Evolution Process and Characteristics of Lower Jingjiang Paleo-Channel in Recent 400 Years

Based on the historical topographic maps of the 1930s and 1950s, the 1954 aerial photo,the 1968 US KH-4B military satellite imagery,and the 2016 domestic GF-1 satellite imagery,in this paper,it comprehensively analyses the paleo-channel under the Jingjiang River. It evolved characteristics and inverted the historical changes of its 400 years since the Ming Dynasty. The results show that the paleo-channel of the Jingjiang River section is frequently oscillated laterally,and is constrained by the hard bank slope and artificial revetment project,there are 20-32 km space sway zone along the paleo-channel plane,the morphological form are two: lateral gradual swing along the main squall line and sudden migration of river channels,which are the bases for the inversion of the paleo-channel in the Jingjiang River. Historically,the shaping of the Lower Jingjiang River has undergone complicated processes,such as overflow,branching and diversion,formation of a single straight channel and evolution and development of meandering. During the period of Hongzhi in the Ming Dynasty,meandering currents mainly occurred in Jianli-Chenglingji section,while the section from Shishou to Jianli was only slightly curved. In the late Ming and early Qing Dynasties,Donggang Lake bend and Haohe River bend were cut and straightened naturally. The meandering channel of the Lower Jingjiang River had been traced back to Shishou in an all-round way and formed a series of meandering bends. In the middle of the 19th century,the development of the meander of the Lower Jingjiang River was characterized by lateral movement,narrowing of the meandering neck,retreat of the concave bank circulation erosion,and high thrust of the convex bank. Since then,there has been no major change. The evolution mode of modern river bend of Lower Jingjiang River includes deposition-propelled in convex bank,collapse-back in concave bank,cut-bank and thrown-away-elbow in convex bank,cut-bend,combing drifting central bar with the bank,cluster ditch-flow in concave bank.The role of the river itself is the main reason for its evolution,but the artificial construction of the levee and large-scale cofferdams are important external factors.