Perceptions of and responses to coastal erosion risks: The case of Cotonou in Benin

https://doi.org/10.1016/j.ijdrr.2020.101882Get rights and content

Abstract

Intensive erosion has affected the coastal zone of Cotonou for several decades. An analysis of satellite images showed an average coastline retreat of 115 m in the study area over the period 2002–2013 with several hundred houses destroyed. Since 2014, a stabilisation of the coastline is observed. This study aimed at identifying the at-risk population and at analysing the perceptions of people who experience and those who manage coastal erosion risk, as well as the responses adopted. Based on four criteria and their hierarchy, we identified five profiles of inhabitants in this risk zone. (1) Wealthy people who leave the zone when they are affected or (2) fall into the category of people in danger in case they cannot migrate. (3) Fishermen who deliberately stay near the sea. (4) The most precarious people, trapped in the risk zone. Finally, (5) poor newcomers who continually increase the at-risk population. With the recent stabilisation of the coastline, the national authorities manage the “hazard” component of the risk. However, the majority of the population is not serene. The anthropogenic stress linked to evictions gradually replaced the stress to be engulfed by the sea. We conclude that the “vulnerability” component of the risk is not yet resolved. All categories of the population in this sensitive area need to be secured. Cooperation among multiple levels of governance, the application of land use planning regulations and of the Kampala Convention and the involvement of local communities are all measures which will enable to meet this objective.

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)

  • B. Sahoo et al.

    Multi-hazard risk assessment of coastal vulnerability from tropical cyclones–A GIS based approach for the Odisha coast

    J. Environ. Manag.

    (2018)
  • S.B. Adamo

    Environmental migration and cities in the context of global environmental change

    Current Opinion in Environmental Sustainaibility

    (2010)
  • E. Osuteye et al.

    The data gap: an analysis of data availability on disaster losses in sub-saharan African cities

    International Journal of Disaster Risk Reduction

    (2017)
  • S. Luo et al.

    Adaptive measures adopted for risk reduction of coastal erosion in the People's Republic of China

    Ocean Coast Manag.

    (2015)
  • R. Black et al.

    Migration, immobility and displacement outcomes following extreme events

    Environ. Sci. Pol.

    (2013)
  • R. Black et al.

    The effect of environmental change on human migration

    Global Environ. Change

    (2011)
  • O. Teka et al.

    Process analysis in the coastal zone of Benin through remote sensing and socio-economic surveys

    Ocean Coast Manag.

    (2012)
  • C. Lemée et al.

    What meaning do individuals give to coastal risks? Contribution of the social representation theory

    Mar. Pol.

    (2019)
  • O. Teka et al.

    Social perception of natural risks by local residents in developing countries-The example of the coastal area of Benin

    Soc. Sci. J.

    (2010)
  • J. Schumacher et al.

    Methodologies to support coastal management - a stakeholder preference and planning tool and its application

    Mar. Pol.

    (2018)
  • O. Coca-Domínguez et al.

    Validation of the hazard and vulnerability analysis of coastal erosion in the caribbean and pacific coast of Colombia

    J. Mar. Sci. Eng.

    (2019)
  • A.K. Armah et al.

    Sea level rise and coastal biodiversity in West Africa: a case study from Ghana

  • I. Boateng et al.

    Mapping vulnerability and risk of Ghana's coastline to sea level rise

    Mar. Geodes.

    (2017)
  • K.M. Dossou et al.

    The vulnerability to climate change of Cotonou (Benin) the rise in sea level

    Environ. Urbanization

    (2007)
  • O.H. Pilkey et al.

    Society and sea level rise

    Science

    (2004)
  • K. Appeaning Addo

    Shoreline morphological changes and the human factor. Case study of Accra Ghana

    J. Coast Conserv.

    (2013)
  • K.Q. Zhang et al.

    Global warming and coastal erosion

    Climatic Change

    (2004)
  • A. Melet et al.

    What dominates sea level at the coast: a case study for the Gulf of Guinea

    Ocean Dynam.

    (2016)
  • B. Touré et al.

    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.

    (2012)
  • C. Codjia

    Application de la télédétection à l'étude des changements urbains et des transformations du littoral à Cotonou (Bénin). Universités francophones

    (1997)
  • C. Kaki et al.

    Evolution of Beninese coastline from 1963 to 2005: causes and consequences

    Br. J. Environ. Clim. Change

    (2011)
  • E.E. Ago et al.

    Analyse des inondations en aval du barrage de Nangbeto sur le fleuve Mono (Togo et au Bénin)

    Geo-Eco-Trop

    (2005)
  • P. Ozer et al.

    Evolution récente du trait de côte dans le Golfe du Bénin. Exemples du Togo et du Bénin

    Geo-Eco-Trop

    (2017)
  • É.H. Prudencio et al.

    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

    (2002)
  • K. Amoani et al.

    Short-term shoreline evolution trend assessment: a case study in Glefe, Ghana

    Jamba: J Disaster Risk Stud

    (2012)
  • Cited by (11)

    • Using of intensity analysis approach in Benin coastal zone (West Africa) to assess land use/land cover change for further decision making

      2022, Heliyon
      Citation 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.

    View all citing articles on Scopus
    View full text