EMPIRICAL TRANSMISSIVITY MODELING OF PEDESTRAL AQUIFER OF IVORY COAST

Abstract

The objective of this study is modeling the transmissivity of the hard rock aquifers from the specific capacity. The areas tested used for this study are the region of N'zi-Comoé (Paleoproterozoic domain) and Guiglo-Duékoué region (Archean-SASCA domains). A large database of transmissivity and specific capacity values was compiled. The methodological approach is based on the study of the relationship between the transmissivity and specific capacity from an empirical procedure of the form T=αQ_s^β. The quality of the developed models was analyzed from the correlation coefficient, the Student t test, the bias on the mean and the square root of the quadratic error. The values of specific capacity in the Guiglo-Duekoué region ranging from 1.427.10^-2 to 2.571 m²/h with an average of 0.279 m²/h and a coefficient of variation of 159%. The medium and high specific capacities represent 61.22%. As for the region of the N'zi-Comoé, the specific capacity range from 7.752.10^-3 to 3.03 m²/h with an average of 0.402 m²/h, a variation coefficient of 116% and a rate of 82% in respect of the medium and high specific capacities. The transmissivity values of Guiglo-Duekoué region fluctuate between 1.779.10^-3 to 1.952 m²/h with an average of 0.283 m²/h and a coefficient of variation of 135%. Average and high drilling transmissivity represent 73.47%. As regards the region of the N'zi-Comoé, the transmissivity varies between 6.2.10^-3 to 1.302 m²/h with an average of 0.196 m²/h and a coefficient of variation of 123%. Drilling with medium and high transmissivity values are estimated at 68.66%. The results of the adjustment showed that the transmissivity and the specific capacity, processed by the log function follows the normal distribution. The distribution of variables according to lognormal therefore possible to envisage a model of the relationship T=f (Q_s). Thus, two powerful empirical relationships have been established. Both models are designed respectively T₁=0.354Q_s^0.8544 with R²=0.70 for the region of N'zi-Iffou-Moronou (region of N'zi-Comoé) and T₂=1.086Q_s^1.187 with R²=0.60 for the Guiglo-Duekoué region. These empirical models may be useful for other aquifers with similar hydrogeological conditions. However, these models could be improved by correcting the specific capacity losses.