The Senegal River delta in West Africa, one of the finest examples of “wave-influenced” deltas, is bounded by a spit periodically breached by waves, each breach then acting as a shifting mouth of the Senegal River. Using European Re-Analysis (ERA) hindcast wave data from 1984 to 2015 generated by the Wave Atmospheric Model (WAM) of the European Centre for Medium-Range Weather Forecasts (ECMWF), we calculated longshore sediment transport rates along the spit. We also analysed spit width, spit migration rates, and changes in the position and width of the river mouth from aerial photographs and satellite images between 1954 and 2015. In 2003, an artificial breach was cut through the spit to prevent river flooding of the historic city of St. Louis. Analysis of past spit growth rates and of the breaching length scale associated with maximum spit elongation, and a reported increase in the frequency of high flood water levels between 1994 and 2003, suggest, together, that an impending natural breach was likely to have occurred close to the time frame of the artificial 2003 breach. Following this breach, the new river mouth was widened rapidly by flood discharge evacuation, but stabilised to its usual hydraulic width of <2 km. In 2012, severe erosion of the residual spit downdrift of the mouth may have been due to a significant drop (~15%) in the longshore sand transport volume and to a lower sediment bypassing fraction across the river mouth. This wave erosion of the residual spit led to rapid exceptional widening of the mouth to ~5 km that has not been compensated by updrift spit elongation. This wider mouth may now be acting as a large depocentre for sand transported alongshore from updrift, and has contributed to an increase in the tidal influence affecting the lower delta. Wave erosion of the residual spit has led to the destruction of villages, tourist facilities and infrastructure. This erosion of the spit has also exposed part of the delta plain directly to waves, and reinforced the saline intrusion within the Senegal delta. Understanding the mechanisms and processes behind these changes is important in planning of future shoreline management and decision-making regarding the articulations between coastal protection offered by the wave-built spit and flooding of the lower delta plain of the Senegal River.

Cette étude présente une analyse diachronique de l’évolution de la ligne de rivage aux abords de Nouakchott (1954-2005) par photo-interprétation. Elle utilise comme références les lignes des pleines mers et du pied de dune. Les variations observées de la position du pied de dune entre 1954 et 1980 témoignent d’un littoral en érosion à un rythme moyen de -0,83 m/an. L’étude de la cinématique de la ligne des pleines mers entre 1980 et 2005 indique des évolutions importantes consécutives à l’aménagement de la jetée du port de Nouakchott en 1986. Le trait de côte a progressé de plus de 800 m en amont-dérive alors qu’au sud de l’épi, en aval-dérive, la côte a reculé de plus de 500 m.Les principales limites de l’approche méthodologique de cartographie de la mobilité du trait de côte résident dans les erreurs d’interprétation des lignes de référence ; celles-ci sont plus spécifiquement liées ici à la qualité des images aériennes utilisées et aux variations à court terme de la position de la limite des pleines mers. Ce sont là autant de sources d’erreur qu’il faut analyser et estimer avant de tirer des conclusions sur la cinématique littorale.

Cette étude, qui porte sur un peu plus d’un siècle (1900-2009), analyse l’évolution spatiale du port de Dakar en le mettant en rapport avec les facteurs politiques, économiques et territoriaux en œuvre depuis sa création. L’analyse cartographique à l’échelle micro-locale a permis de suivre l’évolution des aménagements et des transformations spatiales de la zone portuaire et a fourni quelques pistes d’articulation avec les autres échelles. À cet égard, l’analyse spatio-temporelle du port montre une gestion qui a pu tant bien que mal s’adapter aux évolutions du trafic maritime, grâce à une succession d’aménagements spatiaux et logistiques. La phase d’extension liée d’abord à la fonction d’escale du port, puis au développement commercial et industriel du pays, n’a pu s’effectuer que sur la mer en raison d’une emprise urbaine qui est devenue très tôt une contrainte spatiale insurmontable. Une phase de spécialisation en faveur du trafic conteneur ne s’est opérée qu’en 2000, soit 25 ans après les premières dessertes de ce type de conditionnement sur les côtes ouest-africaines. Le port se trouve maintenant à un point critique de son évolution. En effet, si son espace a pu être occupé à plus de 90 % pendant cette dernière décennie, sa configuration actuelle ne lui permet pas de supporter la croissance future des flux maritimes. L’option de remblais, qui apparaissait comme une réponse à la congestion des terminaux, n’offre plus de garantie quant à la sécurité des navires. Ceci laisse présager une phase de dissociation avec le déplacement des terminaux minéraliers hors de Dakar et le réaménagement des énormes espaces ainsi libérés. Mais cette alternative coûteuse nécessite une stratégie en harmonie avec le développement du pays, et l’implication d’une diversité d’investisseurs.

In the context of growing international recognition of geospatial information as a strategic driver of evidence-based decision-making, digital transformation, and sustainable development, robust assessment frameworks are essential for guiding the development of National Spatial Data Infrastructures (NSDIs). This paper presents the first baseline assessment of Senegal’s NSDI using the United Nations Integrated Geospatial Information Framework (UN-IGIF). Drawing on the UN-IGIF Diagnostic Tool, supplemented by surveys, semi-structured interviews, and multi-stakeholder consultations, the analysis reveals a low overall maturity level (33/100), despite relatively better performance in institutional governance and geospatial data availability. Significant weaknesses persist in the areas of legislation, funding, standards implementation, innovation, partnerships, communication, and capacity building. The findings confirm the relevance of the UN-IGIF for assessing challenges related to geospatial governance in Francophone African countries and identify priority areas for reform, including strengthening coordination mechanisms, legal and regulatory modernization, sustainable financing, and strategic planning. By providing empirical evidence on both the NSDI maturity level and the operational applicability of the UN-IGIF, this study contributes to the international literature on geospatial governance and offers a solid foundation for future reforms in Senegal and other low- and middle-income countries.

During this last decade, urban flooding has become recurrent in Senegal, particularly in the city of Dakar. The causes are multiple and varied, with devastating impacts on population well-being and the urban environment. For sustainable and harmonious urban development, flood risk mapping should be integrated into urban planning policies. This study aims to map areas vulnerable to flooding at regional, departmental and communal scale, using Remote Sensing, Geography Information System (GIS) and Multicriteria Evolution Approach (MCEA). Twelve criteria layers were defined to identify flood-prone areas, including Rainfall, Elevation, Slope, Groundwater level, Soil type, Impervious surfaces, Land use/cover, Population density, Housing type and structure, Humid zones, Drainage density and Standard of living. A Weighted Linear Combination (WLC) technique was applied and adapted in this study to map flood vulnerability. The criteria were scored and weighted according to their relative importance, as defined by local experts. ArcGIS 10.1 software through its extension Weighted sum overlay tool, was used to aggregate criteria layers into three main indicators: “Socio-economic”, “Physical environment” and “Land use/cover”. The results indicate that approximately 60% of the Dakar urban area is highly vulnerable to flooding according to the "Physical environment" indicator, compared to 12% and 10% for the "Socioeconomic" and "Land use/cover indicators, respectively. Overall, the combination all indicators shows that about 50% of Dakar urban environment is vulnerable to flooding. This vulnerability mainly concerns the departments of Pikine, Guediawaye and Keur Massar, where more than 80% of areas are classified as highly vulnerable. At the municipal and departmental scales, vulnerability indices are higher (greater than 0.7) in these areas compared to the department of Dakar (0.37) and Rufisque (0.14). Validation of final flood vulnerability map was conducted by comparing the most vulnerable areas identified in this study with those severely affected by floods observed using Earth Observation Satellite (SPOT) imagery in September 2005 and 2009. The validation results show an overall accuracy approximately 0.95 and 0.90 for the two respective dates. Understanding the level of vulnerability of the Dakar urban environment, as well as the contribution of each factor, can serve as a decision-support tool for rational and localized management of flood-prone areas in the context of climate change.