HR: 16:00h
AN: H24A-03    [Abstracts]
TI: Minimizing the Error Associated With Measurements of Migration-Related Sediment Exchange on Meandering Rivers
AU: * Lauer, J W
EM: laue0050@umn.edu
AF: University of Minnesota Department of Civil Engineering, Saint Anthony Falls Laboratory 2 3rd Avenue S.E., Minneapolis, MN 55414 United States
AU: Parker, G
EM: parke002@umn.edu
AF: University of Minnesota Department of Civil Engineering, Saint Anthony Falls Laboratory 2 3rd Avenue S.E., Minneapolis, MN 55414 United States
AB: The floodplains of meandering rivers represent reservoirs that both store and release sediment. Bed material is generally released from cut banks and replaced in nearby point bars wherever migration occurs. Measuring the associated bed material flux is important for tracing the movement of contaminants that may be mixed with the bed material. Approximations of this flux can be made using a representative channel depth and sequences of aerial photography to estimate average absolute migration rates (or reworked areas) between photographs. Error in the aerial photographs leads to a positive bias in computed release rates. A method for removing this bias is introduced that uses the apparent offset of fixed linear features such as roads (along smaller rivers) or abandoned channel courses (along larger rivers). Measuring the rate of release of fine sediment is important both for predicting the long term morphodynamic evolution of the channel/floodplain system and for tracing the movement of contaminants that may be adsorbed to the fine sediment. While fine sediment can be mixed throughout the depth of the floodplain, it is most concentrated in the upper portion of older parts of the floodplain where it has had time to accumulate through overbank deposition. Its release rate can be estimated using migration rates computed from aerial photography in combination with local measurements of bank topography, both of which are highly variable even within a given reach. Where detailed bank topography is available for an entire reach, estimating the release of fine sediment is relatively straightforward. However, detailed topography is often unavailable along the banks of large lowland rivers, forcing estimates of the fine material flux to be made using a relatively small number of physically surveyed cross-sections. It is not immediately clear how many cross sections are required for a good estimate. This study performs Monte Carlo simulations on a detailed topographic dataset obtained using LiDAR along a 91 km reach of the Pearl River, near New Orleans, Louisiana, to determine the error introduced by sampling only a small number of cross sections. Estimates of both the bed material flux and fine material flux associated with migration are presented for this reach.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2005 Joint Assembly