Sediment Mixing Depth Determination for Steep and Gentle Foreshores


  • Oscar Ferreira
  • Paolo Ciavola
  • Rui Taborda
  • Marcos Bairros
  • J. Alveirinho Dias


Sediment activation, mixing depth, beach slope, fluorescent tracers, rods and holes, morphodynamics, Portugal


Seven field experiments were undertaken on the Algarve coast, southern Portugal, to obtain mixing depths associated to a range of wave heights on steep beach slopes. The analysis of results lead to the identification of a correlation between significant breaking wave height (Hbs) and mean sediment activation depth (Zm) that can be expressed by the relationship Zm = 0.23Hbs . This relationship is similar to previous ones obtained for steep beaches (beach face slope bigger than 0.08) but about 8 times larger than the ones observed on gentle foreshores (beach face slope smaller than 0.08). Through the joint analysis of the collected data and that published by previous authors for both gentle and steep beaches, together with the beach face slope (tan β), the relationship Zm = 1.86Hbstan β was obtained. A good agreement was observed between predicted values using this equation and existent field observations. The relationship between the mean sediment activation depth and the maximum mixing depth (Zmax) showed the existence of a general Zmax/Zm ratio equal to 1.8. The empirical relationships produced in this study find an applicability for a wide range of beach slopes and wave heights.