Drains as a Boundary Condition in Finite Elements

Abstract

Four different methods of representing drain tubes in finite elements for field drainage problems were studied. A finite-element solution to the Richards equation was used to compare the performance of each method for three conditions: flow to parallel drains from a ponded surface, transient drainage, and flow to and past an interceptor drain. Differences in predictions of hydraulic heads and drain flow rates were found among the four methods. A method using logarithmically varying adjustment factors for hydraulic conductivity and a modified grid system in the vicinity of the drain was found to be relatively easy to implement and to produce accurate estimates of drain flow rates and hydraulic heads for the drainage problems simulated.

Single-porosity and dual-porosity modeling of water flow and solute transport in subsurface-drained fields using effective field-scale parameters

“…The sides and bottom of the domain were specified as no-flux boundaries, and the top of the domain had an atmospheric boundary. The subsurface drain was represented as a nodal sink (Šimůnek et al, 1999) with an effective drain diameter, d e , of 1 cm and a reduction of hydraulic conductivities of the square in the finite element mesh surrounding the drain using the correction factor, C d , of four (Mohammad and Skaggs, 1983;Fipps et al, 1986).…”

Bromide transport at a tile-drained field site: experiment, and one- and two-dimensional equilibrium and non-equilibrium numerical modeling

“…To represent the entrance resistance of the drain, the hydraulic conductivities at the nodes adjacent to the drain node were reduced according to the method of Fipps and Skaggs (1986). An effective drain diameter of 4 cm was assumed and the standard correction factor (Fipps and Skaggs, 1986) was applied without additional reduction factor. A zero gradient (Neumann) boundary condition was assumed for solute transport out of the tile drain.…”

A new parabolic variational inequality formulation of Signorini's condition for non‐steady seepage problems with complex seepage control systems

“…To reduce the difficulty in mesh generation associated with the large number of one-dimensional extended drainage holes, numerous modeling approaches are proposed in the literature, including the equivalent medium approach [15], the substructure technique [16,17], the semi-analytical approach [18,19], the point well model [20] and the composite element method [21], etc. Most of the existing models (except the substructure technique), however, fail more or less to precisely describe the details of the boundary conditions of the drainage holes, and thus, sacrifice to some degree the theoretical strictness of solutions [14].…”