Vertical viscosity and diffusivity in EFDC model

In EFDC model, subroutine CALAV calculates vertical viscosity and diffusivity. There are three options available to calculate the vertical viscosity and diffusivity. The three methods are :

a) Galerpin
SFAV0= 0.392010
SFAV1= 7.760050
SFAV3= 6.127200
SFAB0= 0.493928
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Extracting the tidal database from ADCIRC to use as an open boundary in EFDC

In EFDC model, often times we need to do modeling in coastal areas. In coastal areas, the flow exchange takes place between the freshwater and the salt water. So, to model coastal areas we need to use the open boundary condition. Commonly used open boundary condition types are water surface elevation (clamped boundary) and harmonic boundary conditions.

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Using tides in EFDC model

In EFDC there is an option to use the harmonic constituents or tides are the boundary conditions. It is very important to understand all the parameters in the EFDC model. The model allows you to enter the Harmonic constituents symbols and the period and amplitude and phase for each of the tide constituents.

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Converting HECRAS data into x,y,z form

HEC-RAS is a model that allows to perform one-dimensional steady
flow, unsteady flow, sediment transport/mobile bed computations, and water
temperature modeling.

THE data stored as geometry in HECRAS can be output into GIS data.
If the data stored in HECRAS were properly georeferenced while entering the
data the accurate set of data could be extracted from HECRAS.

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Using EFDC Explorer to Set up the EFDC

EFDC Explorer, a pre processor and post processor developed from Dynamic Solutions can be used to faciliate the model input preparation, analysis, calibration etc. There are three versions of EFDC Explorer. They are Web version (free and hydrodynamic part only), trial version (30 days trial with full functions integrated) and full version (hydrodynamic, sediment transport and water quality).

Recently, a latest version of EFDC Explorer is released and the version is EE 6.

You can download EFDC Explorer on this website:

You can ask several EFDC related and EFDC Explorer related questions on their forum. However, the response from the forum is pretty slow.

Another advantage of using EFDC Explorer is that you can create the simple grids easily and you can import the grid created from several third party softwares.

I hope your simulation process gets rolling.

If you know any other non-commercial software or commercial software that can be used to pre process and post process EFDC model, please write in the comments.

Errors in EFDC Model

EFDC model is quite a complex model and can be used for several applications. However, at the same time it is very difficult to debug the model.

In several instances, you may encounter the error messages such as “Negative depth in Cell Centers” and “Maximum Iterations Exceeded in External Solution”. These error mean that the model is not stable. So the things you need to go back and look are initial conditions, bathymetry. Another thing you may try to do is to decrease the time step. By decreasing the time step the model would be able to model for sudden increase in flows.

Another thing you may try is to increase the Smagorinsky coefficient to make the model stable. You may also disable the HMD and you may get the model working fairly.

I think this tip would be very handy to all the EFDC users since I have been a EFDC user for a while.

Do you know any other methods or parameters you can adjust so that you can make your model stable ? Please share your ideas in the comments.

Calibration in EFDC

EFDC is a short form of Environmental Fluid Dynamics Code. It is originally developed by John H. Hamrick and this is now curated by Tetratech Inc.

The model is quite complex in itself. The process of creating grid , selecting appropriate boundary conditions and finding the input necessary for the model is quite burdensome at times.

I have surpassed those hurdles and now prepared for the calibration of the model. I have been through several papers on EFDC and have read what they have done for the calibration. The common parameters the authors have used for quite a bit are as follows :

a) bottom roughness height

b) Wind drag coefficient

c) Solar radiation (increasing or decreasing)

d) WInd sheltering.

e) Adjusting Bathymetry

f) Appropriately using wind series.

Well, if you have developed your model properly, then adjusting these parameters may direct you to the good shape. Sometimes you may encounter the errors such as maximum iterations exceeded etc. Since the model doesn’t exactly tell you what was the error. The probable solution of such kind would be to change the iterations number to some bigger number for eg. say 2000. You may also try using small time step and rerun the model.

After calibration, we need to do some statistical analysis to access whether our model is working properly or not.

The parameters such as NES (Nash Sutcliffe Efficiency) , R square, MBE and RMSE can be used to see whether our model is working properly or not.

I would recommend to use EFDC Explorer since it is visual and you can easily figure out some minor mistakes.