In this study, Hydrologic Engineering Center-Hydrologic Modeling System is used to simulate hydrologic processes in a watershed in Western Black Sea Region that frequently experiences flooding. The region is mountainous with steep hill slopes and receives high precipitation throughout the year. There are three stream gauging stations in the basin whose data are available for calibration and validation of hydrologic parameters. Simulations are performed for different scenarios to investigate the effect of using multiple stream gauging stations' data on catchment wide calibration and validation of hydrologic parameters. Furthermore, performance of using calibrated internal stream gauging stations' flow data in the estimation of hydrologic parameters in an assumed neighboring ungauged basin was assessed. It is found that using data of multiple stream gauging stations for calibration and validation gives satisfactory results for direct runoff hydrograph but the peak discharge predictions are not improved. The study results suggest that using data of internal stream gauging stations enables improved understanding of internal dynamics and transport in the basin and better predicted direct runoff hydrograph for the assumed neighboring ungauged basin.