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The Hydrological Simulation Program - Fortran- HSPF in interface with Better Assessment Science Integrating Point and Nonpoint Sources BASINS v3.0 is being used to quantity the sediment export potential of the watershed and relate it to land use and land use changes in a north-central watershed of Puerto Rico. The first step in using HSPF, hydrologic calibration and validation is discussed here. Calibration and validation of the simulated flows were compared graphically and statistically with USGS gauge data at the watershed outlet for the period from October 1, 1998 through September 30, 2000 and October 1, 1995 through September 30, 1998, respectively. The plot of residuals showed a non-seasonal periodicity in both periods. For the calibration period, Nash Sutcliffe coefficient was 0.53 and 0.84 for daily and monthly intervals respectively; whereas for the validation period, values of 0.73 and 0.96 were obtained. For a two-year calibration period, there was one percent underestimation of discharge and 5 percent overestimation in the three-year of validation. Coefficient of determination of HSPF simulated streamflows versus USGS gauge data were 0.56 and 0.84 daily and monthly intervals for the calibration runs and 0.79 and 0.97 for the validation runs. Validation period presented extreme events, Hortensia and Georges hurricanes and driest year (minus of half of yearly average stream flow). The hydrological calibration and validation showed good fitness with recorded historical data. Sediment sampling and sedigraph monitoring is being carry out to relate it to watershed management strategies.