Thirty-year evolution of the Atlantic coastline using the digital shoreline analysis system: A case study in Tangier, northern Morocco

Abstract

Tangier’s northern Atlantic coastal zone, particularly from Achakar to Sidi Kacem, is under increasing pressure from urbanization and tourism, which exacerbates its vulnerability to coastal erosion. This study aimed to assess spatio-temporal changes, quantify erosion and accretion rates, and identify factors influencing the coastline’s stability or retreat. Potential impacts of this erosion include the loss of coastal habitats and threats to local biodiversity. The methodology combined automatic shoreline extraction using multi-temporal Landsat images (1973–2024) and field-based DGPS surveys. The results show that the coastline is eroding at an average rate of –2.24 m year–1, with erosion rates increasing in severity towards the south. Two beaches, Sidi Kacem and Houara, were studied in detail. Between 1973 and 1990, significant erosion occurred: –6.63 m year–1 at Sidi Kacem and –8.01 m year–1 at Houara. Between 1990 and 2015, erosion (–2.12 m year–1 at Houara) and accretion (+2.24 m year–1 at Sidi Kacem) fluctuated. From 2015 to 2024, alternating dynamics with reduced intensity were observed. While this erosion poses limited immediate threats to critical infrastructure such as the airport and road networks, the study highlights limitations, including satellite image resolution and temporal data gaps. Future research should integrate higher-resolution data (e.g. LIDAR) and evaluate anthropogenic impacts on coastal dynamics, including urban runoff, sand extraction and tourism infrastructure development, to improve management strategies in the Achakar–Sidi Kacem area.