Strategy for borehole depth optimization in hard rock aquifers (Denguele region, northwestern Ivory Coast)
The aim of this study was to conceive a strategy for the optimization of borehole depth in bedrock during hydraulic campaigns in the Ivory Coast. The methodology is based on data acquired in the Ivory Coast and it allows one to establish optimization equations for choosing the depth of the boreholes. It is founded upon statistical methods, notably Principal Component Analysis (PCA), to which multiple linear regressions are added to develop the needed equations. NCSS6.0 software was used for this study. The analysis showed that some borehole parameters, such as the drilling rate in the rock (Vas), the depth at which groundwater is first observed (Pae) and the number of times groundwater is observed (Nae), yield information about the existence of fractured aquifers. Therefore, they are useful in the development of the borehole depth optimization equations. The thickness of the rock drilled (Soc) is added, since this is the parameter to be optimized. The equation was tested on 171 boreholes in the Denguele region and on 43 other boreholes distributed among several geological formations within the Ivory Coast region. The result was positive for 90% of the all the geological formations tested. For a borehole depth of 9220 m, the application of the equation avoided an over-drilling of 728 m, i.e. an economy of 8%. This strategy thus allows a rational management of the budget for borehole drilling projects for village hydraulics, and favours the supply of water to a maximum number of people.