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Figure 1. The framework of the CMS and its components.
Coastal processes simulated by the CMS.
The Coastal Modeling System (CMS) is an integrated two-dimensional (2D) numerical modeling system for simulating waves, currents, water levels, sediment transport and morphology change, and salinity and temperature. The CMS was developed for evaluation of navigation channel performance and calculation of sediment exchange between inlets and adjacent beaches. This PC-based, easy-to-use, accurate, and efficient modeling tool provides planners and engineers with essential information for improving the usage of USACE Operation and Maintenance Funds and designing and managing coastal engineering and navigation projects, for which the system was identified by the USACE Community of Practice (CoP) as a preferred model.
Two major components of the CMS are the CMS-Flow and CMS-Wave models (Figure 1). CMS-Flow is a coupled hydrodynamic and sediment transport model capable of simulating depth-averaged circulation, sediment transport, and salinity and temperature due to tides, wind and waves, and the resulting morphology change. The hydrodynamic model solves the conservative form of the shallow water equations. The terms included in the equations are the Coriolis force, surface wind stress, bottom stress, vegetation flow drag, wave radiation stress, surface wave roller, and turbulent diffusion. The sediment transport is calculated by a non-equilibrium advection-diffusion model. Depth-averaged salinity and temperature are simulated with the standard advection diffusion model. The calculations include freshwater inflows, evaporation and precipitation, and air-water heat exchange.
Two solvers are implemented in the CMS-Flow code. The implicit solver uses the SIMPLEC algorithm on a non-staggered grid to handle the coupling of water level and velocity. Primary variables, u and v velocity components, water levels, are stored on the same set of grid points. Fluxes at cell faces are determined using a Rhie and Chow type momentum interpolation method. The explicit solver uses a staggered grid with velocities at the cell faces and the water levels and water depths at the cell centers. All equations are solved using the finite volume method on a non-uniform Cartesian grid, which is a discretization scheme that has been proven highly successful in approximating the solution of a wide variety of conservation law systems in integral control volume form.
CMS-Wave is a spectral wave transformation model. The finite difference method is used to solve the steady-state wave-action balance equation on a non-uniform Cartesian grid. Shallow water processes in the CMS-Wave model includes wave shoaling, refraction, diffraction, reflection, wind wave generation and growth, dissipation due to bottom friction, white-capping and breaking, wave-current interaction, wave runup, wave setup, and wave transmission through structures.
The Surface-water Modeling System (SMS) provides the coupling interface between CMS-Flow and CMS-Wave, which is also used for data preprocessing, grid generation, model setup, and post-processing of modeling results. The hydrodynamic and wave forcing calculated by the CMS can also drive a stand-alone Lagrangian Particle Tracking Model (PTM) developed at CHL. The linkage between the CMS and the PTM is carried out via the SMS interface as well (Figure 1).
The CMS has been extensively verified with analytical solutions and validated with field and laboratory datasets covering a wide range of conditions. The CMS applications have covered various project sites in the US and around the world. The studies include the analyses of navigation channel performance; design and rehabilitation of jetties and breakwaters for coastal protection; realignment and sediment exchange around coastal inlets and adjacent beaches; determination of best dredging and placement options for improved regional sediment management (Figure 2).
Figure 2. Simulated coastal processes at Merrimack Inlet, Massachusetts.
The CMS executable is available for free from the CMS Release Page, can be run stand-alone or through the SMS interface. CMS help is available through workshops, webinars, on-site training, and wiki pages. For more information, please visit the CIRP website https://cirp.usace.army.mil/.