南通地区江海岸线近40年之变迁——江海岸的侵蚀和淤积

RIVERBANK AND COASTLINE CHANGES IN NANTONG AREA DURING THE LAST FORTY YEARS——EROSION AND SILTING OF RIVERBANK AND COAST

本文根据50—80年代三轮航空照片和卫星照片的解译与野外实地考证,结合50年代以来对该区江海岸线进行动态监测的结果,将南通地区江海岸分为侵蚀型、淤涨型和基本稳定型。从江海岸的形成背景、地质构造、边界条件、江海岸动力,水文泥沙运动以及人类工程诸方面分析了江海岸动态差异的原因。同时指出了在当今海平面不断上升的形势下,本区面临的各种灾害。

Nantong area (in Jiangsu Province), a part of the Yangtze River Delta Plain, is situated on the north side of the Yangtze River mouth. The riverbank and coastline have been unstable and swinging due to erosion and deposition for the last forty years. Through interpretations of aerophotographs and landsat images of different times and also according to field work, changes of the riverbank and coastline from 1950s' to 1980s' have been made clear and the bank and coast can be considered to consist of 3 types: erosion, swinging and basically stable. Coastline from Xinggang Sluice to Dongzhao Port, 123.7km long, is silted forward 50-65m per year, and its intertidal zone is generally 5-15cm wide with a gradient of 0.5-1.2‰. Coastline from the Dongzhao Port to the Haozhi Port, 30km long, is a seriously eroded section with a retreat rate of 150-600m/a. The intertidal zone is 3km in width and has a slope of 2.68‰. Coastline from the Haozhi Port to the Lianxing Port, 45km long, is basically stable, the intertidal zone is 3.5-5.5km in width and the gradient is about 1.1-1.2‰. Riverbank from the Lianxing Port to Jiao Port, totally 165km long, can be divided into 3 parts: from Jiuyu Port to Jiao Port, is a silting-up part; from Yujiao Port to Yingchuan Port, an erosion-depositional part; and the rest is eroded or scoured and has retreated, as far as 200-2200km. A further comprehensive study has been carried out to reveal the mechanism of the riverbank and coastline changes. The factors may be as follows: hydrodynamic conditions of sea and river, transportation of mud and sand, control of geological structures, and bank and coast compositions etc.. The first two are playing the most important roles. The future global sea-level rise will seriously threaten this area and bring about geological disasters, such as collapse and landslide of riverbank and coastline, inundation of sea water and flood and waterlogging. We must take measures to prevent these disasters.