Evaluating the morphodynamics of a spit complex (Punta Rasa, Argentina): Implications for mid‐term evolution of coastal plains

Abstract

The northern boundary of the Barrera Oriental on the Atlantic coast of Argentina holds the spit complex of Punta Rasa, a well-exposed without subsequent coverage, beach-ridge system. Here, the long-term interaction between the sandy beach, an extensive coastal dune field, and a tidal flat system have created a suite of depositional and erosional coastal features, for which storms seem to be the main driver. Thus, the spit complex represents an ideal example to understand the evolution of the beach-ridge system during the Holocene by extrapolating the morphodynamics conditions currently governing the spit. Through the analysis of 15 years (2005–2019) of wave and wind time series and further simulation of hydrodynamic parameters generated by storm events, changes in shoreline position were studied. Furthermore, morphometric attributes of the Holocene beach-ridge system were investigated. Results allowed us to establish two types of main storms (southeasterns and northeasterns) that have shaped the evolution of the spit during the last 20 years. The prevalence of southeastern storms boosts progradation with clockwise rotation of the spit end, while an increase in the frequency of northeastern events reduces sediment supply, making the spit more vulnerable to erosion and causing its retreat and counterclockwise rotation. The combination of morphometric analysis of beach ridges with these morphodynamic scenarios led us to establish four stages of evolution for the Barrera Oriental.