Floodplain Construction on a Braided River. The Islands of Koppangöyene on the River Glomma

Abstract

The last 300–400 years' evolution of the islands of Koppangsöyene on the river Glomma in southeastern Norway is shown. Fluvial processes on the floodplain surface are analyzed, and the surface's construction and bankfull frequency are related to the channels' hydraulic properties. The possibility of testing whether the river belongs to a steady state or not is discussed. The slope of the floodplain surface does not coincide with any actual stream profile, nor do the island relief and a basal coarse-grained surface in the plain. As the bankfull frequency decreases upstream, the floodplain is termed subrecent. Ice damming and a distal backwater curve may complicate that interpretation.