HR: 10:30h
AN: NB22G-01    [Abstracts]
TI: The Missing Link: the Role of Floodplain Tie Channels in Connecting Off River Water Bodies to Lowland Rivers
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
EM: gmd@lihir.com.pg
AF: Dept. Earth & Planetary Science, 307 McCone Hall, University of California, Berkeley, CA 94720 United States
AB: Along lowland river systems across the globe the exchange of water, sediment, carbon, nutrients and biota between main stem rivers and off-river water bodies (ORWB) is facilitated by the presence of stable secondary channels referred to here as tie channels. Sixty five percent of the ORWB along the middle Fly River in Papua New Guinea connect to the river through such channels. A similar percentage of the 37 ORWB located between Baton Rouge and Memphis on the lower Mississippi River at one time were linked to the river by tie or batture (as they are locally known) channels. Levee construction and other alterations aimed at flood control or navigation on the Mississippi have left only a handful of lakes connected to the river, of these, most are heavily altered by dredging or other modifications. Tie channels were also once common along major tributaries to the Mississippi, such as the Red River. In the much less disturbed Alaskan environment, tie channels are still common, especially along Birch Creek and the Koyukuk and Black rivers. Our studies on the Mississippi River, in Alaska and in Papua New Guinea indicate that tie channels possess a common channel form that is stable and self-maintaining for hundreds to possibly a thousand years. Tie channels exhibit narrow width to depth ratios (~ 5.5) and consistently scale in cross-sectional dimensions to the size of the lake into which they flow. Variations in river and lake stage drive flow bi-directionally through tie channels. A local high or sill in the bed of tie channels controls the degree and duration of connection between the river and ORWB, with many lakes becoming isolated during periods of low stage. The life-span of a tie channel depends on the rate of sediment loading to the ORWB. Our research indicates that this rate directly corresponds to the sediment loading in the main stem river. Along the Fly River, for example, a 5 to 7 fold increase in the river sediment load has resulted increases of 6 to 17 times in tie channel progradation rates. In a few instances Fly River tie channels have become filled with sediment following the increase in sediment loading. The precise role of tie channels in the ecology of lowland river systems has yet to be quantified, but given their critical role in connecting rivers with floodplain habitats it is likely they provide an important source of refuge, breeding habitat, and biomass production for many aquatic organisms. As restoration efforts increasingly focus on the improving or reestablishing connectivity between lowland rivers and their floodplains, consideration should be given as to whether tie channels are an important missing component of such systems.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1845 Limnology
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly