Offshore controls on nearshore rip currents

Long, Joseph W.; Özkan-Haller, H. Tuba

doi:10.1029/2005jc003018

Cited by 63 publications

(66 citation statements)

References 19 publications

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“…Previous studies also have shown that nearshore circulation, including the locations of rip currents, can be controlled by nonuniformities in the offshore (i.e., outside the surfzone) bathymetry [Long and Ö zkan-Haller, 2005]. Here, the effect of strong alongshore variations in the incident wavefield (caused by an offshore submarine canyon [Long and Ö zkan-Haller, 2005;Magne et al, 2007;Thomson et al, 2007]) on setup and on alongshore flows in the surfzone is examined using field observations and simplified one-and two-dimensional momentum balances. After the theories are outlined (section 2) and the observations are described (section 3), the results are presented (section 4) and conclusions are given (section 5).…”

Section: Introductionmentioning

confidence: 99%

Wave‐driven setup and alongshore flows observed onshore of a submarine canyon

et al. 2008

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[1] The effect of alongshore variations in the incident wavefield on wave-driven setup and on alongshore flows in the surfzone is investigated using observations collected onshore of a submarine canyon. Wave heights and radiation stresses at the outer edge of the surfzone (water depth %2.5 m) varied by up to a factor of 4 and 16, respectively, over a 450 m alongshore distance, resulting in setup variations as large as 0.1 m along the shoreline (water depth %0.3 m). Even with this strong alongshore variability, wave-driven setup was dominated by the cross-shore gradient of the wave radiation stress, and setup observed in the surfzone is predicted well by a one-dimensional cross-shore momentum balance. Both cross-shore radiation stress gradients and alongshore setup gradients contributed to the alongshore flows observed in the inner surfzone when alongshore gradients in offshore wave heights were large, and a simplified alongshore momentum balance suggests that the large [O(1 kg/(s 2 m)] observed setup-induced pressure gradients can drive strong [O(1 m/s)] alongshore currents.Citation: Apotsos, A., B. Raubenheimer, S. Elgar, and R. T. Guza (2008), Wave-driven setup and alongshore flows observed onshore of a submarine canyon,

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Section: Introductionmentioning

confidence: 99%

Wave‐driven setup and alongshore flows observed onshore of a submarine canyon

et al. 2008

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“…Munk and Traylor, 1947;Shepard and Inman, 1950). The refractive scattering from these canyons induces longshore variations in both wave height and wave breaking, which in turn quite often lead to rip currents (for a recent analysis see Long and Ö zkan-Haller, 2005). Hence, the scattering can play an important role in the nearshore dynamics.…”

Section: Introductionmentioning

confidence: 99%

Wave Reflection from Nearshore Depressions

Michalsen¹,

Haller

Suh

2008

J. Waterway, Port, Coastal, Ocean Eng.

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This study employs an existing finite-difference model based on the hyperbolic form of the Modified Mild Slope Equation (MMSE) to investigate wave reflection near bathymetric depressions such as dredged borrow pits and nearshore canyons. First, the model is tested for numerical limitations on the higher order bottom slope and curvature terms using a idealized cases of a simple depth transition and a symmetric trapezoidal trench, with comparisons of the MMSE to both the traditional Mild Slope Equation (MSE) solution and a shallow water analytic solution. It is demonstrated that the model gives accurate solutions on slopes as steep as 1:1, and that the solutions from all three models agree in the shallow water region. However, for waves in intermediate depths, predicted wave reflection from nearshore depressions is shown to differ significantly between the MMSE and MSE models. Next, geometrical data from a wide range of existing and proposed borrow pits and a submarine canyon are gathered and analyzed for whether wave reflection is an important process near realistic nearshore depressions. The geometric data show that realistic nearshore depressions lie within the tested range of the MMSE model and that borrow pits are generally not in shallow water, which means it is important to use an MMSE-type model to calculate reflection from these features. In addition, storm conditions on average lead to a 50% increase in reflection coefficient in comparison to the mean wave conditions, due to the increase in wave period. Finally, the results also indicate borrow pit design criteria that can be used to ensure minimal reflection.

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“…Wave breaking on alongshore-nonuniform beaches can drive rip current circulation patterns and spatial variations in breaking-wave-driven alongshore flows [Sonu, 1972;MacMahan et al, 2010;Houser et al, 2013;Winter et al, 2014]. The alongshore gradients in wave breaking and setup that drive rip currents may be generated by local bathymetric variations [Bowen and Inman, 1969;Brander and Short, 2001;Haas et al, 2003;MacMahan et al, 2005Bruneau et al, 2009;Austin et al, , 2014, offshore bathymetric variations [Long and Özkan-Haller, 2005], wave-wave interactions [Dalrymple, 1975;Peregrine, 1998;Buhler and Jacobson, 2001], or wave-current interactions [Dalrymple and Lozano, 1978]. In both field and laboratory studies the speed of rip currents near inhomogeneous bathymetry varies with incident wave properties, tidal elevation, and the geometry of the bathymetric depression [Brander and Short, 2001;Bruneau et al, 2009;.…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic and morphodynamic responses to surfzone seafloor perturbations

Moulton¹

2016

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Holes and channels were excavated in the surf zone on an ocean beach near Duck, NC, and observations of the subsequent evolution of waves, currents, and the modified seafloor were used to investigate nearshore dynamics. In one set of seafloor perturbation experiments, deep holes with steeply sloping sides were excavated in the inner surfzone seafloor. Observations of the infilling holes were used to make the first field estimates of the surfzone morphological diffusivity, which describes the rate of seafloor smoothing by downslope sediment transport. To improve the temporal resolution of bathymetric estimates, a mapping method was developed to combine infrequent, spatially dense watercraft surveys with continuous, spatially sparse in situ altimeter estimates of the seafloor location. In another set of seafloor perturbation experiments, channels were dredged across the surf zone with the propellers of a landing craft. Alongshore variations in wave breaking caused by the perturbed bathymetry resulted in strong rip currents in the channels under some conditions, whereas alongshore currents bypassed the channels under other conditions. The dynamics of the circulation response for changing wave forcing, bathymetry, and tidal elevation are investigated using the observations, a numerical model, and a parameter based on wave properties and bathymetry.

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Offshore controls on nearshore rip currents

Cited by 63 publications

References 19 publications

Wave‐driven setup and alongshore flows observed onshore of a submarine canyon

Wave‐driven setup and alongshore flows observed onshore of a submarine canyon

Wave Reflection from Nearshore Depressions

Hydrodynamic and morphodynamic responses to surfzone seafloor perturbations

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