Sandy coastlines in Chile currently have strong erosive tendencies. However, little is known about the morphodynamics of these coastlines; such knowledge would allow us to understand coastline changes and incorporate this knowledge into coastal management. Accordingly, the historical scale of coastal erosion and the morphodynamic characteristics of six beaches of the Arauco Gulf, central-southern Chile (36◦ S), were analyzed to determine the prevailing wave conditions during winter and summer. Historical changes in the relative position of the coastline were determined using DSAS v5.1. The coupled WAVE-FLOW-MOR modules of the Delft3D 4.02 software package were used for the morphodynamic analysis. Using image processing, it was established that erosion predominates in winter seasons for almost every beach analyzed. However, the Escuadrón beach presents this trend both in winter and summer, with rates of up to −0.90 m/year (2010–2021). In addition, accretion was observed in both stations at Tubul beach. On the other hand, numerical models for the dominant conditions predict accretion in the beaches of Escuadrón, Chivilingo, and Arauco, stable conditions for Coronel beach, and erosion in Llico.