Hydrology and Sediment Modeling Using BASINS/HSPF in a Tropical Island Watershed

The Hydrological Simulation Program - FORTRAN (HSPF) in interface with Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) v.3.0 was used to study hydrology, soil erosion, and sediment transport of the Ro Caonillas watershed in Puerto Rico. The HSPF model has been used widely since 1980; however, little is known about the model's performance in tropical island watersheds that have extreme environmental conditions, such as rainfall intensity more than 25 mm h-1 and average soil slope of 38%. Three years (1999-2001) of continuous meteorological, flow, and suspended sediments data were used for model evaluation. The study found that the groundwater recession rate coefficient (AGWRC) was the most sensitive model parameter for both streamflow and sediment transport modeling. The calibrated model explained more than 85% of the monthly variability of streamflows and 70% of the monthly variability of suspended sediment concentrations. Agricultural and barren areas yielded the highest soil losses, contributing 55% and 20% of annual soil erosion, respectively. These results demonstrate that HSPF is capable of simulating hydrology and suspended sediment in the river for tropical island watersheds, principally for analysis on a monthly basis.