Coastal Erosion,Suspended Sediment Distribution And Engineering Protection In The Northern Yellow River Delta

Delta is abundant in marine resources.From the perspective of social value and ecological value,delta also plays an important role in resource utilization,port and shipping construction,green tourism and ecological protection.The northern coast of the Yellow River Delta,as a typical erosive coast,whose state is becoming complicated under the influence of long-term coastal erosion,sediment reduction and frequent extreme weather.The coastal erosion effect has become obvious since the balance of coastal erosion and deposition is damaged to varying degrees.It has become a social and practical task to explore the major influencing factors of typical erosive coastal erosion process in the current situation and to put forward corresponding engineering protection measures for the protection of delta coastal in the future.The paper takes the northern coast of the Yellow River Delta as the research area,which is affected by climate change and extensive human activities over the years.Based on the bathymetric topographic data and remote sensing data,the strong erosion area and its related erosion characteristics can be accurately identified.A reliable inversion model of suspended solids concentration is established to analyze the suspended solids concentration in the study area.In order to provide scientific guidance for coastal erosion protection and coastal engineering construction in the Yellow River Delta,this paper analyzes the design standards of protection engineering under different dynamic environment on the basis of clear erosion characteristics and dynamic law of suspended sediment.The main results are as follows:(1)The erosion rate of the northern shoreline of the Yellow River Delta was the fastest in the early stage of the estuary abandonment,and then decreased to varying degrees.From 1976 to 1996,the coastal erosion in the study area mainly manifested as the shoreline retreat,and the phenomenon eased after 1996.In the northern part of the Yellow River Delta,coastal erosion is caused by seabed erosion.Erosion is dominant in the area with shallow 10 m isobath,erosion and deposition can both be found in the area with 10-15 m isobath,while erosion and deposition are not obvious in the area under 15 m isobath.The main reason for the strong coastal erosion is that the amount of coastline erosion in the front of the mouth is greater than that on both sides of the mouth,and the mouth protrudes to the sea.The accurate identification of the erosion characteristics of the study area provides a basis for the study of suspended sediment's spatial and temporal distribution in the strong erosion area,and effectively defines the key protection areas of coastal engineering.(2)The distribution and diffusion of suspended particulate matter(SPM)in coastal waters have an important impact on water ecological environment,coastal geomorphic evolution,aquaculture and coastal engineering.The northern Yellow River Delta is a strong coastal erosion area due to the diversion of Diaokou course.Revealing the variation characteristics and laws of suspended solids concentration in this area is the basis for maintaining the safety of protection projects.The cross validation results of Landsat-8 and Sentinel-2 satellite images show that the suspended matter concentrations retrieved by the two sensors have strong consistency,and the two satellite data can be used in combination.The seasonal variation of suspended solids concentration in the coastal waters of the study area is obvious.The suspended solids concentration is higher in winter and spring,and lower in summer.Autumn is the season when the suspended solids concentration changes from low to high.In winter and spring,the wind and waves are strong in this area.Under the combined action of wave lift and tidal current transport,the sediment in the bottom bed is strongly re suspended,which is the main source of suspended solids.The construction of spur dike group altered the spatial and temporal distribution of suspended solids to a certain extent.(3)Coastal protection engineering plays an important role in preventing waves and tide.To a certain extent,it has also delayed the rate of coastal erosion.According to the hydrological data of the coastal area in the north of the Yellow River Delta in recent years,the design tide level of the hydraulic structures along the Yellow River Delta is calculated by using the cumulative frequency curve.The design high tide level of the seawall is 1.93 m.The design wave height of the hydraulic structures in the north of the Yellow River Delta is 8.4 m with the return period of 50 years.The new standards of seawall design under the influence of global warming are far higher than the construction states of some Seawalls in the north of the Yellow River Delta,such as Gudong seawall and Zhuangxi seawall,which need to be further strengthened to prevent coastal erosion and inundation in extreme weather.Combined with the advanced coastal protection engineering experience at home and abroad,from the perspective of ocean wave energy weakening,ocean flow field altering and ecological vegetation protection,the protection ideas and measures of coastal engineering in the north of the Yellow River Delta are put forward.The purpose of the research is to further maintain the stability of the coastline,restore the ecosystem of the estuary area,maintain the biodiversity,as well as the stability of the natural coastline,wetland and marine landscape.