Determining Soil Water Characteristics for Application of WEPP Model in South Florida

Abstract

Knowledge of soil water characteristics, such as soil hydraulic conductivity, soil erodibility, and soil water retention, are required for the application of a surface hydrology model in south Florida. However, these data are limited for the soils of south Florida. Also, there are no standard methods for determining soil hydraulic properties such as saturated hydraulic conductivity, erodibility, and water retention values. The objectives of this study were: 1) to calculate soil erodibility using results from rainfall simulation; 2) to compare different methods for calculating soil hydraulic conductivity, soil erodibility, and soil water retention values; and 3) to evaluate how the results from these different methods would affect evapotranspiration, storm water runoff, crop growth, and soil erosion in the model. Three typical soils from the region were used for this study: Krome (sandy loam, moderately well drained), Chekika (silty clay loam, poorly drained), and Perrine Marl (sandy loam, very poorly drained). Field research (including model calibration and rainfall simulation) was used to determine soil water parameters. While using various methods to determine soil parameters (calibrated, measured, and estimated) in a hydrologic model, significant discrepancies of simulated hydrologic variables were observed. Therefore, caution should be exercised when predicting critical parameters for hydrologic models. If a model, such as the Everglades Agro-Hydrology Model (EAHM), is used for comparison of different management practices, slight errors in estimated parameters are acceptable. However, if the model is used to assess possible changes in the hydrologic regime of south Florida, the accuracy of simulated values is important and in need of further investigation.