Morfodinámica costera en la playa Bailén, costa sur del occidente de Cuba, entre los años 2003-2013

Abstract

Due to their geological nature, beaches are susceptible to changes over a relatively short period of time. Composed mainly of recently formed rocks, the scarcely consolidated structure of the substrate makes beaches vulnerable to the action of waves, tides, currents, wind, changes in sea level and human activity. Beach dynamics is marked by different degrees of fragility. In tropical regions, especially in the Caribbean, extreme hydro-meteorological phenomena such as hurricanes and cold fronts associated with extra-tropical storms significantly accelerate the erosion and accretion processes along the coast. The geographical location of the Cuban archipelago, at the margins of the Tropic of Cancer (its northernmost latitude is 27°17’ N), makes it susceptible to the combined action of hurricanes (between June and November) and cold fronts (between November and March). This very fact makes the study of coastal morphodynamic changes a subject of the utmost importance in sustainable-development projects and environmental planning, including the preservation of coastal natural resources. In Cuba, several authors have reported a coastal retreat of 1 to 3 m per year in western beaches, as well as an average loss of sand of about 50 000 m³ per year in the famous Varadero beach. The latter case is mainly due to the extraction of sand from the underwater platform between 1968 and 1978 for construction purposes. This paper addresses the morphodynamic processes taking place at Bailén beach, on the southwestern Cuban coast, as observed during a 10-year period, from 2003 to 2013. Transversal topographic measurements were taken at the beachfront and coastline at 15 observation stations along 2 140 m of beach in 2007, 2010 and 2013. These measurements were then compared to the data available for 2003. Estimated volumes of accreted and eroded sand for the period 2003-2007 indicate remarkable changes in beach morphology and evidence the vulnerability of coastal systems to extreme events, such as those unleashed by hurricane Ivan in 2004. The most important morphological changes observed included an increase of 0.20 to 0.50 m in dune height in some cases, and a decrease in others in the order of 0.15 to 0.40 m. Finally, granulometric tests were conducted to establish the spatial and temporal variations in the diameter of sand grains. To the north side of the beach, the maximum recession rate was 2.0 m per year, and sand grains were larger. Both measurements are indicative of the impact of buildings constructed at the front side of dunes and the beach berm on beach morphology. In the southern sector, on the other hand, the maximum accretion reached 8.0 m per year, whereas the average value was 2.3 m per year. During the 10 years of analysis, beach recovery has been characterized by a low resilience to the impact of hurricanes and other meteorological events. There is a clear spatial correlation between the inadequate location of buildings less than 30 meters from the shore on dunes and berms, where beach dynamics is most intense, and the development of intensive erosive processes, as observed in the northern sector of Bailén beach. The slow recovery of the initial coastline position translates into a steady increase in the average diameter of sediments. The low level of resilience in these beach stretches becomes even more evident when hydro-meteorological events occur. For beach recovery projects through local sand repositioning to be successful, the beachfront must be closely monitored, recording measurements of both sediment dynamics and the effects of wind and water on a transversal profile. Also, to ensure an effective regeneration of this natural resource, an average volume of sand per linear meter of beach must be established. Finally, the demolition of old buildings located at the berm and the front side of dunes, and the prohibition of further construction in these sites, should contribute to restore the morphodynamic balance of this beach and increase the quality of tourism services.