Application of Pumping Tests to Estimate Hydraulic Parameters of Volcanic Aquifers in Lake Tana Basin, Ethiopia

The purpose of this study was to enhance the understanding and sustainable groundwater management of volcanic aquifer systems by estimating key hydrogeological parameters. The transmissivity of a volcanic aquifer system was estimated using analytical solutions based on 68 constant rate and recovery data sets collected from various sources. A combination of hydro-lithostratigraphy and diagnostic plots was employed to identify the aquifer types and flow conditions, which facilitated model selection. Transmissivity of the confined aquifer was modeled using both Theis and Cooper–Jacob methods, with the Theis residual drawdown solution utilized for estimation. For the unconfined aquifer, the Neuman method was used, and the Hantush/Jacob method was employed for leaky aquifers. The results showed that the transmissivity of the Tertiary basalt varied from 0.38 m2/d to 860 m2/d, while the Quaternary aquifer system ranged from 2.33 m2/d to 1.8 × 104 m2/d, indicating an increase in transmissivity with younger volcanic flows. Specific capacity (SC) was estimated for 74 wells and the values ranged from 0.62 to 5860 m2/d. This wide variation of specific capacity and transmissivity showed significant heterogeneity within the volcanic aquifers. This study introduces the innovative application of derivative diagnostic plots in groundwater research, offering an efficient approach for analyzing and interpreting pumping test data to characterize aquifer systems in various hydrogeologic units. This study focuses on aquifer characterization in hard rock formation, demonstrating methods that can be applied to similar geological environments globally. For the Blue Nile basin in general and for the Lake Tana basin in particular, the study result of aquifer characterization will contribute to exploration, development, and improved groundwater management in the region.