We have used a novel techniques to study turbulent diffusion by means of 
digital processing of images taken from remote sensing and video recordings of 
the sea surface. The use of image analysis allows to measure variations of 
several decades in horizontal diffusivity values. There is an increase of 
diffusivity with wave height but only for large Wave Reynolds numbers. Other 
important factors are wind speed and tidal currents. The horizontal diffusivity 
shows a marked anisotropy as a function of wave height and distance from the 
coast.

Measurements have been made near the coast in a series of field experiments 
done at the Trabucador beach in the Ebro Delta, south of Barcelona and in Brazil 
for a variety of weather conditions and there is a strong dependence of 
horizontal eddy diffusivities with the Wave Reynolds number as well as with the 
wind stress measured as the friction velocity from wind profiles measured at the 
coastline. These results have been published recently in Bezerra et al. 1998. 
Both efects are important and give several decades of variation of eddy 
diffusivities measured near the coastline (between 0.0001 and 2 m2/s ). 
Longshore currents are also important near the coast. Experiments of dye 
diffusion such as those performed filming the evolution of sliks allow to 
characterize the ranges of Kx and Ky as a function of the distance to the coast 
and other environmental factors such as Wave height and frequency, wind stress, 
tides and mean currents.

References

Bezerra M.O., Diez M., Medeiros C., Rodriguez A., Bahia E., Sanchez Arcilla A. 
and Redondo J.M., (1998), "Study on the influence of waves on coastal diffusion 
using image analysis", Applied Scientific Research, 59, 127-142.

Rodriguez A., Sanchez-Arcilla A., Redondo J.M and C. Mosso, (1999), 
"Macroturbulence in the Surf Zone: Field and Laboratory Measurements", 
Experiments in Fluids, 26, 82-94.