大河口潮滩地貌动力过程的研究-- 以长江口为例

该文阐述河口潮滩的发育依赖于河流泥沙来源、河口动力和海底地形诸方面的有利条件.长江口潮滩在世界大河三角洲潮滩发育中独具特色.大河口潮滩的平面形态有“长条状”、“裙状”、“沙咀状”和“江心洲”型,横剖面形态有“宽缓型”、“陡岸型”和“侵蚀崖型”.主河道两侧潮滩水流基本上是往复流,但岛屿面向外海一侧的潮滩是旋转流.潮滩近底流速随着高程的增大而减小.虽然潮汐始终是潮滩水动力的控制因子,但径流起着加强落潮流和改变流速不对称性的作用.潮滩上的波能随风力、水深、滩坡和植被状况而变化.长江口潮滩水体属高浑浊水体,悬沙浓度变化于每升几百毫克至每升几万毫克之间.在总体迅速淤涨的背景下,大河口潮滩存在不同时间尺度的冲淤循环.

A Study of Intertidal Flat Morphodynamics of A Large River Mouth: Yangtze River Mouth

The development of intertidal flat in river mouths depends on favorable conditions such as riverborn sediment supply, estuarine hydrodynamics and morphology of seabed. The intertidal flats of the Yangtze River mouth benefit from these conditions. For a large mouth, there are different types of intertidal flats: "attached bar", "spit" and "isolated bar" in relation to the land, and "broad flat", "sharp bank" and "eroded cliff" according to the shape of cross-shore profile. Tidal currents on the flat are basically back and forth along the river channel banks but gyre on the seaward side. The flow speed is gradually reduced with increase in elevation along the cross-shore profile. The river discharge strengthens ebb flows and modifies current asymmetry especially on the lower flat in neap tide, although hydrodynamics over the tidal flat is tide-dominated. Wave height over the tidal flat is normally limited to a few decimeters although it changes with water depth, slope and wind climate. Intertidal flats of the Yangtze River mouth are characteristic of high turbid water (the suspended sediment concentration is from hundreds of mg/l to thousands of mg/l. There are different time-scales of accumulation and erosion on intertidal flats of large mouths, although rapid progradation is a trend.