National Highway Institute (NHI) Safety Inspection of In-Service Bridges Final Assessment Practice Exam

A floodplain is defined as the area adjacent to a river or stream that is subject to flooding. This overbank area, which extends from the edge of the river channel, is primarily composed of sediments that the river deposits during periods of high water. Floodplains serve an essential role in the natural hydrological cycle by allowing excess water to spread out and dissipate over a larger area, which helps to reduce flood impacts downstream and provides various ecological benefits, such as habitat for wildlife and retention of water resources.

In contrast, the other options do not accurately capture the nature of a floodplain. High elevations are typically located away from water bodies and are less likely to experience flooding. An area with minimal water flow would suggest a dry region rather than one prone to flooding. A designated flood control zone may refer to specific areas that have been intentionally managed for flood mitigation, but this does not encompass the broader, naturally occurring floodplain concept, which encompasses all the land adjacent to a flood-prone water body.