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 fromĀ EFDC Explorer website Continue reading

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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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.