STUDY ON THE INFLUENCE OF WAVES ON COASTAL DIFFUSION USING IMAGE-ANALYSIS

A series of novel image analysis techniques have been used to study su rf-zone hydrodynamics taking advantage of recent advances in digital p rocessing of images taken from video recordings of the sea surface nea r the coast. The use of image analysis allows the estimation of both s patial and temporal characteristics of wave fields, surface circulatio n and mixing in the surf zone. The dispersion of blobs of dye released at different distances from the coastline under very different sea co nditions is used to measure surface eddy diffusivities. A preliminary set of field measurements were done in the Ebro Delta where the method ology was tested. Further experiments have been performed at Vilanova, Spain and Recife, Brazil. There is an increase of diffusivity with wa ve height but only if the wave Reynolds number, Rw, is greater than 10 (3). No such trend is observed for Rw greater than 10(6). The other im portant factors are wind speed and tidal and longshore currents.