1998长江全流域特大洪水期河口区床面泥沙运动特征

Micro-features and Their Changes of Bed Configuration in the Changjiang Estuary during the 1998 Disastrous Flood

在 1998长江全流域特大洪水后期用旁侧声纳、热敏式双频测深仪、D .GPS、声学悬沙浓度剖面仪和流速仪等对长江口主航槽南支至南港河段床面泥沙运动进行了走航和定点测量。观测期间为大潮讯 ,水深 13～2 1.3m ,底质粒径 0 0 8～ 0 12 5mm ,平均粒径 0 10mm ;水面以下 1m处流速最大值 2 17cm s、量小值 0 75cm s、平均值 12 9cm s;调查船航速 2 5～ 3.5m s。走航测量获得的大尺度三维底形沙波波长在 2 0～ 30 0m之间 ,波高0 5～ 3.6m之间 ,波长大于 10 0m以上者仅占 7% ,陡坡朝向下游。定点测量获得的连续 14小时沙波平均运移速率为 0 0 9m s。这种罕见的极细砂质大尺度底形沙波由大洪水期强涨落潮流和底沙再悬浮作用所致。伴随着沙波运移实时同步再悬浮的泥沙浓度底部平均值为 0 9kg m3 、最高可达 1 33kg m3 、最低为 0 44kg m3 。它们是长江口下游河槽不稳定的关键因素。

A succession of high\|resolution large\|scale bedform movements composed of very fine sand is shown by the high resolution survey records.They are detected by Thermal Depth Recorder,Sonar Side\|scan,Endeco Current Meter along two profiles,and Optical Suspended Concentration Meter,Acoustic Suspended Concentration Profiler and D.GPS at one fixed station in the Changjiang Estuary during the last period of 1998 disastrous flood.There are several times of those detected during the dry season.These results can provide the practical data about the tremendous quantities of bedload transport,which is the mainly ambiguously long\|standing problem resulting in serious shallowing in docks and navigation channels,especially for the present construction of Deep Water Channel in the Changjiang Estuary.