Evolution analysis of Chongming Dongtan wetland in recent 60 years based on digital nautical chart and remote sensing

Abstract

The spatial variation of Chongming Dongtan wetland was monitored using 10 remote sensing images including Landsat MSS,TM and ETM+ data.Nine nautical charts were employed to analyze the evolution of underwater terrain from 1951 to 2006.With the above/under water topographic changes as an entirety,the authors made quantitative and qualitative analysis of geomorphic evolution in the past 60 years at Chongming Dongtan wetland using waterline method and depth contour overlaying.Some conclusions have been reached: ① The dynamics of Chongming Dongtan tend to be stable,characterized by erosion in the south part,deposition in the north,rapid propagation in the middle and alternate erosion and deposition in some coasts under the stabilities of the current Yangtze estuary;② Human activities made important effect on the wetland.Especially,damn in the Baigang tidal channel accelerated deposition in the wetland.Then the 0 m isobath expanded to the east at a stable rate.Although the wetland area was increasing with the human reclamation year by year,the inter-tidal structure of wetland was deviated from the nature state.The proportion of high tidal flat was decreasing and it showed discontinuous spatial distribution at Chongming Dongtan.Because the damn was directly exposed to the outside marine environment,it would reduce the capability of disaster weather prevention.