The Hydrological Simulation Program - FORTRAN (HSPF) in its personal computer version, release
10.10, was used to perform the hydrological simulation of a sub-watershed of the Occoquan River drainage
basin. The sub-watershed selected was the Cub Run Watershed located in the northern area of the
Occoquan River catchment. A model in the form of a User Control Input (UCI) file was prepared. The
Cub Run Watershed was analyzed considering its geological, edaphic and weather characteristics, and
segmented accordingly. The model was calibrated to adjust simulated results to observed data. Several
calibration runs were executed and a final run was done considering a further segmented watershed. The
simulation results were good even when not all the desired data could be found. The annual percent
difference between the best calibration run and the observed results was 21.28%. The ten-month percent
difference, excluding June and July, was 5.82 %. The first value is a fair result for hydrologic calibration,
the second value is an excellent result for the same type of calibration. Additional segmentation did not
further improve the results obtained during the best calibration run. Differences in the calibration when
considering just a pervious segment or two segments (one pervious and one impervious) could be noted,
indicating the importance of considering impervious surfaces for the simulation. HSPF reacted quite
logically to variations in the calibration parameters and the results from those variations could be predicted
beforehand. In summary, the PC version of HSPF was demonstrated to be a good management tool for
the hydrological simulation of this watershed.
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