In the present work, the impact of watershed processes to the coastal zone quality is studied for a typical sandy beach in the vicinity of a torrent mouth, located in Chalkidiki, North Greece. The shoreline evolution – attributed to the extensive land use changes in the upstream watershed – was studied using the numerical model PELNCON-M developed by the authors; the model incorporates three well known formulae to estimate the longshore sediment transport rate. The calculations within the watershed were performed in GIS environment using the SWAT model, initially calibrated on the basis of PELNCON-M results for the CERC formula. The conclusions derived from the analysis of the results, confirm the correlation of the studied phenomena and support the methodological aspect that watersheds and coastal zones have to be treated as an entity in the framework of Integrated Coastal Zone Management.