Using EFDC Explorer to compare bathymetry between different models

Often times we will end up having two different bathymetry data sources and we would like to know how different those data sources are. Eventually, we will use those data to create bathymetry in EFDC model.

EFDC model allows an easy comparison between bathymetry at two different models.

For example, we will use an EFDC model of Ohio River which can be downloaded from EFDC Explorer website Continue reading

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Dynamic time step in EFDC model

In EFDC Model there is an option to choose the dynamic time step. The subroutine which controls the dynamic time step is CALSTEPD.f90. In this subroutine, there are four method check which determine the time step. They are as follows:

1) Method 1: Upwind difference in momentum equations.
2) Method 2: Positivity of advected material.
3) Method 3: Implicit bottom friction and rotational acceleration damping
4) Method 4: Limit rate of depth change. Continue reading

Calibration parameters and their range in EFDC model

EFDC is not a self calibrated model. There are several parameters that can be tuned in EFDC model to calibrate the parameters. Calibration is a process of comparing the modeled results with the observed data. If the modeled data and observed data match close then it is said that the model is calibrated. There are several parameters that are used to quantify the calibration process. They are average error, relative error, average absolute error, RMS error, Relative RMS error, Nash-Sutcliffe Efficiency Coefficient. 

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.

Continue reading

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: http://www.efdc-explorer.com

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.