长江口北支河槽容积变化特征的定量分析

Quantitative analysis of the characteristics of channel storage changes in the North Branch of the Yangtze River Estuary

北支河槽容积变化是北支河道演变趋势在定量上的直接表现,河道边界条件和河床泥沙运动是影响河槽容积变化的主要因素。收集1986—2013年长江口北支河道年实测地形资料,利用GIS技术建立不同时期水下数字高程模型,进行北支河槽容积变化和河床冲淤变化特征分析。结果表明,北支岸线圈围和泥沙淤积导致了1986年以来河槽容积萎缩。北支河槽0 m线以下容积共减少约7.110亿m^3,岸线圈围引起河槽容积减少4.000亿m^3,占比56.3%;泥沙淤积引起的河槽容积减少3.110亿m^3,占比43.7%。具体而言,北支上段河槽容积萎缩主要是泥沙淤积所致,其航道开发综合利用应遵循上段的泥沙运动规律特点;中段则是边滩圈围和沙洲并岸引起,边界调整后束流作用加强,河床冲刷,断面形态调整后水深条件更加有利于中段的航道利用开发;下段是泥沙淤积和边滩圈围共同影响所致,泥沙淤积影响略大,但下段沿北岸-5 m深槽始终存在且稳定,具备航道开发利用的河势基础,且南侧河道边界仍具有可圈围的余地。

Change of channel storage is a direct quantitative indication of river bed evolution. Boundary conditions and sediment transport are the major factors to change the channel volume. Topographic data of the North Branch of Yangtze River Estuary from 1986 to 2013 is collected for digital underwater elevation model during different periods by GIS technology. With the models channel storage variation and river bed evolution are analyzed in the paper. The re- sults show that the channel volume under elevation 0 meter decreases 711 million cubic meters in the North Branch of Yangtze River Estuary since 1986. Among those, 400 million cubic meters, accounted for 56.3 per cent is caused by enclosure of side foreland and the rest 311 million cubic meters, accounted for 43.7 per cent is the result of sediment deposition. Specifically, in the upper reach, sediment deposition is the main factors for channel storage reduction and comprehensive development and utilization of the waterway ought to be in accord with characteristics of sediment trans- port. In the middle of the branch, reclamation on marginal bank and growth of sandbar towards bank are the main cau- ses of channel storage reduction. With the boundary condition adjustment, it is strengthened of constraint of river flow and erosion in riverbed, and the bathymetry is advantageous to develop and utilize of the waterway after river cross- section adjustment. In the lower reach, both sediment deposition and reclamation on marginal bank are the major rea- sons for river storage shrinks, while the effect of the former is slightly larger than that of the latter. Because the groove under elevation -5 meters stable exists, river regime has basic conditions for development and utilization of the waterway in the lower reach. And there is margin for reclamation in the future on the south bank.