子是盐度、流速、水深和悬沙粒径等，再悬浮泥沙浓度与四个因子的线性回归关系显著，相关系数达0.91。其回归模型可用于预测南港底沙再悬浮泥沙浓度。南槽颗粒态重金属元素可分为三类，重金属元素在该水域进行的是有选择性的置换吸附，且Cu、Zn、As、Cd对重金属污染的贡献率最大。底沙再悬浮能增强水体的自净能力，由于涨、落急阶段再悬浮泥沙浓度高，溶解态重金属浓度较低，水质总体上较转流阶段好。更多还原

【Abstract】 Field measurements of suspended sediment concentration, salinity, water depth, bedforms, grain sizes in the bottom, current velocity at 1 m under water surface were made at four fixed stations in the area that dunes distributed at the South Channel and North Channel, South Passage and North Passage of the Yangtze Estuary in 1998, 2000 and 2002. And the records of viewed near-bed turbulent burst, bed-sediment ejection with a continuous time scale of 14 hours were obtained by Acoustics Suspended Concentration Profiler (ACP). Particulate and dissolved heavy metal concentration were analyzed by Inductively Coupled Plasma-Atomic Emission (ICP-AEC). Statistics methods of correlative analysis, regression analysis, principal component analysis and spectrum analysis are applied for the winnowing of bed-sediment, mechanism, periods and influence of the bed sediment re-suspension. Results show that:1. According to the frequency and intensity of bed sediment re-suspension, three stages within a tide are divided as: (1) during the slack water, the frequency is lower, but the intensity is higher; (2) during the flood or ebb strength, the frequency is higher, but the intensity is lower; (3) during the transition, the frequency and intensity changes positively with the velocity fluctuation. These bed sediment re-suspension ejection characteristics might be due to interval, duration, frequency and intensity of the turbulent burst.2. The winnowing formula of fine-grained gummy sediment particles in the Yangtze Estuary are poly-regression imitated. The correlative coefficients are more than 0.85. The winnowing formula is more applicable than other theoretical and semi-experimental winnowing formula reported in the study area because the particles felt.3. Three remarkable periods of bed-sediment re-suspension in the area appear as:4.2h, 35mmand 2mm.The first peak value 4.2 hperhaps is corresponding to thetidal duration; the second peak value 35 min perhaps is corresponding to medium or large scale sand dunes movement; and the third peak value 2 min perhaps is corresponding to turbulent burst.4. Bed-sediment re-suspension concentration is mainly controlled by four factors as salinity, velocity, water depth and grain sizes. A good linear correlation exists between re-suspension concentration and salinity, velocity, water depth, grain sizes of suspension sediment, and linear correlative coefficient is 0.91. So the regression models are applicable for forecasting the bed sediment re-suspension concentration at the South Channel. The particulate heavy metals at the South Passage can be divided into 3 clusters, and it is also known that heavy metals are exchanged selectively in the area. The water quality is chiefly influenced by the concentration of the dissolved Cu, Zn, As and Cd at the South Passage, and the water quality during the flood or ebb strength is much better than that during the slack water. Therefore, the bed-sediment re-suspension contributes to the water’s self-purification.更多还原