Avoiding Grid Over Refinement in GMS

When building a grid for your groundwater model, it can certainly be tempting to make a really refined grid. While this temptation is understandable, there are certain pitfalls that can result from having a grid that is overly refined. This post will go over some of the reasons to avoid overrefining your grid in GMS.

There are, of course, legitimate reasons to refine portions of your grid. Portions of the grid that are key areas should be refined. This should be done only in areas around wells or other structures that are important to the model. By refining key areas, important areas of the grid will receive more attention during the model run. However, over refining your grid can cause some issues, including some of the following ones listed here.

When you are refining, you are creating more grid cells in your grid. Each of these cells will be used in the model run calculation. A grid that has been over refined generally has a lot of cells that need to be used in the model calculations, many of which are unnecessary. This will cause the model run to go slower and take longer than the same model without the over refinement.

Because an over refined grid contains refined cells in unimportant areas of the project, the data from these areas can sometimes skew the results. The model run does not generally discriminate between important and unimportant parts of the grid. When it encounters a portion of the grid that has a lot of cells, it gathers all the data it can for that area. In an over refined grid, this can mean it gathers more data than the model needs, which sometimes can skew the results.

The biggest issue we most often see is when over refined grids cause the model to fail to converge. Once again, an over refined grid will have too many cells and be collecting too much nonessential data. All of this can overwhelm the model and can cause the model run to diverge. To resolve this, you will need to simplify the grid so that the model run stays focused on the key areas of the model.

Try out some of these tips while refining grids in GMS 10.5 today!