The Rangang Dam faces a significant risk of flooding due to variations in river discharge, especially during the rainy season with high rainfall. As a mitigation effort, the Kadumalik Dam was built as one of the National Strategic Projects located upstream of the Rangang Dam. This study aims to conduct a hydrological analysis to measure the influence of the construction of the Kadumalik Dam on the reduction of flood discharge in the Rangang Dam. The results of the analysis show that the physical characteristics of the watershed greatly influence the flood response. Watersheds with longer rivers (L=130 km) produce sloping hydrographs with a peak discharge (Qp) of 37.21 m³/s/mm. In contrast, watersheds with shorter rivers (L=65 km) showed a faster and sharper response with a peak discharge of 57.81 m³/s/mm. Modeling for the Kadumalik watershed itself, which has an area of 435 km² and a river length of 65 km, resulted in a peak unit discharge (Qp) of 12.29 m³/s/mm, which was achieved within 4.97 hours. Further discussion revealed a crucial fact: the catchment watershed of the Kadumalik Dam only covers 12.4% of the total watershed upstream of the Rangang Dam. This implies that although the Kadumalik Dam is effective in reducing flooding from its own watershed, its effect on overall flood mitigation in the Rangang Dam will be limited.