HR: 1330h
AN: OS12A-0192    [PDF]
TI: The Role of Conjoining (Tie) Channels in Lowland Floodplain Development and Lake Infilling
AU: * Rowland, J C
EM: rowland@eps.berkeley.edu
AF: Dept. Earth \& Planetary Science, 307 McCone Hall University of California, Berkeley, CA 94720 United States
AU: Dietrich, W E
EM: bill@eps.berkeley.edu
AF: Dept. Earth \& Planetary Science, 307 McCone Hall University of California, Berkeley, CA 94720 United States
AU: Day, G
AF: Dept. Earth \& Planetary Science, 307 McCone Hall University of California, Berkeley, CA 94720 United States
AU: Lepper, K
EM: ken.lepper@ndsu.nodak.edu
AF: Dept. of Geosciences, Stevens Hall North Dakota State University, Fargo, ND 58105 United States
AU: Wilson, C J
EM: cjw@lanl.gov
AF: Los Alamos National Laboratory, MS J495 EES-2, Los Alamos, NM 87545 United States
AB: In simple models of lowland river systems, water and sediment enter the main stem via tributary and secondary channels and are only redistributed to the floodplain during overbank and crevasse splay events. Along numerous river systems across the globe, however, water and sediment are regularly exchanged between the river and off river water bodies via stable, narrow channels. These channels, known as tie channels on the Fly River in Papua New Guinea and batture channels along the lower Mississippi, are largely overlooked but important components of floodplain sediment dispersal where they exist. These channels become pathways of sediment dispersal to the floodplain system when elevated river stages force sediment-laden flows into the off-river water bodies. On the Fly River, it is estimated that about 50% of the sediment delivery to the floodplain is via these channels, and along low gradient tributary channels during flood driven flow reversals. During low flow, tie channels serve to drain the floodplain. With the outgoing flows, large amounts sediment can be carried and lost to the floodplain; floodplain lakes progressively infill with sediment as the mouth of these channels steadily prograde lakeward. These lake deposits not only become significant stratigraphic components of floodplains (traditionally referred to as clay plugs), but are important local sinks recording hundreds to thousands of years of river history. As with all sinks, the proper interpretation of these stratigraphic records requires understanding the processes by which sediment is delivered to the sink and how these processes alter the paleohydraulic and climatic signals of interest. We have conducted field investigations of conjoining channels in Papua New Guinea (the Fly and Strickland Rivers), 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 using optically stimulated luminescence (OSL). Across all systems channel morphology is similar and exhibit scale independence, however, channel size and rates of progradation are directly related to the size of the main stem river. Through these studies and ongoing scaled modeling we are examining the morphodynamics that lead to the formation, advancement and stability of these unique self formed channels.
DE: 1824 Geomorphology (1625)
DE: 4558 Sediment transport
DE: 4863 Sedimentation
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting