Evolución durante 141 años (1875- 2016) del retroceso de la línea de costa de la playa del Puntal-Somo-las Quebrantas (Cantabria).

Résumé

The sandbar known as El Puntal is the natural breakwater of the bay of the city of Santander. This coastal relief form is dynamic and is, as a result, subject to the inconvenience that when strong sea storms with large waves (greater than 8 m) coincide with high tide coefficients (greater than 100), they may lead to its partial destruction, in which case it would require restoration with artificial dunes using sand and vegetation. The dynamic of the sand bank must be monitored, since the accumulation of sand underwater in the bay entrance may result in the waters becoming too shallow for ships to come into port. This article, however, only deals with the surface dynamic of the Puntal-Somo-Las Quebrantas beach and not what takes place below the surface of the water. The evolution of el Puntal-Somo was tracked using historical maps (1875, 1908, 1920, 1946, 1950, 1985), which were scanned and geo-referenced in ETRS89. The curves of the level from 0 m and 5 m were then digitalized (the 5 m curve is found between the head and the foot of the slope of the sand front) for each map. The 0 m curves, the head and the foot of the sand slope were restored using the photogrammetric flights of the years 2001, 2005, 2007, 2010, 2014. The flights of 1985, 1988 and 2001 were also digitalized, though without any certificate of camera calibration. From the study of the evolution of the historical maps of El Puntal-Somo beach, geomatic studies were carried out (cartograpy, topography, photogrammetry, terrestrial laser scanner) in the area of Quebrantas. The geomatic studies in the latter began in 1988 (project CICYT, PB87-0800) and it was in the 1988-1993 period when topographic and bathymetric profiles were made which revealed slight changes in the coastline. In order to confirm these changes the evolution of the area was studied by digitalizing the historical maps from 1875 to 1985, and the 1985-2014 period was analysed using photogrammetric techniques. Since 2011 two measurements are taken annually using terrestrial laser scan. For this comparative study, a 400 m stretch of the coast was selected.