Numerical Investigation Of Tidal Flat Dynamic Geomorphology In The Yellow River Delta

The modern Yellow River Delta was formed in 1855 when the Yellow River reflowed into the Bohai Sea from the South Yellow Sea.The Yellow River estuary has undergone many changes in the past 160 years.The recent change was Diaokou Course divert to Qingshuigou course in May 1976.Qing 8 course artificially made the estuary swing northward.Under the background of the Yellow River's huge amount of sediment deposited into the sea,less than 50 years had accumulated to form a large estuary delta,and it had developed a typical silty coast,and its intertidal flats were broad and flat.There were few deltas in the world that were still expanding.The estuary of the Yellow River diverted from the north to the Qing8 River after the estuary continued to extend to the sea,but the original estuary of the Qingshuigou estuary showed a significant erosion and receding trend after losing the supply of sediment,which indicates the current estuary-sub-delta and abandoned-sub-delta tidal beach coast had significant differences in the dynamic properties.This study based on Delft3 D,and usesd hydrodynamic,wave and sedimentary dynamic model to calculate and analyze the marine dynamics under different combined conditions of seawater and sediment and the evolution of geomorphology under the corresponding conditions.Quantitative analysis of the tidal flat dynamic landform evolution between the old and new estuaries.(1)The current estuary had an obvious erosion trend during the dry period,and the siltation trend was obvious during the flat period and flood period.The siltation intensity of the estuary estuary was proportional to the amount of sediment entering the sea.The current estuary had a significant siltation trend under the effect of tidal current.Although the main trend is still siltation under the condition of wave-current coupling dynamics,erosion also exists in some areas.Abandoned estuaries had an erosion trend under different inflows of sand and different dynamic conditions,but the eroded areas under wave-current coupling tend to be more contiguous.(2)The suspended sediment concentration at the current and abandoned estuary were both high,and the suspended sediment concentration under the wave-current coupled dynamic conditions was generally higher than the tidal current dynamic conditions.The current estuary of the Yellow River was the main Yellow River estuary,and a large amount of sediment entering the sea will be deposited near the estuary.Therefore,the source of high suspended sediment concentration at the current estuary was the injection of the Yellow River.There was no sediment flow in abandoned estuary of the Yellow River,but it was still a distribution area with high suspended sediment concentration.The reason is that the prominence of the abandoned estuary had intensified the current and wave movement.The waves resuspended a large amount of sediment,and the current will move the resuspended sediment to the offshore direction.Therefore,the high suspended sediment concentration at the abandoned estuary was mainly caused by the re-suspension of waves and the lateral transport of re-suspended sediment by tidal current.(3)In the context of the reduction of sediment into the sea from the Yellow River,the current morphological dynamics of the estuary were obviously driven by tidal currents.The morphological dynamics of abandoned estuaries were mainly dominated by waves.This dynamic difference did not change with the changes of the conditions of seawater and sediment.The current amount of sand entering the estuary was closely related to the evolution of estuary geomorphology.The input sediment was mainly transported laterally under the tidal current.Most of the sediment was deposited near the estuary,which made the current estuary shallower and the underwater bank slope tend The trend of slowing and silting was obvious.Although the wave protrudes from the estuary to the current estuary near shore,the wave energy gradually decreases with the depth of the water,and the Yellow River runoff will offset some of the wave energy after entering the ocean.In most cases,the waves have little effect on the current near-shore landforms.There is no river runoff and sediment input at the abandoned estuary,and the prominence of the estuary exacerbates the wave motion.Therefore,the wave would directly affect the near shore of the abandoned estuary,causing the re-suspension of the bottom sediment to increase the suspended sediment concentration and re-suspend sand will leave the place with the lateral flow or tidal current,and the water depth at the abandoned estuary will increase,the underwater bank slope will become steep,and it will tend to be eroded.