Assessment of coastal changes following the construction of a groyne using satellite and drone imagery along the Mediterranean coast of northwest Tunisia (Rafraf, Bizerte)

This study aimed to assess the vulnerability of the Rafraf coastline in northwestern Tunisia as well as some of the environmental impacts following the construction of a coastal protective structure (groyne). This coastline has experienced severe erosion, which was detected using satellite images taken in 2004, 2013, 2015, and 2017. To prevent erosion, the coastline was protected between 2016 and 2018 by building a 370-m-long groyne and adding sand to nourish it over a 2-km stretch. The coastal response to this management and the groyne performance were tracked using imagery obtained in 2018, 2019, and 2020 as well as UAV aerial photography and ultrahigh-resolution digital elevation models (DEMs) provided by Inspire 2 Pro drones equipped with Zenmuse X4S payloads. Results show that the coastline retreated at rates ranging from 1 to 11.78 ± 0.31 m/year during 2013–2015. However, after the management actions (in 2019 and 2020), the coastline advanced by 18–21 ± 15.22 m/year updrift of the groyne. Sediment accumulation also occurred at shallow depths of − 1 m and − 2 m, indicating a triangular zone where corresponding isobaths diverge from the coast, thus demonstrating the groyne's effectiveness. This study could be used to evaluate the effectiveness of installing groynes as part of coastal management projects.