长江口浑浊带近底泥沙浓度变化

Variations of near-bed suspended sediment concentration in South Passage of the Changjiang Estuary

基于近底边界层四角架系统观测的水沙过程完整资料,对近底悬浮泥沙浓度的变化及其动力响应关系进行了分析。结果表明:1)近底悬浮泥沙浓度变化过程的特征是多峰性。在一个潮周期内,一般会出现四次明显的悬浮泥沙浓度峰值;2)水体中始终存在一个背景含沙浓度;3)流速的大小并不是决定近底悬浮泥沙浓度大小的唯一决定性因素。潮流加速度、憩流阶段形成的背景泥沙浓度以及床面可供起动的泥沙量同样起重要的作用;4)泥沙浓度变化和动力的响应关系可以归为四类:第一类正响应过程(悬浮泥沙浓度随流速的增大而增大)、第一类负响应过程(悬浮泥沙浓度随流速的增大而减小)、第二类负响应过程(悬浮泥沙浓度随流速的减小而增大)和第二类正响应过程(悬浮泥沙浓度随流速的减小而减小)。综合分析紊动扩散作用、泥沙的起动和沉降作用及床面泥沙的供应率,对近底层悬浮泥沙浓度和动力响应变化的四个过程进行了详细的解释。

Based on the data measured by the TETRAPOD system, we analyzed the variations of suspended sediment concentration （SSC） in the bottom boundary layer （BBL） and its response to dynamics in Turbidity Maximum of the Changjiang Estuary, China. The results show that 1 ） the concentration curve has the characteristic of multi-peak,generally four peaks with a single tidal period; 2） near-bed suspended sediment concentrations are always greater than a certain value, which means there is a base concentration in the water body no matter the current is in slack or rapid state; 3） the inconsistency between the maximum tidal current speed and peak values of near-bed SSC indicated that the quantity of velocity is not the only factor to determine the SSC. The factors, such as the available erosion sediments, the tidal acceleration and deceleration, etc, are also very important; 4） after the detail analysis of the relationship between the SSC and depth-averaged velocity, the response of near-bed SSC to dynamics can be summarized as four kinds of response processes： the first kind of positive-response process in which the SSC increases with the increase of tidal current speed, the second kind of negative-response process in which the SSC decreases with the increase of tidal current speed, the second kind of negative-response process in which the SSC increases with the decrease of tidal current speed, and the second kind of positive-response process in which the SSC decreases with the decrease of tidal current speed.