Oyapock et Maroni

Guyana, delimited by its border rivers, the Oyapock and the Maroni, is a French Amazonian territory in South America, remarkable for its rich biodiversity. The Guyanese coastline, which stretches for 350 km between the estuaries of these two rivers, is extremely unstable, constantly modified by mud banks formed by sediments carried from the Amazon delta in Brazil which move along sides. One of the best preserved mangroves in the world is developing there, at the heart of considerable ecological challenges due to its role as nursery and nursery for many species and its ability to store carbon. Very productive in terms of fishing, the Guyanese maritime fringes are under heavy pressure on fishery resources while numerous socio-environmental changes are taking place under the effect of strong demographic growth and significant human migration. Guyana must therefore meet many environmental, human and economic challenges today. This richly illustrated book is both a showcase of the Guyanese coastline and these exceptional estuaries, and an invitation to rethink the interactions between man and his environment

Mud bank colonization by opportunistic mangroves: A case study from French Guiana using lidar data

Mud bank colonization by mangroves on the Amazon-influenced coast of French Guiana was studied using light detection and ranging (lidar) data which provide unique information on canopy geometry an sub-canopy topography. The role of topography was assessed through analysis of vegetation characteristics derived from these data. Measurements and analyses of mangrove expansion rates over space and time led to the identification of two distinct colonization processes. The first involves regular step-by-step mangrove expansion to the northwest of the experimental site. The second is qualified as ‘opportunistic’ since it involves a clear relationship between specific ecological characteristics of pioneer Avicennia and mud cracks affecting the mud bank surface and for which probabilities of occurrence were computed from terrain elevations. It is argued from an original analysis of the latter relationship that mud cracks cannot be solely viewed as water stress features that reflect desiccation potentially harmful to plant growth. Indeed, our results tend to demonstrate that they significantly enhance the propensity for mangroves to anchor and take root, thus leading to the colonization of tens of hectares in a few days. The limits and potential of lidar data are discussed with reference to the study of muddy coasts. Finally, the findings of the study are reconsidered within the context of a better understanding of both topography and vegetation characteristics on mangrove-fringed muddy coasts

Dynamique morpho-sédimentaire d'un littoral sous influence amazonienne (Impact des forçages hydrosédimentaires sur la migration des bancs de vase et la mangrove côtière)

Cette thèse a pour but d'améliorer la compréhension des interconnexions entre les processus hydro-sédimentaires et l'évolution morphologique du littoral guyanais, formés à partir des énormes apports sédimentaires amazoniens. Elle s'appuie sur trois échelles spatiales : la côte des Guyanes, le banc de vase et la vasière. L'amortissement des houles à la côte ainsi que les processus de migration des bancs ont été étudiée à l'échelle de la côte des Guyanes. Ce travail apporte une vision structurelle des zones subtidales des bancs et met aussi en évidence les différents processus et forçages (houle, courant) responsables du transport sédimentaire, en fonction de la bathymétrie (> 5 m et < 5 m). L'évolution morphologique du banc de Kourou et des surfaces de mangrove côtières associées, ont aussi été étudiées. Un lien a ainsi été exposé entre, l'implantation des palétuviers, les régimes de courant et la topographie de la vasière. Cette relation a permis d'aborder l'aspect prédictif de l'expansion des surfaces de mangrove côtière. À l'échelle de la vasière, les zones intertidales sont divisibles en deux secteurs géographiques avec des dynamiques sédimentaires bien distinctes : le front de mer et les zones internes. La morphologie des vasières est abordée, tout comme les processus sédimentaires ayant lieu au niveau de la zone interne. Une méthode de reconstitution des apports sédimentaires de la zone interne est aussi proposée. Cette étude souligne l'importance des interactions entre les sédiments cohésifs et la houle, qui modèlent la morphologie du littoral. Les influences des forçages hydrométéorologiques sur la morphodynamique des bancs de vase et l'évolution du trit de côte sont soumises à discussion.The aim of this work is to improve the knowledge of the interconnections between hydro-sedimentary processes and Guianese's coastal morphology evolution, formed by the sedimentary Amazon discharge. This subject follows three spatial scales : the Guianese's Coast, the mud bank and the mudflat. Coastal waves damping by mud and migration process have been studied at the Guianese's Coastal scale. This study also gives a structural vision of subtidal part of banks and highlights the various processes and hydrodynamics conditions needed for sedimentary transport, for two bathymetric areas (> 5 m and < 5 m depth). The morphological evolution of Kourou's mud bank and the associated surfaces of coastal mangrove are also analysed. A link between mangrove colonisation, currents and the mudflat topography is highlighted. This relation allows a discussion about predictive aspect of the mud banks colonisation by mangrove. At the mudflat scale, intertidal part is divided in two areas with different sedimentary dynamic processes : sea front and internals zones. The morphologycal structure and the sedimentary processes of internals zones are analysed. An historical reconstitution method of sedimentary supplies is also proposed. This study underlines morphological coastal changes sensitivity to hydro meteorological forcing and interactions between cohesive sediment and swells which seems to lead the morphological coastal evolution.DUNKERQUE-SCD-Bib.electronique (591839901) / SudocSudocFranceF

Chenier Morphodynamics on the Amazon-Influenced Coast of Suriname, South America: Implications for Beach Ecosystem Services

The 350-km long coast of Suriname, South America, is part of a unique system in the world characterized by large-scale mud supply from the Amazon and exposed to Atlantic waves. Large banks migrate alongshore from the Amazon to the Orinoco delta, separated by ‘inter-bank’ zones. Banks dissipate waves, partially weld onshore, and are colonized by mangroves, whereas waves in inter-bank areas cause shoreline erosion, mitigated where rare cheniers develop. Cheniers assure coastal protection and recreational and ecosystem services, notably providing nesting sites for marine turtles. Cheniers are also under pressure from sand mining. In order to gain a better understanding of how these cheniers form and evolve, a study was conducted on Braamspunt beach, a major turtle-nesting chenier in Suriname constructed from sand supplied by the Maroni River. Satellite images between 1987 and 2018 show a reduction of the alongshore extent of the chenier, following sand supply cut-off from the Maroni by a mud bank migrating westward towards the mouth of the Suriname River, exacerbated by mud-blanketing of sand. Commercial sand mining has further affected the beach, but mined volumes are not known. Field surveys (high-resolution topography, drone photogrammetry, wave measurements) conducted in February, 2016 highlight two chenier types depending on sand availability, transport and wave reworking: a high-tide reflective/low-tide dissipative and longshore transport-dominated type 1 exhibiting berm scarping, and a low, overwash-dominated type 2. As the mud-bank’s leading edge impinges on the inter-bank trailing edge, sand sequestering by mud and storage in type 2 washovers entail less available sand downdrift. Type 1 lost over 4200 m3 of sand in just 3–4 days. An increasingly deficient budget induces progressive change to type 2, morphodynamically better adapted to diminution of available sand, and epitomizing chenier fragmentation and isolation within the muddy Guianas coastal plain. By affecting the morphology and sand budget of Braamspunt, these changes lower opportunities for turtle-nesting. Further reduction of the length of exposed chenier is apparently halted near the Suriname River mouth where mud is liquefied by the outflowing river and tidal jet, but the continued existence of this preserved beach could be endangered by sand mining

Les paysages urbains de l’île de Cayenne, Guyane française

A urbanisação da ilha de Cayenne rãvéa das fomas inesperado para um departamento françês um meio dificil, uma mosaico de população de condição socia-economico muito desigual, da forma muito heterogéneo. As consequências d’uma urbanisação desordenada tem muito e da muita cidade do país do sul.Cayenne, the capital of French Guiana, shows forms of urbanization that are atypical for a French Department. The heterogeneous urban landscape of Cayenne is the joint product of a harsh equatorial environment and juxtaposed ethnic groups exhibiting marked socioeconomic differences. The consequences of this disorderly urbanization are numerous and akin to those of many Third World cities.L’urbanisation de l’île de Cayenne revêt des formes inattendues pour un département français. Un milieu contraignant, une mosaïque de populations, de conditions socio-économiques très inégales, ont façonné un paysage urbain très hétérogène. Les conséquences d’une urbanisation désordonnée sont nombreuses et génériques à de nombreuses villes des pays du Sud.Gardel Antoine. Les paysages urbains de l’île de Cayenne, Guyane française. In: Mappemonde 63, 2001/3. pp. 16-21

Monitoring of coastal dynamics in French Guiana from 16 years of SPOT satellite images

International audienc

De l’analyse des cartes anciennes à l’altimétrie laser aéroportée : l’évolution des techniques de suivi du trait de côte. Exemples sur la Côte d’Opale

International audienc