BOTTOM BOUNDARY-LAYER SPECTRAL DISSIPATION ESTIMATES IN THE PRESENCE OF WAVE MOTIONS

Turbulence measurements are an essential element of the Sediment TRans port Events on Shelves and Slopes experiment (STRESS). Sediment transp ort under waves is initiated within the wave boundary layer at the sea bed, at most a few tens of centimeters deep. The suspended load is car ried by turbulent diffusion above the wave boundary layer. Quantificat ion of the turbulent diffusion active above the wave boundary layer re quires estimates of shear stress or energy dissipation in the presence of oscillating flows. Measurements by Benthic Acoustic Stress Sensors of velocity fluctuations were used to derive the dissipation rate fro m the energy level of the spectral inertial range (the -5/3 spectrum). When the wave orbital velocity is of similar magnitude to the mean fl ow, kinematic effects on the estimation techniques of stress and dissi pation must be included. Throughout the STRESS experiment there was al ways significant wave energy affecting the turbulent bottom boundary l ayer. LUMLEY and TERRAY [(1983) Journal of Physical Oceanography, 13, 2000-2007] presented a theory describing the effect of orbital motions on kinetic energy spectra. Their model is used here with observations of spectra taken within a turbulent boundary layer which is affected by wave motion. While their method was an explicit solution for circul ar wave orbits aligned with mean current we extrapolated it to the cas e of near bed horizontal motions, not aligned with the current. The ne cessity of accounting for wave orbital motion is demonstrated, but var iability within the field setting limited our certainty of the improve ment in accuracy the corrections afforded.