Mapping regional discontinuities and identification of their role in underground hydrodynamics in a base zone: case study of the Dimbokro-Bongouanou region, Ivory Coast

This study aims to investigate a methodology to map regional discontinuities, based on a combined analysis of radar and optical images, to assess if they play a noticeable role as groundwater flow paths. This method is implemented in the region of Dimbokro-Bongouanou (Ivory Coast). In a first step, the methodological approach consists of spatial analysis of the regional lineaments likely to be related to the fracturing of the basement by means of combined analysis of radar (Radarsat) and optical (Landsat) images, and then validating these lineaments with the mean geological data. In the second step, analysis is proposed that enables the role of these lineaments in ground-water circulation to be identified. This consists of determining the correlation between the major lineament traces and the location of boreholes. The yield of boreholes is analysed as a function of their distance from the nearest lineament, which shows that borehole yield decreases proportionally with the distance between the lineament and high-yield boreholes (discharge greater than 5 m super(3)/h). No correlation between distance to the lineament and low-yield boreholes (discharge less than 5 m super(3)/h) is noticed. The negative correlation between the productivity of high-yield boreholes and the distance to the closest lineament confirms that these lineaments are surface traces of regional discontinuities and act as main groundwater flow paths.Original Abstract: Ce travail a pour objectif de proposer une methodologie de cartographie des accidents regionaux, basee sur une analyse combinee d'images radar et optique, afin de determiner leur role dans les ecoulements souterrains. Cette methodologie est mise en oeuvre en zone de socle, dans la region de Dimbokro-Bongouanou (Cote d'Ivoire). Dans un premier temps, cette demarche methodologique consiste a spatialiser les lineaments regionaux susceptibles d'etre en relation avec la fracturation du socle a partir de l'analyse combinee d'images radar (Radarsat) et optique (Landsat), puis a valider ces lineaments aux moyens de donnees geologiques. Dans un second temps, une analyse permettant d'identifier le role de ces lineaments dans les circulations souterraines est proposee. Celle-ci consiste a etudier les correlations entre la position des forages et le trace des lineaments regionaux. Plus precisement, le debit des forages est analyse en fonction de leur distance au lineament le plus proche, ce qui permet de constater une augmentation du deb