This study aims to evaluate the performance of the drainage system along Jalan Diponegoro-Yos Sudarso, Samarinda, which frequently experiences flooding due to the complex interaction between the Mahakam River’s tidal effects and urban stormwater runoff. The methodology includes collecting channel elevation data using RTK technology and drones, and conducting two-dimensional hydrodynamic modeling with HEC-RAS to simulate flood scenarios. The results indicate that tidal water intrusion from the Mahakam River into the drainage channels, especially during high tides, creates a backwater effect that hinders efficient stormwater discharge, leading to surface overflow onto the streets. The affected area covers approximately 1,307 m2. This study highlights the importance of redesigning the drainage system to address these hydrological challenges and protect the road infrastructure in Samarinda.