Studies On The Evolution Of The Yangtze Estuary In The Past 35 Years And The Underwater Shipwreck Space Management System

The Yangtze Estuary is the third largest estuary in the world,adjacent to China's economically developed the Yangtze River Delta urban agglomeration.Affected by the natural changes of the basin and the high-intensity human activities,since the mid-1980s,the sediment flux of the Yangtze River into the sea had shown a significant downward trend.This had a huge impact on the evolution of the Yangtze Estuary.In this context,the evolution of the Yangtze Estuary lacked a systematic summary and comparison.Since ancient times,the Yangtze Estuary has occupied an important position in China's waterway transportation,created a rich and profound historical and cultural heritage of the Yangtze Estuary.The excavation work of the underwater relics of the Yangtze Estuary had made a series of important progress since its launch.In recent years,with the continuous decrease of sediment coming from the upstream,the number of underwater relics surveys had increased,and the erosion and deposition of topography may affect the changes of underwater burial conditions.However,there is little research on this aspect,and the application of efficient management of underwater relics in China is not much.Based on this,this study collected the nautical chart data of the Yangtze Estuary from 1982 to 2017,reconstructed the digital elevation model of the Yangtze River estuary,discussed the lateral and longitudinal changes of each channel,and quantitatively calculated the evolution of erosion and deposition in each channel.Based on the measured data and remote sensing inversion of suspended sediment concentration data(SSC),the evolution of the turbidity maximum zone(TMZ)was analyzed.Based on the underwater shipwreck data provided by the Shanghai Cultural Relics Bureau,combined with the quantitative analysis of the river regime evolution,the terrain scouring and siltation and cultural relics burial conditions changes were discussed and initially established the Shanghai underwater shipwreck geographic information management system.The development of the research is of great significance for understanding the changes of the Yangtze Estuary in response to human activities and natural driving effects.It is of great significance for the maritime security department to ensure navigation safety and the systematic development and protection of underwater relics by the cultural relics department.The main findings are as follows:1.The recent overall evolution of the Yangtze Estuary continues the historical evolution of the estuary's outward extension and narrowing,and local sand changes affect the Yangtze Estuary and channel stability.In the past 35 years,the 0 m,-2 m and-5 m contour lines of the Yangtze Estuary have clearly e xtended outwards in the Nanhui east beach.Chongming east shoal,Hengsha east shoal,Jiuduan shoal and Hengsha east shoal have continued to accumulate in the southeast.In the situation,the sand changes in the local river section,such as the siltation of the Biandan sand,the continuous erosion of the sand body in the Ruifeng sand,and the siltation of the sand dune in the south of the Jiangyan land,affect the stability of the river and the channel.2.The change of erosion and deposition in the underwater delta of the Yangtze Estuary shows obvious spatial and temporal differences.From 1982 to 2002,the area in the scouring state accounted for 62%of the total area of the Yangtze Estuary.The North Channel and the mouth bar'section were obvious,and the average annual scour rate of North Channel reached 10-14 cm/a.In 2002-2013,the proportion of areas in the scouring state fell to 47%.Due to a large number of silt-promoting cofferdam projects in Chongming east shoal,Hengsha shoal,Jiuduan shoal and Nanhui east beach,the sediment was concentrated in the estuary area.The net siltation volume of this year was 1.01×10~9 m~3,and the net siltation area was 455 km~2.The scouring and silting of the study area reached a relative balance,and the erosion degree of the mouth bar was reduced.In 2013-2017,the proportion of areas in the scouring state increased by 55%,and the scouring trend of the Yangtze Estuary increased relatively.The scouring mainly occurred in the main channel of the South Branch and the mouth bar of the North Channel.3.In the past 30 years,the characteristics of TMZ in the Yangtze Estuary were still significant.In the vertical direction,the SSC increased with the increase of water depth,and the maximum SSC was in the vertical direction appears,but in the background of continuous reduction of sediment into the sea,compared with 1982,the SSC in TMZ decreased by about 50%in 2012.The SSC of the near-measured points in the dry season decreased to varying degrees compared with that in 1982,and The increase of SSC had also been significantly reduced.The sharp decrease of SSC in the Yangtze Estuary was the main reason for the difference in the distribution characteristics of SSC in the two phases.4.In the absence of artificial dredging channels,changes in burial conditions of underwater shipwreck,especially depth changes,reflected local scouring and silting conditions.Taking the No.2 shipwreck in the Yangtze Estuary and the No.3shipwrecks in the North Channel as example,when the sea-sweeping survey was carried out in the water near the shipwrecks to find out the obstacles of navigation,the hull was not exposed,the surface of the riverbed was flat,and no sound was seen through the side-scanning sonar and multi-beam sonar.During the underwater archaeological survey in 2016,it was found that some of the hulls were exposed to the riverbed after scouring,and the burial conditions of the shipwreck changed,and the shipwreck position was finally determined.5.Developed the Shanghai underwater shipwreck geographic information management system and realized the systematic management.According to the needs of the Shanghai Cultural Relics Bureau to realize the mana gement of underwater shipwreck geographic information system,Visual Studio 2010 is used as the development platform,SQL Server 2008 is the system database,and the Shanghai underwater shipwreck geographic information system is developed by using Visual C#language and ArcGIS Engine 10.0 components.The management system provides system support for the relevant management personnel of the Cultural Relics Bureau and realizes operational operation.