Géomorphologie Dynamique: Analyse Systémique De La Morphodynamique Hydrique Continentale Par Ravinement

L’histoire de la géomorphologie a connu une grande révolution paradigmatique avec les travaux de WiliamMoris Davis. Il a défini le système géomorphologique comme l’ensemble de toutes les formes de la surface de la terre subissant des transformations et étant la fonction des trois variantes : structure, processus et temps. Cependant, le positionnement d’emblée des réflexions géomorphologiques dans l’analyse systémique conduit à élargir les problématiques du champ disciplinaire de cette science. Dans le cas de la géomorphologie dynamique, ce type d’analyse conduit à concevoir des recherches intégrées au sein des bassins versants afin de mieux mettre en lumière certains processus morphodynamiques. En l’absence de zone d’étude précise, l’étude est basée sur un balayage des connaissances bibliographiques à travers le domaine continental dans sa globalité. Ainsi, l’article montre que l’analyse systémique demeure une approche efficace pour lire en intégralité le fonctionnement des processus morpodynamiques hydriques continentales en géomorphologie, en particulier le ravinement. La caractérisation du ravinement sur un bassin versant grâce à l’analyse systémique doit se fonder sur trois caractéristiques essentielles : hydrologique, morphogénique et anthropique. Chaque critère correspondant à l’une des notions géographiques fondamentales : Temps, Espace et Société. The history of geomorphology has undergone a great paradigmatic revolution with the work of Wiliam Moris Davis. He defined the geomorphological system as the set of all forms of the earth’s surface undergoing transformation and being the function of three variants: structure, process and time. However, the immediate positioning of geomorphological reflections in systemic analysis leads to widening the problems of the disciplinary field of this science. In the case of dynamic geomorphology, this type of analysis leads to the design of integrated research within watersheds in order to better highlight certain morphodynamic processes. In the absence of a precise study area, the study is based on a sweeping of bibliographic knowledge across the continental domain as a whole. Thus, the article shows that systemic analysis remains an effective approach to fully read the functioning of continental water morphological processes in geomorphology, in particular gullying. The characterization of gullying on a watershed using systemic analysis must be based on three essential characteristics: hydrological, morphogenic and anthropogenic. Each criterion corresponding to one of the fundamental geographic concepts: Time, Space and Society

Caractérisation Spatiotemporelle Et Analyse De La Tendance Des Températures Au Sénégal

La connaissance de la variation spatiotemporelle des températures et l’analyse de leur tendance constituent un aspect essentiel dans la compréhension des changements climatiques et le développement de stratégies d’adaptation et de mitigation. L’objectif de ce travail est de contribuer à la connaissance de l’évolution des températures au Sénégal. De façon spécifique, il s’agit d’abord, de faire une caractérisation spatiotemporelle des températures, ensuite, de déterminer les anomalies et enfin de détecter les tendances des températures au Sénégal. Pour ce faire, les données mensuelles de températures maximale et minimale de 20 stations synoptiques sont utilisées. La méthodologie adoptée consiste à cartographier les températures (maximale, minimale et moyenne) aux échelles mensuelle et annuelle, détecter les anomalies par l’application de l’indice de Lamb et d’analyser les tendances par le test de Mann Kendall et la pente de Sen. Les résultats montrent que les températures moyennes varient de 19°C à 35°C et les mois de mars et avril sont les plus chauds. Du point de vue spatial, plus on s’éloigne des côtes, plus les températures sont élevées. La détection des anomalies révèle une hausse de 0,68°C et 1,27°C des températures maximale et minimale sur la période 1960 - 2015. L’analyse de tendance montre une augmentation significative des températures maximale et minimale annuelles et saisonnières sur la période 1960 - 2015 sur la quasi-totalité du pays. Les résultats montrent aussi une augmentation plus vite des températures minimales que celles maximales. Il serait donc important d’analyser la tendance des autres paramètres climatiques pour comprendre le pourquoi les températures minimales augmentent plus vite que celles maximales. Il serait intéressant aussi d’étudier les impacts de la hausse des températures sur les systèmes biophysiques et socioéconomiques du Sénégal. Knowledge of the spatiotemporal variation in temperatures and the analysis of their trend is an essential aspect in understanding climate change and developing adaptation and mitigation strategies. The objective of this work is to contribute to the knowledge of the evolution of temperatures in Senegal. Specifically, it is first of all to do a spatiotemporal characterization of temperatures, then to determine anomalies and finally to detect temperature trends in Senegal. For this, monthly data of maximum and minimum temperatures from 20 synoptic stations are used. The methodology adopted consists in mapping the temperatures (maximum, minimum and average) on monthly and annual scales, detecting anomalies by applying the Lamb index and analyzing the trends by the Mann Kendall test and the slope of Sen. The results show that average temperatures vary from 19 ° C to 35 ° C and the months of March and April are the hottest. From a spatial point of view, the further away from the coast the higher the temperatures. The detection of anomalies reveals an increase of 0.68 ° C and 1.27 ° C in maximum and minimum temperatures over the period 1960 - 2015. Trend analysis shows a significant increase in annual and seasonal maximum and minimum temperatures over the period 1960 – 2015 in almost the all country. period 1960 - 2015. The results also show a faster increase in minimum temperatures than maximum ones. It would therefore be important to analyze the trend of other climatic parameters to understand why minimum temperatures are increasing faster than maximum ones. It would also be interesting to study the impacts of rising temperatures on Senegal's biophysical and socioeconomic systems. &nbsp

Caractérisations Granulométrique et PaléoEnvironnementale des Sédiments d’un Bassin Versant à Forte Dynamique Structurale dans un Contexte de Ravinement: Bassin Versant de Ourossogui (Nord du Sénégal)

L’intérêt de cette caractérisation sédimentaire par granulométrie, est de faire une reconstitution paléo-environnementale des sédiments du bassin versant de Ourossogui. Ainsi, la méthodologie est basée sur des analyses granulométriques au laboratoire. Le traitement des données s’est fait grâce à des indices granulométriques et des diagrammes de K-Sk de Friedman et de Mz-Sk de Moiola et Weiser. Lesrésultats montrent que les faciès lithologiques superficiels observés dans le bassin versant de Ourossogui sont en majorité composés de particules sableuses. Quant au diagramme de K-Sk de Friedman, il renseigne que les sédiments sont apportés par les eaux courantes, alors que celui de Mz-Sk de Moiola et Weiser a montré que les sédiments sont intégralement d’origine continental, avec cependant une légère présence de sédiments d’origine marine. Ils correspondent à des apparitions de faciès de calcaires phosphatées au niveau des éboulis situés sur les lits des ravins du bassin versant. Ce contexte paléo-environnemental du bassin versant est à l’origine de sa forte dynamique structurale, marquée par une réactivation de la morphodynamique hydrique. The interest of this sedimentary characterization by granulometry, is try to do a paleo-environmental reconstitution of the sediments of the watershed of Ourossogui. For this reason, the methodology is based on granulometric analyzes in the laboratory. Data processing was done using grain size indices and Friedman K-Sk and Moiola and Weiser Md-Sk diagrams. The results show that the superficial lithological facies observed in the Ourossogui watershed are mostly composed of sandy particles. As for the Friedman K-Sk diagram, it indicates that the sediments are brought by running waters, while that of Mz-Sk of Moiola and Weiser showed that the sediments are entirely of continental origin, with however a slight presence sediments of marine origin. They correspond to occurrences of phosphated limestone facies in the scree on the beds of the watershed ravines. This paleo-environmental context of the watershed is at the origin of its strong structural dynamics, marked by a reactivation of the water morphodynamics

La Grande Niaye de Pikine, un espace humide à haute valeur agronomique au cœur de l’agglomération urbaine de Dakar : analyse des enjeux socioéconomiques

La croissance urbaine à l’échelle planétaire s’accompagne de défis tels que l’autonomisation, l’aménagement et la résorption du chômage en milieu urbain. En Afrique de l’Ouest et plus particulièrement dans la région des Niayes au Sénégal, le maraîchage emploie bon nombre de jeunes et de femmes. A Dakar, ces espaces agricoles subissent un recul depuis plusieurs années. Dans la Grande Niaye de Pikine qui constitue le plus grand bassin de production horticole de l’agglomération dakaroise, les maraîchers sont menacés par la pression foncière, malgré les enjeux liés au maintien de l’activité agricole. Cette étude est une contribution à la connaissance des enjeux socio-économiques autour du maraîchage dans la Grande Niaye de Pikine. La méthodologie adoptée procède par des enquêtes auprès des maraîchers et des vendeurs de produits de la Grande Niaye.Les résultats montrent une charge familiale importante chez ces deux catégories d’acteurs, mais également une précarité foncière des exploitations qui facilite les expropriations. Ceci menace l’équilibre de la chaîne de valeurs qui semble être entretenue par la proximité du bassin de production.Urban growth on a global scale is accompanied by challenges such as empowerment, urban planning and the eradication of unemployment. In West Africa and more particularly in the Niayes region of Senegal, market gardening employs a large number of young people and women. In Dakar, these agricultural areas have been declining for several years. In the Great Niaye of Pikine, which is the largest horticultural production area in Dakar agglomeration, market gardeners are threatened by land pressure, despite the issues related to the maintenance of agricultural activity.This study is a contribution to the knowledge of socio-economic issues around market gardening in the Great Niaye of Pikine. It proceeds through surveys of market gardeners and sellers of Grande Niaye products.The results show significant family burdens for these two categories of actors, but also land precariousness of the farms that facilitate the expropriations. This threatens the balance of the value chain that seems to be maintained by the proximity of the production basin

Analyse Par Approche Hydrogeochimique De La Distribution Spatiale De La Salinite Des Eaux De La Nappe Et Des Sables Quaternaires Du Secteur Des Niayes Du Gandiolais (Littoral Nord Senegalais)

Dans le Gandiolais, la nappe des sables quaternaires, fortement salée sur la majeure partie de la zone, est utilisée pour irriguer les cultures et pose de véritables difficultés pour la durabilité du système maraicher. La salinisation secondaire du sol irrigué et la réaction du complexe absorbant dépendent principalement des paramètres intrinsèques, particulièrement la texture du sol. L’objet de cet article est d’analyser la distribution spatiale de la salinité en tenant en compte les caractéristiques granulométriques du complexe absorbant. L'approche hydrogéochimique basée sur les relations de concentration permet d'apprécier les modalités de conservation in situ entre les eaux d'irrigation et le sol exploité. Les résultats obtenus ont confirmé que la texture grossière de type sables moyens à fins permet un lessivage rapide des sels solubles sur tout le profil. Les sols restent globalement calcimagnésiens même si les eaux d'irrigation sont globalement chlorurées sodiques et potassiques ou sulfatées sodiques. Cependant, cette forte perméabilité du complexe constitue un risque de surconcentration ionique dans la nappe. Les retours d'irrigation associés aux engrais accentuent la minéralisation de la nappe des sables quaternaires. In the Gandiolais, the groundwater of the quaternary sands, heavily salted over most of the area, is used to irrigate crops and poses real difficulties for the sustainability of the market gardening system. Secondary salinization of the irrigated soil and the reaction of the absorbing complex depend mainly on the intrinsic parameters, particularly the texture of the soil. The purpose of this article is to analyze the spatial distribution of salinity taking into account the particle size characteristics of the absorbent complex.The hydrogeochemical approach based on the relations of concentration makes it possible to appreciate the process of conservation in situ between the irrigation water and the exploited soil. The results obtained confirmed that the coarse texture of medium-to-fine sand type allows rapid leaching of soluble salts over the entire profile. Soils remain globally calcimagnesian although the irrigation water is globally sodium chloride and potassium or sodium sulphated. However, this high permeability of the complex constitutes a risk of ionic overconcentration in the aquifer. Irrigation returns associated with fertilizers accentuate the mineralization of the groundwater of the quaternary sands

Delivery strategies for malaria vaccination in areas with seasonal malaria transmission

BACKGROUND: Seasonal vaccination with the RTS,S/AS01E malaria vaccine given alongside seasonal malaria chemoprevention (SMC) substantially reduces malaria in young children. The WHO has recommended the use of RTS,S/AS01E, including seasonal vaccination, in areas with seasonal malaria transmission. This study aimed to identify potential strategies to deliver RTS,S/AS01E, and assess the considerations and recommendations for delivery of seasonal malaria vaccination in Mali, a country with highly seasonal malaria. METHODS: Potential delivery strategies for RTS,S/AS01E in areas with seasonal malaria were identified through a series of high level discussions with the RTS,S/AS01E plus SMC trial investigators, international and national immunisation and malaria experts, and through the development of a theory of change. These were explored through qualitative in-depth interviews with 108 participants, including national-level, regional-level and district-level malaria and immunisation programme managers, health workers, caregivers of children under 5 years of age, and community stakeholders. A national-level workshop was held to confirm the qualitative findings and work towards consensus on an appropriate strategy. RESULTS: Four delivery strategies were identified: age-based vaccination delivered via the Essential Programme on Immunisation (EPI); seasonal vaccination via EPI mass vaccination campaigns (MVCs); a combination of age-based priming vaccination doses delivered via the EPI clinics and seasonal booster doses delivered via MVCs; and a combination of age-based priming vaccination doses and seasonal booster doses, all delivered via the EPI clinics, which was the preferred strategy for delivery of RTS,S/AS01E in Mali identified during the national workshop. Participants recommended that supportive interventions, including communications and mobilisation, would be needed for this strategy to achieve required coverage. CONCLUSIONS: Four delivery strategies were identified for administration of RTS,S/AS01E alongside SMC in countries with seasonal malaria transmission. Components of these delivery strategies were defined as the vaccination schedule, and the delivery system(s) plus the supportive interventions needed for the strategies to be effective. Further implementation research and evaluation is needed to explore how, where, when and what effective coverage is achievable via these new strategies and their supportive interventions

The duration of protection against clinical malaria provided by the combination of seasonal RTS,S/AS01E vaccination and seasonal malaria chemoprevention versus either intervention given alone

BACKGROUND: A recent trial of 5920 children in Burkina Faso and Mali showed that the combination of seasonal vaccination with the RTS,S/AS01E malaria vaccine (primary series and two seasonal boosters) and seasonal malaria chemoprevention (four monthly cycles per year) was markedly more effective than either intervention given alone in preventing clinical malaria, severe malaria, and deaths from malaria. METHODS: In order to help optimise the timing of these two interventions, trial data were reanalysed to estimate the duration of protection against clinical malaria provided by RTS,S/AS01E when deployed seasonally, by comparing the group who received the combination of SMC and RTS,S/AS01E with the group who received SMC alone. The duration of protection from SMC was also estimated comparing the combined intervention group with the group who received RTS,S/AS01E alone. Three methods were used: Piecewise Cox regression, Flexible parametric survival models and Smoothed Schoenfeld residuals from Cox models, stratifying on the study area and using robust standard errors to control for within-child clustering of multiple episodes. RESULTS: The overall protective efficacy from RTS,S/AS01E over 6 months was at least 60% following the primary series and the two seasonal booster doses and remained at a high level over the full malaria transmission season. Beyond 6 months, protective efficacy appeared to wane more rapidly, but the uncertainty around the estimates increases due to the lower number of cases during this period (coinciding with the onset of the dry season). Protection from SMC exceeded 90% in the first 2-3 weeks post-administration after several cycles, but was not 100%, even immediately post-administration. Efficacy begins to decline from approximately day 21 and then declines more sharply after day 28, indicating the importance of preserving the delivery interval for SMC cycles at a maximum of four weeks. CONCLUSIONS: The efficacy of both interventions was highest immediately post-administration. Understanding differences between these interventions in their peak efficacy and how rapidly efficacy declines over time will help to optimise the scheduling of SMC, malaria vaccination and the combination in areas of seasonal transmission with differing epidemiology, and using different vaccine delivery systems. TRIAL REGISTRATION: The RTS,S-SMC trial in which these data were collected was registered at clinicaltrials.gov: NCT03143218

Impact of seasonal RTS,S/AS01E vaccination plus seasonal malaria chemoprevention on the nutritional status of children in Burkina Faso and Mali.

BACKGROUND: A recent trial in Burkina Faso and Mali showed that combining seasonal RTS,S/AS01E malaria vaccination with seasonal malaria chemoprevention (SMC) substantially reduced the incidence of uncomplicated and severe malaria in young children compared to either intervention alone. Given the possible negative effect of malaria on nutrition, the study investigated whether these children also experienced lower prevalence of acute and chronic malnutrition. METHODS: In Burkina Faso and Mali 5920 children were randomized to receive either SMC alone, RTS,S/AS01E alone, or SMC combined with RTS,S/AS01E for three malaria transmission seasons (2017-2019). After each transmission season, anthropometric measurements were collected from all study children at a cross-sectional survey and used to derive nutritional status indicators, including the binary variables wasted and stunted (weight-for-height and height-for-age z-scores below - 2, respectively). Binary and continuous outcomes between treatment groups were compared by Poisson and linear regression. RESULTS: In 2017, compared to SMC alone, the combined intervention reduced the prevalence of wasting by approximately 12% [prevalence ratio (PR) = 0.88 (95% CI 0.75, 1.03)], and approximately 21% in 2018 [PR = 0.79 (95% CI 0.62, 1.01)]. Point estimates were similar for comparisons with RTS,S/AS01E, but there was stronger evidence of a difference. There was at least a 30% reduction in the point estimates for the prevalence of severe wasting in the combined group compared to the other two groups in 2017 and 2018. There was no difference in the prevalence of moderate or severe wasting between the groups in 2019. The prevalence of stunting, low-MUAC-for-age or being underweight did not differ between groups for any of the three years. The prevalence of severe stunting was higher in the combined group compared to both other groups in 2018, and compared to RTS,S/AS01E alone in 2017; this observation does not have an obvious explanation and may be a chance finding. Overall, malnutrition was very common in this cohort, but declined over the study as the children became older. CONCLUSIONS: Despite a high burden of malnutrition and malaria in the study populations, and a major reduction in the incidence of malaria in children receiving both interventions, this had only a modest impact on nutritional status. Therefore, other interventions are needed to reduce the high burden of malnutrition in these areas. TRIAL REGISTRATION: https://www.clinicaltrials.gov/ct2/show/NCT03143218 , registered 8th May 2017