FIELD OBSERVATIONS OF SAND-MIXING DEPTHS ON STEEP BEACHES

A series of field studies were carried out on three Portuguese beaches (Garrao, Fare and Culatra) to assess sandmixing depths under a range of wave heights (0.34-0.80 m), wave periods (5.1-7.0 s) and mean grain sizes (0.26 and 0.38 mm). All the studied beaches had a reflective pr ofile with a steep upper foreshore (tan beta of 0.10-0.14) and a more gentle low-tide terrace. In all experiments, plunging waves were break ing on the beach face. The study has identified a linear correlation b etween significant wave height at breaking (H-b), and average sand-mix ing depth (Z(m)), whereby Z(m)=0.27H(b). The empirical relationship is ten times larger than a previous one proposed by other authors workin g on gentle-slope dissipative beaches, and confirms previous findings on similar reflective beaches carried out in the USA. It was also conf irmed that Z(m) is related to wave period, but does not seem to be a f unction of mean sand size. (C) 1997 Elsevier Science B.V.