Grain Size Characteristics And Dynamic Deposition Of Surface Sediments In Tidal Flat Of The Yellow River Delta

Due to the high sediment concentration of the Yellow River and the flat terrain and loose soil in the lower reaches of the Yellow River,the channel at the end of the Yellow River frequently swings in the alluvial fan of the Yellow River Delta.Under the interaction of land and sea,the front of the Yellow River Delta developed a wide tidal flat.As an important reserve land resource in China,tidal flat plays an important role in improving coastal protection capacity,increasing potential land resources and protecting biodiversity.However,under the influence of climate change and human activities,the flow-sediment processes and hydrological conditions in the Yellow River Delta have undergone dramatic changes,as have the geomorphological evolution,sedimentary processes,hydrodynamic characteristics,water and sediment relationships,and the movement characteristics of particulate matter in the tidal flat.Therefore,the analysis of grain size characteristics and dynamic deposition of surface sediments in Yellow River Delta tidal flat can deepen the understanding of the evolution law of coastal dynamic geomorphology in Yellow River Delta,and provide geomorphology basis for the protection and restoration of Yellow River Delta tidal flat.In this thesis,the tidal flat of the Yellow River Delta was taken as the research area,and the region was divided according to the evolution state of coastal landform and the state of scour and silt.And the grain size of 229 tidal flat surface sediment samples were used to analyze the grain size characteristics of different sub-delta tidal flat surface sediments.Combined with measured spectral data and remote sensing image data,a quantitative remote sensing inversion model of surface reflectance,grain size components and grain size parameters of surface sediments were established,and were compared the spatial distribution characteristics of sediment types and grain size parameters on the surface of tidal flats in different sub-deltas.On this basis,the two-dimensional grain size trend model(GSTA model)was used to simulate the grain size trend of surface sediments in the study area,and the relationship between the distribution of tidal flat surface sediments and the hydrodynamic conditions of the Yellow River Delta was discussed in combination with the flow channel changes of the Yellow River,the variation characteristics of sediment into seawater,the changes of the delta shoreline and the hydrodynamic conditions of the ocean.The results show:(1)Through particle size analysis of collected sediment samples,it was found that the sediment samples had the highest content of silt components,followed by sand components,and the lowest content of clay components.According to Sheppard triangular classification,sediment samples are classified into 4 types,namely silty sand,sandy silt,silty sand,and clay silt.Using graphical methods to calculate the grain size parameters of sediment samples,the average particle size distribution range is 2.97Φ～7.34Φ,with an average value of 4.96Φ;the distribution range of sorting coefficient is 0.78～2.91,with an average value of 1.27;the distribution range of skewness coefficient is-0.41～0.50,with an average value of 0.34.According to the Fleming’s triangle diagram method,the particle size data of sediment samples are distributed in areas I,II,and III,indicating that the hydrodynamic conditions of the tidal flat in the Yellow River Delta are generally strong.(2)Based on the correlation analysis of surface reflectance,grain size component content,and grain size parameters of sediment samples,the band with the highest correlation was selected as the characteristic band,and 3 quantitative remote sensing inversion models for grain size components and grain size parameters of surface sediment in the northern abandoned delta tidal flat,the Qingshuigou sub-delta tidal flat,and the southern abandoned delta tidal flat was constructed.These models were the derivative spectral reflectance model based on measured spectral data,the single band factor regression model based on hyperspectral remote sensing image data,and the support vector machine model.The ability of each model in the inversion of sediment particle size composition and particle size parameters was evaluated.Through the comparison and analysis of the inversion accuracy of the above three models,according to the principle of the maximum correlation coefficient(R~2)and the minimum root mean square error(RMSE),the support vector machine model was finally selected as the quantitative remote sensing inversion model for the grain size components and grain size parameters of the surface sediments in the tidal flats of each subregion of the Yellow River Delta.(3)Support vector machine(SVM)model was used to retrieve the percentage content of grain size components in the surface sediments of tidal flats in various regions of the Yellow River Delta,and the spatial distribution of sediment types was obtained using the Shepard triangle classification method.The grain size components of the surface sediments of the tidal flats in each region of the Yellow River Delta are mainly composed of silt,followed by sand,and the clay component is the least.The content of clay and silt gradually increases and sand gradually decreases from sea to land.The surface sediment types of the northern abandoned delta tidal flat include 3 types:silt,sandy silt,and silty sand,mainly composed of sandy silt;the main type of surface sediment on the Qingshuigou sub-delta tidal flat is silt;the surface sediment types of the southern abandoned delta tidal flat include 3 types of silt,sandy silt,and silty sand,mainly composed of silt.(4)The spatial distribution characteristics of surface sediment particle size parameters in tidal flats of the Yellow River Delta were retrieved using a support vector machine model.The average grain size,sorting coefficient,and skewness coefficient of surface sediments from the northern abandoned delta tidal flat are 4.59Φ,1.23,and 0.31,respectively.The Qingshuigou sub-delta tidal flat are 5.22Φ,1.60,and 0.20,respectively;The southern abandoned delta tidal flat are5.16Φ,1.21,and 0.20,respectively.By comparing the grain size parameters of tidal flat sediments in various regions,the average grain size of the surface sediment in each zone’s tidal flats is as follows:Qingshuigou sub-delta tidal flat>southern abandoned delta tidal flat>northern abandoned delta tidal flat,it is found that the surface sediment particles of the northern abandoned delta tidal flat are the coarsest,while the surface sediment particles of the Qingshuigou sub-delta tidal flat are the smallest.The sorting coefficient of tidal flat surface sediment in each division is between 1 and 2,indicating that the sorting of tidal flat surface sediment in each division of Yellow River Delta is poor.The average skewness coefficient of the surface sediment of the northern abandoned delta tidal flat is between 0.3 and 1,indicating a very positive skewness.The surface sediment of the southern abandoned delta tidal flat and the Qingshuigou sub delta in the south is between 0.1 and 0.3,indicating a positive skewness.The spatial distribution characteristics of particle size parameters in the surface sediments of tidal flats in various zones are relatively consistent,showing a trend of gradually increasing average particle size from sea to land,slowly decreasing sorting coefficient first and then slowly increasing,and slowly decreasing skewness coefficient.(5)By simulating the particle size trends of grid sampling points with a sampling interval of250 m at different feature distances,the optimal feature distance is determined using image similarity discrimination method.Considering the average width of tidal flat in Yellow River Delta and previous research experience,when the grid sampling point spacing is 250 m and the characteristic distance is 375 m,it can better reflect the migration trend of sediment particle size in the study area.(6)On the basis of remote sensing inversion of grain size parameters of surface sediments in tidal flats of Yellow River Delta,the spatial distribution map of grain size parameters was resampled to 250 m,and the characteristic distance was 375 m.The two-dimensional grain size trend model(GSTA model)was used to simulate the grain size migration trend of surface sediments.The surface sediments of tidal flats in various regions of the Yellow River Delta generally exhibit a migration trend towards the north and northeast,which is consistent with the grain size trend of the measured samples.The surface sediment transport trends of the northern abandoned delta,the Qingshuigou sub-delta and the southern abandoned delta are SW–NE,SE–NW and SW–NE respectively.By analyzing the particle size trend of surface sediment on typical tidal flats,it is shown that the particle size migration trend of surface sediment on tidal flats is jointly influenced by factors such as the inflow of water and sediment from the Yellow River,marine hydrodynamic conditions,and human activities.(7)Based on the spatial distribution characteristics of grain size and the migration trend of grain size,combined with the changes of the Yellow River flow path,the variation characteristics of sediment entering seawater,the changes of the delta shoreline and the hydrodynamic conditions of the ocean,the relationship between the distribution of tidal flat surface sediment and the hydrodynamic conditions of the Yellow River Delta was discussed.The northern abandoned delta tidal flat face both normal and strong wave directions,with strong wave action.The tidal current is controlled by the tidal waves in the Bohai Bay and moves in an E-W direction,with the ebb tide dominating the sediment transport.Under the combined influence of waves and currents,a large amount of fine sediment is lifted by the waves and washed away with the currents,causing strong erosion of the coast and continuous erosion of the shoreline.The Qingshuigou sub-delta tidal flat is mainly affected by runoff,wind waves,and tidal currents.In the current estuary area,runoff and ocean dynamics are basically in equilibrium;in the old estuary area,due to the existence of a high velocity zone in the sea area near the east side,the wind wave and tidal current erosion in the front edge of the sand mouth is strong,fine sediment is lifted and washed away,and the shoreline is constantly eroded.The southern abandoned delta tidal is mainly influenced by the tidal current field on the west bank of Laizhou Bay.The northward rising tide on the west bank of Laizhou Bay and the southwestward rising tide on the south side of the Yellow River mouth support each other,and some sediment deposits on the south side of the Yellow River mouth.Due to the fact that the flow velocity of the rising tide is smaller than that of the falling tide,and the falling tide flows in the northeast direction,the falling tide has an advantage in sediment transport,and sediment is transported in the northeast direction.