LINKFLOW, A WATER-FLOW COMPUTER-MODEL FOR WATER-TABLE MANAGEMENT .1. MODEL DEVELOPMENT

A computer simulation model, LINKFLOW, was developed to calculate the movement of water during various water table management practices, nam ely subsurface drainage, controlled drainage, and subirrigation. The m odel can simulate water movement through a heterogeneous and anisotrop ic saturated soil and includes an unsaturated flow component with a zo ne of water extraction by plant roots. The computer program links a ne wly developed one-dimensional unsaturated water flow model to an exist ing but modified three-dimensional saturated water flow model, MODFLOW . The water movement is simulated for a region of the field, and resul ts obtained define water conditions in the root zone for a wide range of soil, topography, drain location, and weather conditions. LINKFLOW is unique among soil waterflow models because of the following feature s: I) it can simulate soil-water conditions beneath a crop on land wit h varying topography; 2) it can determine 3-D flows from drains in a h eterogeneous, anisotropic soil; and 3) it can simulate the effects of different automated control strategies for subirrigation. Results can be presented in tabular format, contour map format, and/or a 3-D surfa ce format to help understanding flow behavior of the system. A subirri gation case simulation is presented to illustrate just one example of the model's use in water table management studies. This article focuse s on the development of the simulation model.