Estimation of turbulence-dissipation rates and gas-transfer velocities in a surf pool: Analysis of the results from WABEX-93

: Two major research activities were carried out during this grant period. The first was participation in the DUCK94 field experiment to investigate nearbed fluid motions and resulting sediment resuspension in the surf zone. Data were collected over two three-week periods, in August and October 1994, and included concurrent measurements of velocity and suspended sediment profiles at three cross-shore locations and under a variety of wave and current conditions. The second activity was participation in a controlled wave basin experiment to investigate turbulence generated under breaking waves (galley proof attached). Vertical profiles of turbulence intensity were estimated from velocity fluctuations. Beneath broken waves, turbulence intensity was found to be high throughout the water column and to increase both toward the bed (due to boundary shear) and the sea surface (due to wave breaking). In a simple model using eddy viscosity profiles determined from the turbulence intensities, the surface turbulence generated by wave breaking would cause suspended sediments to be distributed higher into the water column than existing models would predict considering turbulence generated only at the bottom boundary. This redistribution of suspended sediment would have a significant impact on sediment flux in the surf zone. At present we are analyzing the DUCK94 data set in two ways. First, the eddy viscosity profiles from the wave basin experiment are being used to understand observed suspended sediment profiles and particle flux. Second, cross-shore flux divergence of sediment is being used to explain observed changes in the beach profile (i.e., net deposition and erosion).