Analysis of Three-Dimensional Flow and Transport

Version 1.5 (January 1995)
Order No: TPS 26
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MULAT is a program for the analysis of three-dimensional steady-state groundwater flow, and the advective transport of particles, including linear adsorption and desorption. The model assumes flow in the aquifer to be mainly horizontal, with vertical flow from one aquifer to another through the resistance layers. The model handles up to six layers. The aquifers may be confined or unconfined, and may also be partly confined and partly unconfined. The flow of groundwater may be influenced by various types of wells, line sources, line drains and line screens (impermeable walls).

The geometry of the problem can be described in a two-dimensional network of triangular elements in the x,y-plane. The model area is divided in a number of triangular zones, each of which is homogeneous with respect to soil properties (permeability, porosity and retardation factor) and infiltration rate. Each of the zones is subdivided in a large number of triangular elements. This refinement is automatically performed by the program based on user-defined zone-refinement strategy.

In vertical direction, the model is based on the generalized Dupuit assumption, which states that the groundwater head in each aquifer is independent of the vertical coordinate within that aquifer. However, the vertical component of the fluid velocity in the aquifer is not neglected. This component is directly calculated from the equation of continuity, resulting in a vertical velocity varying linearly with depth. This information, together with the horizontal velocity, derived by applying Darcy's law to the head distribution, is used to trace three-dimensional flow paths.

Adsorption and desorption is represented by a transport retardation factor. The particles, representing transport of pollutants, can be traced both in a forwards mode (downstream direction) and a backwards mode (upstream direction). Travel times can be marked on pathlines.

MULAT is user-friendly, easy-to-run program It has a text-based user interface for program control and data input and editing. Results of mesh generation, head distribution and pathlines in two or three dimensions are displayed on screen or may be routed to a HPGL plotfile. MULAT includes its own DOS extender which uses all RAM resources available on the computer and therefore should not be run under MS Windows.


Intel 80386 based microcomputer or compatible with mathcoprocessor, at least 640 Kb conventional RAM, DOS 5.0 or higher, a hard disk with at least 2 Mb free disk space for program and example files, VGA graphics.

Optional, but highly recommended: At least 3 Mb additional extended memory (MULAT automatically uses all available extended memory).

Author: A. Verruijt, Delft University of Technology, The Netherlands.