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Michal

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  1. Michal

    Animation over multiple Model Runs

    Hi, I think it is not directly posible through MODFLOW, but maybe you could create the second drawdown dataset in postprocessing using GMS data calculator. Just compute difference in head between the first timestep of the first simulation and the transient head dataset of the second sim. That should be the drawdown you are looking for.
  2. Michal

    Constituent across each cell face

    You are welcome. I suggest you to read the MT3DMS v5.3 supplemental manual here: http://gmsdocs.aquaveo.com/mt3dms_v5_supplemental.pdf There is a section about the new TOB package. If you need data for each cell of the boundary condition, then you would probably have to prepare the input files by hand and include each BC cell as a mass-flux object/group for which the budget data are going to be saved.
  3. Michal

    Constituent across each cell face

    Hi Lalith, In the MT3D output file, there is cumulative mass budget associated with each BC type already listed. If you need more control then there is TOB package for MT3D. https://www.xmswiki.com/wiki/GMS:Transport_Observation_Package
  4. Michal

    Flow Budget

    Hi bokuhata, I assume you have maped a general head boundary (GHB) at the coastline. When you select an arc representing this boundary you see, in the tooltip area of GMS, a flow across this boundary to/from an external reservoir. On the other hand, the Zone flow in Zonebudget is the flow between the two zones in the model. From this you see it has to be different.
  5. Michal

    Stratigraphy

    Hi Aly, I think there is no straight forward way to do this in GMS. I would suggest the following procedure: 1. Create the profile as a regular 3d grid with high enough resolution to carry the material information (1 row, many columns, many layers) 2. Export your grid into a text file with the following format: Cell_id X Y Z Y coordinate should be constant for all cells. 3. Swap Y<->Z 4. Import into GIS 5. Digitize the material polygons in GIS in X-Y space 6. Select the cell centers according to the material polygon and asign material ID into a new column in the atribute table (spatial join) 7. Export the atribute table into a text file 8. Copy the material column into a new file and format the new file as GMS 3d dataset format (see GMS wiki for details) 9. Import the new material dataset to the existing 3d grid 10. Select cells in GMS according to the material dataset and specify material properties as you like
  6. Michal

    Flow budget in an unconfined aquifer (MODFLOW)

    Yes, but if the model is steady, than the best approach is to set the initial heads high, because during the consecutive aproximation of the solution the chance of making cell inactive as a result of undershoot is lower. It can happen anyway, but in your case it looks fine. Btw. I think the cells never get rewetted because they are initialy dry.
  7. Michal

    Flow budget in an unconfined aquifer (MODFLOW)

    This result looks good to me. There seems to be no more flooded cells. What about the budget? The wetting capability is turned on in the LPF or BCF package. I usually use the default values first unless there is a problem with convergence.
  8. Michal

    Flow budget in an unconfined aquifer (MODFLOW)

    Hi, what about the dry cells in the above picture? Couldn't it be the explanation for what you observe? This could cause reduction in aquifer thickness and reduction of volumetric flow rate therefore. Is rewetting on?
  9. Michal

    Dry cells in steep mountain terrain

    I would say that MF-USG is very different in terms of how the solution to the flow equation is aproached compared to the traditional structured modflow. However it is usually not too difficult to set up a MF-USG simulation in GMS. There are some tutorials out there that could help. I would recommend reading the MF-USG manual as well to grasp the internal differences. Regarding your second question. I believe there are other people here that could provide more accurate answer. The problem comes from the way MODFLOW solves the groundwater flow equation, that is by numerical approximation. During these approximations (in MF-2005) if head in a cell falls bellow the cell bottom the cell is assumed dry and is inactivated (becomes no-flow cell). However in subsequent approximation the cell could become wet and active again if certain criteria are met. For instace if head in the cell below (i,j,k-1) is 0.1 m above the cell (ijk) bottom. The 0.1 m would be the user specified threshold for conversion from dry to wet. This whole process brings instability into the solution and may cause convergence problems especialy if poor initial head values and low threshold values are specified. However MF-NWT adressed this issue in a brilliant way. It does not deactivate dry cells, but instead it uses upstream weighting approach to limit flow from dry cell to a neighboring partialy saturated cell. It also uses additional smoothing for conductance and storage functions which allows the use of newton numerical method for outer iterations. It therefore provides a continuous solution for all unconfined groundwater flow conditions and is very robust. However if you have steep aquifer your problem is different. Consider two neighboring cells of 10 m thickness. Lets say, under extremely steep conditions they share only 1 m thickness. However structured modflow will assume 10 m anyway and would not modify transmissivity accordingly. Such a solution would be incorrect. That is why I recommend using MF-USG in your case as mentioned earlier in my previous post. For literature I suggest reading the manuals published by USGS for modflow 2000, 2005, NWT and USG. There are plenty of further references there too.
  10. Michal

    Dry cells in steep mountain terrain

    Hi, MODFLOW assumes flat continuous aquifer. You could probably overcome the drying/wetting problem by using Newton linearization implemented in MODFLOW-NWT. However, if there are large not negligible differences in elevation between two horizontaly adjacent cells MODFLOW results will be incorrect. Fortunately the finite volume formulation in MODFLOW-USG adressed this issue - it involves true interface area into the calculation. If I remember it right, this is supplied for each cell connection in the DISU file somewhere. If you use GMS, this should be done automaticaly for you. You could use the upstream weighting (LPF package) and newton linearization (SMS package) for a more robust solution. With this setup the model should converge to a correct solution.
  11. Michal

    confused in output control

    Hi Mina, the output control file should look like this: HEAD PRINT FORMAT 15 HEAD SAVE FORMAT (20F10.3) LABEL HEAD SAVE UNIT 30 COMPACT BUDGET FILES DRAWDOWN PRINT FORMAT 14 PERIOD 1 STEP 1 PRINT HEAD 2 6 PRINT DRAWDOWN PRINT BUDGET SAVE BUDGET SAVE HEAD PERIOD 1 STEP 7 SAVE HEAD 1 3 5 PRINT DRAWDOWN SAVE BUDGET PERIOD 2 STEP 5 PRINT HEAD PRINT BUDGET SAVE BUDGET SAVE HEAD See this page for detailed input instructions.
  12. Michal

    How to import/read a binary *.hds file?

    Ok, I see your dilemma, since the model was already calibrated. Try loading the .nam file via Read Solution command. It should have the same format as .mfn and it should load the binary output data referenced there. You could also try to run the model with the MF executable that worked through GMS via custom Run dialog.
  13. Michal

    Importing XYZ data and attribute (pressure)

    Hi T, I didnt understand what you do, so forget my last comment :). I dont know much about this topic. It would be nice if GMS would allow us to do "Interpolate to modflow layers" command with RIV package (to prepare the river bottom/elev dataset and head), but i think only Head in GHB package could be distributed this way. If you decide to model it with RIV, which would be my choice, you need to prepare the package outside GMS.
  14. Michal

    Changes to MODFLOW-USG?

    It may be a long shot as I dont have much details about the model itself, but there might have been some changes in the default values for the solver between MF versions.
  15. Michal

    Importing XYZ data and attribute (pressure)

    If I understand it right, you have raster dataset of measured heads and you basicaly want your model to reproduce these as close as possible. Why not just convert the raster data to points a treat each point as observation point? Then you can formulate the inversion problem as usual.
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