Internal Wave Model Option
- Kester Scandrett
- Former user (Deleted)
In general the influence of wind on the flow velocity field is important while studying hydrodynamics and sediment transport in lakes, estuarine and coastal areas. Wind effects not only induce the flow current, but also generate surface waves with a 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 imported 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 ViewPlan.
The Wave Parameter & Options form 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 release of EE5 there has been the ability to internally generate wind-induced wave 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 Tab: Internal/External Linkage to SWAN Wave Model