Detection and analysis of historical variations in the shoreline, using digital aerial photos, satellite images, and topographic surveys DGPS: case of the Bejaia bay (East Algeria)

Abstract

The Bejaia coastline is one of the most beautiful and attractive coastlines in Algeria; this is due to its landscape and ecological diversity running along it. The eastern coast of Bejaia is formed by a wide stretch of sand, occupying the bottom of the bay. Its beaches are fed by sediments carried by two main wadis that debouch into the bay: Soummam in the west and Agrioun in the east. The undertaken work in this article focuses on the study of coastal erosion, which has a significant damage on the natural patrimony. This erosion risk in perpetual evolution, by location, is dramatically affecting the beautiful sandy beaches and various infrastructures over all the coast length of the Bejaia bay. In order to map and evaluate this risk, a methodological approach has been followed. This approach is mainly based on a diachronic variation analysis in the position of the shoreline over a period of 60 years; based on a series of ortho-rectified aerial photos, satellite images, as well as DGPS topographic surveys on the ground. The results revealed significant variations in the position of the shoreline during the last 60 years, especially on both sides of Soummam and Agrioun wadis. The most observed retreat of the shoreline is in the western part of the coast, where the rate of evolution reached −7.89 m/year (beach of Sidi Ali Lebhar), whereas the shoreline retreat reached −1.75 m/year in the center of the bay and −2 m/year toward the east.