Abstract
Rip currents are a leading cause of drowning on beaches worldwide. How bathers caught in a rip current should attempt to escape has been a subject of recent debate. A numerical model of human bathers escaping from a rip current flow field is applied to a 2-km-long section of the open beach of Biscarrosse, SW France. The study area comprises 4 rip channels that visually appear similar from the beach, but exhibit different morphologies. Simulations are run for 2 representative hazardous summer wave conditions. Results show that small changes in the bar/rip morphology have a large impact on the rip flow field, and in turn on the alongshore variability of the optimal rip current escape strategy. The overall flow regime (dominant surf-zone exits versus dominant recirculation), which is found to be influenced by the alongshore dimensions of the sand bars adjacent to the rip channel, is more important to rip current escape strategy than rip velocity. Flow regime was found to dictate the success of the “stay afloat” strategy, with greater success for recirculating flow. By comparison, the dominant longshore feeder current and rip-neck orientation determined the best direction to “swim parallel” towards. For obliquely incident waves, “swim parallel” downdrift then swim onshore with breaking waves was highly successful and can become a simple safety message for beach safety practitioners to communicate to the general public. However, in SW France where rip spacing is large (\(\sim\)400 m), surf-zone eddies have large spatial scales of the order of 100+ m, requiring a large distance (100+ m) to swim to reach safety, therefore requiring good swimming ability. This also shows that in addition to rip current intensity, rip flow regime and the depth of adjacent sand bars, rip spacing is important for defining rip current hazard and the best safety message. Our results also indicate that for normal to near-normal wave incidence, rip current hazard and best rip current escape strategy are highly variable alongshore due to subtle differences in bar/rip morphology from one rip system to another. These findings challenge the objective of developing a universal rip current escape strategy message on open rip-channelled beaches exposed to normal to near-normal wave incidence, even for seemingly similar rip channels.
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References
Almar R, Castelle B, Ruessink BG, Sénéchal N, Bonneton P, Marieu V (2010) Two- and three-dimensional double-sandbar system behaviour under intense wave forcing and a meso-macro tidal range. Cont Shelf Res 30:781–792
Arozanera I, Houser C, Echeverria AG, Brannstrom C (2015) The rip current hazard in Costa Rica. Nat Hazards 77:753–768
Austin M, Scott TM, Brown JW, Brown JA, MacMahan JH (2009) Macrotidal rip current experiment: circulation and dynamics. J Coast Res 56:24–28
Austin M, Scott TM, Brown JW, Brown JA, MacMahan JH, Masselink G, Russell P (2010) Temporal observations of rip current circulation on a macro-tidal beach. Cont Shelf Res 30:1149–1165
Austin M, Scott TM, Russell PE, Masselink G (2013) Rip current prediction: development, validation and evaluation of an operational tool. J Coast Res 29(2):283–300
Austin M, Masselink G, Scott TM, Russell PE (2014) Water-level control on macro-tidal rip currents. Cont Shelf Res 75:28–40
Bonneton P, Bruneau N, Castelle B, Marche F (2010) Large-scale vorticity generation due to dissipating waves in the surf zone. Discrete Contin Dyn Syst Ser B 13(4):729–738. doi:10.3934/dcdsb.2010.13.729
Bowen AJ (1969) Rip currents: 1. Theoretical investigations. J Geophys Res 74:5479–5490
Branche CM, Stewart S (2001) Lifeguard effectiveness: A report of the Working Group. Atlanta
Brander RW, Short AD (2001) Flow kinematics of low-energy rip current systems. J Coast Res 17:468–481
Brander RW, Bradstreet A, Sherker S, MacMahan JH (2011) The behavioural responses of swimmers caught in rip currents: new perspectives on mitigating the global rip current hazard. Int J Aquat Res Educ 5:476–482
Brander RW, Dominey-Howes D, Champion C, Del Vecchio O, Brighton B (2013) A new perspective on the Australian rip current hazard. Nat Hazards Earth Sci Syst Sci 13:1687–1690
Brewster BC (2010) Rip current misunderstanding. Nat Hazards 55:161–162
Brighton B, Sherker S, Brander RW, Thompson M, Bradstreet A (2013) Rip current related drowning deaths and rescues in Australia 2004–2011. Nat Hazards Earth Sci Syst Sci 13:1069–1075
Bruneau N, Castelle B, Bonneton P, Pedreros R (2009a) Very low frequency motions of a rip current system: observation and modeling. J Coast Res 56:1731–1735
Bruneau N, Castelle B, Bonneton P, Pedreros R, Almar R, Bonneton N, Bretel P, Parisot JP, Sénéchal N (2009b) Field observations of an evolving rip current on a meso-macrotidal well-developed inner bar and rip morphology. Cont Shelf Res 29:1650–1662
Bruneau N, Bonneton P, Castelle B, Pedreros R (2011) Modeling rip current circulations and vorticity in a high-energy meso-macrotidal environment. J Geophys Res. doi:10.1029/2010JC006693
Bruneau N, Bertin X, Castelle B, Bonneton P (2014) Tide-induced flow signature in rip currents on a meso-macrotidal beach. Ocean Model 74:53–59
Butel R, Dupuis H, Bonneton P (2002) Spatial variability of wave conditions on the French Atlantic coast using in situ data. J Coast Res 36:96–108
Castelle B, Bonneton P (2006) Modelling of a rip current induced by waves over a ridge and runnel system on the Aquitanian Coast, France. Comptes Rendus Geosci 338:711–717
Castelle B, Coco G (2013) Surf zone flushing on embayed beaches. Geophys Res Lett 40:1–5. doi:10.1002/grl.50485
Castelle B, Bonneton P, Sénéchal N, Dupuis H, Butel R, Michel D (2006) Dynamics of wave-induced currents over an alongshore non-uniform multiple-barred sandy beach on the Aquitanian Coast, France. Cont Shelf Res 26:113–131
Castelle B, Bonneton P, Dupuis H, Sénéchal N (2007) Double bar beach dynamics on the high-energy meso-macrotidal French Aquitanian Coast: a review. Mar Geol 245:141–159
Castelle B, Michallet H, Marieu V, Leckler F, Dubardier B, Lambert A, Berni C, Bonneton P, Barthelemy E, Bouchette F (2010) Laboratory experiment on rip current circulations over a moveable bed: Drifter measurements. J Geophys Res. doi:10.1029/2010JC006343
Castelle B, Marieu V, Coco G, Bonneton P, Bruneau N, Ruessink BG (2012) On the impact of an offshore bathymetric anomaly on surfzone rip channels. J Geophys Res. doi:10.1029/2011JF002141
Castelle B, Reniers AJHM, MacMahan JH (2014) Bathymetric control of surf zone retention on a rip-channelled beach. Ocean Dyn 64:1221–1231
Castelle B, Marieu V, Bujan S, Splinter KD, Robinet A, Senechal N, Ferreira S (2015) Impact of the winter 2013–2014 series of severe Western Europe storms on a double-barred sandy coast: Beach and dune erosion and megacusp embayments. Geomorphology 238:135–148
Dalrymple RA, MacMahan JH, Reniers AJHM, Nelko V (2011) Rip currents. Annu Rev Fluid Mech 43:551–581. doi:10.1146/annurev-fluid-122109-160733
Drozdzewski D, Shaw W, Dominey-Howes D, Brander RW, Walton T, Gero A, Sherker S, Goff J, Edwick J (2012) Surveying rip current survivors: preliminary insights into the experiences of being caught in rip currents. Nat Hazards Earth Syst Sci 12:1201–1211
Drozdzewski D, Roberts A, Dominey-Howes D, Brander RW (2015) The experiences of weak and non-swimmers caught in rip currents at Australian beaches. Aust Geogr 46:15–32
Feddersen F (2014) The generation of surfzone eddies in a strong alongshore current. J Phys Oceanogr 44:600–617
Gallagher EL, MacMahan JH, Reniers A, Brown J, Thornton EB (2011) Grain size variability on a rip-channeled beach. Mar Geol 1–4:43–53
Gensini VA, Ashley WS (2009) An examination of rip current fatalities in the United States. Nat Hazards 54:159–175
Haller MC, Dalrymple RA, Svendsen IA (2002) Experimental study of nearshore dynamics on a barred beach with rip channels. J Geophys Res. doi:10.1029/2001JC000955
Houser C, Barrett G, Labude D (2011) Alongshore variation in the rip current hazard at Pensacola Beach, Florida. Nat Hazards 57:501–523
Houser C, Arnott R, Ulzhofer S, Barrett G (2013) Nearshore circulation over transverse bar and rip morphology with oblique wave forcing. Earth Surf Process Landf 38:1269–1279
Idier D, Castelle B, Charles E, Mallet C (2013) Longshore sediment flux hindcast: spatio-temporal variability along the SW Atlantic coast of France. J Coast Res 65:1785–1790
Inman D, Trait R, Nordstrom C (1971) Mixing in the surf zone. J Geophys Res 76:3493–3514
Johnson D, Stocker R, Head R, Imberger J, Pattiaratchi C (2004) A compact, low-cost GPS drifter for use in the oceanic nearshore zone, lakes, and estuaries. J Atmos Ocean Technol 20(12):1880–1884
Lafon V, Dupuis H, Howa H, Froidefond JM (2002) Determining ridge and runnel longshore morphodynamics using SPOT imagery. Oceanol Acta 25:149–158
Lafon V, Dupuis H, Butel R, Castelle B, Michel D, Howa H, De Melo Apoluceno D (2005) Morphodynamics of nearshore rhythmic sandbars in a mixed energy environment (SW France): II. Physical forcing analysis. Estuar Coast Shelf Sci 65:449–462
Long JW, Ozkan-Haller HT (2005) Offshore controls on nearshore rip currents. J Geophys Res. doi:10.1029/2005JC003018
Loureiro C, Ferreira O, Cooper JAG (2012) Extreme erosion on high-energy embayed beaches: influence of megarips and storm grouping. Geomorphology 139–140:155–171
MacMahan JH, Thornton EB, Stanton TP, Reniers AJHM (2005) RIPEX: observations of a rip current system. Mar Geol 218:113–134
MacMahan JH, Thornton EB, Reniers AJHM (2006) Rip current review. Coast Eng 53:191–208. doi:10.1016/j.coastaleng.2005.10.009
MacMahan JH, Brown JW, Thornton EB (2009) Low-cost handheld global positioning system for measuring surf-zone currents. J Coast Res 25:744–754
MacMahan JH, Brown JW, Brown JA, Thornton EB, Reniers AJHM, Stanton TP, Gallagher EL, Morison J, Austin MJ, Scott TM, Senechal N (2010) Mean lagrangian flow behavior on an open coast rip channeled beach: a new perspective. Mar Geol 268:1–15. doi:10.1016/j.margeo.2009.09.011
McCarroll RJ, Brander RW, MacMahan JH, Turner IL, Reniers AJHM, Brown JA (2013) RIPSAFE: rip current swimmer and floater experiments, Shelly Beach, NSW, Australia. J Coast Res 65:784–789
McCarroll RJ, Brander RW, Power HE, T IL, Mortlock TR (2014a) Lagrangian observations of circulation on an embayed beach with headland rip currents. Mar Geol 355:173–188
McCarroll RJ, Brander RW, MacMahan JH, Turner IL, Reniers AJHM, Brown JA, Bradstreet A, Sherker S (2014b) Evaluation of swimmer-based rip current escape strategies. Nat Hazards 71:1821–1846
McCarroll RJ, Castelle B, Brander RW, Scott T (2015) Modelling rip current flow and bather escape strategies across a transverse bar and rip channel morphology. Geomorphology 246:502–518
Miloshis M, Stephenson WJ (2011) Rip current escape strategies: lessons for swimmers and coastal rescue authorities. Nat Hazards 59:823–832
Ozkan-Haller HT, Kirby JT (1999) Nonlinear shear instabilities of the longshore current: a comparison of observations and computations. J Geophys Res 104:C11. doi:10.1029/1999JC900104
Pattiaratchi C, Olson D, Hetzel Y, Lowe R (2009) Wave-driven circulation patterns in the lee of groynes. Cont Shelf Res 29:1961–1974. doi:10.1016/j.csr.2009.04.011
Reniers AJHM, MacMahan JH, Thornton EB, Stanton TP, Henriquez M, Brown JW, Brown JA, Gallagher E (2009) Surf zone retention on a rip-channeled beach. J Geophys Res. doi:10.1029/2008JC005153
Reniers AJHM, MacMahan JH, Beron-Vera FJ, Olascoaga MJ (2010) Rip-current pulses tied to lagrangian coherent structures. Geophys Res Lett. doi:10.1029/2009GL041443
Roelvink JA, Reniers AJHM, van Dongeren A, de Vries JV, McCall R, Lescinski J (2009) Modelling storm impacts on beaches, dunes and barrier islands. Coast Eng 56:1133–1152. doi:10.1016/j.coastaleng.2009.08.006
Schmidt WE, Woodward BT, Millikan KS, Guza RT, Raubenheimer B (2003) A GPS-tracked surf zone drifter. J Atmos Ocean Technol 20:1069–1075
Scott T, Austin M, Masselink G, Russell P (2016) Dynamics of rip currents associated with groynes field measurements, modelling and implications for beach safety. Coast Eng 107:53–69. doi:10.1016/j.coastaleng.2015.09.013, http://www.sciencedirect.com/science/article/pii/S0378383915001702
Scott TM, Russell PE, Masselink G, Austin MJ, Wills S, Wooler A (2011) Rip current hazards on large-tidal beaches in the United Kingdom. In: Leatherman S, Fletemeyer J (eds) Rip currents: beach safety, physical oceanography, and wave modelling, CRC Press, London, pp 225–242
Scott TM, Masselink G, Austin MJ, Russell PE (2014) Controls on macrotidal rip current circulation and hazard. Geomorphology 214:198–215
Sénéchal N, Gouriou T, Castelle B, Parisot JP, Capo S, Bujan S, Howa H (2009) Morphodynamic response of a meso- to macro-tidal intermediate beach based on a long-term dataset. Geomorphology 107:263–274
Shepard FP, Emery KO, La Fond EC (1941) Rip currents: a process of geological importance. J Geol 49:337–369
Short AD (2007) Beaches of the New South Wales coast: a guide to their nature, characteristics, surf and safety. Sydney University Press, Sydey, Australia
Suanda SH, Feddersen F (2015) A self-similar scaling for cross-shelf exchange driven by transient rip currents. Geophys Res Lett 42(13):5427–5434. doi:10.1002/2015GL063944
Tellier E (2014) Noyades sur le littoral océanique girondin: étude rétrospective des conditions de noyade en 2011–2013. PhD thesis, Université de Bordeaux, in French
Thornton EB, MacMahan JH, Sallenger AH Jr (2007) Rip currents, mega-cusps, and eroding dunes. Mar Geol 240:151–167
Tipton M, Reilly T, Rees A, Spray G, Golden F (2008) Swimming performance in surf: the influence of experience. Int J Sports Med 29(11):895–897
Van Leeuwen BR, McCarroll RJ, Brander R, Turner IL, Power HE, Bradstreet AJ (2015) Examining rip current escape strategies in non-traditional beach morphologies. Nat Hazards. doi:10.1007/s11069-015-2072-4
Winter G, van Dongeren AR, de Schipper MA, van Thiel de Vries JSM (2014) Rip currents under obliquely incident wind waves and tidal longshore currents. Coast Eng 89:106–119
Wright LD, Short AD (1984) Morphodynamic variability of surf zones and beaches: a synthesis. Mar Geol 56:93–118
Acknowledgments
This study was performed in the framework of Project DECA (INSU/EC2CO). Additional funding was provided by the Australian Research Council (ARC), Surf Life Saving Australia through Linkage Project LP110200134 and the programme “Invited Scholar” (Idex, University of Bordeaux), the latter funding the stay of RJM and RWB at University of Bordeaux. We thank the 3 anonymous reviewers for their comments and constructive criticism.
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Castelle, B., McCarroll, R.J., Brander, R.W. et al. Modelling the alongshore variability of optimum rip current escape strategies on a multiple rip-channelled beach. Nat Hazards 81, 663–686 (2016). https://doi.org/10.1007/s11069-015-2101-3
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DOI: https://doi.org/10.1007/s11069-015-2101-3