长江河口枯季河床沉积物与河床沙波现场观测研究

Field observations on bed sediments and sandwaves in dry season in Changjiang Estuary

于 2 0 0 2年 3月利用浅地层剖面仪、双频道测深仪、旁侧声纳和ADCP流速剖面仪、ENDECO海流仪、OBS测沙仪在江阴至横沙岛航行 1 50km ,取得河床沉积物、河床形态和与此相关的动力因子实测资料。采用沉积学和泥沙运动力学相结合的方法进行研究 ,结果表明 :观测期间该河段河床沉积物颗粒组成以细砂为主 ,中值粒径为 2 φ左右 ,分选较好 ;河床泥沙以单颗粒群体跳跃运动为主 ,在河床上形成沙波形态 ,并发育良好 ;其河床沙波的形成、发展和消失与河床沉积物颗粒度特征和涨落潮水流强弱息息相关。

A series of advanced instruments were applied to get the field data of bed sediments, riverbed shapes and relevant dynamic factors of the 150-km-long reach from Jiangyin to the Hengsha Island in March 2002. The fine sand predominates the bed sediments in terms of granularity of bed sediment on the surface from Jiangyin to the Hengsha Island, the granularity becomes finer and finer from land to ocean. From the cumulated distribution of the bed sediments in the Changjiang estuary, we found that the rolling grains were absent in dry season and the saltation grains jumped twice.The first group was in majority and well-sorted because of the ebb tide, and the second group was in minority and bad-sorted because of the flood tide. The suspended sediment was also in minority and bad-sorted. There was stronger flow and the longer duration during the ebb tide in dry season and the grains could saltate fully and continuously. The form of sandwave was related to the interaction of tidal current and sediment, the sandwaves grew well in the reach from Jiangyin to north of Zhangjiagang port, the lower reach of Nantong and south channel of the Changjiang estuary and so on in dry season, and which became the major type of bed sediment transporting in estuary. In the Hengsha Island, the bed sediments were composed of fine sands and the sandwaves mostly dispersed to the upper reach, but the bed sediments were composed of clayey silt and sandwaves couldn't form in the following north and south passages, which was accordant with the theory of dune formation on the bed. The direction of sandwave was normally vertical to the flow direction, the longitudinal form of sandwave might be symmetry or asymmetry, and the latter had the sharp slope in the lower reach and the slow slope in the upper reach. Near the tidal interface, the tidal current was greater during the ebb tide than that during the flood tide and the forms of sandwaves of the estuary were similar to those of rivers. But in the lower reach of the estuary, the quantities of transportation to the upper and lower reaches were both large, the sandwaves had symmetry forms and round crests. In conclusion, the sandwaves had more complicated influencing factors in the Changjiang estuary than those in the river, and which became the major form of bedload transportion in the Changjiang estuary.