Etude de l’impact de la dynamique de l’occupation du sol sur les ressources naturelles dans le sous-bassin de l’Okpara à Nano au Nord Bénin

Au Bénin, les pratiques agricoles actuelles caractérisées par l’agriculture itinérante sur brûlis, continuent de soumettre l’environnement à une pression anthropique importante. L’objectif de la recherche est d’apporter une contribution à la gestion des ressources naturelles et de l’occupation du sol dans le sous-Bassin versant de l’Okpara Nano. L’approche méthodologique adoptée a consisté à une description, et à une étude analytique des facteurs de la dynamique de l’occupation du sol et leurs implications sur la gestion des ressources naturelles du sous-Bassin. L’analyse des résultats a été faite à l’aide du modèle PEIR « Pression-Etat-Impact-Réponse ». Les résultats obtenus ont révélé qu’en une vingtaine d’années (1992-2012), la population des communes du sous-Bassin de Nano ont connu une augmentation de 74,48 %, passant ainsi de 155 164 habitants en 1992 à 608 015 habitants en 2012. Cette situation a conduit à une extension des espaces bâtis au sein du sous-Bassin avec un taux d’accroissement de l’ordre de 3,9 %. Aussi, a-t-il été constaté une évolution des unités d’occupation du sol entre les années 1985 et 2014 dans le sous-Bassin versant de Nano, une nette régression des unités de végétation naturelle ou artificielle, excepté les mosaïques de cultures qui sont en augmentation. In Benin, current agricultural practices characterized by shifting slash-and-burn agriculture continue to subject the environment to significant human pressure. The objective of the research is to make a contribution to the management of natural resources and land use in the Okpara Nano sub-watershed. The methodological approach adopted consisted of a description and an analytical study of the factors of land use dynamics and their implications on the management of the natural resources of the sub-basin. The results were analyzed using the PEIR "Pressure-State-Impact-Response" model. The results obtained revealed that in about twenty years (1992-2012), the population of the municipalities of the Nano sub-basin experienced an increase of 74.48%, from 155,164 inhabitants in 1992 to 608,015 inhabitants in 2012. This situation has led to an extension of built-up areas within the sub-basin with an increase rate of around 3.9%. Also, it was noted an evolution of the units of land use between the years 1985 and 2014 in the sub-basin of Nano, a clear regression of the units of natural or artificial vegetation, except the mosaics of cultures which are increasing

Flood Hazard Assessment in Agricultural Areas: The Case of the District of Pélébina in the Municipality of Djougou, Bénin

Flood is a natural disaster and causes loss of life and property destruction. Its impacts are large on agriculture especially in West African countries where smallholder farmers account for 80% of all the farms. The objective of this study was to assess flood risks in the inland valley of Dosir located in the district of Pélébina, northern Benin. Rainfall, discharge and water level in the riverbed were monitored using rain gauge, acoustic current meter and pressure sensors, respectively. The hydrological functioning of the inland valley was simulated using the Integrated Flood Analysis System (IFAS) model. The calibration was done based on the land use map (GlobalMap) and the soil water holding capacity map (UNEP). Our study demonstrated the existence of a high flood hazard in the inland valley of Dosir which reacts very quickly to rainfall solicitations. The IFAS model has shown a good performance in simulating the runoff in the riverbed of the inland valley with a coefficient of determination of 0.65. The IFAS model can be used to design a flood management system in the district of Pelebina. Further studies are needed to assess the exposure and vulnerability of farmers to flood risk

Modelling the hydrological balance of the Okpara catchment at the Kaboua outlet in Benin

Rapid population growth and industrial development create problems with water management that can lead to contamination and scarcity of water resources. The primary aim of the modeling in this study was to assess annual renewal rates of water resources and erosion rates in the Okpara catchment at the Kaboua outlet. The SWAT 2003 model was selected as the most appropriate for the purpose of this study; it was calibrated and validated for the study basin. Digital elevation model, daily climatic data for 1968-2007, soil and land use maps, physical characteristics of soil, physical parameters of crops were all incorporated in the model that divided the whole catchment in to sub-basins and Hydrological Responses Units (HRU). Calibration and validation of data demonstrated that precipitation in the watershed was 1,075.8 mm/a. Surface runoff was 106.6 mm/a (10% of precipitation), and the total recharge of aquifers was 225.4 mm/a (21% of precipitation). The actual rate of evapotranspiration was 759.8 mm/year (71% of precipitation). The total volume annually produced in the catchment was about 4 billions m3; this amounted to more than 500 times the needs of the population, but paradoxically it still suffered from severe water scarcity. Regarding erosion, an average value of 7t/ha/year was obtained for the watershed with a maximum value for cropland (16.85t/ha/a) and the minimum value for bushed savannah (0.64t/ha/a). Moreover, agricultural practices most susceptible to reduce soil loss were those ridges perpendicular to a slope. Based on these results, some suggestions were made for more sustainable use of land and water resources in the catchment

Evaluation of Household Knowledge on Water Supply, Hygiene and Sanitation Practices in So-Ava District (South Benin)

The adoption of good practices in access to water, hygiene and sanitation is very important for the well-being and socio-economic development of any community. The objective of the study was to evaluate the knowledge and practices that households adopt regarding water supply, hygiene and sanitation. For this, a survey was conducted among 386 households in the seven districts of the commune of Sô-Ava. The data collected was analyzed using the XLSTAT 17 software and the Excel Spreadsheet. The results obtained show that in the commune of Sô-Ava, drilling is the most used water source and that nearly 66.33% of households do not cover their containers during the transport of water with a rate that varies from 2.85 to 25.39% from one borough to another. Sô-Ava is the district that has the highest number of latrines is that with a rate of 3.11%. In addition, most households dispose of their garbage and wastewater either in the wild or in the water body in the absence of a waste collection system. The low level of hygiene and sanitation observed could affect the quality of drinking water and hence the health of the population

Utilisation du Modèle GR4J pour la Simulation des Débits d’Etiage du Fleuve Mono (Bénin, Togo) à l’Exutoire d’Athiémé

RésuméLa gestion des ressources en eau recouvre des questions telles que l’hydrologie, les besoins des populations, la planification et la réalisation des infrastructures, la préservation de la ressource et sa gouvernance. Des méthodes d’investigations pour une meilleure connaissance des ressources en eau existent pour une meilleure description et une gestion des problèmes à l’échelle bassin versant par l’exploitation des données hyrodroclimatiques et la mise en œuvre de mécanismes de gestion durable des ressources du bassin (Zannou, 2011 ; Fofana, 2015).L’objectif de la présente étude est de simuler les débits d’étiage du fleuve Mono à l’exutoire d’Athiémé en prévision de l’utilisation durable des ressources en eau à des fins agricoles. Les données hydroclimatiques journalières (Pluie, Evapotranspiration, Débits), sur la période de 1970 à 2019, ont été recueillies et exploitées avec l’utilisation de la version Perrin et al., (2003) du modèle Génie Rural à 4 Paramètres Journaliers (GR4J) à l’aide du logiciel R.Les valeurs du critère de Nash-Sutcliffe avant la construction du barrage en 1988, sont de l’ordre de 70% (sous-estimation) en calage et validation et les valeurs de KGE (Gupta et al., 2009) de 0,8317 et 0,8421 (proches de 1). Ces valeurs traduisent une bonne performance et robutesse du modèle GR4J sur le bassin du Mono. Mais ces valeurs sont très dégradées sur la période après barrage du fait du régime hydrologique modifié par les lâchers d’eau lors du turbinage, contrariées par le caractère lacunaire des observations sur cette période.Ces résultats appellent à une meilleure attention et à des investissements conséquents pour une meilleure connaissance des ressources en eau, base d’une planification de leur utilisation durable.Mots clés : Athiémé, Bassin du Mono, Débits d’étiage, Hydrologie, GR4J.     Abstract :Simulation of low flooded of Mono river watershed (Benin and Togo)  at Athiémé outlet with GR4J model.Water resources management involved varied implications such hydrology, people needs, infrastructures planning and establishment, basin resources conservation and institutional management. Strategies and policy management for better knowledge of water resources by diagnostic of matter of the basin using hydroclimatic data and the implementation of integrated water resources management (Zannou, 2011; Fofana 2015).This study aims in order to simulate low flow of Mono watershed at Athiémé outlet to evaluate water availability for agricultural uses. Therefore daily hydroclimatic data (rianfall, recharge and flow were collected (1971-2019) and analyzed with Perrin and al., (2003) GR4J model unsing R software.Results showed a good performance of the model to simulate low flow before the construction of Nangbeto dam in 1988, according to Nash-Sutcliffe, RMSE and KGE (Gupta et al., 2009) criteria. Criteria values of Nash-Sutcliffe before dam establishment in 1988 are around 70% both in calibration and validation where KGE values (Gupta et al.., 2009) showed 0,8317 et 0,8421 (near 1). A worst performance of the model is noticed for the period after the dam establishment due to the change in the hydrological regime due to water jets for energy production and lack of historical data for this period.This situation calls for serious attention and investment for all activities related to a better known of water resources, which is reliable tool for their sustainable use.Key words : Athiémé, Mono watershed, Low flood, Hydrology, GR4J

IAHS2022 -Variability and change across space, time, extremes, and interfaces Comparison of one-site vs. multi-sites calibration schemes for hydrological modelling of nested catchments in the West African Sahel

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