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Found 10 results

  1. We are about to start a 3D dam seepage model. We have done several similar models over the last few years in a finite element, unstructured mesh model code similar to FEMWATER. This time, we've decided to start with a MODFLOW model due to funding and scheduling issues. I've been wondering if a MODFLOW-USG model will meet our needs, and eliminate the need to switch to an FEM model sometime in the future. I took a MODFLOW-USG class several years ago, and have been looking for an opportunity to use it, but have not stayed up to date with the current condition of the interface in GMS. I've done a little testing over the last few days, and I see two possible hindrances. I think I've got workarounds for both, but wanted to see if anyone else had additional ideas. 1. We definitely need to be able to look at a cross-section of the dam and show head contours on the cross-section. With a regular grid, this is straight forward as long as your cross-section is along a row or column. I don't see any cross-section cutter in the USG model. With an unstructured mesh, we are used to using the control key to select a line of elements to isolate. I do not see that that hotkey is available with an unstructured grid, but it looks like we can select and isolate a group of cells and get a similar effect - either draw a box or select with a polygon. Is that our best bet? 2. Once we have the model solution, we compute a factor of safety against uplift at all the surface nodes in the FEM model - basically we need the gradient for upward flow. We have an external code that will automatically do this for an unstructured mesh by comparing heads and elevations at nodes located at the same x,y location. If we use a regular structured gridded MODFLOW, the computation is pretty trivial using the MODFLOW arrays for the centroid elevations and computed heads and the data calculator. I am not finding the same options in the unstructured grid. I realize that the grid is not required to have layers and that the computational points are not necessarily at exactly the same x,y locations, but it seems that the only way to build the unstructured grid in GMS is with layers, so if you're using the GMS interface, it's likely a layered USG. At this point, I'm thinking writing an external code or maybe an excel macro may be my only option here and I can probably steal code from the routine we use on unstructured meshes. Is there anything I'm missing in the GMS interface that could help me here? Thanks for your advice.
  2. Hello, For a very long time, I have been trying to create a numerical model of an aquifer with complex hydrogeology (by using borehole-to-Ugrid option). I had several layers of 4 different materials. But all my efforts were trash. Because, I have never obtain a successful Modflow-usg run. They never converged. Although wetting option was on, the aquifer had so many dry cells. And these dry cells were always at same locations (not near/at the location of wells). It was meaningless. I couldn't run the PEST. So I decided to make my system more basic and created a one-layer model with HK zones. It worked well without the wetting. I have applied pilot points approach for the calibration. And pest is working because the forward run has a successful result. However, this time the calculated residual is too high. I have done many things to decrease the error. But the best result until now is about 7000 (Sum of Squared Weighted Residual Head+Flow) and for Root mean squared residual it is 16. These values are so big. Interestingly, the computed vs. observed head plot (attached) looks not so bad that there should be a way to fit them to the line. I only have head observations in my hand and I don't have any flow observations data. May this be the problem? Or what may be the problem? Could you please help me on this? I would be so happy to hear your recommendations to lower my calibration error to an acceptable value. Note: The computed heads are higher than the measured heads. The boundary conditions are ; specified head along the coast and GHB condition was assigned to some part of the boundary. The model is steady-state. Thank you! Best, Cansu
  3. Hi, I'm having some problems tracking particles in a USG groundwater model, because the particles stops in the edge of the cell and don't continue. Checking de mod-PATH3DU.exe file, the version in GMS is 1.0.6, but the latest one is 1.1.1. And if i replace it, GMS stop working and the sorfware close. What can i do? Another problem is with display options, because i tried to activate label in contour options (Ugrid), but it doesn't appear in the model, so maybe is a bug of GMS Thanks, Bastian
  4. Hi all. I have a problem mapping recharge to MODFLOW-USG within GMS (version 10.2.4). My MODFLOW-USG model has multiple layers. Layer 1 pinches out to expose layer 2 at the surface, and similar for deeper layers (that's how GMS created the 3D grid from horizons and TINS etc). When I map recharge to MODFLOW (steady state rates for now, but will use transient rates later), GMS maps the recharge fine to the surface where layer 1 is exposed, but will not map anything to the surface where layer 2 (and below) is exposed. So only part of the recharge is mapped to MODFLOW. I have discussed this with GMS support, and they have suggested that I add a thin upper layer (a new layer 1) to the model over the whole model domain, and set this layer to inactive. Recharge would then map to this new layer 1, and pass through this inactive layer (if the right settings are selected) to the first active cell below. However, I also have a SFR2 coverage that needs to map to the uppermost layer, and this will not map to inactive cells. This also creates errors with river bed inverts passing below the bottom elevation of layer 1 cells. I therefore don't think this is a suitable solution. GMS support have been very helpful, but they are very busy and response times are long. Therefore, I was wondering if anybody else has had this issue arise, and if they have found an alternative work around. Is it a GMS mapping problem or a MODFLOW-USG limitation? I would have thought that having underlying layers outcrop to the surface is not uncommon, and so it would be unusual for MODFLOW-USG to not support this. Any help would be appreciated. Thanks.
  5. Dear Members, I have never used modflow-usg before. I am wondering if MT3DMS is compatible with the Modflow-USG "Ugrid" flow model and the CLN well package? In other words, if I create a flow model using the UGrid in Modflow-USG and wells using the CLN package, would I be able to simulate solute transport using MT3DMS in GMS? I look forward to hearing from you. Cheers Mahmoud
  6. Is there plans to implement more capabilities for the CLN process in GMS beyond just CLN Wells? In theory CLNs can be used in MODFLOW-USG to simulate a 3D tunnel network. Over 50% of the modeling we do could use CLNs to simulate tunnels or adits in dewatering/recovery analyses. Please let me know if this is in the works and if there is a projected release of expanded CLN capabilities in GMS. Thank you - Greg B.
  7. Currently you can not get cell to cell flow budgets with MODFLOW-USG. This is a feature that can really help troubleshoot problems and analyze if the model is behaving correctly. Any plans in providing this in MODFLOW-USG?
  8. Is there a way to split a UGrid layer into multiple layers in GMS 10.0 or 10.1?
  9. Please let us know when the CLN Package in MODFLOW-USG will be available in GMS. I have many projects that I could use this on. One is just starting up, with 2-3 starting later this year. The other request I have is for GMS to develop a scheme to allow for Time Varient Material Properties. I understand that MODFLOW does not allow for TVM properties, but it seems like there could be a sub routine that the GUI could implement to make it significantly easier to model projects where the aquifer properties are altered.
  10. Hi All, I am in the planning phase for a groundwater flow model of an underground mine dewatering project to evaluate mine inflows and effect on water resources in the area of the proposed mine. The mine plan consists of using paste backfill throughout all of the stopes. It is estimated that the hydraulic conductivity of the paste back fill will be 2-3 orders of magnitude lower than the native rock (storage will also change). I have worked with models that implement changing material properties by use of cascading models (export heads from transient model run, change material properties and run next stress period and repeat). This is tedious and I have never been too comfortable with the stability of the model between the model runs as you are not importing steady state heads into the next model. I would like to use MODFLOW to complete this analysis, but have concerns with drying up cells (which I hope will be better with MODFLOW-USG using the NWT re-wetting) and stability of model between model runs. Can anyone give advice as to MODFLOW being appropriate to conduct this analysis or if there are alternatives to using a cascading model approach in MODFLOW? I know this could be modeled using a finite element-variably saturated flow model in FEFLOW, but for many reasons (one being the client does not want to go there) I would like to avoid it if I can. Thank you for any input in advance. - Greg
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