Rip currents and alongshore flows in single channels dredged in the surf zone

Moulton, Melissa; Elgar, Steve; Raubenheimer, Britt; Warner, John C.; Kumar, Nirnimesh

doi:10.1002/2016jc012222

Cited by 37 publications

(41 citation statements)

References 84 publications

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“…Brander, 1999;MacMahan et al, 2005;Castelle et al, 2006;Austin et al, 2010;Bruneau et al, 2011;Winter et al, 2014) and tide elevation (Aagaard et al, 1997;MacMahan et al, 2006;Bruneau et al, 2009;Austin et al, 2014). Surf zone morphology is also critical to rip activity, with deeper rip channels resulting in more intense rips (Brander, 1999;Aagaard and Vinther, 2008;Moulton et al, 2017a;McCarroll et al, 2018). Given that rip speed is an effective proxy for the physical hazard posed by rips (Moulton et al, 2017b), and that warm sunny days with low winds typically result in increased beach attendance and beachgoer exposure to hazards (Ibarra, 2011), rip risk predictors based on simple correlations between meteorological, oceanographic conditions and the incidence of rip related rescues were developed (Lushine, 1991;Lascody, 1998, Dusek andSeim, 2013).…”

Section: 5% Of Leading Cause Of Rescue Inmentioning

confidence: 99%

Environmental controls on surf zone injuries on high-energy beaches

Castelle¹,

Scott²,

Brander³

et al. 2019

Preprint

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Abstract. The two primary causes of surf zone injuries (SZIs) worldwide, including fatal drowning and severe spinal injuries, are rip currents (rips) and shore-break waves. SZIs also result from surfing and body boarding activity. In this paper we address the primary environmental controls on SZIs along the high-energy meso-macrotidal surf beach coast of SW France. A total of 2523 SZIs recorded by lifeguards over 186 sample days during the summers of 2007, 2009 and 2015 were combined with measured and/or hindcast weather, wave, tide and beach morphology data. All SZIs occurred disproportionately on warm sunny days with low wind likely because of increased beachgoer numbers and hazard exposure. Relationships were strongest for shore break and rip related SZIs and weakest for surfing related SZIs, the latter being also unaffected by tidal stage or range. Therefore the analysis focussed on bathers. Shore-break related SZIs disproportionately occur during shore-normal incident waves with average to below-average wave height (significant wave height Hs = 0.75–1.5 m) and around higher water levels and large tide range when waves break on the steepest section of the beach. In contrast, rip related drownings occur disproportionally near neap low tide, coinciding with maximized channel rip flow activity, under shore-normal incident waves with Hs > 1.25 m and periods mean wave period longer than 5 s. Additional drowning incidents occurred at spring high tide, presumably due to small-scale swash rips. The composite wave and tide parameters proposed by Scott et al. (2014) are key controlling factors determining SZI occurrence, although the risk ranges are not necessarily transferable to all sites. Summer beach and surf zone morphology is highly interannually variable, which is critical to SZI patterns. The upper beach slope can vary from 0.06 to 0.18 between summers, resulting in low and high shore-break related SZIs, respectively. Summers with coast-wide highly (weakly) developed rip channels also result in widespread (scarce) rip related drowning incidents. With life risk defined in terms of the number of people exposed to life threatening hazards at a beach, the ability of morphodynamic models to simulate primary beach morphology characteristics a few weeks/months in advance is therefore of paramount importance to predict the primary surf-zone life risks along this coast.

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Section: 5% Of Leading Cause Of Rescue Inmentioning

confidence: 99%

Environmental controls on surf zone injuries on high-energy beaches

Castelle¹,

Scott²,

Brander³

et al. 2019

Preprint

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“…However, less efforts have been devoted to investigating beach evolution after coastal structures removal. Recent studies have focused on investigating the morphodynamic responses to seafloor artificial perturbations (e.g., excavated holes and channels) in the nearshore [19][20][21]. Moulton et al [20] investigated the mechanisms controlling the infill of large excavated holes in the surf zone, finding that downslope gravity-driven bedload transport was important in morphological evolution for bathymetric features with large slopes.…”

Section: Introductionmentioning

confidence: 99%

Field and Numerical Study of Resistance and Resilience on a Sea Breeze Dominated Beach in Yucatan (Mexico)

Medellín

Torres-Freyermuth

Tomasicchio

et al. 2018

Water

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The understanding of the beach capability to resist and recover from a disturbance is of paramount importance in coastal engineering. However, few efforts have been devoted to quantifying beach resilience. The present work aims to investigate the shoreline resistance and resilience, associated to a transient disturbance, on a sandy beach. A temporary groin was deployed for 24 h on a micro-tidal sea-breeze dominated beach to induce a shoreline perturbation. Morphological changes were measured by means of beach surveys to estimate the beach perturbation and the further beach recovery after structure removal. An Empirical Orthogonal Function (EOF) analysis of the shoreline position suggests that the first EOF mode describes the spatial-temporal evolution of the shoreline owing to the groin deployment/removal. A new one-line numerical model of beach evolution is calibrated with the field surveys, reproducing both the sediment impoundment and subsequent beach recovery after the structure removal. Thus, a parametric numerical study is conducted to quantify resistance and resilience. Numerical results suggest that beach resistance associated to the presence of a structure decreases with increasing alongshore sediment transport potential, whereas resilience after structure removal is positively correlated with the alongshore diffusivity.

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“…Although the comprehensive risk assessment of rip currents could be properly related to long-term observation statistics (Scott et al, 2014), the evolution and mechanism of this multi-channel rip system still remains insufficiently understood (Castelle et al, 2016b). Extensive previous research was focused on artificial topography with only one or two idealized rip channels (Haller et al, 2002;Haas et al, 2003;Moulton et al, 2017b;Hur et al, 2019). Present paper explores the dynamicity of multi-channel rip currents interlaced with rhythmic sandbars.…”

Section: Motivationmentioning

confidence: 99%

Dynamicity of multi-channel rip currents induced by rhythmic sandbars

Zhang

Xiao

et al. 2020

Preprint

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Abstract. In response to frequent fatal beach drownings, China's first operational attempt on the rip current hazard investigation was made by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches were found developing rip currents interlaced with rhythmic sandbars, varying by season and location evidenced by satellite images and morphodynamic calculation. Considering insufficient understanding of the multi-channel rip system, case analysis and numerical study were conducted to explore its dynamicity and circulation characteristics under various wave climates in present work. The strength of rip currents was generally proportional to wave height and channel width under certain limits. Increasing wave height was not always a promotion and could even weaken the rip current due to the strong wave-current shear. Interesting pump and feed interactions between adjacent rip currents in the multi-channel system were observed. The rip current might be totally absent in narrow channels when the majority of water flows through neighboring broader pathways. The rip current was highly sensitive to the incident wave angle. Alongshore currents prevailed over the rip current when the wave angle reached 11 degrees to shore normal, which was not favorable to the existence of channeled sandbars. Vortices appeared around the edge of the bar owing to nonuniform wave breaking over rapid-varying bathymetry. The setup water was created shoreward by the sandbar array and substantially increased as the wave deviated from the normal incidence. The water surface depression in the rip channel was not observed as the wave angle increased, which fundamentally explained why the rip current could not persist when the incident wave became slightly oblique. In future, incident wave angle should be further incorporated into empirical formulas or probabilistic models to predict the rip current for expected improvement in accuracy.

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Rip currents and alongshore flows in single channels dredged in the surf zone

Cited by 37 publications

References 84 publications

Environmental controls on surf zone injuries on high-energy beaches

Environmental controls on surf zone injuries on high-energy beaches

Field and Numerical Study of Resistance and Resilience on a Sea Breeze Dominated Beach in Yucatan (Mexico)

Dynamicity of multi-channel rip currents induced by rhythmic sandbars

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