Abstract <p>Dams are vital hydraulic infrastructure with spillways to control floods by reducing downstream discharge and flood risk. Flooding is among the most frequent disasters in Indonesia, with climate change worsening its impacts. By 2019, flooding became the third most common disaster, emphasizing the need to improve flood control measures for dams like Tapin Dam. Located on the Tapin River in South Kalimantan, Tapin Dam aims to prevent flooding in the Tapin District. However, flooding persists, prompting the Ministry of Public Works (PUPR) to demand improvements. Specifically, the dam must maintain sufficient freeboard (≈0.75 m) during probable maximum flood discharge (Q_PMF) and manage downstream river capacity (≈100 m³/s) during a 25-year return period (Q₂₅). An early release strategy was chosen to address these constraints. HEC-RAS was used to model the current conditions and simulate two early release scenarios. Scenario 1 proved optimal, considering early release time and downstream capacity limits. It involves installing a 3 × 3 m sluice gate at an elevation of +140.5 m. This gate will reduce the reservoir’s normal water level (+145.5 m) to the required water level (+142 m) within 4 days, 22 h, and 51 m. A volume-checking analysis confirmed the model’s accuracy, with a 2.43% error, well below the 5% threshold. This validates Scenario 1 as an effective solution to improve Tapin Dam’s flood control capabilities.</p>