The issue of gully erosion is of major concern in the south-eastern part of Nigeria. This study adopts Geographic Information Systems (GIS) as a tool to identify and study gully erosion hazards in Abia state. 171 gully erosion sites were coordinated using GPS receivers and overlaid on the soil and geological maps of the study area. Spatial database for erosion sites was created using relational database model. Additional 35 gully erosion sites were identified from the processed digital elevation model (DEM) and ground verification carried out. Result shows that gully erosion sites were well dispersed around false bedded sand stone geological formation. The slope characteristic was ascertained to be greater than 15 o which encourages gully erosion activities. An erosion hazard map was produced showing risk and vulnerability of settlements and infrastructure. This study shows that GIS is an efficient and effective tool in the study and mapping of gully erosions.
IntroductionThere have been a number of clinical studies on diagnosed Stroke disease. However, there have been few studies on the geographical disparities for stroke. This study investigates the spatial pattern of stroke disease reflecting socio-demographic characteristics in the State.MethodsStroke patients' admissions for 22 years (from 1990 to 2012) were examined. Their socio-demographic characteristics were extracted from their health records and analyzed. The location of the stroke patients were categorized by Local Governments Areas (LGAs). Spatial maps were generated and produced in a Geographical Information System (GIS) environment. It involves the analysis of the distribution of stroke cases in relation to their underlying population to determine the areas of high and low density of diagnosed cases across the state.ResultsThe result highlighted the spatial distribution of diagnosed stroke cases and also highlighted the areas of concern regarding their spatial distribution within the state. Social inequalities in stroke were persistent as incidence rates in urban areas (North) were around 3 times higher than in the rural areas (South). However, this could be due to better healthcare access in the urban areas than in the rural areas as there were disparities in the distribution of healthcare facilities involved in administering care to stroke patients in Osun State.ConclusionThe outcome of this study appears to indicate that spatial inequalities in the access to Stroke healthcare is a concern that needs to be addressed in order to manage the disease adequately.
During the wet season, the Benue River overflows its banks and sometimes, extreme floods also occur in Adamawa catchment. Intensification of agriculture in some areas and urban growth in other areas has exposed a large population to flood risk. Little is known about localities or areas liable to flood at various peak flows and how land use and soil permeability affects the severity of flood in Adamawa catchment. This study seeks to analyse the exposures of land use/land cover and soil permeability to flood and model flood peak zones for three flow rates (2 years, 5 years and 10 years) using geospatial techniques and HEC-RAS model. Results of 2 years flood show that at least eight localities in the study area are highly prone to flood. This means that the probability of a flood of this calibre to occur and affect those localities in a given year is 50%. The number of localities prone to flood increases for Annual Exceedance Probability of 20% and 10%. The probability of 10% flood to occur and affect those localities in a given year is relatively low compared to both the 2yr and 5yr flood. Modelling results generated a curve number grid map which shows the permeability levels within the study area. Areas with more infiltration capacity recorded 50% (very high) and 20% (high). Moderate permeability score 16%. Very low and low levels account for 7.6% and 5.2% respectively. The implication is that 70% of the total area experience reduced surface runoff whereas 12.9% are more prone to water logging.
Gully erosion remains a major threat to the people of Benin City. This study applies Analytical Hierarchical Process (AHP) and geospatial techniques to evaluate vulnerability to gully erosion in Benin City, Nigeria. Five essential criteria were identified based on literature, and evaluation by experts. Pairwise Comparison Matrix (PCM) was obtained and weights for each of the PCM were determined using AHP. The consistency of generated weights obtained is not above 0.07. The method resulted in a gully erosion vulnerability model. Analysis of the model revealed that 52.1% (488.69Km2) of the area is vulnerable to gully erosion, while 3.4% (32.37 Km2) was found to be highly vulnerable to gully erosion. Fieldwork was conducted to establish the people’s perception and identify the causes and control measures for the gully erosion problem in the area. Findings on the major contributing factor that leads to the gully erosion formation showed that lack of drainage system accounts for 56.25%, improper land use practice account for 25%, and bad road construction (18.75%). About 50% of the respondents are of the view that an adequate drainage system would go a long way to mitigate the gully erosion. This present study has provided information on the state of gully erosion vulnerability in Benin City through mapping of vulnerable areas. L’APPLICATION DES TECHNIQUES PHA ET GEOSPATIALES POUR L'EVALUATION DE LA VULNERABILITE A L'EROSION DES RAVINS DANS LA VILLE DE BENIN, DANS L’ETAT D’EDO, AU NIGERIA.Cet article a évalué l'érosion des ravins à l'aide des méthodes de télédétection et de SIG ainsi que la méthode du processus hiérarchique analytique (PHA) pour déterminer les zones vulnérables et sensibles à l'érosion en ravins et analyser qualitativement la perception des habitants de ladite ville, leurs mécanismes d'adaptation à l'érosion du ravin (et leurs facteurs causatifs) dans la ville de Benin. Cinq critères essentiels (la Lithologie, l’Utilisation des terres/Couverture des terres, la Densité de drainage (DD), les Pentes et sols) ont été identifiés sur la base de la littérature. La méthode du processus hiérarchique analytique (PHA) a étéutilisé pour déterminer les poids pour chacune des matrices de comparaison par paires. La cohérence des poids générés n’était pas supérieure à 0,07 reflétant ainsi, un résultat valide. Un travail de terrain a également été mené pour établir la perception des gens et identifier les causes et les mesures de contrôle du problème d'érosion en ravins dans la région, 100 questionnaires ont été distribués en utilisant des méthodes d'échantillonnage systématique aux habitants autour des sites de ravins identifiés. Le modèle de vulnérabilité à l'érosion en ravins développé dans cette étude a révélé que jusqu'à 44,4% de la superficie totale étaittrès vulnérable à l'érosion en ravins, 52,1% (488,69Km2) de la zone est vulnérable à l'érosion en ravins, tandis que 3,4% (32,37 km2) s'est avéré moins vulnérable à l'érosion en ravins. Les résultats sur le principal facteur contributif qui conduit à la formation d'érosion en ravine ont montré que le manque de système de drainage représente 56,25%, les pratiques inappropriées d'utilisation des terres représentent 25 % et la mauvaise construction des routes (18,75 %). Environ 50 % des répondants sont d'avis qu'un système de drainage adéquat contribuerait grandement à atténuer l'érosion des ravins. Cette étude a fourni desinformations sur l'état de vulnérabilité à l'érosion des ravins dans la ville de Bénin par la cartographie des zones vulnérables et nous recommandons que la planification et le développement urbain dans la ville de Benin soient basés sur la prise de décisionéclairée, nous recommandons également la construction de systèmes de drainage appropriés et efficaces et nous suggérons que des pratiques collaboratives et intégrées d'utilisation des terres soient maintenues dans la ville de Bénin. Mots clés: Techniques géospatiales, Érosion en ravins, PHA, vulnérabilité
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