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Bonou, F.; Angnuureng, D.B.; Sohou, Z.; Almar, R.; Alory, G., and du Penhoat, Y., 2018. Shoreline and beach cuspsdynamics at the low tide terraced Grand Popo beach, Bénin (West Africa): A statistical approach. In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 138–144. Coconut Creek (Florida), ISSN 0749-0208. This paper presents the description of a 2-dimensional shoreline and 3-dimensional shoreline behaviour around a 'storm free' microtidal beach from a 3-year video observation using empirical orthogonal function (EOF) analysis. The EOF method is applied successfully to delineate 2D and 3D developments that show the beach evolution influenced by the action of waves and tides. The EOF model results are in agreement with measurements that reflect the morphological concepts for the 2D and 3D cases: the first temporal EOF mode which accounts for an overwhelming 80% of shoreline variation reflects the alongshore-averaged cross-shore migration (2D) largely influenced by waves while the higher eigenfunctions with 20% shoreline variation reflect beach deformation/irregularities (3D). Shoreline location is correlated to cross-shore energy flow from waves, while 3D is associated to the longshore energy flow. The influence of wave height increases cross-shore uniform migration and beach seasonality. The results show that with EOF method, beach cusps are clearly identified for 3D developments to be evaluated. Beach cusps are well observed at low tides on video images. Tide and cusps increase the importance of short term events and deformation; at the lowest high tide mark, beach cusps were observed on higher spatial functions of EOF. This indicates that a study of these morphological features as a coupled system, promotes their contribution in predicting 2D and 3D shoreline changes. [ABSTRACT FROM AUTHOR]

Hounguè, G.H.; Kounouhéwa, B.B.; Almar, R.; Sohou, Z.; Lefebvre, J-P.; Houépkonhéha, M., and Tokpohozin, B., 2018. Waves forcing climate on Bénin coast, and the link with climatic index, Gulf of Guinea (West Africa). In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 130–137. Coconut Creek (Florida), ISSN 0749-0208. Bénin's coastline is currently undergoing very marked erosion. This erosion is the consequence of the impact of swells from the South Atlantic and is accentuated by human development. These swells, from weak to moderate energies, drive Bénin's coastline evolution. Although crucial, the characteristics of this forcing are not accurately defined. From instantaneous outputs of ERA40 and ERA-Interim's sea state parameters, the annual and seasonal average of significant wave height (Hs), peak period (Tp) and direction (Dir) were determined to characterize wave forcing and extreme event on Bénin Coast after a validation using the data of the ALIZEE buoy installed 6 km off the coast of Bénin in December, 2015. Hindcast data analysis indicates an important if increasing trend of Hs and Tp. A weak trend of peak direction towards the South West clockwise is observed between 1957 and 2016. The intra-annual variability of Hs shows a marked seasonality, the first one characterized by strong swells from April to October and the second one by moderate swells from October to April. Offshore wave height is positively correlated with AMO (Atlantic Multidecanal Oscillation). [ABSTRACT FROM AUTHOR]

The first large nearshore field experiment in the Gulf of Guinea was conducted at Grand Popo Beach, Benin, in February 2013, on an open wave-dominated micro- to meso-tidal coast, located mid-way between Cotonou and Lome harbours. The overall project aims at understanding at multi-scale (from event to interannual) the causes of the dramatic erosion observed throughout the Bight of Benin, and caused by the interaction of a large littoral drift with human engineering works. Grand Popo 2013 experiment was designed to measure the processes over the short term and to test the ability of an installed video system to monitor the evolution of this stretch of coast over the longer term. The beach, characterized by a low-tide terrace and a high tide reflective part, experiences a long swell (Hs=1.6 m, Tp=16 s, oblique incidence ~15-20°). Topographic surveys showed a double beach cusp system interaction and repeated surf-zone drifter runs revealed high flash and swash rip activity driven by wave dissipation over the terrace and energetic swash dynamics at the upper reflective beach. Swash was measured over a cusp system at two locations using video poles. Wave reanalyses (ERAInterim) were used to determine the wave climate and its variability, and to quantify sediment transport. This robust methodology is thought to be replicated elsewhere in different coastal environments in West Africa, in particular with the objective to monitor various sites within the framework of the new West African Coastal Observatory. [ABSTRACT FROM AUTHOR]