HR: 1340h
AN: H53D-0490    [Abstracts]
TI: Bed load transport in gravel-bed rivers lacking constraints on sediment availability
AU: * Gomez, B
EM: bgomez@indstate.edu
AF: Indiana State University, Geomorphology Laboratory, Terre Haute, IN 47809 United States
AB: G.K. Gilbert and R.A. Bagnold made the analogy between a river and a machine, relating the rate at which bed load is transported to the rate of energy expenditure in the channel, such that i_b = ω e_b / tan α where: (in mass units) i_b is the transport rate of bed load measured as immersed mass per unit width; ω is the stream power per unit width; e_b is the bed load efficiency; and α is the angle of internal dynamic friction of the sediment. In circumstances where there are no limitations on the supply of incoming sediment to a reach rivers become very efficient at transporting bed load, and i_b has been hypothesized to vary as particle size (D)^-0.5. Considering averages of measurements made in four rivers where there is a high availability of sediment in relation to runoff, and comparable data that represent the high end of the range of transport conditions achieved in three laboratory flumes, a coherent regression relation (R² = 0.99) between efficiency and median particle size emerges. Assuming 0.63 is an appropriate value for tan α, substituting the regression relation for e_b in the above equation gives i_b = ω 0.0105 D₅₀^-0.532 / 0.63, which is a straightforward scale correlation that can be used to estimate the magnitude of bed load transport in gravel-bed rivers under conditions where sediment transport is not constrained by the supply of sediment to, or the amount of sediment available in the channel. Although not an authoritative test of its applicability, there is a good correspondence between average observed and predicated transport rates during the large magnitude, September 1994 flood in the Rio Cordon, Italy, and in the Pasig-Potrero River following the 1991 eruption of Mount Pinatubo (i_{b observed} / i_{b calculated} = 1.1 and 0.9, respectively).
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1815 Erosion
DE: 1817 Extreme events
DE: 1856 River channels (0483, 0744)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: Fall Meeting 2005