A flat area of land adjacent to a river that is subject to periodic flooding. Floodplains serve as natural storage areas for excess water during high flow events.
A floodplain is the relatively flat area of land bordering a river channel that is formed by the deposition of sediment during periodic flooding events. It represents the area that would be inundated when streamflow exceeds the capacity of the main channel. Floodplains are created through long-term geomorphic processes including lateral channel migration, point bar formation, and overbank sediment deposition. They serve critical ecological and hydrological functions, including flood attenuation, sediment storage, nutrient cycling, groundwater recharge, and provision of habitat for diverse plant and animal communities. Regulatory floodplains are defined by agencies such as FEMA based on flood frequency analysis, with the 100-year floodplain being the most commonly used planning boundary. Development on floodplains increases flood damage potential and reduces natural flood storage capacity. Modern floodplain management integrates structural measures (levees, floodwalls) with non-structural approaches (zoning, flood insurance, wetland restoration) to reduce risk while preserving ecological functions.