Shoreline Changes and Coastal Erosion: The Case Study of the Coast of Togo (Bight of Benin, West Africa Margin)

Abstract

The coastal strip between the Volta River delta and the westernmost portion of Benin (West Africa Margin of Atlantic Basin) is highly populated (e.g., Lomé) due to migrations from inland areas. The coastal zone has proved to be very vulnerable because of the potential development of sometimes catastrophic events related to different and interacting causes, resulting in negative effects on natural ecosystems and socio-economic conditions. The main problem is the marked erosion of large coastal sectors with maximum retreat rates of the order of 5 m/year. The continuous loss of territory leads to a progressive impoverishment of activities and human resources and to the increase of geological risk factors. The coastal erosion is induced both by natural and anthropic causes and can be controlled only by means of prevention programs, detailed scientific studies and targeted technical interventions. The main erosional processes observed in the study area are triggered by the presence of the Lomé port and other human activities on the coastal strip, including the water extraction from the subsoil, which induces subsidence and the use of sediments as inert material. These elements, together with the reduction of the solid supply from Volta River (caused by the realization of the Akosombo dam) are among the main factors that control the medium and long-term evolution of the area. Also relative sea level changes, which take into account also tectonic and/or isostatic components, can contribute to the process. In order to have a real understanding of the coastal dynamics and evolution, it would be necessary to develop a scientific structure through the collaboration of all countries of the Bight of Benin affected by coastal erosion. The aim should be primarily to collect the interdisciplinary quantitative data necessary to develop a scientific knowledge background of the Bight of Benin coastal/ocean system. In conclusion, some proposals are presented to reduce the vulnerability of the coastal area as for example to plan surveys for the realization of appropriate coastal protection works, such as walls, revetments, groins, etc. A possible expansion of the port of Lomè is also considered. Proposals comprise the constitution of a Supranational Scientific Committee as a coordinating structure on erosion for both the study of phenomena and planning interventions.

Designing Coastal Adaptation Strategies to Tackle Sea Level Rise

“…The appropriate governance scale has been addressed through the notion of sediment cell, based on the scale of the physical phenomenon of sediment transport (Cooper and Pontee, 2006), considering that human interventions in each jurisdiction will affect neighboring jurisdictions; for example, sediment reduction from dams will impact the sediment cell they are part of, and deep-water ports will block sediment drift downstream (Almar et al, 2015;Guerrera et al, 2021). This issue has prompted several communities to cooperate in order to avoid the transfer of impact caused by gray infrastructure.…”

Coastline modification at worldwide

“…Koukouvelas en su estudio mencionó la tasa de recesión aproximada de 35 mm/año en los acantilados de la Isla de Lefkada en Grecia (Koukouvelas et al, 2020). Tras estudios realizados en la Costa de Togo (Ensenada de Benin, margen de África occidental por Guerrera y otros autores se ha identificado que se presentan tasas máximas de retroceso del orden de 5 m/año (Guerrera et al, 2021). Por otra parte, Borkai Boye y Bani Fiadonu han estudiado el retroceso de las costas de Ghana donde se evidencio un promedio de 0,78 m/año durante un período de 31 años (Borkai Boye & Bani Fiadonu, 2020).…”

Monitoring Spatial and Temporal Scales of Shoreline Changes in Lahou-Kpanda (Southern Ivory Coast) Using Landsat Data Series (TM, ETM+ and OLI)

“…A coastal zone is a transition area between the land and water. It represents a very important natural and economic resource [1][2][3], despite the fact that it is constantly changing. In addition, this microcosm is a highly complex environment in which erosion phenomena, and therefore the retreat or advance of the coastline, are influenced by a wide range of meteorological, geographical, biological, and anthropogenic influences [4][5][6].…”