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 profile 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 breaking on the beach face. The study has identified a linear correlation between significant wave height at breaking (H-b), and average sand-mixing depth (Z(m)), whereby Z(m)=0.27H(b). The empirical relationship is ten times larger than a previous one proposed by other authors working on gentle-slope dissipative beaches, and confirms previous findings on similar reflective beaches carried out in the USA. It was also confirmed that Z(m) is related to wave period, but does not seem to be a function of mean sand size. (C) 1997 Elsevier Science B.V.