| The coastal and estuarine areas are located in the intersection between land and sea,densely populated,industrial developed and rapid economic development,where human activities are frequent and the hydrodynamic conditions are complicated under the combined action of runoff and tidal currents at the same time,made their water and ecological environment worsen.Shallow lakes are an important part of the earth's water circulation system.The ecological structure and hydrological processes of lakes have undergone profound changes.The evolution of the lake water cycle is affected by various factors such as wind,topography,aquatic plants and human activities.It is of great significance to study the two-dimensional flow movement and sediment transport in coastal,estuarine and lakes.Combining the characteristics of shallow water,the Navier-Stokes equations are simplified to two-dimensional shallow equation.A depth-averaged two-dimensional mathematical model with explicit format for shallow water is established.The model is based on the unstructured triangular mesh,using the finite volume method to discrete equation,and applied to the hydrodynamic simulation of Dalian Bay with complex boundaries.Model predictions are compared to field observation of water levels and tidal currents.The experimental results are in good agreement with the measured values.A detailed analysis of the flood and ebb tide field near Dalian Bay was conducted.It was found that the tides around Dasanshan Island and Xiaosanshan Island are rotated,the rest is basically reciprocating and there is reflux in the bay.The results show that the model can accurately reflect the changes of hydrodynamic environment in the Dalian Bay within the simulated section,which can be used to simulate and analyze the dynamic conditions of the offshore waters.Taking Lake Taihu as the research object,depth-averaged two-dimensional shallow water equation of the lake with the vegetation is established.The numerical simulation of the hydrodynamic characteristics of the Lake Taihu under the prevailing wind field is carried out.The results indicate that wind plays a major role in forming flow of Lake Taihu,wind speed and wind direction have a great influence on the flow velocity and flow structure,which is an important factor in the formation of the wind-current of Lake Taihu.When the wind speed is large,the flow velocity is large,the wind speed is small,and the flow velocity is small.With the same wind speed and opposite wind direction,the lake current has similar flow patterns and opposite flow direction.Lake Taihu formed different circulation systems under different winds,and the simulated flow structure was the same as previous simulation results.In addition,by using multi-source remote sensing data(Landsat8),the information extraction of aquatic vegetation in Lake Taihu was carried out,and the vegetation and water information of lake wereextracted.The model incorporates the effects of vegetation on flow drag,parameterized by the stem height,diameter and plant density.Based on the numerical simulation of wind-driven currents,the effect of wind-current-vegetation interaction on the flow velocity of Lake Taihu was studied.The results showed that the flow velocity of the Lake Taihu with vegetation distribution was significantly smaller than that of the non-vegetation distribution.In the area of vegetation distribution in Lake Taihu,the flow rate of Lake Taihu is negatively correlated with the parameters of vegetation.In this paper,the MIKE 21 Hydrodynamics(HD)and salinity coupling model of the Liao River estuary was established in association with the collected river hydrological data,and the measured water level and salinity.The model has been employed to study the change of water level,tidal current and salinity in Pink Beach wetland,and the flow field characteristics and distribution are also given.The distribution of vegetation,such as Phragmites communis and Suaeda heteroptera in Panjin area,was obtained utilizing the remote sensing technology derived from Landsat TM satellite for the period 28 th to 29 th June 2017.The influence of vegetation on the hydrodynamic of estuarine wetland was simulated by the varying of Manning coefficient in the bottom friction.The results exhibit that the MIKE 21 hydrodynamic-salinity mathematical model can simulate the water level process,the tidal current process and the distribution of salinity,and the error is within the acceptable range.Wind stress is also one of the important factors that affect the water depth of wetland.The water depth increases obviously driven by the wind.Due to the existence of wetland vegetation,the energy flowing through the vegetation is consumed and the resistance of the flow is increased,which leads to the change of the flow direction in the vegetation area and the obvious decrease of the flow velocity.The simulation of the Pink Beach wetland water flow under different vegetation densities and drag coefficient shows that the flow velocity decreases with the increase of vegetation densities in the areas.What's more,when the density is constant,the increase of the drag coefficient of vegetation leads to the decrease of flow rate in the vegetation area.The flow velocity in the vegetation area has a negative correlation with the vegetation density and the drag coefficient of the vegetation.The results demonstrate that including the effects of vegetation in a numerical model is vital in simulating the hydrodynamic conditions over tidal flat wetland.Runoff exerts a significant effect on salinity changes.When the runoff is low,the salinity of the upstream freshwater runoff pose dilution effect on station is weak,and the plentiful runoff is opposite.Under the same runoff conditions,the vertical distribution of salinity in the pink beach wetland shows a tendency that increase from upstream to downstream.The results of this study can provide scientific reference for the hydrodynamic and salinity conditions for the normal growth of wetland vegetation in Liao River estuary,and will be crucial to wetland conservation. |
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