HR: 17:15h
AN: OS14B-06    [Abstracts]
TI: Laboratory observations of waves and turbulence over a barred beach
AU: * Maddux, T B
EM: tbmaddux@engr.orst.edu
AF: Oregon State University, O.H. Hinsdale Wave Research Laboratory 202 Apperson Hall, Corvallis, OR 97331-2302
AU: Scott, C P
EM: scottc2@engr.orst.edu
AF: Oregon State University, O.H. Hinsdale Wave Research Laboratory 202 Apperson Hall, Corvallis, OR 97331-2302
AU: Cox, D T
EM: dan.cox@oregonstate.edu
AF: Oregon State University, O.H. Hinsdale Wave Research Laboratory 202 Apperson Hall, Corvallis, OR 97331-2302
AB: Turbulence in the surf zone plays an important role in many nearshore processes. Turbulence generated by wave breaking dominates wave dissipation and affects the drag felt by waves as they move towards shore. Turbulence may also play an important role in unsteady effects important to cross-shore sediment transport over barred beaches. These effects, which are not incorporated into quasi-steady models for cross-shore sediment transport, include the interactions of breaking wave turbulence with the bed and forward phase shifts of bed shear stress relative to the fluid velocity outside the boundary layer. It is difficult to obtain spatially dense observations of turbulent stresses in the field. Furthermore, separation of turbulent motions from wave-induced motions is technically difficult, and existing field-applicable techniques (Trowbridge, 1998; Trowbridge & Elgar, 2001) for this separation have not been directly compared with laboratory techniques such as phase-averaging. A rigid, impermeable barred beach bathymetry was setup in the large wave flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University for these purposes. The flume is 104 m long, 3.7 m wide, and 4.6 m deep. The bar is modeled as a feature of elevation atop an underlying 1:36 slope, with a 0.45 m crest height and an 0.69 m water depth over the bar crest. Regular and random waves corresponding to an approximately 1:3 scale of field observations at Duck, NC were run over the barred beach. Waves and vertical profiles of velocity were measured at many cross-shore locations. Results to be presented include comparisons of the different techniques for estimation of Reynolds stress components and evaluations of the errors associated with each technique. The cross-shore distribution of near-bed estimates of Reynolds shear stress will be compared with acceleration-based parameterizations for boundary shear stress in the nearshore. The balance of turbulent kinetic energy fluxes with turbulent production and dissipation will be explored along with comparisons of observed stress and dissipation estimates with those arising from turbulent closure or drag coefficient approximations.
DE: 4546 Nearshore processes
DE: 4558 Sediment transport
DE: 4560 Surface waves and tides (1255)
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting