Taking into Account the Role of the Weathering Profile in Determining Hydrodynamic Properties of Hard Rock Aquifers

Abstract

The present study aims at understanding the role of the structure and the geometry of the weathering profile on the hydrodynamic behavior of hard rock aquifers. We first described 2D geophysical cross sections of weathering profiles realized and validated on an experimental site. Next, we implemented five long-term pumping tests in wells drilled at various locations of these cross sections. Finally, we chose the appropriate analytical solutions to determine the hydrodynamic parameters in consistence with the structure and the geometry of the weathering profile. Results reveal that land covers, weathering type and thickness, presence of no flow boundaries, etc. are all factors that explain the flow regime, which appears therefore much less unpredictable. In other words, the 2D geophysical data are enough to locate the best permeable areas, or the areas where the structure of the aquifer without impervious boundaries and with leakage favor a good long-term behavior of the well. The values of aquifer's transmissivity vary between 5.10 −3 and 4.10 −5 m 2 /s. The storage varies between 0.06 and 7.10 −7. The variability of these parameters from site to site reflects the high heterogeneity of hard rock aquifers.

Groundwater Storage Change Estimation Using Combination of Hydrogeophysical and Groundwater Table Fluctuation Methods in Hard Rock Aquifers

“…At the outlet, the specific yield estimated only by sample analysis is 1.8%. On the other hand, the value of S y estimated by MRS in the central valley is lower than that obtained by Koïta et al [39] by pumping test which is 6%. This difference would probably be related to the conceptual model of the aquifer chosen to interpret the pumping data.…”

Magnetic resonance sounding measurements as posterior information to condition hydrological model parameters: Application to a hard-rock headwater catchment

“…Characterizing the heterogeneity of the hydraulic parameters in the subsurface and the geometry of the subsurface layers is still a challenge in hydrology (Salve et al, 2012;Koïta et al, 2017;Comte et al, 2019). A proper characterization is nonetheless critical to reduce equifinality issues when using models that describe the water cycle at the catchment scale.…”

“…The use of geophysical methods, such as electrical resistivity, seismic tomography, or ground penetrating radar, provides insights into the structure of subsurface systems and allows for defining zones of different properties, including the thickness of hydraulically-active layers (Koch et al, 2009;Befus et al, 2011;Cassidy et al, 2014;Holbrook et al, 2014;Parsekian et al, 2015;Soulsby et al, 2016;Olyphant et al, 2016;Orlando et al, 2016;Koïta et al, 2017;Flinchum et al, 2018a). Time-lapse experiments also inform on the processes driving the water circulation along hillslopes or in a catchment (Cassiani et al, 2009;Angermann et al, 2017;Jackisch et al, 2017;Scaini et al, 2018;Hübner et al, 2017;Kotikian et al, 2019).…”

In Situ Observations and Lumped Parameter Model Reconstructions Reveal Intra‐Annual to Multidecadal Variability in Groundwater Levels in Sub‐Saharan Africa

“…No pumping test data are available for the remaining three sites (Dingasso, Binde, and Ouda), and no data for unconfined storage coefficients are available for any of the sites. The resultant calibration ranges for K and S (Table 2) therefore represent a "best estimate," encompassing the K estimates derived above and considering the pumping test data quality and ranges reported for weathered basement aquifers in Africa (MacDonald et al, 2008;Ouedraogo et al, 2016;Wright, 1992) and West Africa specifically (Bianchi et al, 2020;Dickson et al, 2019;Koïta et al, 2017; SNC-Lavalin/INRS, 2011). Mackay et al (2014) and Jackson et al (2016) report significant interaction in AquiMod between hydraulic conductivity and the discharge elevation and aquifer length parameters.…”