Hydrogeological Assessment of the Merti Aquifer, Kenya

The Government of Kenya has approached the Dutch investment company ORIO to support the investment in infrastructure for the Habaswein-Wajir Water Supply project. The project proposes to draw water from the Merti Aquifer to supply the city of Wajir with drinking water, through a 120 km pipeline. The proposed well-field is located near Habaswein and will be used for urban water supply for Habaswein as well. This documents reports the outcomes of a hydrogeological assessment that determines the risk of groundwater depletion as a result of the proposed well-field. It is a technical report published in the framework of ARIGA - Assessing Risks of Investment in Groundwater Development in Sub-Saharan Africa. The principles of Applied Information Economics are used to develop a decision model for the water supply intervention. The results of the hydrogeological study are used in that decision model.

The hydrogeological study aims to predict the effect of the pipeline project on the groundwater system, while also stating the uncertainty in the predictions. This study focusses on the prediction of drawdown of groundwater levels, ultimately leading to boreholes falling dry, and deteriorating water quality as a result of displacement of saline water in the aquifer in a 30 year time period. Process-based models, that conceptualize the physical processes in the groundwater system, are combined with stochastic methods. This approach provides the probabilistic characteristics of the model outcomes to support decision-making.