Recent Coastal Geomorphological Evolution in the Negro River's Mouth (41°S), Argentinean Patagonia

Abstract

This paper analyzes the geomorphological evolution of the Negro River's mouth to understand how aerodynamic and hydrodynamic states of the Atlantic coast have developed to this date. Accordingly, the morphometry of the beach and the historical river flow record were studied. The results indicate a dichotomous state for this coast. The SW area is characterized by cliffs with an average recession rate of 0.69 m/y during the 1959-2011 period, whereas the NE area is characterized by beaches in stable and accretion states. In the latter zone, a relatively fast coastal accretion was corroborated with the advance of a berm of up to 170 m between 1986 and 2014; furthermore, the beach extension grew to 760 m during 1986-2004. Since 1936, a completely new phenomenon was observed at the Negro River's mouth: the displacement and accretion of intertidal banks toward the coast provoked the closure of the channels of fluvial discharge and tidal currents. This activity at the Negro River's mouth could be due to the reduction of river discharge during the 20th century, which increased the preponderance of littoral current over the river discharge.