Modelling of Infiltration-Exfiltration Effects of Cross-Shore Sediment Transport in the Swash Zone

Abstract

The effects on the sediment transport rate due to inclusion of seepage process in the mass of the beach sand in the swash zone are investigated numerically. A higher order Boussinesq model for breaking and non-breaking waves is extended in the swash zone and is coupled with a porous flow model which is based on the shallow water equations. To take into account of the infliltration-exfiltration processes in the sediment transport, a modified Shields parameter is used to account the effects of stabilization or destabilization of the surface layers and boundary layer thickening or thinning. The numerical results indicated that for fine sediments, the time-averaged onshore transport is decreased, while the offshore transport is increased. For coarser sediments the time-averaged onshore transport is increased, while the offshore transport is decreased. The above results are in agreement with field measurements as well as with experimental data. The exact value of the critical grain size changeover point is no straightforward to estimate. Present numerical experiments indicate that the value of the critical grain size changeover point appears to lie somewhere between 0.4 and 0.6 mm. Relatively small changes in the estimation of the friction factor might change the direction of the apparent influence of infiltration-exfiltration.