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Rob Virtue

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  1. Is it possible in NWT for the hydraulic characteristic of an HFB to change over time? If so it would be useful to have this as a transient option, much like GHB conductance, to simulate the installation of HFBs over time and their degradation long-term.
  2. Rob Virtue

    Modflow - modpath

    Arto, hydraulic conductivity determines how much volume flows through fro a given aquifer for a given area an gradient. Imagine a block of aquifer and a block of water being extruded out of the side as it flows. If the aquifer was all space (porosity of 1) a particle of water would flow through the aquifer at the same rate is is extruded out the side. If the porosity is only half (0.5) and everything else remains the same, the velocity of a particle in water in the aquifer has to flow twice as fast to keep the block of water moving out. If your porosity is 0.01 for the same K, it has to move 100 times as fast. This is expressed in the Darcy flow velocity equation V=K*(dh/dl)/Pe where V = velocity K= hydraulic conductivity dh/dl = hydraulic gradient Pe = effective porosity. Particle flow velocity is inversely proportional to effective porosity, if all other parameters remain the same. This may seem counter intuitive, because you are thinking that less pore space means lower flow, but remember, you are keeping hydraulic conductivity the same, so the volumetric water flow stays the same.
  3. What conductance value are you using for the drain and what are the Kh & Kv of the high conductivity layers? A higher drain conductance is required to fully drain a higher conductivity layer.
  4. How are the drains mapped? If they are from arcs, the elevations will not necessarily follow the variation in topography, especially if topography is irregular and node spacing wide relative to the grid. If as a polygon, for the same reason, elevations may not match if topography is irregular and the grid and raster resolution are not similar. Solutions are : Use the automatic layer range allocation with "Auto-assign BC to one cell", so they can go into the layer below if below the top layer (if that is conceptually acceptable) If using arcs, redistribute vertices more finely along the arc, to a similar spacing to the grid, convert them to nodes so it can have more variation over distance. Simplest and most robust option is to use a Seepage Face rather than Drain, so that the drain elevation in the grid is set relative to the upper cell top elevation. In your case set the “elevation offset” set to -1m.
  5. Can you please add the new Australian mapping datum, GDA2020, to the projection options.
  6. In Windows 7 (and presumably other versions) , it depends on the font size selected under Control Panel\All Control Panel Items\Display.
  7. Dunaj, Check under HELP>REGISTER> that you have the TIN module enabled.
  8. I used to get this a lot but it's been a while. If it is a transient model, make sure there are no observations in the first time step (or maybe first stress period?) . This can stop the model running or the head file saving properly.
  9. Rob Virtue

    ET surface

    Kirk, We had the same issue recently (18 September 2015), with the option for "2D Dataset -> Array" being greyed out, and were given this work-around from Jack at Aquaveo support. It seems to have worked. "Currently the option to use the "2D Dataset -> Array" command for U-Grids is not available, however I believe that the developers are working to implement it in future versions of GMS. I've got a possible work-around for you. This assumes that your topographic surface can be represented as a 2D scatter set or TIN. In this case right-click on your U-Grid and select 3D->2D, and then select layer 1 so as to make a 2D U-Grid of the top layer of your 3D U-Grid. This ensures that the cell IDs of layer 1 in your 3D U-Grid line up with the cell IDs of the 2D U-Grid. Now select the 2D U-Grid to ensure that it is the active U-Grid, and select the topographic surface data that you have and convert it to a 2D scatter set. Then interpolate that 2D scatter set to the 2D U-Grid. Now you will right-click on the interpolated dataset on the 2D U-Grid, and select "View Values". Copy the column of f values here, click ok to exit that dialog and bring up the dialog for the EVT package on the 3D U-Grid. Now paste in those values to the array for the EVT package. You can check to make sure that the cell IDs are the same and line up all right. If you have trouble doing this, please let us know."
  10. Mina, I suspect you have specified head cells with the head elevation set below the base of the cell, which causes a terminal error. Use the automatic layer assignment option to ensure the elevations are set at the uppermost cell ("Auto assign to one cell") or the uppermost and all underlying cells ("Auto-assign including lower cells") where the elevation is above the base of the cell. If you are using transient heads, be aware that automatic layer assignment seems to use the elevations from the first stress period.
  11. Mgozdor, This occurs if you have the "use to define model boundary (active area)" box checked in ANY coverage in addition to your activation coverage. This is a common problem at the moment, because if you select "layer range" in a coverage, it automatically checks the "..active area)" box. A bit annoying really. It will cause the activation errors whether you map the coverage to the model or not, so make sure you check ALL of your coverage.
  12. Rob Virtue


    I am having the same problem (GMS 10.0.6). It appears that PEST is looking for flow observations for DRN and CHD boundaries, even though there are no coverages with flow observations in the current model.
  13. If you have a high conductance value for the general head boundary relative to the cell K, it will act as a variable head cell as there is not a significant restriction to flow. If you drop the conductance to a very low value relative to K (conductance can be varied over time just like head) flow is restricted so that the is negligable exchange to and from the GHB term. By varying the conductance, the GHB can be used like adding or removing a constant/variable head boundary, without the need to stop and start the model.
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