CAPE VERDE BEACH HAZARDS

Abstract

Coastal Marine Applied Research (CMAR) have been commissioned by Adam Wooler to assess physical bathing hazards at Praia de Lacacao, Boa Vista, Cape Verde. A number of bathing injuries have occurred at the beach adjacent to the RIU Touareg Hotel, and this report seeks to estimate the wave and beach morphology conditions at the times of the bathing incidents, as well as to identify typical bathing conditions that occur throughout the year at the beach. Through a process of expert judgement using a combination of wave analysis, and assessment of in-situ and satellite imagery, the beach at Praia de Lacacao is expected to be consistently at the ‘reflective’ end of the beach morphology spectrum. The likely beach profile gradient in the area of wave breaking is expected to be consistently within the range 0.1 – 0.2 (slope of 1-in-10 to 1-in-5), which represents a steep beach profile. Steep beaches exposed to small wave heights with long wavelengths experience plunging or surging/collapsing wave breakers, which break intensely over a short part of the beach profile, or dissipate their energy entirely at the shoreline. Given the expected beach morphology and wave breaker types, shore-break impact injuries are expected to be the primary beach hazard type at Praia de Lacacao. From processed wave model data, breaking wave heights at the site are predicted to vary from 0.5 – 3 m, but only exceed 1.7 m 10% of the time. Wave conditions do not vary significantly throughout the year, and average summer and winter breaking wave heights vary from 0.9 – 1.0 m, with peak wave periods of 10.2 – 11.0 s. Wave breaking is predicted to be consistently within the ‘plunging’ to ‘surging/collapsing’ regimes. In-situ photographs of waves breaking at Praia de Lacacao confirm that waves typically break very close to the beach, and under larger waves (breaking wave height, Hb > 1 m) break as plunging breakers with considerable breaking intensity and power at the shoreline. During five of the six bathing incidents, the wave conditions are predicted to have been below the average breaking wave height for the season in which they occurred, ranging from Hb = 0.6 m – 0.9 m. During one of the six incidents, the wave conditions are predicted to have been Hb = 2 m – a wave height which is above average for the season and is exceeded less than 10% of the time at Praia de Lacacao. During all of the incidents, plunging to surging/collapsing breakers are predicted to have been occurring on the beach.