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Georgios Tziatzios

MT3DMS calibration

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I am using Modflow 2000 code in GMS 10.2.6 64bit version for the simulation of groundwater flow and MT3DMS for the transport and fate of nitrates in a aquifer study area. The study of the aquifer’s pollution by nitrates is carried out at the level of Municipal Districts (30 Municipal Districts, each has a unique polygon). Τhe reason why I'm communicating with you is that I have a problem with MT3DMS calibration.

  1. I follow all the steps along with the default times described in the tutorial of MT3DMS Conceptual Model Approach to set up my MT3DMS simulation which runs successfully. 
  2. The sensitivity analysis indicates that the nitrate leaching parameter is the most uncertain parameter. As a result, the calibration is based on the nitrate leaching rate using a trial and error method, but every time I change the nitrate leaching, no significant difference noted to any polygons .
  3. Ιt may be a silly mistake that I can not figure out.
  4. Μaybe the answer would be to do an observation point to each polygon? but it is a whole area with consists of polygons.
Kind Regards,
Georgios Tziatzios

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Hello Georgios, could you be more specific in the problem you are solving? I suppose you are modeling the process of landfill leaching. The flow model is in a steady state with assigned recharge from the landfill that has associated nitrate concentration. The problem is, when you manualy change the value of recharge you see no response in the concentration dataset. To analyze the problem you could try to use the TOB package and check the Compute mass flux at sources/sinks in the TOB package dialog. Then when you run the model and select the polygon associated with the landfill recharge you should be able to see the mass flux for a given stress period in the status bar in GMS. Alternatively you should be able to look into the .mfx file that is writen by the TOB package in the MT3DMS folder. The mass flux data for each source/sink in the conceptual model should be listed there. Once you are able to observe the mass flux associated with the landfill recharge polygon, you could change the recharge value and see if the mass flux changes. If it does, the problem is probably somewhere in the flow velocity magnitude and/or stress period time setting. If it does not change, than there is some principal problem in the model.

Edited by Michal

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