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Chongming Dongtan salt marsh near-bottom water and suspended sediment change process research

Author: CaoHui
Tutor: HeBaoGen；WenJiaHong
School: Shanghai Normal University
Course: Physical Geography
Keywords: Chongming Dongtan Salt marsh near-bottom Level of velocity Shear stress Suspended sediment concentration Average particle size Suspended sediment grading
CLC: P333.4
Type: Master's thesis
Year: 2008
Downloads: 141
Quote: 2
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Abstract

With the rapid development of the cities in the Yangtze River Delta, the Yangtze estuary intertidal salt marsh potential use of resources and ecological environmental benefits more and more people are concerned, their research also gaining the attention of experts and scholars. Tidal flat salt marsh by the land and sea interactions, the strong role of trend hydrodynamic, sediment transport and material exchange frequent. It not only plays a coastal barrier protection response is also very sensitive to environmental changes at the same time. Near bottom of the salt marsh tidal flat sediment suspended, settlement, the most direct exchange places, its flow and sediment transport mechanism is the hot issue of the tidal flat erosion and deposition and material circulation research. Chongming Dongtan salt marsh area as a study area, select the observation period, near the end of the three-dimensional flow rate, water level by the measured trend in spring (May) and summer (July-August), the near-bottom suspended sediment concentration and average a number of indicators such as particle size, salt marsh plant Scirpus Scirpus role in the tidal process near the bottom of the water and suspended sediment characteristics changes, the following main conclusions: (1) the measured data of the spring and summer small salt marsh near the underlying trend of the average flow rate of the overall 3.24cm/s-7.29cm/s, significantly less than the average vertical velocity (11.75cm / s); the tide flow rate greater than the neap tide, about 1.5-2.1 times; Fluxes average flow rate of (5.73 cm / s) much the ebb (4.03cm / s). Tide ebb phase, respectively, to form a peak phase of the onshore and offshore flow rate, which is more obvious to the peak of velocity; neap tide peak ebb stage was not significant, the flow rate of the basic trend of the mid-larger. Utilize Vectrino flow meter measured three-dimensional velocity data, through the the TKE method nearly underlying flow turbulence energy and shear stress near the bottom of the tide of the average near-bottom shear stress (1.2N / m ~ 2) greater than neap (0.7N / m ~ 2). Neap near the bottom shear stress in the process diagram presents \shear stress (1.33N / m ~ 2) is slightly larger than the ebb (1.08N / m ~ 2). The near-bottom shear stress with neap tide level rises increases, larger values ??generally appear in the trend of the mid. (2) the use of Solitax sc100 Turbidimeter measuring salt marsh near the underlying trend of turbidity value, suspended sediment concentration data obtained through on-site sediment calibration method. The spring tidal cycle average suspended sediment concentration 2.45g / L, the average of the high tide stage suspended sediment concentration (2.64g / L) is greater than the ebb stage (2.25g / L); summer tidal cycle average suspended sediment concentration of 0.8g / L, tide stage average suspended sediment concentration (0.79g / L) is slightly less than the ebb stage (0.8 g / L). LS 13 320 laser diffraction particle size analyzer measurement collecting water samples hanging sand tidal cycle synchronization. Salt marsh near bottom suspended sediment particles generally smaller average particle size of 15.2μm, the average particle size of the tide cycle (16.6μm) larger than the small tidal cycle (13.8 μm); suspended sand gradation of fine silt and clay content, accounting for 69.9% of the total volume. (3) through regression analysis found that the salt marsh near the bottom shear stress (or turbulent energy) was a significant positive correlation with the level of velocity, the correlation coefficient R2 ranged from 0.57 to 0.83. Not found in the salt marshes near the underlying direct relationship between suspended sediment concentration and level of velocity significantly, but at the high water mark of the tide cycle stage, smaller tidal current velocity, Near bottom suspended sediment concentration peak, the upper layer of the spring high-water stage suspended sediment sedimentation obvious. Near the bottom of the salt marsh suspended sediment particle size changes with the level of the flow rate there is a positive correlation, two quarters of the correlation coefficient R2 of 0.77 and 0.66, respectively. Change with the flow rate of change of the average particle size of suspended sediment in the tidal cycle similar: an average particle size of more than presents \Mainly coarse particles suspended sediment gradation in coarse silt sediment content changes significantly the velocity response. (4) neap tidal cycle by two quarters of data comparison, the height of the spring marsh surface salt marsh vegetation Scirpus Scirpus (13.9cm) and density (1056 / m ~ 2) were significantly less than in the summer (21cm, 1854 / m2), the the the spring salt marsh near the bottom of the average velocity (5.47cm / s) and shear stress (1.27 N / m to 2), suspended sediment concentration (2.45g / L), and the average particle size (20μm) are greater than the average tidal cycle summer (4.56cm / s, 0.79N / m ~ 2, 0.8 g / L, 12.6 μm). The results show that with the plants, the slow flow of salt marsh vegetation, energy dissipation, and the role of adhesion and interception of suspended sediment gradually.

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