Dynamique De La Mangrove De Thiobon Dans L’estuaire De La Casamance (Sénégal) Entre 1972 Et 2017

In the village soil of Thiobon in lower Casamance (southern Senegal), site being established as Marine Protected Area (MPA), the main activities of the population (rice growing, harvesting of fish products, salt production, …), happens in mangrove zone. These mobilize the population for several months in the year. This mangrove ecosystem, vulnerable and fragile, has undergone profound changes since the 1960s under the combined actions of rainfull variability and main. This study proposes to analyze the spatio-temporal dynamics of Thiobon mangrove. The method used is based on the processing and analysis of satellite data (Landsat imagery acquired in 1972, 1986, 2000 and 2017), rainfall data (1960 to 2017), and on the perception of populations of change in their terroir (field investigation). Map results indicate an overall decline on 52% in mangrove area in tanne during drought years (1970 to the late 1990s). During 2000–2017, characterized by the almost normal return of the rainfall and activities of reforestation done by the local population, about 69% of the mangrove areas lost between 1972 and 2000 regenerated. This dynamic is the result of external and internal forces exerted on this ecosystem and evolve since the early 1970s

Évolution du trait de côte à Nouakchott (Mauritanie) de 1954 à 2005 par photo-interprétation

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.This paper presents a diachronic analysis of shoreline changes (1954-2005) around Nouakchott by interpretation of aerial photographs. Two shoreline indicators are used: the dune foot and the high water line. The comparison of the dune foot location between 1954 and 1980 shows a coastline in erosion with an average rate of -0,83m/year. The study of the high water line kinematics from 1980 to 2005 points out large evolutions consecutive to the construction of the harbour jetty in 1986. Thus the shoreline has progressed more than 800m in the updrift while in the downdrift side (South of the groin) it has retreated over half kilometer. The main limits of the method are the misinterpretation of the reference lines due to the poor quality of some aerial photographs and the short-term variability in the high water line position. All that may lead to errors that must be analysed and assessed before drawing conclusions on coastal evolution

Analyse Granulometrique et Cartographie des Sediments Superficiels de la Lagune Cotiere au Benin (Afrique de L’Ouest)

The current study is part of the wide-ranging issue related to the sedimentary dynamics of paralic hydro systems. This study aims to characterize the sedimentary cover of the coastal lagoon, one of Benin's four main water bodies, using the granulometric analysis procedure. Based on shallow sediment samples’, following 48 transects in the lagoon, a few laboratory processes have been undertaken, including granulometry, statistical calculus acting upon the Folk & Ward textural parameters through Excel and Origin 6.0 software, and also sandy feature mapping, while considering the ArcGIS 10.3 software performance. The grain size indexes of these facies indicate a second or poor-rate classification of medium sands, almost symmetrical, with mesokurtic acuity. The Passega diagram describes a saltation or rolling transport of these sands. The combination of Friedman’s, Moiola’s and Weiser’s diagrams reveals fluvial-origin sediments and remobilization from the coastal dune zones flanking the lagoon. At the level of the coastal lagoon, a hydrodynamic zoning is established, characterized by some insubstantial hydro dynamism of the eastern sector, impacted by the influence of the so-called Ouidah lagoon and a relatively strong hydro dynamism of the western sector corresponding to the Grand- Popo lagoon, with a speed ranging between 0.78 to 1.4 m / s towards the bottom and a flow rate of 429 m3 / s, at the Avlo beach station. Ultimately, this study made it possible to underscore the state of hydrodynamic variations observed in the lagoon, notably an opposition between eastern and western sectors, the diversity of sedimentary input sources and the design of the first lithological facies map of this paralic environment, which now stands as a vital tool for its follow-up and monitoring, in the current context of upcoming changes and unremitting alteration.Cette étude s’inscrit dans la problématique de la dynamique sédimentaire des hydrosystèmes paraliques. Elle se base sur les techniques granulométriques pour caractériser les sédiments de la lagune côtière, l’un des quatre principaux plans d’eau paraliques du Bénin. A partir des prélèvements de sédiments superficiels sur 48 transects, des travaux de laboratoire, des calculs de paramètres texturaux de Folk & Ward sur Excel et le logiciel Origin 6.0 ainsi que la cartographie des faciès via ArcGIS 10.3., ont été effectués. Les indices granulométriques de ces faciès indiquent un classement médiocre de sables moyens, presque symétrique, avec une acuité mésocurtique. Le diagramme de Passega décrit un transport par saltation ou roulement de ces sables. La combinaison des diagrammes de Friedman, Moiola et Weiser montre des sédiments d’origine fluviatile et ceux remobilisés à partir des dunes côtières adjacentes à la lagune. Un zonage hydrodynamique est également noté, caractérisé par un hydrodynamisme faible du secteur oriental ou lagune de Ouidah et un hydrodynamisme relativement fort du secteur occidental ou lagune de Grand-Popo, avec une vitesse de l’ordre de 0,78 à 1,4 m/s vers le fond et un débit de 429 m3 /s, à la station de Avlo Plage. En définitive, ce papier fait ressortir l’état de variations hydrodynamiques de la lagune, notamment une opposition entre secteurs oriental et occidental, la diversité des sources d’apports sédimentaires et la réalisation de la première carte des lithofaciès de cet environnement aquatique, outil indispensable à son suivi face à des changements futurs et à un contexte en mutation perpétuelle

Using the nexus between public participation and institutional arrangements for conflicts prevention in the senegal river basin

Water management forms the most critical process in such semi-arid land, as it impacts livelihood, food security, land tenure, productivity and social stability. Though generally quoted as a successful case of regional cooperation, the nature of the Senegal River Basin (SRB) cooperative management is being strained by the impacts on the most vulnerable groups of its community. The scarcity of resources, unilateral short term gains, recent transformation of social networks, and lack of public participation had raise old and new types of disputes and social unrest in recent years. This paper, a step in what is hoped to be a continued exploration of disputes and cooperation over the SRB, offers the opportunity for institutional and administrative reform to acquaint local stakeholders in the decision making process to cope with social and environmental conflicts and, the discontinuities, such as extreme climatic events or sudden institutional changes. Even if some tremendous progress have been achieved in some sectors, several indicators point out that, to date, the majority of the stakeholders have not yet benefited from the output since the entire management approach has been sectoral without serious options for dialogue, consensus building, public participation or recognition of the local knowledge in the decision making process. The priority is no longer to make development projects profitable at all costs according to the narrow economic criteria of connected state bureaucracy and donors, integrated water management should be based on the awareness and constructive communication, responsibility sharing and consider the basin and its people as an inextricable part of the ecosystem

Pejoration climatique et degradation des formations forestieres en haute-casamance (senegal)

The objective of this study is to analyze climatic changes and forest degradation in Haute-Casamance, one with the highest biomass productivity of the country. This climatic analysis was performed using rainfall, temperature and evaporation data collected from to the Senegal National Meteorological Agency. Data of potential evapotranspiration (PET) was used to better characterize the evolution of the water balance. The results show changes in climatic conditions through an important rainfall deficit, particularly in the course of 1971-1980 and on 1981-1990 decades and an increase in temperatures. The deterioration of climatic conditions combined with unsustainable land use systems (brush fires, clearance, extension of cultures for private income, overexploitation,) had seriously disturbed the ecosystem and socioeconomic conditions of the Haute-Casamance. The land use mapping of two protected forest formations (Guimara in the north and Kayanga in the south), deducted from the interpretation aerial photographs, shows that forest degradation is more accentuated in the north in accordance with a north-south gradient of the rain gauge stations distribution in the study zone

Evolution récente des côtes sableuses d'Afrique de l'Ouest par traitement d'images Landsat

National audienceCet article décrit l'évolution du trait de côte entre 1978 et 2001, intervenue sur les estrans sableux ouest-africains, de la Mauritanie à la Guinée-Bissau. Les images Landsat utilisées, d'accès libre, font l'objet d'un traitement par équidensitométrie et classification non supervisée (ISODATA). Cependant, les résultats sont partiels du fait de la résolution spatiale des images (30 m à 79 m) inadaptée à la mise en évidence de taux d'évolution relativement bas de l'essentiel des côtes sableuses (1 à 6 m/an). Ils sont donc limités aux formes très mobiles associées aux systèmes estuariens (flèches, petites îles et cordons sableux isolant des mangroves). Ainsi, seuls 7,5% du linéaire côtier sableux régional montrent une évolution mesurable avec les données disponibles. Sur ce pourcentage, 73,4 % sont en progradation et 26,6 % en érosion avec des vitesses moyennes d'évolution variant généralement de +15 à +140 m/an et de -13 à -47 m/an

Analyse de la dynamique spatiale du port de Dakar de 1900 à 2009 : enjeux multi-scalaires et aménagements

International audienc