Determining soil water characteristics for application of WEPP model in south Florida

Knowledge of soil wafer characteristics, such as soil hydraulic conductivit y, soil erodibility, and soil water retention, are required for the applica tion 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 cond uctivity, erodibility, and water retention values. The objectives of this s tudy were: 1) to calculate soil erodibility using results from rainfall sim ulation; 2) to compare different methods for calculating soil hydraulic con ductivity, soil erodibility, and soil water retention values; and 3) to eva luate how the results from these different methods would affect evapotransp iration, storm water runoff, crop growth, and soil erosion in the model. Th ree typical soils from the region were used for this study: Krome (sandy lo am, moderately well drained), Chekika (silty clay loam, poorly drained), an d Perrine Marl (sandy loam, very poorly drained). field research (including model calibration and rainfall simulation) was used to determine soil wate r parameters. While using various methods to determine soil parameters (cal ibrated, measured, and estimated) in a hydrologic model, significant discre pancies of simulated hydrologic variables were observed. Therefore, caution should be exercised when predicting critical parameters for hydrologic mod els. If a model, such as the Everglades Aaro-Hydrology Model (EAHM), is use d for comparison of different management practices, slight errors in estima ted parameters are acceptable. However if the model is used to assess possi ble changes in the hydrologic regime of south Florida, the accuracy of simu lated values is important and in need of further investigation.