The Kosi river in north Bihar plains, eastern India presents a challenge in terms of long and recurring flood hazard. Despite a long history of flood control management in the basin for more than 5 decades, the river continues to bring a lot of misery through extensive flooding. This paper revisits the flooding problem in the Kosi river basin and presents an in-depth analysis of flood hydrology. The study integrates the hydrological analysis with a GIS-based flood risk mapping in parts of the basin. Typical hydrological characteristics of
the Kosi river include very high discharge variability, and high sediment flux from an uplifting hinterland.