Column evaporation study conducted on fly ash for the evaluation of evaporation routines of three numerical water budget models

Results from a fly ash column evaporation study were compared to computer-simulated values of HELP2, UNSAT1D, and the Wetting Front model. All three models used the same input data. The Wetting Front model showed the best agreement between the experimental value and the computed values, within 6.3% for Colbert fly ash and 5.4% for Kingston fly ash. Modeled results for HELP2 and UNSAT1D showed a range difference of 53 to 36% and 95 to 97% respectively, for Colbert and Kingston fly ash. Default values used by the HELP2 model when compared to fly ash suggested that differences between fly ash and soils existed. These differences were shown as the evaporation coefficients. As a result of the column evaporation study, codes that simulate soil-water movement should be analyzed before they are used to estimate the water budget of fly ash. Based on the comparison of cumulative evaporation between actual measured data and modeled data, codes derived from the Richards equation had an advantage over other models developed from empirical equations based on field studies.