Improvement of aquifer transmissivity assessment in crystalline and metamorphic fractured rocks in Bondoukou area, North-Eastern Côte d’Ivoire

Abstract

This study is performed in the Bondoukou area located in north-eastern Cote d’Ivoire. The aim of this study was to improve the assessment of transmissivity of the highly fractured aquifers of Bondoukou area using kriging techniques. A previous estimation of the transmissivity was conducted with aquifer transmissivity of crystalline rocks (n = 62). These transmissivities were later supplemented by 78 samples of aquifer transmissivity of metamorphic rocks. The results of this study were compared with those obtained in crystalline rock aquifers. In both cases, the variogram exhibits a large nugget effect representing respectively 63 and 70% of total dispersion. The nugget effect of this study is less important than the previous study. The range is equal to 12 km and is larger than that obtained in the previous study. The structuring of the variogram is enhanced when we consider the aquifer transmissivity of metamorphic rocks. Transmissivity estimated in both studies varies between 4.00E-06 and 1.72 E-06 E-05 m 2 .s -1 and between 3.86 E-06 and 1.84 E-05 m 2 .s -1 respectively in the previous study and in this study. In both cases, the observed and estimated transmissivities values are comparable and are spread over two orders of magnitude. Kriging maps showed that the estimation of transmissivity in Bondoukou area is better in this study. The results obtained in this study are interesting because they showed improved estimate of the transmisssivity in the Bondoukou area. Key-words: crystalline basement, fractured aquifers, Bondoukou, transmissivity, variogram, kriging.