Procedure Run finite element model and calculate conductance of each stream tube. Link each saturated streamtube to a one dimensional solution of Richard's equation above the water table. Lower boundary flow of each one-dimensional streamtube is determined by water table height in vertical streamtube and conductance of each streamtube. Calculate Specifics of the finite element model Construction of grid - Nieber gridding program with 9 regions. Movement of elements around drain - radial movement around drain, vertical movement far from drain.
Solution blows up as the nodes go around the corner.
Model validation Numerical models should be compared with analytical models for validation. Kirkham's analytical solution of two-dimensional flow to subsurface drains was bounded by the impermeable layer and the drain elevation. The streamtubes had no resistance to flow. In this section, Subdrain is compared with the analytic solutions developed by Kirkham with no resistance to flow. To validate the numerical model, this chapter compares numerical and Kirkham function results for the position of the water table in sheds with steady state regime.