@article{fdi:010075139,
  title = {{C}ontrols on flash rip current hazard on low-tide terraced tropical beaches in {W}est {A}frica},
  author = {{S}cott, {T}. and {C}astelle, {B}. and {A}lmar, {R}afa{\¨e}l and {S}enechal, {N}. and {F}loc'h, {F}. and {D}etandt, {G}.},
  editor = {},
  language = {{ENG}},
  abstract = {{F}lash rip currents are transient non-fixed offshore-directed jets of water often associated with migrating surf-zone eddies. {T}hey can occur on featureless (alongshore-uniform) beaches and are essentially hydrodynamically controlled. {D}ue to their unpredictable nature, they represent one of the most significant hazards to bathers across surf zones worldwide, especially in {T}ropical {W}est {A}frica, where high levels of flash rip activity and a lack of a lifeguard service lead to high drowning rates. {R}ecent work has shed light on two contrasting driving mechanisms for non-fixed rips: (1) cascading vortices generated by wave breaking, and (2) shear instabilities of the longshore current. {T}his research provides the first quantitative scientific understanding of wave-driven currents in {T}ropical {W}est {A}frica. {S}pecifically, the study focussed on the dynamics of flash rips occurring along alongshore-uniform beach morphology, through the collection of unique {L}agrangian field measurements of flash rips. {D}uring two periods, {F}ebruary 2013 and {M}arch 2014, 13 days of field data collection occurred at {G}rand {P}opo beach on the southerly-facing {B}ight of {B}enin coast ({G}ulf of {G}uinea, {W}est {A}frica). {T}he experiments measured flash rip currents, nearshore hydrodynamics and morphology at a moderately energetic (long-term average significant wave height, {H}s = 1.36 m, and peak wave period {T}p = 9.4 s), sandy alongshore-uniform low-tide terraced beach exposed to {S}outh {A}tlantic groundswells and local wind-waves. {A} suite of {GPS} drifters, dye-tracking and video confirmed the presence and characteristics of low high energy flash rips (up to 0.7 m/s) in the surf zone, while in-situ acoustic wave and current measurements from the surf zone and inner shelf provided metocean forcing conditions (0.8<{H}s<1.6 m; 8<{T}p<14 s; 1 <{D}p<21 degrees (from shore normal)) and longshore current velocities (0.2-0.8 m/s in surf zone). {T}hroughout a range of wave conditions (height/period/angle/directional-spreading) contrasting flash rip behavioural responses were observed (surf zone exits/offshore extent/offshore-directed velocities). {T}his study (1) supports findings of the first rip experiment conducted at this site ({F}eb 2013) suggesting that flash rip activity is likely to be driven by wave breaking vorticity generation (flash rip activity high under shore-normal wave forcing) and (2) provides further quantitative insights into the role of specific wave/tide forcing characteristics on flash rip activity, specifically the importance of reduced directional spreading and tidal level in controlling increases in offshore extent of flash rip currents. {F}inally, (3) the observed ubiquity of significant hazardous transient flash rip activity and identification of key behavioural controls can provide a foundation for any future development of rip hazard prediction tools and effective lifeguarding in {W}est {A}frica.},
  keywords = {{R}ip currents ; suif zone circulation ; lagrangian drifters ; tropical ; {W}est {A}frica ; beach hazard ; coastal hydrodynamics ; {AFRIQUE} {DE} {L}'{OUEST} ; {BENIN} ; {GRAND} {POPO}},
  booktitle = {},
  journal = {{J}ournal of {C}oastal {R}esearch},
  numero = {81 {N}o sp{\'e}cial},
  pages = {92--99},
  ISSN = {0749-0208},
  year = {2018},
  DOI = {10.2112/si81-012.1},
  URL = {https://www.documentation.ird.fr/hor/fdi:010075139},
}