DOCUMENTATION AND SIGNIFICANCE OF THE PERIRHEIC ZONE ON INUNDATED FLOODPLAINS

The transfer of water, sediment, and other materials to floodplains is a function of the hydrology of inundation. Inundation of floodplains by regional water, that is, overbank flow from the main river channel, and local water, that is, groundwater, hyporheic water, local tributa ry water, and direct precipitation onto the floodplain, is such that s ome rivers inundate dry floodplains, while other rivers inundate fully saturated floodplains. Remote sensing and field data from the large r ivers Missouri, Mississippi, Amazon, Ob'-Irtysh, Taquari, and Altamaha show a variety of water types on inundated floodplains, including are as of mixing of river and local water defined as the ''perirheic zone. '' For the rivers examined here, only the Missouri River flooded its e ntire valley with sediment-rich river water. Therefore the floodplains of these large rivers from the Arctic to the Amazon are only partiall y inundated with river water during floods and the corresponding perir heic zones may encompass a significant floodplain ecotone.