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Greg Nelson

MT3DMS Transport Observation Package in GMS

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I am using GMS version 6.0 and am familiar with using the Observation coverages for MODFLOW. I have read in the tutorials and help that the MT3DMS concentration observation package is available (TOBS). I am unable to figure out how to create a concentration observation coverage in the Map module or to use the TOBS package in GMS.

When in the Grid module, under the MT3D menu, there is an item titled "Transport Observation Package". This opens a dialogue box. I check the "Compute concentrations at observation points" box and get the message, "No observation coverages defined." I thought by chance, if I created a "head" observation coverage, by default the concentration coverage would be created; this is not the case - I still get the same message.

I am familiar with MT3DMS and with how to use the TOBS package. But I would prefer not having to go to all of that hard work in text editors outside of GMS. The GMS help menu says this option is available:

"Transport Observation Package

"The Transport Observation Package (TOBS) package is used to provide summaries of simulated concentrations at observation wells and mass fluxes at source sink objects.

"Observation Wells

"With previous versions of GMS, it was possible to associate observed concentrations (in addtion to heads) at observation wells. When a transport solution computed by MT3DMS was read into GMS, the simulated concentrations at the observation well were found by interpolating from the surrounding cell centers to the obesrvation well location. This interpolation was peformed internally to GMS at the instant the file was imported. With the new TOBS package, the interpolation and summation of the simulated concentrations is performed internally to MT3DMS.This provides a number of advantages, including the following:

"The summation of the simulated concentrations is weighted by MT3DMS according to the size and location of the well screen, similar to how simulated heads are summed by MODFLOW.

"The interval at which the simulated concentrations are reported can be at a different interval than that used to save the concentration data for contouring. The output interval for observation wells can be quite small without requiring a large amount of disk space.

"When an MT3DMS solution is read into GMS, the simulated concentrations are automatically associated with the proper observation wells and the concentration residuals can be plotted. Furthermore, the global error norms (mean error, mean absolute error, root mean square error, etc.) are stored with the MT3DMS solution and can be viewed by right-clicking on the solution in the Project Explorer."

How do I get this option to work in GMS?

Greg

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Here are the steps to create an observation coverage using the mt3d map tutorial in GMS 6.5.

1. Create a new coverage

2. In the coverage setup dialog under the "Observation Points" section toggle on "leachate"

- this creates the proper columns for the points in the coverage

3. Near the bottom of the coverage setup dialog is the "3D grid layer option for obs. pts.:" This is where you decide how you want the observation points assigned to layers in the grid. The easiest option to use is "By layer number".

4. Create a new observation point and then edit its properties and make sure to set the layer number to the appropriate layer. For this tutorial setting the layer to 1 should be fine.

5. Now if you go into the MT3D Transport Observation Package the coverage will appear.

6. Save and Run MT3D.

If you run MT3D and read in the solution you should see an observation target appear next to your point. The target should change as you change time steps on your concentration data set.

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It sounds like the conceptual model hasn't been initialized with the transport option set to active.

If you right click on the conceptual model and go to properties, the "Transport" toggle should be checked - also, "Leachate" should be defined under the "Species" button.

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It sounds like the conceptual model hasn't been initialized with the transport option set to active.

If you right click on the conceptual model and go to properties, the "Transport" toggle should be checked - also, "Leachate" should be defined under the "Species" button.

Thanks, I knew there had to be an easy solution.

Edited by Key

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Hi,

I have a similar problem. I am working in version 5.1 and in here there is no option of choosing the "Transport Observation Package". Was this simply not included in this old version? If not do you know how I can work through this?

Thanks.

Mette

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Greg cited: "The interval at which the simulated concentrations are reported can be at a different interval than that used to save the concentration data for contouring."

I tried, but get only output at the times concentration data for contouring are stored. Neither do I see the TOB data in the project explorer.

On the disk there is a file with extension .OCN that contains computed concentrations per MT3D time step. Can these data be used in GMS 7.1.8?

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Greg cited: "The interval at which the simulated concentrations are reported can be at a different interval than that used to save the concentration data for contouring."

I tried, but get only output at the times concentration data for contouring are stored. Neither do I see the TOB data in the project explorer.

On the disk there is a file with extension .OCN that contains computed concentrations per MT3D time step. Can these data be used in GMS 7.1.8?

GMS only keeps in memory the times that match the mt3d solution data set times.

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Hello Bill,

Thank you very much for your prompt reply.

I run MODFLOW and generated groundwater head from UGrid. Further, I want to run MT3D by using file that i created from said grid. Is there any way to initialize and run MT3D based on existing file (file from UGrid) beside initialize and run MODFLOW again from 3D grid?

Thank you,

Ratha

Edited by Doung Ratha

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