HR: 08:15h
AN: OS11A-02    [PDF]
TI: Morphodynamic Modeling of the Co-evolution of Channel and Floodplain in Large, Sand-bed Rivers
AU: * Lauer, J
EM: laue0050@umn.edu
AF: St. Anthony Falls Laboratory, Mississippi River at 3rd Ave SE, Minneapolis, MN 55414 United States
AU: Parker, G
EM: parke002@umn.edu
AF: St. Anthony Falls Laboratory, Mississippi River at 3rd Ave SE, Minneapolis, MN 55414 United States
AB: The Strickland River, Papua New Guinea, provides an example of a dynamic large, lowland sand-bed river in which channel and floodplain have co-evolved. We are developing a general model to predict such co-evolution. The key new element of the analyis concerns fine-grained material, which heretofore has been considered as wash load and assumed to play no morphodynamic role. In the model described here sand plays the role of bed material load and mud plays the role of floodplain material load. In the present simple implementation only two grain sizes are used, one for the sand and one for the mud. Three active and one passive sediment reservoirs are considered; a) the active layer of the bed, b) a basal floodplain layer, c) an upper floodplain layer and d) the (passive) substrate below these layers. An enforcement of conservation of sediment mass in each of the active reservoirs makes it possible to model the evolution of bed and floodplain elevation, and the fractions of sand and mud in each reservoir and the water column. Flux of sediment from the channel to the floodplain is modeled in terms of an overbank sediment deposition model. Flux of sediment from the floodplain to the channel is modeled in terms of a net loss associated with channel meander migration. The model offers an explanation of bankfull channel characteristics. That is, when the channel is too shallow, (the floodplain elevation is too low), the river floods frequently, so that overbank deposition overwhelms the loss of sediment associated with channel migration and mean floodplain elevation increases in time. When the channel is too deep, (the floodplain is too high), overbank deposition is so infrequent that it is overwhelmed by floodplain removal due to channel migration, causing mean floodplain elevation to decrease in time. In the absence of bed elevation changes, the channel evolves toward a depth where overbank deposition just equals floodplain erosion due to migration. We present preliminary results of the model. Although it is too early to apply the model directly to the Strickland and Fly Rivers in Papua New Guinea, our ultimate goal is to extend the model to this case, so as to include a) multiple grain sizes, b) channel aggradation/degradation and c) base level rise.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1869 Stochastic processes
DE: 1886 Weathering (1625)
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting