overbank

Overbank, in fluvial geomorphology, refers to the land adjacent to a river channel that becomes submerged when water exceeds the channel capacity during high flows. The term also describes the process of water spilling across the banks onto the floodplain during floods.

Overbank flow occurs when discharge surpasses bankfull capacity, allowing water to breach the channel boundary and spread over the floodplain. The extent of overbanking is influenced by flood magnitude, channel morphology, sediment deposits, and man-made structures such as levees, which can confine or divert flow.

During overbank events, sediment is deposited on the floodplain, forming features such as natural levees and crevasse splays. Recurrent overbank floods supply nutrients, create diverse habitats, and maintain dynamic soil and vegetation patterns that sustain floodplain ecosystems.

In flood risk management and river restoration, overbank processes are considered to evaluate flood hazards, design flood defenses, and restore connectivity between rivers and their floodplains. Bankfull discharge is used as a hydrologic threshold in modeling, while restoration projects seek to reestablish natural overbanking where feasible.