The Krueng Pirak River, which is located in North Aceh Regency, has relatively very high rainfall. From these implications, it is estimated that there can be changes in the river environment which can certainly affect the dynamics of changes in its morphology. The flooding occurred after heavy rains hit the North Aceh and Bener Meriah regencies, causing the krueng keureuto and krueng pirak rivers to overflow. Therefore, the purpose of this study is to analyze the capacity of river basins using the HEC-RAS application, as well as provide suggestions for effective cross-sectionaltamps. The only river under review is the Krueng Pirak river which is limited from the lower end to 11 km to the upstream. This study used only secondary data obtained from relevant agencies. The area of the catchment area is 221 km² with a river slope of 0.0022. Rain data comes from Malikussalhe Station for 15 years (2007-2021). Flood discharge is calculated by the Haspers method, used re-periods of 2, 5, and 25 years with flood discharge magnitudes of 119,044 m3/sec, 159,335 m3/sec, and 218,401 m3/sec. This flood discharge data is then input into the HEC-RAS and juxtaposed with the existing data of the river for running. The results of running on the existing river with the discharge input showed overtopping in some parts of the river. The flood mitigation method used is only the structural method, that is, the normalization of the river. From the results of running after normalizing the river, there was no overtopping in the entire cross section of the river, so that the Krueng Pirak River was safe from flood runoff for a 25-year re-period.