Multi-scale Time Series Analysis Of The Yellow River Delta Area And Study On The Distribution Of Suspended Sediment

As an important link between the sea and the land,the coastal zone contains abundant natural resources,and the systematic research and analysis the coastline and the changing trend of the water environment of its surrounding sea areas is of great significance for the rational utilization and development of the coastal zone.Therefore,this paper uses the Google Earth Engine(GEE)remote sensing big data platform,combined with GIS technology,to explore the variation law of suspended sediment in the coastline of the Yellow River Delta and its adjacent waters and their influencing factors in recent years.Compared with the traditional manual field monitoring to collect data and the interpretation of satellite images using other remote sensing image processing software,this method is relatively time-saving and fast updating,and is suitable for monitoring and analysis of large area long time series.In this paper,the Yellow River Delta and its adjacent waters are taken as the research area,and multi-source remote sensing images such as Landsat TM,ETM,OLI,and ERA5 datasets are used as data sources to extract shoreline data from 1984 to 2018 and invert surface suspended sediment concentration data from 2014 to 2020.Combined with the runoff and sediment transport data from Lijin Station,wind field,temperature,surface sediment type in the study area,the temporal and spatial law of the total area of the Yellow River Delta,the area of each bank segment,the distribution of surface suspended sediment on the adjacent area and their influencing factors are analyzed.The main contents and conclusions of the study are as follows:1.Temporal and Spatial Variation Characteristics and Causes of the Yellow River Delta AreaThe Yellow River Delta is divided into four areas according to the location and characteristics of the bank section-Diaokou river bank section,Gudong bank section,new river mouth bank section and Laizhou Bay bank section.The following conclusions are drawn: The area of new river mouth bank section shows an increasing trend,but with the decrease of water and sediment supply,the growth rate gradually slows down,and sediment transport and runoff have lag effect on the area of new river mouth bank section.In the early stage,The area of Diaokou river bank section showed a downward trend due to the loss of water and sediment supply after the Yellow River diversion and erosion by the dynamic action of seawater.In the later stage,the decrease rate of the area gradually slowed down due to the increase of artificial shoreline.The area of Laizhou Bay bank section and Gudong bank section is basically stable due to the construction of the shore-fixing project.From 1984 to 2018,the total area of the Yellow River Delta showed a trend of first increasing and then decreasing gradually,and the turning point occurred in 1998.In general,the amount of sediment and runoff into the sea are important factors affecting the area of the Yellow River Delta.However,with the increase of human activities in the coastal zone,unnatural factors have an increasing impact on the area of the Yellow River Delta.2.Qualitative inversion of suspended sediment concentration based on GEEBy analyzing the spectral curve of the sediment-laden water body in the study sea area,a sediment index inversion model was established.After comparing with the previous research results,the same variation trend of suspended sediment distribution was obtained,which verified that the sediment index model can be used to qualitatively invert the surface suspended sediment concentration in the adjacent waters of the Yellow River Delta.According to this inversion model,an online inversion software for surface suspended sediment distribution in the Yellow River Delta was developed based on GEE,which can accurately and quickly invert the surface suspended sediment concentration in the adjacent waters of the Yellow River Delta on a specified date,and using the software obtained the results of the suspended sediment distribution in the wet and dry periods of the study area from 2014 to 2020 to study the temporal and spatial distribution of the surface suspended sediment concentration.3.Spatial and temporal distribution characteristics and causes of suspended sediment concentration in the adjacent waters of the Yellow River DeltaUsing the method of geodetector,combined with factors such as water and sediment volume at Lijin Station,wind field,temperature and type of sea surface sediments,the spatiotemporal characteristics of surface suspended sediment concentration in the adjacent waters of the Yellow River Delta were analyzed,and the following conclusions were drawn: In terms of time distribution,from 2014 to 2020,the distribution range of high-concentration suspended sediment in the study area was larger in the dry season than in the wet season,and the area proportion of high-concentration suspended sediment showed a decreasing trend year by year.In terms of spatial distribution,the surface suspended sediment forms an obvious high concentration area in the new river mouth bank section,and it shows a decreasing trend from the nearshore to the far sea.The results obtained by the geodetector method show that the correlation between the concentration of wind speed and the distribution of surface suspended sediment concentration is the largest,and there is a significant interaction between the influencing factors.At the same time,the temporal and spatial distribution of surface suspended sediment is also affected by natural factors such as tides,residual currents,storm surges,and human activities.