A numerical model solving the Reynolds-Averaged Navier-Stokes equations, with a volume of fluid-tracking scheme and turbulence closure, is employed for estimating hydrodynamics in the swash zone. Model results for run-up distance, water depth, and near-bed velocity are highly correlated (r2 > 0.97) with ensemble-averaged dam-break-driven swash data. Moreover, modeled bed shear stresses are within 20% of estimates derived from measured velocity profiles. Dam-break-driven swash simulations are conducted to determine the effect of foreshore characteristics (bed roughness and foreshore slope) on bore-induced swash-zone hydrodynamics and bed shear stresses. Numerical results revealed that the boundary layer vanishes during flow reversal, grows during the backwash, and becomes depth limited at the end of the swash cycle. In general, the uprush experiences larger shear stresses but for a shorter duration than the backwash. Some variability in this pattern is observed depending on the bed roughness, foreshore slope, and cross-slope location in the swash zone, implying that large spatial gradients in shear stresses can occur on the foreshore. The mean tangential force per unit area supplied to the bed is offshore directed for the simulated cases, with the exception of the mild-slope (1:25) cases, owing to the skewed nature of swash flows. The temporal evolution of the momentum balance inside the swash zone shows an important contribution to the total force from turbulence and advection at the early/final stage of the swash cycle, whereas the local acceleration does not appear to be a significant contribution.
This work was supported by the National Council of Science and Technology of Mexico (CB-167692 and M0023-08-06-106400), UNAM (Instituto de Ingenieria Proyecto Interno A2 and DGAPA UNAM PAPIIT IB102012-2), the National Science Foundation CAREER Award (OCE-0845004), and the University of Delaware. Tom Baldock and two anonymous reviewers are thanked for helping to improve the manuscript. We thank one anonymous reviewer for his/her suggestion to investigate flow vorticity during uprush as a possible way to determine the applicability of the log-law model during that phase of the swash cycle.
- swash zone