The Effect of Grid Resolution on Hydrodynamic Modeling of Estuarine Water Surface Elevation: Balancing Efficiency and Accuracy

Water surface elevation (WSE) is a fundamental state variable in the hydrodynamic modeling of estuaries. WSE varies with time due to physical processes such as tides, waves, wind, storm surges, and river discharge. WSE is used to predict the extent and duration of flooding events and to assess the impact of sea-level rise on coastal communities. Therefore, the accurate simulation of water surface elevation is essential for understanding hydrodynamics, managing water resources, and protecting coastal communities from natural hazards. Environmental Fluid Dynamics Code Plus (EFDC+) is a hydrodynamic model that has been proven effective in simulating WSE. For efficient and accurate modeling of WSE and other hydrodynamic parameters, a suitable grid resolution is required. EFDC+, developed by Dynamic Solutions International, is a successor to the Environmental Fluid Dynamics Code (Hamrick, 1992). It is a popular 3D finite-difference surface water hydrodynamic model used to simulate WSE based on physical principles in rivers, lakes, and estuaries. This model uses a numerical grid to divide a water body into discrete cells, and the mass and momentum conservation equations are solved for each cell at each time step to simulate the changes in water surface elevation over time. EFDC+ uses numerical grids to divide the spatial domain into discrete sections, or cells. Each grid cell represents a specific volume and the properties of water in that volume, such as depth, water surface elevation, salinity, and temperature. A curvilinear grid is a type of grid that has been adopted by some studies due to its various features. A curvilinear grid is a structured grid with cells that are cuboids or quadrilaterals rather than rectangles or rectangular cuboids. It is the only structured grid supporting non-rectangular/square spaces. Hence, cylindrical or spherical forms can be wrapped in a curvilinear grid to simulate or visualize their form accurately. This study used curvilinear grids of different numerical grid resolutions in the EFDC+ hydrodynamic models due to the efficiency of curvilinear grids in simulating hydrodynamic processes. Numerical grid resolution refers to the size of the computational grid used in the EFDC+ hydrodynamic model to simulate water flow and other related processes. A finer grid resolution means that the model can capture smaller features and details in the flow, while a coarser grid resolution means that the model can only represent larger-scale features and may miss some of the smaller-scale processes. The grid resolution can have a significant impact on the accuracy of the model results. A coarser grid resolution may lead to inaccuracies in the simulation of small-scale features, such as eddies or turbulence, which can affect the overall flow patterns and transport of water and model accuracy. Conversely, a very fine grid resolution can lead to high computational costs. The objective of this study is to compare modeled WSE using three grid resolutions: fine, medium, and coarse. Surprisingly, each of the three resolutions performed similarly. Future work will investigate the effect of grid resolution on modeling salinity and develop and compare even coarse grid resolutions.