Dynamics of the swash zone and effluent line on sandy beaches

Features of overall swash climate were examined over a range of beaches including reflectlve, intermediate and dissipative types.Both reflective and dissipative beaches have swashes, wlth respectively short and long penods, that cross the effluent h e or groundwater table outcrop a t all states of the tlde.Intermediate beaches experience more swashes crossing the effluent line at hlgh tide.Total swash upwash is greatest on intermediate beaches whereas the frequency of upwashes reaching unsaturated sand above the effluent line is greatest on reflective beaches.The 3 beach types are well separated on the basis of total upwash distance as a percentage of intertidal distance, this being 95 to 125 % on reflective beaches, 25 to 55 % on intermediate and 7 to 35 % on dissipative beaches.Similarly, reflective beaches are marked by 2 to 5 effluent line crossings min-' as opposed to 0 to 2 for intermediate and 0 to 1 for dissipative beaches.Many features of swash climate show good correlations with beach slope and morphodynamic state but not with wave energy.All beach types exhibit similar proportions of saturated vs unsaturated sand, this being 5 to 30 O/O at low tide and 80 to 95 O/O at high tide.It 1s concluded that changes in the dynamics of the effluent line and swash climate from reflective to dissipative beach types may be responsible for changes in interstihal conditions and the types of macrofauna inhabiting the different beaches.