Coupling an unstructured grid three‐dimensional model with a laterally averaged two‐dimensional model for shallow water hydrodynamics and transport processes

Abstract

AbstractThis article presents a dynamically coupled 3D‐2DV hydrodynamic model, which combines an unstructured Cartesian grid three‐dimensional hydrodynamic model named UnLESS3D with a laterally averaged model for estuaries (LAMFE). Both UnLESS3D and LAMFE are shallow water models, which solve unsteady Reynolds‐averaged Navier–Stokes equations. The coupled hydrodynamic model, named UnLESS, is very suitable and efficient for rivers, lakes, and estuaries, which have not only large waterbodies but also long, meandering, and narrow tributaries. The dynamic coupling of UnLESS3D and LAMFE is facilitated with a semiimplicit scheme called the free‐surface correction (FSC) method. The resulting coupled model UnLESS is unconditionally stable with respect to the gravity waves, bottom shear stress, and vertical eddy viscosity terms. The UnLESS model was tested with an idealized estuary case which has a large basin and two narrow tributaries, providing freshwater flow to the basin. Model results using UnLESS were compared with those using the UnLESS3D model. It was found that the UnLESS model can reproduce the model results of UnLESS3D. The UnLESS model was also applied to Charlotte Harbor, with its major tributaries flowing to its northern part being included in the simulation domain. A good agreement of model results of water level, current, salinity, and temperature simulated by the UnLESS model with real‐time data measured in Charlotte Harbor and its tributaries suggest that the method presented here is robust in dynamically coupling the 3D unstructured Cartesian Grid model UnLESS3D with the laterally averaged model LAMFE.