Seepage Modeling with SEEP/W - GeoStudio 2007 version 7.22

Chapter 3: Geometry and Meshing
SEEP/W
relative to the orientation of the triangular elements. Also, dealing with plant root zones in the
VADOSE/W model necessitates that element nodes in the surface layer all fall on vertical lines.
Moreover, using quadrilaterals greatly reduces the number of elements required, an important
consideration when dealing with situations that will be very computationally intensive.
Figure 3-21 Illustration of a surface layer mesh
Surface layers have special viewing options. Consider the two meshes illustrated in Figure 3-22. The left
diagram shows a surface layer without all the cluttering details as illustrated on the right. When many thin
elements are located in a close proximity to each other, they can appear indistinguishable when viewed
from a far away scale. By optionally turning off the surface mesh details a clearer image of the structure
of the near surface soil layers can be viewed.
Figure 3-23 is another illustration of this optional viewing concept. The left diagram in the figure shows
the detailed mesh and soil layers across the 0.75m thick surface region and the right diagram leaves the
details out, but still shows the layer colors. A couple of additional key points can be made in regards to
the figure. Notice that bottom two elements of the left diagram are the same soil type as the main
underlying soil. This is a good mesh design strategy – that being to have the bottom most layer of the
surface mesh be made of the same soil as the existing ground. Consider if the bottom layer of the surface
soil was VERY different from the underlying soil. If a finely spaced mesh was placed directly on top of
the different underlying soil then the numerical integration of material properties at the common mesh
node between the two soils would be less accurate because of the influence of the large element area from
the material below the common nodal point. By having the bottom layer of the surface layer be the same
as the underlying soil, the element shapes are very similar in size and aspect at the common nodal point
between the two very contrasting soils.
The second point to node from Figure 3-23 is that in the right diagram the nodes that are located at the
interface between two soils are still viewable even though the main mesh details are not. This is
intentional so that you can easily see and graph data at nodes that are used for automatic tracking of
interlayer fluxes in the VADOSE/W model.
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