Swash-zone morphodynamics

Hydrodynamic forcing with respect to sediment transport and morphologic change, paying particular attention to relevant swash asymmetries, is reviewed. The hydrodynamics are categorized into their individual effects: high- and low-frequency motions, bores and turbulence, in/exfiltration, shear stresses and friction coefficients. Individual effects are then related to their potential for driving or influencing sediment transport and morphological change. Additional concepts such as settling/scour lag and sediment advection that have largely been ignored are also discussed. A simple framework is presented for the morphological response of the beachface under swash zone hydrodynamic processes. The framework acknowledges that the beachface cannot be considered in isolation from the surf zone and that the two zones are strongly linked through feedback processes. The swash zone itself is also a morphodynamic system and morphological response occurs as a result of disequilibrium between the beachface gradient and asymmetries in the swash hydrodynamics. Any beachface morphological development in response to such equilibrium will have direct and indirect effects on swash hydrodynamics and sediment transport processes. It is concluded that the two issues requiring most urgent research attention with regards to swash zone sediment transport processes are the roles of sediment advection and longshore swash motion.