INLET TEST CASE
This coupled example demonstrates the significance of wave-current coupling and includes ROMS coupled to SWAN. The application and methodology was originally developed and implemented as decribed in Warner, Perlin, and Skyllingstad (2008) "Using the Model Coupling Toolkit to couple earth system models", Environmental Modelling & Software, 23, p. 1240-1249.
The test case is a simple tidal inlet system, based on a rectangular basin domain that is 15 km wide by 14 km in length, with a uniform initial depth of 4 m. Model setup parameters are shown in Table 1. The domain is separated into two regions. The seaward (top) region has northern, western, and eastern edges that are open with radiation boundary conditions. The backbarrier region (bottom) is enclosed with four walls and is connected to the seaward region through a 2 km wide inlet. The model is forced by a tide and waves. An oscillating water level is imposed on the northern edge with a tidal amplitude of 1 m. Waves are also imposed on the northern edge with a height of 1 m, directed to the south with a period of 10s.
In the paper as The model is run with two configurations: 1) one-way coupled with wave information passed to the circulation model and 2) two-way fully coupled where the ocean model sends water velocities, water level, and bottom morphologic change to the wave model, and the wave model sends wave height, period, and wave length to the ocean model. The model hydrodynamics were simulated for a period of 2 days with a morphologic scale factor of 10, simulating a 20 day period. In the one-way coupled system, wave heights evolve to a steady state, decreasing southward toward the inlet and showing no effect from the inlet currents (Figure 3). The contour of wave height is straight across the inlet opening showing no sign of current interaction. At the peak of the ebb tide the combined wave-current bottom stresses are maximum near the location of maximum currents. As the tidal currents transport sediment and evolve the sea floor, the bathymetric evolution produces flood and ebb tidal shoals, with a larger ebb shoal. By contrast for the the two-way coupled model results, the wave heights are greatly increased in front of the inlet. The wave height contour lines show increased wave amplitudes in the inlet as the approaching wave interacts with an opposing current. The increased wave heights create combined bottom stresses that are greater than the one-way coupled system, and the peak bottom stresses are located near the maximum wave heights. The morphology evolves a stronger ebb shoal due to the higher stresses and the shoal is displaced slightly further seaward. The coupling of the wave and ocean models demonstrates an important feature that the nearshore wave and circulation dynamics are mutually interactive and accurate modeling of this type of system should include these communications.
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Table 1. Model parameters for the ROMS-SWAN test case 1.
Model Parameter Variable Value length, width, depth Xsize, Esize, depth 15000 m, 14000 m, 4.0 m number of grid spacings Lm, Mm, Nm 75, 70, 10 bottom roughness zob 0.015 m time step dt 10 s simulation steps Ntimes 17280 steps (2 day) morphology factor morph_fac 10 (= 20 day scaled simulation) settle velocity ws 11.0 mm s-1 erosion rate E0 5x10-3 kg m-2 s-1 critical stresses cd, ce 0.10 N m-2 porosity 0.50 bed thickness bed_thick 10.0 m northern edge tide A, Tt 1.0 m, 12 hour northern edge wave height Hsig 2m northern edge wave period T 10 s northern edge wave direction from 00
cpp options:
To compile this test case the user is required to activate:
SWAN_COUPLING ?= on
MPI ?= on
