Visual Modflow vs. SEVIEW
This issue provides a comparison between SEVIEW and Visual Modflow.
Although both of these packages can be used to develop site-specific cleanup objectives, they are
very different. SEVIEW contains the SESOIL and AT123D analytical models while Modflow is a
numerical groundwater model. Numerical models are like weather forecasting models and, as such,
need a great deal of information. For instance, to predict the temperature at a location
I would need data like cloud cover, wind speed, and any approaching fronts.
Analytical models are much simpler and use much less data. For example, a model that predicts temperature
in a solar collector may only require the intensity of the sunlight and the albedo of the material.
Both types models can provide accurate results.
When to Use Which
Exactly which type of model should be used depends on the complexity of site conditions. For instance, AT123D can be used at sites with relatively simple hydrologic conditions. While numerical models like Modflow should be used to simulate complex hydrological conditions like pumping and injection.
A decision as to which type of model to use is also dependent upon the process simulated by the model. There is no question that Modflow can simulate more complex groundwater conditions than AT123D. However, Modflow is not a vadose zone model. Processes controlling the transport and fate of contaminants in the vadose zone are typically far more complex than those in the saturated zone. Groundwater models like Modflow are simply not designed to handle the seasonal dependent processes within the vadose zone.
Ease of Use
It is easy to run analytical models. For instance, grid spacing in AT123D has no effect on the results. This is because results at each point are solved independently. In fact it is possible to run AT123D with only a single grid node. With its simplified model setup and reports SEVIEW makes modeling easy enough to be done by almost any environmental professional. Using SEVIEW, modeling can be completed in as little as 10 minutes to several days at the most.
This is not true of numerical models like Modflow where it typically takes days or even months to complete the work. Grid design becomes an important step of the modeling process as results are dependant on the grid spacing. Basically, even though software like Visual Modflow has made numerical modeling much easier, it is still best left to experienced professionals. In addition, due to data requirements, numerical modeling is beyond the scope of the average site.
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