Perpustakaan Digital ITB

The Upper Citarum Sub-Watershed plays an important role in water resources management in the Bandung Basin. One of the key hydrological components in this area is baseflow, which represents streamflow sustained by shallow groundwater discharge. Baseflow estimation is commonly conducted using hydrograph separation methods, such as the Arnold Recursive Digital Filter. However, the results are strongly influenced by the selected alpha value, which is often determined empirically. This study aims to produce a physically based baseflow estimation using a physically based SWAT+ model in the Upper Citarum Sub-Watershed, which is subsequently used as a physical reference for calibrating the alpha value of the Arnold Recursive Digital Filter. Model 1 was developed as the main hydrological model and was calibrated and validated against observed discharge at the Nanjung gauging station. Daily recharge from Model 1 was then used as the main input for Model 2, which was modified using CN_Zero, PERCO = 1, and LATQ_CO = 0 to isolate the baseflow component. The discharge generated by Model 2 was used as a physically based reference for alpha calibration. The results show that Model 1 performed well, with NSE values of 0.8886 during calibration and 0.6732 during validation. The average annual recharge was 640.5 mm/year. Model 2 indicated that baseflow contributed approximately 46% of the total discharge at Nanjung. The optimal alpha value was ? = 0.963, with KGE of 0.578, NSE of 0.437, PBIAS of ?27.5%, and BFI of 0.590. These findings indicate that the physically based SWAT+ model successfully produces a baseflow estimation that can serve as a reference for digital filtering parameter calibration.