Sediment mixing depth determination for steep and gentle foreshores

Seven field experiments were undertaken on the Algarve coast, southern Port ugal, to obtain mixing depths associated to a range of wave heights on stee p beach slopes. The analysis of results lead to the identification of a cor relation between significant breaking wave height (H-bs) and mean sediment activation depth (Z(m)) that can be expressed by the relationship Z(m) = 0. 23H(bs). This relationship is similar to previous ones obtained for steep b eaches (beach face slope bigger than 0.08) but about 8 times larger than th e ones observed on gentle foreshores (beach face slope smaller than 0.08). Through the joint analysis of the collected data and that published by prev ious authors for both gentle and steep beaches, together with the beach fac e slope (tan beta), the relationship Z(m) = 1.86H(bs) tan beta was obtained . A good agreement was observed between predicted values using this equatio n and existent field observations. The relationship between the mean sedime nt activation depth and the maximum mixing depth (Z(max)) showed the existe nce of a general Z(max)/Z(m) ratio equal to 1.8. The empirical relationship s produced in this study find an applicability for a wide range of beach sl opes and wave heights.