TY - JOUR

T1 - The Roles of Bathymetry and Waves in Rip-Channel Dynamics

AU - Christensen, D. F.

AU - Raubenheimer, B.

AU - Elgar, S.

N1 - Publisher Copyright: © 2024. American Geophysical Union. All Rights Reserved.

PY - 2024

Y1 - 2024

N2 - The behavior and predictability of rip currents (strong, wave-driven offshore-directed surfzone currents) have been studied for decades. However, few studies have examined the effects of rip channel morphology on the rip generation or have compared morphodynamic models with observations. Here, simulations conducted with the numerical morphodynamic model MIKE21 reproduce observed trends in flows and bathymetric evolution for two channels dredged across a nearshore sandbar and terrace on an ocean beach near Duck, NC, USA. Channel dimensions, wave conditions, and flows differed between the two cases. In one case, a strong rip current was driven by moderate height, near-normally incident waves over an approximately 1-m deep channel with relatively little bathymetric evolution. In the other case, no rip was generated by the large, near-normally incident waves over the shallower (∼0.5 m) channel, and the channel migrated in the direction of the mean flow and eventually filled in. The model simulated the flow directions, the generation (or not) of rip currents, and the morphological evolution of the channels reasonably well. Model simulations were then conducted for different combinations of the two channel geometries and two wave conditions to examine the relative importance of the waves and morphology to the rip current evolution. The different bathymetries were the dominant factor controlling the flow, whereas both the initial morphology and wave conditions were important for channel evolution. In addition, channel dimensions affected the spatial distribution of rip current forcings and the relative importance of terms.

AB - The behavior and predictability of rip currents (strong, wave-driven offshore-directed surfzone currents) have been studied for decades. However, few studies have examined the effects of rip channel morphology on the rip generation or have compared morphodynamic models with observations. Here, simulations conducted with the numerical morphodynamic model MIKE21 reproduce observed trends in flows and bathymetric evolution for two channels dredged across a nearshore sandbar and terrace on an ocean beach near Duck, NC, USA. Channel dimensions, wave conditions, and flows differed between the two cases. In one case, a strong rip current was driven by moderate height, near-normally incident waves over an approximately 1-m deep channel with relatively little bathymetric evolution. In the other case, no rip was generated by the large, near-normally incident waves over the shallower (∼0.5 m) channel, and the channel migrated in the direction of the mean flow and eventually filled in. The model simulated the flow directions, the generation (or not) of rip currents, and the morphological evolution of the channels reasonably well. Model simulations were then conducted for different combinations of the two channel geometries and two wave conditions to examine the relative importance of the waves and morphology to the rip current evolution. The different bathymetries were the dominant factor controlling the flow, whereas both the initial morphology and wave conditions were important for channel evolution. In addition, channel dimensions affected the spatial distribution of rip current forcings and the relative importance of terms.

U2 - 10.1029/2023JF007389

DO - 10.1029/2023JF007389

M3 - Journal article

AN - SCOPUS:85181713472

VL - 129

JO - Journal of Geophysical Research: Earth Surface

JF - Journal of Geophysical Research: Earth Surface

SN - 2169-9003

IS - 1

M1 - e2023JF007389

ER -