19 research outputs found
Water supply and Sanitation in Burkina Faso : Current status and research perspective to contribute to the Millennium Development Goal achievement
No full textDe la méso-échelle à la micro-échelle : désagrégation spatio-temporelle multifractale des précipitations
No full textWe present a study performed in the framework of the EDF project on the use of seasonal meteorological forecasts to improve hydro-electrical resources management. Due to the difference of space and time scales, it is indispensable to downscale the (meso-scale) GCM rainfall to the (micro-) scale of the hydrological models. To preserve the scaling properties of the rainfall field, as well as its close interrelation with the dynamics at all scales, we develop a multifractal downscaling algorithm based on the idea that the rain rate cascades from large to small scale in a multiplicative manner: a scale invariant random multiplicative increment determines the rate fraction forwarded from a parent structure to a child one. Firstly, we proceeded to a rather exhaustive space and time analysis of the Météo-France PRECIP data base (about 10 years of high resolution data for 243 rain gages distributed over France territory) in order to estimate the universal multifractal parameters α, C1 as well as the exponent Ht of the scaling anisotropy of time versus space. The latter was empirically estimated to be in full agreement with its theoretical value: Ht=1/3. Secondly, we develop a cascade model defined with these parameters from space-time pixels corresponding to 243km×243km×32days, close to those of the GCM, which are of the order of 250km×250km×30 days, i.e. 35km×35km×25days. This choice is done in agreement with the value of Ht. In conclusion, we discuss how to take into account the orographic effects.Le passage de la méso-échelle, échelle des modèles de circulation générale GCM, de l'anglais "General Circulation Models", à la micro-échelle (échelle hydrologique), pour les précipitations, est un exercice assez complexe. Les champs de précipitations comme la plupart des champs géophysiques turbulents obéissent au concept d'invariance d'échelle, qui est une caractéristique principale des champs multifractals. Par ailleurs, il a été prouvé que le transfert d'énergie des grosses structures aux plus petites structures au sein d'un phénomène géophysique turbulent s'effectue de façon multiplicative (Kolmogorov, 1962; Mandelbrot, 1974 ...): un facteur aléatoire déterminant la fraction de flux transmis d'un gros tourbillon à un plus petit. Le travail que nous présentons ici s'inscrit dans le cadre du projet EDF "Prévisions saisonnières et Hydraulicité" dans la gestion de son parc hydroélectrique et a pour objectif la construction d'un modèle de désagrégation basé sur le principe d'invariance d'échelle des champs de précipitation, donc utilisant les propriétés des champs géophysiques mentionnées ci-dessus. Dans un premier temps, nous conduisons une analyse multifractale (Schertzer et Lovejoy , 1991) sur des séries pluviométriques de la France (243 séries pluviométriques au pas de temps de six minutes, constituées sur une dizaine d'années distribuées sur la France métropolitaine), ce qui nous permet de déduire les paramètres multifractals, dans le temps, dans l'espace ou dans le cas spatio-temporel. La seconde étape consiste à construire des cascades multifractales, à partir des valeurs saisonnières de pluies avec les paramètres déterminés dans la première étape. Le principe de cette deuxième partie consiste, à partir d'une prévision mensuelle sur des mailles de dimensions 243km×243km×32jours (correspondant à une anisotropie espace-temps de l'ordre de H=2/3 :x=y=t (3/2) ) voisines de celles des modèles de circulation générale (dimensions de l'ordre de 250km×250km×30jours) et à conduire la cascade multifractale, avec les paramètres multifractals préalablement déterminés, pour atteindre des valeurs de prévision sur des mailles de l'ordre de 1km×1km×1j. Les résultats obtenus devront faire l'objet d'un conditionnement orographique avant d'être comparés avec les valeurs réelles obtenues
De la méso-échelle à la micro-échelle (désagrégation spatio-temporelle multifractale des précipitations)
No full textPARIS-MINES ParisTech (751062310) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF
Hydrodynamic behavior of the sedimentary aquifer of the Kou catchment in the southwest of Burkina Faso
No full textL’Afrique de l'Ouest est sujette à une variabilité climatique importante et elle connaît une longue période de sécheresse depuis les années 1970 dont l’impact sur les ressources en eau souterraine reste peu étudié. La présente étude porte sur le bassin versant du Kou au Burkina Faso qui abrite une grande réserve d’eau souterraine à l’origine de sources exceptionnelles. Cette ressource, essentielle pour les besoins de la population, présente pourtant des signes d'épuisement qui soulèvent une question essentielle : quelle est la part du climat et celle des prélèvements dans l’épuisement de cette ressource ? Pour répondre à cette question, nous avons utilisé des méthodes d’analyse statistique et la modélisation hydrogéologique. Les méthodes statistiques ont été appliquées aux chroniques de données climatiques, hydrométriques et piézométriques. Elles ont permis de décrire la réponse des eaux souterraines aux forçages du climat et d’identifier les facteurs explicatifs du comportement de la nappe. La modélisation hydrogéologique a pallié certaines limites de ces méthodes statistiques par une meilleure prise en compte de l’hétérogénéité spatiale de l’aquifère. Elle a en particulier montré que les pompages ont un impact significatif sur la ressource en eau. En somme, les déficits de précipitation, combinés aux pompages en croissance continue, mettent en péril la ressource. La gestion de cette dernière dans une perspective durable devrait donc revêtir une attention particulière.West Africa is prone to critical climate variability and since the 1970s has been experiencing a long period of drought whose impact on groundwater resources is little studied. This study focuses on the Kou catchment in Burkina Faso which holds a large groundwater resource that lies at the root of exceptional springs. This resource, essential to fulfill the populations’ needs, shows signs of depletion that raises a critical question: what is the share of climate and that of withdrawals in the depletion of the resource? To answer this question, we used statistical analysis methods and hydrogeological modeling. The statistical methods were applied to climatic, hydrometric and groundwater level time series to describe the groundwater’s response to climate forcing and to identify explanatory factors of the groundwater’s behaviour. The hydrogeological modeling overcame some of the statistical methods limitations by better heeding the spatial heterogeneity of the aquifer’s characteristics. Particularly, it revealed that pumping have significant impact on the resource. To sum up, rainfall deficits combined with growing pumping endanger the resource. Hence, sustainable management of the resource should be a critical issue to pay attention to
Impacts of climate change and pumping on groundwater resources in the Kou River basin, Burkina Faso
No full textWest Africa is subject to climatic variability with a long period of drought during the 1970s–1990s whose impact on groundwater remains poorly studied. This work focuses on the Kou basin in Burkina Faso, which holds a large groundwater resource resulting in exceptional springs. This resource shows signs of depletion that raise a critical question: What is the share of climate and that of withdrawals in the depletion of the resource? To answer this question, we used a hydrogeological model calibrated in steady state and in transient regime (monthly time step 1995–2014; annual time step 1961–2014). The results showed that pumping has a significant impact on the resource, especially in the vicinity of the pumping areas, and caused approximately 30% of the observed decrease in spring discharge. Drought periods and consecutive years without recharge also led to a decrease in groundwater levels. Thus, precipitation deficits and variability, combined with increasing pumping, have endangered the resource
Multifractal analysis of the evolution of simulated precipitation over France in a climate scenario
No full textNational audienceMultifractal techniques are applied to the study of rainfall daily time series over France simulated by the climate model CNRM-CM3 of Meteo France in a coupled climate scenario A2 over the period 1860-2100. We quantify the scaling variability of the simulated rainfall with the help of a few relevant multifractal exponents characterizing the intermittency and multifractality of the field. These multifractal exponents are determined by the Double Trace Moment (DTM), which shows a scaling range from one day to about 16 days. The opposite trends found in the evolution of the intermittency and multifractality exponents have contradictory effects on the evolution of the extremes. However, a refined analysis shows that due to the dominant effect of intermittency increase, we may expect an effective increase of rainfall extremes for the next hundred years
Méthodologie d’étude des digues anciennes en terre de latérites au Burkina Faso
No full textInternational audienceIn Burkina Faso, hydro-agricultural production and the need in water for domestic use require the construction of many retention basins, with earth dams. These works, which also support roads, are mostly built with lateritic materials that are locally very abundant. They are therefore regularly subjected to road loads, runoff phenomena and internal flows. The knowledges of the team allow them to begin the complex study of internal erosion from laboratory tests and numerical approch. In situ observations on a site near the institution will be realised to establish a methodology, which could be used for all the national earth damsAu Burkina Faso, la production hydroagricole et le besoin en eau à usage domestique requièrent la construction de nombreux bassins de rétention, grâce à des digues en terre. Ces ouvrages supportant aussi des routes, sont pour la plupart construits avec du matériau latéritique de grande variabilité (à l’état induré à meuble). Ils sont donc régulièrement soumis à des charges routières, à des phénomènes de ruissellement et de l’érosion interne. La bonne connaissance des matériaux latéritiques de l’équipe leur permet d’aborder l’étude complexe de l’érosion interne à partir d’essais de laboratoire et de modélisation. Des observations sur un ouvrage réel proche du site seront entreprises pour établir une méthodologie de diagnostic pour tous les ouvrages en terre de cette catégorie
Impacts of climate change and pumping on groundwater resources in the Kou River basin, Burkina Faso
No full textWhy Do Small Earth Dams Deteriorate: Insights from Physical Investigations in the West African Sahel
No full textIn West Africa, the construction of small earth dams is common against water scarcity. Burkina Faso, an inland country in West Africa, is home to 1001 dams that serve agricultural and pastoral needs. These embankments are predominantly made of compacted laterite, a cost-effective material abundant in over 2/3 of the country. However, these dams degrade over time, hindering their functionality. This study aims to establish a catalog of typical degradation occurring on small dams in Burkina Faso, which is virtually non-existent in the region while identifying and analyzing the potential causes. The study uses a diagnostic analysis followed up with technical visits on a representative sample of 24 dams in the Centre and Centre-South regions as a basis for future studies. The results reveal that these dams were constructed between 1965 and 2018, with capacities ranging from 150,000 to 4,740,000 m3. 33% of these dams have undergone total failure, likely attributed to factors such as internal erosion, pore overpressures, settlement, and deformation. Although 67% of the dams remain functional, their structural integrity could be improved. Erosion observed in riprap indicates vulnerability during high flood periods. Additionally, the absence of proper maintenance, as shown by the vegetation development weakening embankments, contributes to deterioration. The analysis also suggests that variability in construction techniques and lateritic material properties across time and regions may further exacerbate degradation. These findings inform infrastructure improvements and policy development for sustainable water resource management in Burkina Faso and similar regions
Climate Variability and Groundwater Response: A Case Study in Burkina Faso (West Africa)
No full textWest Africa experiences great climate variability, as shown by the long-lasting drought since the 1970s. The impacts of the drought on surface water resources are well documented but remain less studied regarding groundwater resources. The nexus between climate variability and groundwater level fluctuations is poorly documented in this area. The present study focuses on the large reserve of groundwater held by the Kou catchment, a tributary of Mouhoun river (formerly the Black Volta) in the southwest of Burkina Faso, in the Sudanian region. Analyses were undertaken using climatic time series (1961–2014), two rivers’ hydrometric data (1961–2014), and 21 piezometers’ time series (1995–2014) applying statistical trend (Mann–Kendall) and break (Pettitt) tests, correlation analysis, and principal component analysis. The analyses showed that rainfall in the area underwent a significant break in 1970 with an 11%–16% deficit between the period before the break and the period after the break that resulted in a deficit three times greater for both surface and base flows. This significant deficit in flow results from the combined effect of a decrease in rainfall and an increase in evapotranspiration. The response of the catchment to the slight increase in rainfall after 1990 was highly dependent on hydrological processes. At Samendéni, on the Mouhoun River, the flow increased with a slight delay as compared to rainfall, because of the slow response of the base flow. Whereas at Nasso on the Kou river, the flow steadily decreased. The analysis showed that the groundwater level responds to rainfall with a delay. Its response time to seasonal fluctuations ranges from 1 to 4 months and its response time to interannual variations exceeds the timescale of one year. This response is highly dependent on the local aquifer’s physical characteristics, which could explain the spatial heterogeneity of the groundwater response
