Internal Wave Model

In general, the influence of wind on the flow velocity field is vital while studying hydrodynamics and sediment transport in lakes, estuary, and coastal areas. Wind effects not only induce current but also generate surface waves with wave height up to several meters. To calculate the total bed shear stress in such areas, the model must take the wave factor into account. The wave parameters such as wave height, wave direction, and wave period are calculated by the SMB (Sverdrup, Munk, and Bretschneider, see Zhen-Gang Ji, 2008) model. The wave direction is the same as the wind direction. This means that the effects of refraction, diffraction, and reflection are not taken into account in this internal wave model.

The internal wave model option doesn't require an external wave to simulate wind-generated wave effects on bed shear stress and wave-induced currents (Dang Huu Chung and P.M.Craig, 2009). The fetch for each cell by wind sector may be viewed in the 2DH View

The Wave Parameter & Options frame allows the user to specify Ks, the Nikuradse sand roughness value as shown in Figure 1. This can be estimated as Ks = 2.5 x d50. The Nikuradse roughness is not the same as the hydrodynamic roughness (i.e., bottom roughness, Z0) used by EFDC to solve the hydrodynamic equations. The Nikuradse roughness is a grain roughness and represents more of a local scale phenomenon.

For the cases of ISWAVE=3 and ISWAVE=4, available only in EFDC+, the wind time series provided in the WSER.INP file is used to compute the instantaneous values of wave parameters with fetch calculated for each cell in sixteen directions. The effect of shoreline and EFDC internal masks are included in the fetch calculations. The resulting wave parameters are then used to calculate total bed shear stress, with bed shear stress linked to the current generated shear stress via the Grant Madsen approach.

From the release of EE5, there has been the ability to internally generate wind-induced waves for bed shears only (ISWAVE=3). This can also include the radiation stresses for the whole water column (ISWAVE=4). These options allow the simulation of wave effects and re-suspension of sediments inside EE.

Figure 1  Waves Module: Internal Wave Model.

As default, the number of wave cells is the same as the model active cells. However, the user can define the number of wave cells by using the Use Subset of Computational Grid checkbox option. When the option is checked, the user then needs to browse the polygon file. The wave cells are defined within the polygon. To allow EE to properly update the Number of Wave Cells, click OK button to exit the Wave form, then LMC to reopen the Waves module, then the Number of Wave Cells is updated on the Wave form as shown in Figure 2.

Figure 2  Waves Module: Internal Wave Model with using subset polygon.

Some parameters setting inside the Wave Parameters & Options as Rotational Radial Stress, Irrotational Radial Stress and Moving Bed Effectactivated options can be used by checking on the option checkboxes.