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 tributary water, and direct precipitation onto the floodplain, is such that some rivers inundate dry floodplains, while other rivers inundate fully saturated floodplains. Remote sensing and field data from the large rivers Missouri, Mississippi, Amazon, Ob'-Irtysh, Taquari, and Altamaha show a variety of water types on inundated floodplains, including areas of mixing of river and local water defined as the perirheic zone. For the rivers examined here, only the Missouri River flooded its entire valley with sediment-rich river water. Therefore the floodplains of these large rivers from the Arctic to the Amazon are only partially inundated with river water during floods and the corresponding perirheic zones may encompass a significant floodplain ecotone.¿ 1997 American Geophysical Union