Hi all, I recently modeled temperature in a reservoir using EFDC Explorer 7( Web version), but experienced some strange problems.

My model consists of 184 cells, the cells have a size of 150m by 150m approximately, the reservoir has a total inflow of 4 million cubic meters per day, average velocity for the whole reservoir is 0.8 cm/s.

The problem is:

1) When modelling flow only, i.e. ISTRAN = 0 for all constituents in card image 6 in the efdc.inp file, the simulated vector field appears normal.

2) When adding temperature, i.e. ISTRAN = 1 for TEM, and ISTRAN = 0 for other constituents in card image 6 in the efdc.inp file, the simulated vector field appears abnormal, seems unstable.

3) Above two cases using measured bathymetry data for model bottom elevation. When modelling temperature with a flat bottom, the simulated vector field appears normal again.

By the way, when adding salinity calculating, I got the same problem.

I also conducted the modelling using EPA EFDC derived from EPA offical websit, and got the same problem.

Why this happened? Could anyone give me some help. Thank you.

Sincerely.

BadMicro

How many layers does you model have? If it is a 3D model then there are certain well known issues with the sigma coordinate transformation. EFDC uses the Ssgma stretch model for vertical layering which can induce numerical errors in horizontal pressure gradient force in the case of stratified flow over steep topography. These issues exist with other models such as POM, ECOM3D, DELFT-3D. DSI has recently developed a “sigma-zed” (EFDC_SGZ) model. This allows for the number of vertical layers to vary over the model domain, thereby reducing the traditional pressure-gradient error associated with the normal implementation of the sigma stretch vertical layering system. The new version is also computationally more efficient than a similarly configured sigma stretch grid, thus making models with 20 to 50 layers or more practical for typical projects.

Thank you for your reply.

The model is a depth-averaged two dimensional test case model, with only one vertical layer.

Please provide a link to your model (input files only) or upload your model and we will try to have a look at it if we can.

As I understand, you are using Full heat balance option on the computational option for temperature. Can you try to run using “CEQUQLW2 method” for computation and see whether you see normal values. Can you show the input files for the model ?

If you cannot share the input files, can you define abnormal velocity vector. Can you show the comparison plot of the results from all models i.e., model with flow only and model with temperature and model with flat bottom ? That way we can find out what might be the issue.

Thanks.

Janesh

Thank you for your replies, I uploaded the model results in the attachment. Thank you! {REMOVED by Admin}

Hi there,

What are the in/outflow in your model? If it is small I think you better to reduce your grid cell-size to have better stabilization of velocity field… Please feed back to us your new results.

Thank you,

// Tinh

Thank you for your reply.

The in/outflow is about 4 million cubic meters per day.

The model I uploaded in the attachment has 754 cells, I conducted a case with only 184 cells, but got the same results. So I think the cell size may not be the problem.