APPLICATION OF AHP AND GEOSPATIAL TECHNIQUES FOR EVALUATING GULLY EROSION VULNERABILITY IN BENIN CITY, EDO STATE, NIGERIA

This paper assessed gully erosion using Remote Sensing and GIS methods as well as Analytical Hierarchical Process (AHP) method to determine areas vulnerable and susceptible to gully erosion and Analysed qualitatively the perception of city dwellers, their coping mechanisms to (and the causative factors of) Gully Erosion in Benin City. Five essential criteria (Lithology, Land-use/Landcover (LULC), Drainage Density (DD), Slope and Soil) were identified based on literature. AHP was used to determine weights for each of the Pairwise Comparison Matrix (PCM) obtained. Consistency of generated weights obtained was not above 0.07 reflecting a valid result. Field work was also conducted to establish the people’s perception and identify the causes and control measures for the gully erosion problem in the area, 100 questionnaire was distributed using purposive systematic sampling methods to inhabitants around identified gully sites. The gully erosion vulnerability model developed in this study revealed that as high as 44.4% of the total area was highly vulnerable to gully erosion, 52.1% (488.69Km2 ) of the area is vulnerable to gully erosion, while 3.4% (32.37 Km2 ) was found to be less vulnerable to gully erosion. Findings on the major contributing factor that leads to the gully erosion formation showed that lack of drainage system account 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 adequate drainage system would go a long way to mitigate the gully erosion. This study has provided information on the state of gully erosion vulnerability in Benin City through mapping of vulnerable areas and we recommend that planning and urban development in Benin-City be based on the informed decision making, we also recommend the construction of proper and efficient drainage systems and suggest that collaborative and integrated land-use practices be upheld in the city of Benin.