Bedload Transport on Sloping Beds in the Surf Zone
Calantoni, J., and Drake, T.G., 1999, Bedload transport on
sloping beds in the surf zone: EOS Trans. AGU, 80 (17), Spring
Meeting Suppl., S194. (Special session: Bedform Patterns and Processes)
Non-horizontal
beds are ubiquitous in sedimentary environments. Although the
bed is approximately horizontal in many cases, often it is not;
for instance, in the swash zone on coarse-grained beaches or on
such bedforms as dunes and megaripples. In particular, the effect
of bed slope on bedload transport processes in nearshore and fluvial
environments is poorly understood. Results from three-dimensional
discrete-particle computer simulations of bedload transport rates
in oscillatory flows over a plane bed contradict predictions of
commonly used energetics-based bedload transport formulae. For
beds sloping parallel to the direction of wave propagation, both
onshore and offshore, simulations predict a linear dependence
of the time average bedload transport rate on the bed slope for
slopes less than about 7 degrees. For bed slopes greater than
about 7 degrees the slope dependence of the time-average bedload
transport rate is nonlinear. Simulations used three waveforms
having a maximum near-bed fluid velocity of 1 m/s and a grain-size
distribution having a mean diameter of about 1 mm. The waveforms
vary from a Stokes-like wave to a sawtooth wave. For a given
waveform and slopes less than about 7 degrees, the constant of
proportionality between the time-average bedload transport rate
and the bed slope increases with increasing wave asymmetry.
Supported by the Coastal Dynamics Program of
the Office of Naval Research.