Modélisation de la Relation Pluie-Débit dans un Contexte de Gestion en Eau : Cas du Sous Bassin Versant du N’zi en Côte d’Ivoire

Cette étude s’inscrit dans un contexte de modélisation pluie-débit pourune optimisation des ressources en eau de surface. L’objectif principal estd’appliquer le modèle du Génie Rural (GR) sur le bassin versant de la régiondu N’zi afin de comprendre la relation pluie-débit dans ce bassin versant.L’utilisation des différents pas de temps mensuel(GR2M) et journalier (GR4J)ont permis de déterminer d’une part le meilleur modèle GR et d’autre part, lesparamètres optimaux des stations de la zone d’étude. Une période de 18 ans apermis de déterminer les paramètres optimaux du bassin. Les critères de Nashobtenus pour le modèle GR4J varient de 40,80 à 67,40 % pour les débitsélevés, de 34,10 à 61% pour les débits moyens et de 8,80 à 30,90 % pour lesdébits faibles. Cependant, les critères de Nash du modèle GR2M sont trèsfaibles. Ils évoluent de 25,20 à 36,30 % pour les débits élevés, de 08,20 à 14,60% pour les débits moyens et de -41 à -31,40% pour les débits faibles. Le modèle GR4J simule mieux les écoulements du bassin que le modèle GR2M.En fait, les deux modèles simulent de façon acceptable la variation des débitsobservés en termes d’allure, mais ce sont les écarts qui existent entre les débitsobservés et simulés qui les distinguent. Le modèle GR4J serait mieux indiquerpour faire des prévisions sur les périodes d’inondation. Le coefficientd’échange X2 négatif, explique la raison pour laquelle le N’zi se vide dans lebassin de Bocanda, alors que la baisse de la pluviométrie est négligeable. This study is part of a rain-flow modeling context for optimizingsurface water resources. The main objective is to apply the flow simulationmodel, that of Rural Engineering (GR) on the watershed of the N’zi region inorder to understand the rain-flow relationship in this watershed. The use ofdifferent monthly (GR2M) and daily (GR4J) time steps made it possible toidentify, firstly the best GR model and scondly, the optimal parameters of thewatershed. An 18 year period has therefore permitted to determine the optimalparameters of the watershed. The Nash criteria obtained for the GR4J modelvary from 40.80 to 67.40% for high flow rates, from 34.10 to 61% for mediumflow rates and from 8.80 to 30.90% for low flow rates. On the other hand, theNash criteria of the GR2M model are very weak. They range from 25.20 to36.30% for high bit rates, from 08.20 to 14.60% for medium bit rates and from-41 to -31.40% for low bit rates. The GR4J model better simulates the flowsof the watershed than the GR2M model. In fact, both models simulate in an acceptable manner the variation of the observed flows in terms of pace, but itisthe differences which exist between the observed and simulated flows whichdistinguish them. The GR4J model would be bettersuited for forecasting floodperiods. The stall period should be relatively short for best results. Theexchange coefficient X2 negative, explains why the N'zi empties into theBocanda Basin, while the decrease in rainfall is negligible

Aptitudes À L’agriculture Des Eaux Souterraines Du Departement d’Agboville (Sud-Est De La Côte d’Ivoire)

In the department of Agboville, farmers are interested in the using of groundwater to improve the performance of their crops. But they didn’t know the effects of this water on the crops without. The main objective of this study is to determine the quality of groundwater to prevent the risk of soil alkalinization and salinization in the department of Agboville. Hydrochemical analysis of 28 wells used for irrigation of crops was carried out. The dry residue (RS), the osmotic pressure (π), Sodium Absorption Ratio (SAR), the percentage of sodium exchange (ESP), salinity potential (SP), and the coefficient or the Kelly ratio (RK) were determined. Wilcox diagram was also applied for this study. The results show that groundwater department are soft and lightly mineralized wiht a low salinity. 75% of samples from groundwater haves low salinity and 25% have an average salinity. The values of the Salinity Potential (SP <5), Kelly Ratio (RK <1) and SAR (SAR <10 méq/L) show that all sampled groundwater are good qualities for agriculture. According to Wilcox diagram, groundwaters are excellent quality for agriculutre. The osmotic pressure ( ), the dry residue (RS) and the conductivity values 75% of the sampled waters are excellent quality and 25% average quality for agriculture. Groundwaters from the department of Agboville have a low risk of alkalizing and can be used in irrigation for most crops

Variation Saisonnière De La Qualité Physico-Chimique Des Eaux Souterraines Des Aquifères d’Altérites Du Département d’Agboville (Sud-Est De La Côte d’Ivoire)

The main objective of this study was to evaluate the seasonal quality to explain the phenomena at the origin of the mineralization of groundwater in the department of Agboville. Hydrochemical analysis was performed in 24 wells located throughout the study area. Hydrochemical different methods and techniques of multivariate statistical analysis were used to study these waters. The physicochemical analyzes show that the water is acidic with an average pH of 6.09 in the rainy season and 6.29 in the dry season. Overall, these waters are soft and slightly mineralized with an average electrical conductivity of 172.92 μS / cm in the rainy season and 196.71 μS / cm in the dry season. These waters are mineralized in the dry season than rainy. The hydrochemical classification of water from the Piper diagram showed one hydrofacies is calcium chloride-facies. Quality chemical parameters are mostly below the WHO (2011) guideline values, except for some points (29.17%) where levels of nitrites and ammonium sometimes exceed the guide values. The various processes responsible for the acquisition of the chemistry of groundwater are studied: the residence time of water in contact with the host rock, the redox infiltration of substances linked to human activities and litter decomposition. In the mineralization mechanisms, hydrolysis of silicates is the dominant process

Apport Du SIG Et De L’analyse Multicritère Dans La Prospection Hydrogéologique Du Socle Précambrien De Gagnoa (Centre-Ouest De La Côte d’Ivoire)

Côte d’Ivoire is constituted in more than 97.5% of crystalline basement which contains the main part of groundwater resources of the country. These resources are contained in the weathering material and fissured aquifers. Gagnoa area located at the Central West of Côte d'Ivoire, on crystalline and metamorphic basement. In this area, surface water and groundwater are exploited for the water supply of the populations. However surface water are often doubtful quality and can affect the health of these populations. Thus find water resources in sufficient and good quality amount is a necessity in this area. The study aims to identify favourable areas for the archievement of drillings with important discharge using geomorphologic, hydrogeological data and remote sensing. Multi-criteria analisys methods were used in this study. The database is constituted by various data in particular, data sheets of drillings, hydroclimatic statements and satellite image. This database was stored, analyzed, treated and managed using ARCGIS 10.2. software. Various treatments allowed to establish various thematic maps (accessibility, exploitability, availability). The synthesis of all information inside a SIG allowed to establish the maps of favourable areas to achieve drillings with large discharges. The classes of good and excellent sensibility cover 26% of the study area. These favourable areas for the achievement of drillings with important discharge are located at the center and south of the study area. Validation of this map showed that 66% of the water points (drillings) with discharge superior to 5 m3/h overlap on the good and excellent classes of sensibility. The various zones of productivity of Gagnoa area were able to be characterized. These results are very interesting and useful for the hydrogeological prospecting. They contribute to a better knowledge and a groundwater resource management