Analysis Of Reclamation In The Modaomen And Its Effects On Hydrodynamic Environment And Morphological Change

The Modaomen estuary belongs to the Xijiang River Basin of the Pearl River Basin.It is the main channel of the Pearl River system to the sea,and it is the largest port in the Pearl River estuary to transport water and sediment.For 45 years,Modaomen Tidal Flat reclamation area in Doumen District,Zhuhai has reached 179 km2.Reclamation has changed the boundary conditions of the Modaomen River estuary,and the hydrodynamic conditions such as runoff,tide,wave,and coastal flow in the estuary area have changed,causing problems such as tidal surges and saline backflow.Both sides of the Modaomen Estuary are economically developed and densely populated.The Modaomen Estuary Reclamation is used as a sample to study and analyze the changes in the hydrodynamic environment of the estuary and affect the erosion and deposition process of the riverbed.Issues such as evolution lay the foundation and provide a reference for the future development of the Modaomen Estuary and the regulation of the river channel.This article uses 45 years of remote sensing data and measured hydrological and topographic data of the Modaomen estuary to analyze the impact of the Modaomen tidal flat reclamation on the estuary landform,and uses MIKE21 FM to build a two-dimensional mathematical model of the Modaomen tidal current.The changes of average tidal level,high and low tidal level,tidal difference,fluctuation velocity,tidal flux and residual current before and after reclamation in the mudflats of the Damenmen Estuary were analyzed and analyzed by erosion and siltation of the Modaomen Estuary through inversion of measured bed sand data and remote sensing images of suspended sediment.Combined with the comparative analysis of the measured topographic data,the erosion and deposition characteristics of the Modaomen Riverbed in the Pearl River Estuary before and after the 1970～2018 tidal flat reclamation and river channel remediation project were implemented to prove the rationality of the calculation results.the result shows:(1)The reclamation project is the main reason for the change of the Modaomen River port line.The reclamation of Sanzao Island,Hengzhou Island and Hengqin Island led to the shrinkage of the inner sea area of the Modaomen estuary,forming a "one master and one branch" channel structure.From 1973 to the present,the Modaomen Estuary extends to the sea about 17 km,and the estuary reclamation area is about 179 km2.(2)The characteristics of the spatial evolution of the Modaomen estuary channel vary in different periods.Before the modaomen estuary reclamation,the modaomen channel topography evolved relatively stable;from 1984 to 2008,the channel narrowed and the river bed undercut;the single channel outside the Hengzhoukou developed into a branch channel,and in recent years,the east channel has gradually shrunk and the west channel The road develops and extends westward.(3)The Modaomen reclamation project resulted in an increase in the runoff flow rate in the main channel and a large erosion of the undercut channel.The average residual flow rate in the west channel is greater than that in the east channel,and the intensity of the east side residual flow decreases.The trajectory of residual current on the west side of the Hengzhoukou moved to the southwest.In recent years,the runoff has shifted westward after flowing out of the river channel.(4)After reclamation at the Modaomen estuary,the sediment in the main channel during the flood season was substantially washed away,causing the channel to undercut,and the discharge and sediment transport in the west channel were greater than those in the east channel.Suspended sand in the dry season accumulates in the slow flow area formed by the intersection of the falling tide and the coastal current,and the silt is deposited,causing the Dongcha to gradually shrink.The north slope of the bar and sand receded,and the beach top and the south slope were silted.