Perceptions of and responses to coastal erosion risks: The case of Cotonou in Benin
Introduction
Coastal erosion is defined as the invasion of land by the sea, or as the tendency of the coastline to retreat, generating significant loss of beaches, land and ecosystems that are used for human activities [1]. Sea level rise can trigger coastal and riverbank erosion, flooding and saltwater intrusion into lakes [[2], [3], [4]]. Moreover, waves that break closer to the shore cause beach erosion in discrete time steps in the form of storms [5,6]. Human influence in the coastal area has been generally identified as a major cause of shoreline morphological change, which ultimately drives coastal erosion [7,8]. In the future, this type of erosion will very likely be amplified by sea level rise, changes in wave conditions and more frequent storms as consequences of global warming [3,[8], [9], [10], [11], [12]]. Amongst the coastal areas that are particularly at risk of climate change, those located on the Gulf of Guinea in West Africa rank very high [13,14]. According to Touré et al. [15]; the West African coasts are undergoing a significant erosive process, which can be impressive in some places with average retreats exceeding 10 m per year. The city of Cotonou, the economic capital of Benin, is built on alluvial sand with a maximum thickness of 4 m [4] between Lake Nokoue in the North and the Gulf of Benin1 in the South (Fig. 1). In the east of the harbour, the coastline of Cotonou retreated by 400 m between 1963 and 1997 according to Codjia [16]. Based on a detailed analysis of remote sensing data and verified ground truth, Kaki et al. [17] observed a coastal erosion of nearly 500 m between 1963 and 2005 in the same area. In this case, the coastal erosion is mainly due to (i) the obstruction of the littoral transit by the deep-water harbour and its pier built in the early 1960s, (ii) the decreasing transport of river sediments from the upstream catchment (Mono River) since the construction of the Nangbéto Dam in 1987, and (iii) the decrease in sedimentary inputs from the West because of diverse coastal protection structures [[18], [19], [20]]. Moreover, activities of sand quarries and beach sand mining [17,21] have amplified the phenomenon in Benin, as in Ghana [[22], [23], [24]].
Defined as the potential of a given area to be harmed by the impact of erosion and quantified by comparing the intensity of the impact with the adaptability of the system [25], the vulnerability to coastal erosion is particularly high in West Africa. The Gambia, Ghana, Togo, and Benin and Nigeria have the most vulnerable coastal communities with people suffering tremendous economic losses, destruction of homes, livelihoods and cultural artefacts [26]. Urbanisation in African cities is shaped by the combination of past and current governmental planning practices, traditional land ownership systems, private development interests, direct foreign investments, and migration. The interaction of these drivers creates hazard-prone areas in settlements facing an increase in the risk of natural disasters [27]. Coastal erosion and sea flooding are serious problems that affect the safety and livelihoods of many dwellers along the West African coast [28]. As in other parts of the world, the coast of the Gulf of Guinea concentrates the biggest cities of the region and a large proportion of the population [[29], [30]]). Coastal areas, characterised by high-density populations [31,32] are growing rapidly, notably because of rural-urban migration inflows [20,33]. Worldwide, a large proportion of urban expansion is taking place as informal settlements in areas exposed to environmental hazards (low-lying places, coastal areas …) [34,35]. The rapid increase in coastal populations imposes more pressure on coastal lands through alteration of natural habitats and leads to increased erosion [7,36]. People living in these coastal areas that lack basic infrastructure and services are disproportionately affected by the impacts of climate change [37,38]. Moreover, both, rapid demographic growth and inadequate resources for urban development exacerbate their vulnerability. Actually, population growth in coastal areas places more people potentially at risk from natural hazards, which could mean that post-disaster displacement and migration from coastal areas will increase in the future [[38], [39], [40]]. Sea level rise is expected to cause most migration in the next decades [42]. According to Appeaning Addo [7]; various studies have quantified the rate of landward change with regard to the position of the coastline but not much work has been done to estimate the rate at which human settlements are moving closer to the coastline. In addition, there is a large research gap regarding the responses of households, communities, and states towards coastal erosion and sea level rise [43].
The main objectives of this study are to identify populations living in a coastal area of Cotonou affected by rapid erosion for several decades and to analyse the perceptions of and responses to risks by those who experience the risks and those who manage the risks.
The study area comprises 8 km along the sea (Gulf of Benin) to the east of the Siafato groyne2 built in 1962–1963 just after the harbour (Fig. 1). This zone has been significantly eroded since the early 1960s. Prior to this, the coastline was linear. In 2013, seven groynes, one at every kilometer from the Siafato groyne, have been implanted along the coast as coastal protection measures (see Fig. 1, below, Groyne 1 to Groyne 7) and two additional intermediate groynes (the first one between Groyne 1 and Groyne 2 and the second one between Groyne 6 and Groyne 7) have recently been integrated (April 2018). As shown in Fig. 1, the series of groynes have been constructed up to the administrative limit of the municipality of Cotonou, neighboured by the municipality of Sèmè-Podji. The study area is also characterised by high-density housing to the limits of the beach. As shelter types, we find standing houses, permanent houses, makeshift houses and some plots of land free of any construction. While some zones of the coastal area are more endowed with permanent houses and other zones are more dedicated to temporary housing, we mainly observe a mix of these dwellings, especially closer to the coastline. Whether it is due to the construction of the groynes (storage of materials) or sanitation of the area, the authorities have regularly forced demolition of makeshift shelter and eviction of the inhabitants.
Section snippets
Methodology
We used the triangulation method to obtain data and adopted a multidisciplinary approach to analyse the social and management problems posed by coastal erosion. The triangulation method allows the acquisition of data from various angles, while taking into account the scale of the research study [26]. The multidisciplinary approach focuses primarily on the different disciplines and the diverse perspectives they bring to understand an issue. In practice, to meet our objectives, we proceeded in an
From 2002 to the installation of seven groynes in 2013
Between 2002 and 2013, we measured a generalised coastline retreat in the study area of about 115 m with local variations from 38 to 145 m (Fig. 2). On these estimations of coastline regression measurement, we considered 5 m as a margin of error that may arise from natural influences on the position of the coastline (winds, tides), imprecisions related to the images (ortho-rectification, mosaic) and measurement uncertainties (digitalisation and photo-interpretation). Our estimations are
Discussion of results
The coastal erosion recorded in Cotonou, leading to coastline retreat and subsequent land loss, would not be an issue of concern if it had not affected local populations, infrastructures and economic development. In this part, we successively discuss the (im-)mobility of people in the risk zone and the comparison between people who experience the risk and those who manage the risk.
Final remarks
Coastal erosion and sea flooding, as urban floods in Africa, occur as the results of multiple interacting social and environmental processes that are poorly monitored [27]. The coastal area of Cotonou, highly urbanised, clearly is a risk-prone zone as affected by a fast erosion for several decades. The speed of coastal erosion over the last two decades was impressive and temporary stabilisation concerned only a few kilometres of coastline. Our results also show that the vulnerability of the
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The research leading to these results has received funding from the European Union Seventh Framework Programme FP7/2007-2013 under grant agreement no. 603864 and from the Commission de la Coopération au Développement de l’Académie de Recherche de d’Enseignement Supérieur (ARES-CCD). The authors gratefully acknowledge all the respondents, residents and stakeholders for time, experience and confidence. Many thanks to anonymous reviewers for relevant and insight comments and to Carolin Mayer for
References (73)
Social and economic costs of sea level rise
Int. Geophys.
(2001)- et al.
A quantitative assessment of human interventions and climate change on the West African sediment budget
Ocean Coast Manag.
(2018) - et al.
Assessment of coastal vulnerability to multi-hazardous events using geospatial techniques along the eastern coast of Bangladesh
Ocean Coast Manag.
(2019) - et al.
Sea level projections to AD2500 with a new generation of climate change scenarios
Global Planet. Change
(2012) - et al.
Effective sea level rise and deltas: causes of change and human dimension implications
Global Planet. Change
(2006) - et al.
Management strategies for coastal erosion problems in West Africa: analysis, issues, and constraints drawn from the examples of Senegal and Benin
Ocean Coast Manag.
(2018) - et al.
Vulnerability to beach erosion based on a coastal processes approach
Appl. Geogr.
(2019) - et al.
Vulnerability to coastal erosion in the Gambia: empirical experience from Gunjur
International Journal of Disaster Risk Reduction
(2020) - et al.
Institutional bricolage and the production of vulnerability to floods in an urbanising delta in Accra
International Journal of Disaster Risk Reduction
(2017) Exploring the dynamics of migration to mega-delta cities in Asia and Africa: contemporary drivers and future scenarios
Global Environ. Change
(2011)
Multi-hazard risk assessment of coastal vulnerability from tropical cyclones–A GIS based approach for the Odisha coast
J. Environ. Manag.
Environmental migration and cities in the context of global environmental change
Current Opinion in Environmental Sustainaibility
The data gap: an analysis of data availability on disaster losses in sub-saharan African cities
International Journal of Disaster Risk Reduction
Adaptive measures adopted for risk reduction of coastal erosion in the People's Republic of China
Ocean Coast Manag.
Migration, immobility and displacement outcomes following extreme events
Environ. Sci. Pol.
The effect of environmental change on human migration
Global Environ. Change
Process analysis in the coastal zone of Benin through remote sensing and socio-economic surveys
Ocean Coast Manag.
What meaning do individuals give to coastal risks? Contribution of the social representation theory
Mar. Pol.
Social perception of natural risks by local residents in developing countries-The example of the coastal area of Benin
Soc. Sci. J.
Methodologies to support coastal management - a stakeholder preference and planning tool and its application
Mar. Pol.
Validation of the hazard and vulnerability analysis of coastal erosion in the caribbean and pacific coast of Colombia
J. Mar. Sci. Eng.
Sea level rise and coastal biodiversity in West Africa: a case study from Ghana
Mapping vulnerability and risk of Ghana's coastline to sea level rise
Mar. Geodes.
The vulnerability to climate change of Cotonou (Benin) the rise in sea level
Environ. Urbanization
Society and sea level rise
Science
Shoreline morphological changes and the human factor. Case study of Accra Ghana
J. Coast Conserv.
Global warming and coastal erosion
Climatic Change
What dominates sea level at the coast: a case study for the Gulf of Guinea
Ocean Dynam.
L’influence des actions anthropiques dans l’évolution historique d’un littoral sableux à forte dérive sédimentaire: la baie de Port-Bouët (Abidjan, Côte d'Ivoire)
Géomorphol. Relief, Process. Environ.
Application de la télédétection à l'étude des changements urbains et des transformations du littoral à Cotonou (Bénin). Universités francophones
Evolution of Beninese coastline from 1963 to 2005: causes and consequences
Br. J. Environ. Clim. Change
Analyse des inondations en aval du barrage de Nangbeto sur le fleuve Mono (Togo et au Bénin)
Geo-Eco-Trop
Evolution récente du trait de côte dans le Golfe du Bénin. Exemples du Togo et du Bénin
Geo-Eco-Trop
Vulnérabilité de la zone côtière du Bénin à un rehaussement relatif du niveau marin: état de la question et préconisations/Vulnerability of the Coastal Zone of Benin to a Relative Sea level Rise: state of the Problem and Recommendations
Annales de géographie, JSTOR
Short-term shoreline evolution trend assessment: a case study in Glefe, Ghana
Jamba: J Disaster Risk Stud
Cited by (11)
Traditional vs. novel approaches to coastal risk management: A review and insights from Italy
2023, Journal of Environmental ManagementUsing of intensity analysis approach in Benin coastal zone (West Africa) to assess land use/land cover change for further decision making
2022, HeliyonCitation Excerpt :Remote sensing and geospatial techniques now provide tools to assess changes in coastal landscapes (Davidson et al., 2018). In West Africa and particularly in Benin, studies have been conducted on different themes such as: coastline dynamics (Assogba et al., 2021; Hounguè et al., 2018; Ndour et al., 2018); coastal risk management (Florence de Longueville et al., 2020; Guerrera et al., 2021; Ndour et al., 2018); assessment of vulnerability and perception of risks by coastal populations (Dossou and Gléhouenou-Dossou, 2007); land use change (Padonou et al., 2017). Studies on land use/cover change have been carried out in two coastal cities in Benin (Teka et al., 2012a,b) however, understanding the basis of the patterns and processes driving land-use change throughout all coastal areas in Benin remains to be elucidated.
Shoreline evolution along Benin coast using satellite data through CASSIE Tool
2024, Research SquareCommunity-based assessment of coastal erosion in Lagos, Nigeria
2022, Natural Hazards