HR: 1340h
AN: H43A-0350    [Abstracts]
TI: Probability Distribution of Bed Elevation in a Bedform-Dominated Large River
AU: * Leclair, S F
EM: leclair@tulane.edu
AF: Department of Earth and Environmental Sciences,Tulane University, Dinwiddie Hall, New Orleans, LA 70118 United States
AU: Miller, J Z
EM: jmiller1@tulane.edu
AF: Department of Earth and Environmental Sciences,Tulane University, Dinwiddie Hall, New Orleans, LA 70118 United States
AB: Recent research on morphodynamic models for bedform-dominated rivers has strongly indicated the need to improve our knowledge of the nature of dune height and trough-scour depth variation in time and space. The probability distribution of dune-bed elevation (Ps) is a key element of these new depth-continuous models (i.e., with no distinct active bed layers) in which elevation-specific formulations for sediment transport were developed. For now, these models are theoretical frameworks and there exist only limited experimental data to implement them. This paper presents much needed data from the field. We surveyed a set of two km-long bed profiles of the Mississippi River where flow depth averaged 20 m. One profile followed the sailing line at a major river crossing and the other was located in the center of the channel. Bed profiles show multi-scale bedforms. We constructed Ps curves for the entire bed profiles and for selected stretches. We find that Ps curves are asymmetric relative to mean bed level, with a larger probability of deep bed elevations. This is comparable to previous experimental results at relatively high sediment-transport stage. Otherwise, Ps curves of entire profiles reflect the tri-dimensionality of macro-scale bedwaves that scale with channel width (1 km) and planform. The upper-limit elevation always approximates the ratio of observed mean dune height over mean flow depth. This ratio is lower for the deep dunes than for those migrating on point bars. Comparative analysis of these Ps curves with those constructed from USACE 2001 data at the same site brings some insight on sediment deposition and erosion over time. Our preliminary results also show the potential of Ps curves for studies integrating multi-scale bedform characteristics. Future research will include relating Ps curves to vertical sorting, velocity profiles and estimates of sediment transport from acoustic measurements, as well as associated stratigraphy.
DE: 4558 Sediment transport
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting