MORPHOLOGY AND IMPORTANCE OF FLOODPLAIN TIE-CHANNELS

Largely overlooked and poorly documented, tie channels represent an important and common feature of lowland floodplain systems around the world. In these lowlands systems, tie channels are sinuous but non-meandering channels which connect the main stem river to floodplain lakes. These channels allow the bi-directional transfer of water, sediment, biota, carbon and contaminants between river and lakes. As a primary link between rivers and floodplains, tie channels influence floodplain sedimentation (both the quantity and pattern), hydrology, ecology, geochemistry and stratigraphic evolution of lowland river systems.

We have conducted field investigations of tie channels in Papua New Guinea (the Fly River), Louisiana (Raccourci Old River ~ 65 km upriver of Baton Rouge) and Alaska (Birch Creek). These field investigations include extensive surveys of both cross and along channel morphological trends, grain size characteristics, water levels and geochronological sampling for optically stimulated luminescence (OSL) dating. In all three systems, both the planform and cross-sectional morphology of the channels show remarkable similarities over scales which range by an order of magnitude. The similarities in channel form suggests a commonality of tie channel morphodynamics across a wide range of scales and hydrological settings. Our results also suggest that size of tie channels and possibly the rates of tie channel development systematically scale to the size of the river system along which they occur.

Morphologically, tie channels share many similarities with tidal, submarine and deltaic channels. Determining the hydrodynamics that control the observed tie channel morphologies should provide critical insights into the controls on alluvial channel formation and morphology for a range of settings.