长江河口北槽浮泥消长过程的现场观测

FLUID MUD PROCESSES IN THE NORTH PASSAGE OF THE CHANGJIANG ESTUARY

2 0 0 0年 8月 2 1～ 2 4日 (小潮汛 )和 9月 3～ 6日 (派比安台风过后 ,寻常潮 )在长江河口北槽下段通海航槽中进行定点观测浮泥潮周期变化过程及影响要素 ,本文对这些现场观测资料进行了描述和综合分析。长江河口北槽浮泥由细颗粒粘粒泥沙组成 ,中值粒径为 7.2 3μm ,小于 4 μm极细颗粒泥沙占 32 .7% ;浮泥的发育和运动存在明显的大小潮和涨落潮周期和风暴潮变化规律 ,实测小潮落憩浮泥厚为 0 .96m ,涨憩为 0 .78m ,涨急为 0 .2 0m左右 ,寻常潮落憩浮泥厚为 0 .73m ,涨憩为0 .5 3m ,涨急为 0 .17m左右。若遇小潮汛大风 ,因水位低 ,流速小 ,风浪对潮滩冲刷强 ,带入河槽泥沙多 ,河槽浮泥发育良好 ,反之 (大潮 )浮泥发育差。可见 ,北槽浮泥形成、发育和消失与泥沙来源、水流速等因素有关 ,若遇盐水楔入侵 ,更有利于浮泥充分发育 ;北槽浮泥容重均较小 (γs <1.2 5t/m3) ,而且活动性较大 。

Field measurements of fluid mud (FM) variations during a tidal cycle were conducted in the North Passage of the Changjiang Estuary. The thermal depth sounder recorder Model 449 was used to observe bed features in August and September 2000.The median size of FM was 7.23 μm including 32.7 percent of clay.Near bed FM reached 0.96 m at slack water of ebb tide ,0.78 m at slack water of flood tide and 0.2 m at tidal flood strength during neap tide .During the mean tide the FM reached 0.73 m, 0.53 m and 0.17 m respectively. This suggests the generation of FM by strong wind and low energy of tide. The abundance of FM in the North Passage increases by the front of the salt water wedge. This is consistent with the conclusions of FM with density value of 1.24 t/m\+3 is begin easy to be transported. Especially in navigation channels this phenomenon may occur, as flow of FM on adjacent slopes is enhanced by gravity.