HR: 0830h
AN: H51E-1130    [PDF]
TI: Numerical Model for the Erosion, Transport and Deposition of Tracer Stones in Gravel-bed Rivers
AU: * Wong, M
EM: wong0228@umn.edu
AF: St. Anthony Falls Laboratory, Mississippi River at 3rd Ave SE, Minneapolis, MN 55414 United States
AU: Gary, P
EM: parke002@umn.edu
AF: St. Anthony Falls Laboratory, Mississippi River at 3rd Ave SE, Minneapolis, MN 55414 United States
AB: Passive tracer stones (e.g. painted stones or stones imbedded with a magnet) have been used to characterize gravel transport in mountain and upland rivers. A key feature of the quantification of transport in this way is the concept of virtual velocity, i.e. the average velocity of a stone including the time it spends at rest either on the bed surface or buried within the bed, in addition to the time it spends moving as bedload. Until recently the only way to model this exchange between the bed and the bedload was through the use of an active layer formulation of the type introduced by Hirano in 1971. Recently, however, a more physically oriented probabilistic approach has been developed. This approach considers the fact that bed elevation is constantly fluctuating in time and space, and specifies this fluctuation in terms of a vertical distance y relative to the mean bed elevation. It includes probability densities of a) a particle at elevation y being exposed, b) a particle at elevation y being entrained into bedload transport and c) a particle being deposited at elevation y. Here this formulation is developed to describe the erosion, transport and deposition of tracers under conditions of a) equilibrium transport, b) aggradation or degradation and c) a hydrograph. The formulation naturally links tracer conservation with conservation of gravel as a whole. In addition, it links vertical exchange of sediment (including tracer particles) with streamwise transport. Finally, it provides a means for predicting virtual velocity in terms of a set of functions describing bedload transport and the probability densities described above. By applying the model to a full hydrograph, it is possible to predict the probability density function of tracer concentration at the end of a flood. A simple moment formulation allows a prediction the mean and variance of distance moved over the hydrograph. Sample implementations of the formulation are given with the aid of experimental results obtained at St. Anthony Falls Laboratory.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1869 Stochastic processes
DE: 1886 Weathering (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting