江苏中部海岸潮沟形态对滩涂围垦的响应

Rapid response of tidal creek network patterns to the reclamation on the central Jiangsu coast

根据2001-2013年江苏中部海岸的遥感影像和野外观测数据,对滩涂围垦影响下潮沟的形态演变过程进行分析。结果显示,研究区潮沟在大规模滩涂围垦影响下整体有明显的退化和消亡趋势,潮沟集水面积由2001年的293.94km2逐渐降低到2013年的103.40km2,潮沟长度随着其集水面积的缩减呈幂函数减小(R^2=0.98),而潮沟宽度随着潮沟长度和集水面积的变小呈指数方式变窄(R^2分别为0.87、0.93),总体上研究区每围垦1km2滩涂,潮沟长度和宽度分别减小约2.60km和0.67m,在整个滩涂围垦过程中,落潮后期潮滩的主要排水方式逐渐由潮沟排水向滩面排水方式转变。江苏中部海岸潮沟形态在统计上具有多尺度分形结构,总体上研究区分纬值从大到小依次为潮沟分维值、各潮沟系统分维值、单支潮沟分维值。研究区潮沟的分维值(无标度区间25~210内)在滩涂围垦影响下呈波动性降低,由2001年的1.26逐渐降低到2013年的1.13,各潮沟系统的分维值随着其分汊个数减少呈线性降低(R^2=0.89),各单支潮沟的分维值随着其蜿蜒性减小呈线性降低(R^2=0.86)。根据潮沟的退化和消亡过程反推潮沟的起源和发育过程,本研究认为研究区最早出现的一类潮沟可能是陆源水流侵蚀型潮沟,而滩面水流冲刷型和潮流辐聚侵蚀型潮沟是随着潮滩淤积变宽过程逐渐发育的,其最初的发育形态可能是潮滩下部的冲刷凹地。

Tidal creek system,one of the most particular geomorphology units in muddy flat,is widely developed on central Jiangsu coast.This paper focuses on their evolutionary process in response to reclamation activities using TM/ETM＋data of 2001-2013 and field investigation.The watershed area of tidal creeks decreased from 293.94km2 in 2001 to 103.40km2 in 2013 following sequential reclamation,which caused the decreasing of tidal creekslength with power function and tidal creekswidth with exponential function.The average change rate of tidal creekslength and width was 2.60 km and 0.67 mwith 1km2 reclamation.The drainage pattern of tidal flat was changed from tidal creeks to beach,which implied that the tidal creeks systems in study area have a retrograde and demise tendency.The fractal dimension value Dof each single tidal creeks and tidal creek systems were calculated from box-counting method.Results of calculation and analysis indicated that the fractal dimension value Din the region is greater than that of each tidal creek systems,followed by each single tidal creek.The fractal dimension value Din the region is positively correlated with the bifurcation ratio of tidal creek systems,and decreased from1.26 in 2001to 1.13 in 2013with influences of reclamation.The fractal dimension value Dof single tidal creek is positively correlated with the meandering of tidal creek.According to the retrograde and demise process of tidal creeks studied the results suggested that the tidal creek inheriting the runoff from land was the earliest tidal creeks,followed by the tidal creek scoured by the currents on tidal flat and tidal creek scoured by the converged tidal currents,whose primary form could be eroded indentation.