Rip current likelihoods and predictions on 2 different bathymetries observed within 1 week on the same beach in Duck, NC

A rip-current prediction model based on Boussinesq numerical simulations (FUNWAVE) that quantifies rip-current likelihoods is applied to two nearshore bathymetries on the Outer Banks of North Carolina, near the town of Duck. The model is skillful (Brier skill score > 0.5) in reproducing the maximum offshore-directed currents observed with 28 current meters deployed across and along the surfzone for 1 month. During ~1 week within the application period, the observed surfzone bathymetry evolved from relatively alongshore uniform to alongshore inhomogeneous with channels and crescentic sandbars, affecting the likelihood of dangerous rip currents with the same incident wave conditions. Although the maximum difference in rip current likelihoods between the two bathymetries reached approximately 20%, the hazard indices, predicted by averaging likelihoods from a wide range of observed incident wave conditions, varied by only 6 to 7%. The results suggest that at beaches with evolving bathymetry, conservative rip current warnings should be based on 3D survey data collected during periods of greater alongshore inhomogeneity, when the strongest rip currents are expected.