长江口潮滩沉积物抗剪强度分析

Shear strength of sediment on tidal flat in Yangtze River Estuary

河口潮滩沉积物抗剪强度的大小,直接影响到河口潮滩泥沙运动和冲淤强度,进而对潮滩湿地生态系统产生影响。河口海岸区域沉积物抗剪强度的现场观测研究,长期以来少有定量成果。本文通过对长江口潮滩沉积物的抗剪强度进行现场观测和分析,得到长江口崇明东滩潮滩沉积物抗剪强度大小分布规律和控制因素。结果表明:由陆向海,北部光滩区域抗剪强度逐渐减小,变化范围在0.22～7.04kpa之间;中部光滩区域抗剪强度是先减小后增大,变化范围在0～9.14kpa之间;南部光滩区域抗剪强度是逐渐增大,变化范围在0.36～4.29kpa之间。由北向南,滩地抗剪强度都呈逐渐增大趋势,光滩区域由0.43kpa增加到2.88kpa,植被区域由1.14kpa增大到2.72kpa。由表层到底层,沉积物抗剪强度随着深度的增加而变大。沉积物粒度特征和水动力条件决定了崇明东滩南、北区域沉积物抗剪强度数值的不同。植被根系的加筋作用使得沉积物抗剪强度增大,其值是光滩区域的1.2～4.3倍。随着沉积物密实度的增加,沉积物抗剪强度相应地增大。

There are few quantitative results of shear strength in estuarine and coastal areas of China. The shear strength of sediments on tidal flats has impacts on sediment erosion and deposition processes. Based on the field observation test and analysis of the sediment on eastern Chongming Island in the Yangtze Estuary, the shear strength and its variations are discussed and conclusions are reached. （ 1 ） From the upper to lower flat, the shear strength decreases gradually in the range of 0.22 -7.04 kpa along the northern profiles. It increases in the range of O. 36 -4.29 kpa along the southern profiles. Along the eastern profiles, the shear strength de- creases firstly and then increases in the range of 0 - 9.14 kpa. （2） From north to south, the shear strength has an increasing trend. It varies from O. 43 to 2.88 kpa over bare flats and 1.14 to 2.72 kpa in the salt marsh areas. （3） Below the surface, the shear strength increases with the thickness of deposit. The sediment proper- ties and the hydrodynamics are responsible for the spatial variations of the shear strength. The shear strength in the salt marsh is 1.2 - 4. 3 times larger than that on the bare flat. In addition, the shear strength becomes smaller with decreasing deposit compactness.