Evaluation of the Correlation Between Surface Geophysical and Subsurface Hydraulic Parameters: A Case Study from Raya Valley, Northern Ethiopia

Abstract

Reliable estimation of aquifer transmissivity (T) is fundamental for groundwater assessment, development, and sustainable management. Although pumping tests provide the most reliable estimates of transmissivity, their application is often constrained by the limited availability of wells and the high cost of testing, particularly in data-scarce regions such as the Raya Valley, northern Ethiopia. This study evaluates the potential of electrical transverse resistance (Tr), derived from Vertical Electrical Sounding (VES), as a proxy for estimating transmissivity in unconsolidated aquifers. A total of 44 VES datasets integrated with pumping test data from nearby wells were used to develop empirical T–Tr relationships. The Schlumberger electrode array was employed with a maximum current electrode spacing (AB) of 1000 m, while an additional 263 VES datasets acquired between 1996 and 2024 were analyzed to characterize subsurface electrical variability. The results reveal strong linear relationships between transmissivity and transverse resistance. Normalization of transverse resistance to account for pore-water resistivity produced comparable relationships, with differences of only 1–3%, indicating that normalization provides limited additional benefit. Independent validation using 16 pumping-test datasets demonstrated excellent agreement between measured and estimated transmissivity values (R2 = 0.99). The transmissivity values used to develop the empirical equations ranged from 120 to 1180 m2/d. These relationships were derived specifically from unconsolidated aquifers within the Raya Valley and should therefore be applied within this hydrogeological context. Their applicability to confined sedimentary aquifers and fractured volcanic formations, which were not represented in the present dataset, remains uncertain. Further studies involving these hydrogeological settings are needed to evaluate and potentially extend the applicability of the proposed relationships. The developed T–Tr relationships provide a reliable and cost-effective approach for estimating transmissivity in saturated unconsolidated aquifers where pumping-test data are limited and may be transferable to hydrogeologically similar environments.