TITLE:
Assessment of Groundwater Resources in a Complex Volcanic Reservoir with Limited Data Sets in a Semi-Arid Context Using a Novel Stochastic Approach. The Goda Volcanic Massif, Republic of Djibouti
AUTHORS:
Ibrahim M. Ahmed, Mathieu Le Coz, Mohamed Jalludin, Paul Sardini, Moumtaz Razack
KEYWORDS:
Water Resources, Stochastic Modeling, GLUE, Volcanic Systems, Goda Aquifer, Djibouti
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.10 No.1,
January
31,
2018
ABSTRACT:
This work focuses on the modeling and evaluation of water resources in complex
aquifer systems and the use of scarce data. The modeling work is developed
based on the GLUE (Generalized Likelihood Uncertainty Estimation)
method. This method is still little used in hydrogeology, although its applications
in other disciplines such as hydrology proved quite efficient. The study
site, located in the Republic of Djibouti (Horn of Africa), is represented by the
volcanic massif of Goda. The hydraulic properties of this massif are highly
heterogeneous since they are associated with fracturing and weathering of the
geological formations. The data are too few to enable a conventional modeling
approach of this volcanic system. The implementation of the GLUE method
in a numerical groundwater flow model allowed developing a stochastic analysis
of the spatial distribution of the hydraulic conductivity and the recharge
modalities of this complex volcanic system. The hydraulic conductivities range
from 10-6 to 10-8 m·s-1 for the basalt and the rhyolite formations (values are
yet generally lower for rhyolites) and are higher than 5 × 10-7 for the sedimentary
formations. In addition, considering diffuse recharge as the main
mechanism by which the precipitation reaches the aquifer results in more
consistent groundwater head simulations than considering only indirect recharge.
The average recharge amount estimated for the Goda aquifer system is
28 mm·yr-1. The results led to a numerical representation of this system, with
the least uncertainty. This model was able to estimate the available water resources
of this system. This result is important because the Goda system supplies water to the city of Tadjourah. Assessment of available resources is vital
for the future development of this city. From a methodological point of view,
the GLUE method proved very promising for water resources assessment in
complex hydrogeological systems for which little data are available.