| The purpose of this study was to modify the UNSAT2 model (saturated and unsaturated two-dimensional finite element model, Neuman et. al., 1974) to allow more precise calculation of evaporation and transpiration and to improve presentation of results. The purpose was achieved by the following: (1) adaptation of the UNSAT2 model to an IBM compatible PC; (2) modification of the model to allow graphical output; (3) conversion of the model from a one-dimensional to a two-dimensional root distribution function; (4) modification of the model to include the calculation of evaporation and transpiration within the model from weather data; (5) modification of the model to allow both surface and subsurface node evaporation rather than evaporation from the top surface only; (6) and, inclusion of the effect of soil surface microadvection of heat energy from dry soil surfaces to more moist soil surface areas. The modified UNSAT2 model was evaluated during simulation of measured field data after each modification to determine the effect of each modification independently. It was found that using a two-dimensional root distribution function had the greatest effect on model results when compared to field measurements. The use of surface and multi-subsurface evaporation nodes did not significantly affect results because the lower nodes contributed only a small percentage of the total evaporation. Adding the microadvection effect was important in improving agreement between the simulations and field measurements.; The modified UNSAT2 model can be used to show the effect of root density characteristics and distribution, and the effect of irrigation method and practice. It also can be used as a valuable teaching tool, enabling farmers to visualize the results of excessive irrigation and the amounts of lost water, in order to promote more efficient irrigation. |
