近期长江河口冲淤演变过程研究

基于长江河口1997年以来数字地形图和近期水文泥沙实测资料,分析研究了近期长江河口大量人工整治工程和流域水库工程建造影响下的河口河道自动调整过程。结果表明:1997-2013年河口段中上游河道微冲刷、拦门沙滩顶仍保持淤积外移、口门外侧近海域冲刷的态势略有增强,而其影响原因与历史时期的自然因素影响为主略有差异,近期人类高强度活动的影响贡献率增大。首先,南支至南港和北港中上游河段河床普遍发生冲刷,河床沙活动较活跃,床面微地貌沙波发育更明显,而口门外侧海域地形略有冲刷蚀退,这些变化与流域来沙锐减有直接关系;北支、北港口门、南槽和北槽河道拦门沙河段呈淤积,尤其北槽主航道的拦门沙河段6m水深浚深为12.5m后回淤量很大,这些与拦门沙河道动力结构环境、河口和海域再悬浮泥沙补给有关;局部河段出现强冲和强淤现象,与近期河口工程建造有关。所以,长江河口近期正处在对自然因素变化和人类活动增强的自我缓慢地自动调整和适应过程之中。

Study on recent bed changes of erosion and siltation in Yangtze River Estuary

Based on the digital nautical charts since 1997 and recent hydrologic field observations,the variations of erosion and siltation in Yangtze River Estuary under the influence of artificial regulation engineerings and basin reservoirs are analyzed. The results indicate that since 1997,(1) the morphological features have been undergone by slightly erosion in upper estuary,(2) the mouth bar crest still received deposition and moved seaward,and (3) the nearshore seabed have been increasingly eroded. And the dominant cause on those phenomena has been changed from the original nature factors to recent intensive human activities. Firstly,the riverbed in South Branch (SB),South Channel (SC) and the upper and middle reaches of North Channel (NC) has been eroded overall. The sediment above bed was very active and surface sediment was coarsened. Bed surface sand wave was becoming more distinct,and the nearshore seabed outside river mouth is being eroded slightly. These variations mentioned above are attributed to river runoff and sediment load. Secondly,there was a sediment deposition in the reaches of North Brach (NB),the mouth of NC and the mouth bars of North Passage (NP) and South Passage (SP),especially for the main channel of NP,which matches a big quantity of back silting after the Deep Waterway Project. The reasons why caused these variations are not only changes in the dynamic structure in estuarine mouth bars,but also variations for the supply of sediment resuspension in local area and offshore area. In addition,the severe erosion and siltation in some reaches is closely related to those estuarine engineering constructions. In a word,the Yangtze River Estuary is in slow adjustment and adaptation under changing natural factors and intensive human activities recently.