Modelling of heterogeneities of aquifer geometry in a fractured basement in Korhogo (Ivory Coast)

Raymond Bile and Fabienne Trolard and Sophie Viseur and Jean-Patrice Jourda and Guilhem Bourrié. ( 2011 )
in: Proc. 31st Gocad Meeting, Nancy

Abstract

In Korhogo region (Ivory Coast), aquifers consist of alterites developed in fractured basement. Major directions of fracturation are N-S, N60-70, N50-60 and N110-120. g cad was used on a set of drilling data aimed at obtaining water resources and funded by a Non Governmental Organization (“Don Japonais”), in which the nature and depth of alterites, the depth of contact with the basement were described. It was corrected with the digital elevation model. gOcad was used to model the surface of contact between the overlying alterite and the fractured basement, and the variations of the thickness of alterites. The surface of contact between the alterite and the underlying basement was first modelled, and the thickness of alterite was obtained by subtracting the altitude of the surface from the topographic altitude. As a result, a central elevation zone was localized, which separates areas with deeper alteration. The small thickness (< 10 m), intermediate (10–30 m) and large thickness alterites occupy respectively 52 %, 33 % and 12 % of the area, with 3 % alterites of uncertain thickness. Alterites of larger thickness are aligned on NNE-SSW, NE-SW, NW-SE and N-S directions, in coincidence with fracturation. The literature indicates that water flows obtained by pumping are insignificant when alterite thickness is less than 10 m, are regular from 10 to 50 m, with larger flows from 30 to 50 m, but decrease at larger thickness probably due to clogging of fractures by clay minerals, which does not happen when alterites were eroded. This study shows the interest of g cad to guide the survey of water resources in an heterogeneous fractured aquifer.

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BibTeX Reference

@inproceedings{BileGM2011,
 abstract = { In Korhogo region (Ivory Coast), aquifers consist of alterites developed in fractured basement. Major directions of fracturation are N-S, N60-70, N50-60 and N110-120. g cad was used on a set of drilling data aimed at obtaining water resources and funded by a Non Governmental Organization (“Don Japonais”), in which the nature and depth of alterites, the depth of contact with the basement were described. It was corrected with the digital elevation model.
gOcad was used to model the surface of contact between the overlying alterite and the fractured basement, and the variations of the thickness of alterites. The surface of contact between the alterite and the underlying basement was first modelled, and the thickness of alterite was obtained by subtracting the altitude of the surface from the topographic altitude. As a result, a central elevation zone was localized, which separates areas with deeper alteration. The small thickness (< 10 m), intermediate (10–30 m) and large thickness alterites occupy respectively 52 %, 33 % and 12 % of the area, with 3 % alterites of uncertain thickness. Alterites of larger thickness are aligned on NNE-SSW, NE-SW, NW-SE and N-S directions, in coincidence with fracturation. The literature indicates that water flows obtained by pumping are insignificant when alterite thickness is less than 10 m, are regular from 10 to 50 m, with larger flows from 30 to 50 m, but decrease at larger thickness probably due to clogging of fractures by clay minerals, which does not happen when alterites were eroded.
This study shows the interest of g cad to guide the survey of water resources in an heterogeneous fractured aquifer. },
 author = { Bile, Raymond AND Trolard, Fabienne AND Viseur, Sophie AND Jourda, Jean-Patrice AND Bourrié, Guilhem },
 booktitle = { Proc. 31st Gocad Meeting, Nancy },
 title = { Modelling of heterogeneities of aquifer geometry in a fractured basement in Korhogo (Ivory Coast) },
 year = { 2011 }
}