The Turbulence Options frame displays the current settings for various hydrodynamic options such as Horizontal Viscosity and Vertical Viscosity and the Standard Computational Scheme for vertical turbulence. These options and parameter settings can be selected and modified by clicking on the Modify button. These options are described in the following sub-sections.

Turbulent Diffusion

Figure 1  shows the main form for the computational options for the horizontal and vertical eddy viscosities and diffusivities.  The parameters and options have been grouped according to which dimension they are used for, i.e. horizontal or vertical. 

Figure 1   Hydrodynamics Options: Turbulent Diffusion.

The Horizontal Kinematic Eddy Viscosity and Diffusivities Options form provides an option box which is used to enable the Horizontal Momentum Diffusion (HMD) capability of EE.  If the Disable HMD option is selected, the HMD is set to the Background/constant Horizontal Eddy Viscosity (AHO) set by the user. This is equivalent to the ISHM flag set to 0. 

EEMS supports a spatially variable AHO option.  When the Spatially Vary checkbox is selected, EFDCPlus will compute a separate AHO for each cell using the expression .  This approach reduces the numerical diffusion error when the models have a large range of cell sizes.

The user should set AHD, Smagorinsky’s Coefficient, in the Eddy Diffusivity (Dimensionless) dialog box when using the Activate HMD with Smagorinsky option. When Activate HMD with Smagorinsky is selected (ISHMD=1) then EE will apply the background HMD as well as Smagorinsky’s subgrid if AHD>0. With this option the contaminant diffusion is off and not accounted for.  If AHD=0 then the Constant Viscosity option will be used.  

EEMS also supports a spatially variable AHD option The user needs to check both of the Spatially Vary checkboxes, in which case the Assign button is also enabled.  Selecting the Assign button displays the form shown in Figure 2.  EE uses a new file called AHMAP.INP to store a cell by cell list of AHO and AHD.  If the AHO in the AHMAP file is a negative number, EFDCPlus will use the cell area times the input value to compute the cell’s AHO according to the equation above.

Typically, a user wouldn’t have data for spatially interpolated AHO and AHD, rather it is expected to use this function to assign constant values to certain regions. The AHO and AHD values can be assigned to the whole model domain using operators or constant values. They can also assign values of AHO and AHD to certain regions using polygon files.  Load the polygon file, select the value for AHO or AHD, and select Apply. When the user saved the project EE will create an AHMAP.INP file.

To ensure that the correct values have been assigned to the correct regions, the AHO and AHD may also be visualized in ViewPlan using the Fixed Params viewing option.

Figure 2  Setting spatially varying AHO and AHD. 

When Activate HMD with Smagorinsky, Wall Drag and WC Diffusion is selected (ISHMD=2), then the full HMD is used as well as wall effects. This option also applies diffusivities to all constituent transport, which includes salinity and temperatures. This option should be used when simulating a very uniform flow system is constituent transport is needed. The resulting horizontal diffusivity from these options can be viewed from within ViewPlan provided velocities are also available.  The vertical eddy viscosities and diffusivities (AV & AD arrays in EFDC, respectively) can also be viewed if the user configures the Internal Array Viewer (See Appendix A) to include these arrays. 

The Vertical Eddy Viscosities & Diffusivities frame allows the user to set the Time Advance Filter and Vertical Eddy Viscosity as well as Vertical Molecular Diffusivity.  The Maximum Magnitude for Diffusivity Terms allows the user to set the Maximum Kinetic Eddy Viscosity as well as the Maximum Eddy Diffusivity.

Turbulent Intensity

Figure 3 shows the Turbulent Intensity tab. Generally, only the Vertical Turbulence Options will be changed. At the current time, production runs should set the Advection Scheme to 1 and the Sub-Option to either Galerpin (Sub-option=1), Kantha and Clayson (Sub-option=2) or Kantha (Sub-option=3).

The Vertical Turbulence Limiting Options provide a drop down menu that allows the user to choose from three options: no length scale and RIQMAX limitation; to limit RIQMAX in the stability function only; and finally, to limit both the length scale and RIQMAX. When using multi-layer models and vertical turbulence is limiting, the Limit Length Scale and Limit RIQMAX option provides runs with less likelihood of model crashes.

The Wall Proximity Function also allows the user three options: no wall proximity effects on the turbulence; to be parabolic over depth wall proximity; and finally open channel wall proximity.

The Turbulence Closure Constants may be changed after the Modify check box is selected. However, these constants should not be changed without good justification.

Figure 3  Turbulent Intensities.

Miscellaneous Options

Further turbulence modification options are also available under the Miscellaneous Options tab shown below in Figure 4. These options allow various momentum corrections which may be enabled with the Momentum Correction Flag. When the flag is set to zero momentum corrections are disabled; when set to 1 they are enabled.

Figure 4  Miscellaneous Tab – Momentum Correctors