Morphological Changes Induced by Coastal Protection on the Coast of Maputo City, Mozambique

Abstract

Coastal change has merited attention because of heated arguments in the literature on this subject at national, regional, southern African, and international levels. The city of Maputo, the capital of Mozambique, which had been undergoing intense coastal erosion actions, was the target of large-scale intervention aimed at halting the advance of the sea and the consequent destruction of infrastructure. Coastal protection consisted of soft forms, artificial feeding, and heavy, longitudinal and transversal structures. This study was carried out along the protected line, about 3 km long, and aims to understand the morphological transformations in the Maputo city shoreline that occurred after the coastal protection. For that, the following technical methods were used: observation, a topographic survey of the beach cross-sections, and the shoreline evolution before and after coastal protection using 2008 and 2010 Google Earth satellite imagery prior to protection 2015, project completion year and 2018 monitoring year. The findings of the study revealed that the causes of coastal erosion persist, like constant removal by deflation of the borrowed sediment. Besides, vertical structures (groynes) intensify erosion in the downdrift while adherent structures interrupt the return of sediment deposited on the sidewalk and the road. The beach that experienced a positive sedimentary balance with artificial feeding has been losing more sediment than it gets. The transversal profiles show the beach shore has depressions that are submerged in the presence of high tides, bringing the sea closer to the adherent structure. Despite the sped up erosion observed, embryonic dunes were detected in some parts of the beach, signs of the establishment of dynamic equilibrium, becoming sites of sand accumulation and sediment source to the beach, through the exchange between the dune and the beach. With these results, a pilot station for artificial dune construction is being designed for beach stability.