Screening Model for Flow and Transport in Soils

Version 1.30 - August 1989

CHEMFLO is a one-dimensional screening level model for simulation of the movement of water and chemicals in unsaturated soils. Water movement is described using Richards equation. The equation describing the movement of chemicals includes advective and dispersive transport, first-order decay in the liquid and solid phase, zero-order production or decay, and linear equilibrium adsorption (using a retardation coefficient. These equations are solved using the finite difference method. The model handles three types of boundary conditions for flow. At the upper boundary, the conditions may be constant potential, constant flux, mixed type condition, or rainfall. The latter condition is a mixed type with the given flux equal to the rainfall rate and the given head equal to zero. For a finite soil system, the conditions at the lower boundary may be: constant potential, constant flux, or mixed type. Results of the water model can be displayed in the form of graphs of water content, matrix potential, driving force, conductivity, and flux density of water versus distance or time. Graphs of concentration and flux density of chemical as functions of distance or time can also be displayed. Cumulative fluxes of water and chemical and total mass of chemical in the soil can be displayed as functions of time.

The program has a menu driven preprocessor for data input and editing. It produces output in both tabular and graphical formats. Public domain CHEMFLO is distributed on DOS-formatted disks containing executable image and example data sets. The user's manual includes data input instructions and example problems.


Intel 80i86 based computer, 640 Kb RAM, about 1 Mb free disk space, and CGA or EGA graphics; math co-processor recommended.


Developers: D.L. Nofziger, K. Rajender, S.K. Nayudu, and P.Y. Su (Oklahoma State Univ.) for U.S. EPA CHEMFLO