HR: 0800h
AN: H51I-0904    [Abstracts]
TI: Effect of Comminution on Bed – Sediment Size in a Fluvial System With a Flood Hydrograph
AU: * Fambrough, B A
EM: bfambrou@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, University Park, PA 16802, United States
AU: Slingerland, R L
EM: sling@geosc.psu.edu
AF: The Pennsylvania State University, Department of Geosciences, University Park, PA 16802, United States
AB: During transport in a fluvial system, sediment grains undergo comminution, thereby modifying the dis-equilibrium sediment transport rates of various size fractions in the bed. It would be useful to predict the relative effects of comminution and differential dis-equlibrium transport on bed composition and slope for steady and variable hydrographs. We have conducted a series of numerical experiments simulating fluvial transport and deposition of sand-sized heterogeneous quartz (Qtz), feldspar (F), and other heavy mineral mixtures (Hm) under varying flood hydrographs with and without comminution. The experimental design consists of a standard steady-state control run to which are compared various runs of simulated floods with discharge (Q) and sediment discharge (Qs) in varying ratios. The sediment supply is a temporally and spatially constant grain size distribution of Qtz:F:Hm equal to 70:25:5 with a feed rate at capacity with Q. The steady state results with constant boundary conditions show that the bed coarsens, the bed slope degrades and bed composition becomes more quartz rich compared to the initial conditions of the uniform feedstock. The results for a flood hydrograph with a matching capacity Qs show that a dynamic steady state is achieved in which the bed alternates between aggradation and degradation. The average bed concavity is greater than the standard case, and the bed composition and texture are more quartz-rich and finer. When grains are allowed to comminute the dis-equilibrium sediment transport rates of the various size fractions increases, leading to a larger deviation about a scenario's given average in the dynamic steady state scenario. The dynamic equilibrium case with comminution is finer and has a larger variance about a mean composition and texture relative to the same setup without comminution.
DE: 0798 Modeling
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1825 Geomorphology: fluvial (1625)
DE: 1862 Sediment transport (4558)
DE: 4558 Sediment transport (1862)
SC: Hydrology [H]
MN: 2007 Fall Meeting