Geological Structural Controls on Groundwater Potential in Volcanic Aquifers of the Upper Blue Nile Basin

ABSTRACT Understanding geological structures, which primarily control groundwater distribution, potential, and flow systems, is essential for sustainable groundwater management. The objective of this study is to investigate the influence of geological structures within volcanic rock units on the region's groundwater potential and borehole and spring yields, providing practical and relevant insights. Furthermore, this study identifies the structural controls that impact the groundwater potential and distribution in the study region. Various methodological approaches, including data collection through intensive fieldwork, evaluation of previous works, satellite image interpretation, and an inventory of groundwater sources (boreholes and springs) from regulatory datasets, were employed to achieve the study's objective. Borehole (23) and spring (22) data collection for validation, along with a detailed assessment of published and previously unpublished works, contribute to the study region's condensed results and interpretations. The analysis results show that structural dynamics have been passed through persistent tectonics and deformation. Those imprints can be found in the study region, thus determining groundwater occurrence and flow. From the 22 boreholes reported in the study region, nine boreholes (40%) were abandoned, mainly in the western part of the Blue Nile River (8 boreholes) and one borehole in the Zenzelma area. The springs primarily concentrate on lithologic contacts and along the fault lines in the southern section of the study area. Among the productive wells (60%), a significant variation in well yield is observed, ranging from 2.5 L/s to 60 L/s, making the controlling factor very complex. The primary geological structures that govern groundwater flow systems are the deep‐seated NE–SW, NW‐SE, and N‐S faults, the N‐S‐trending radial dike, the NE–SW‐trending radial fracture, and the NW‐SW chain of cinder cones. The upper section of the Andasa area (Adiet‐Gonj Kolela), characterised by a thick, structurally undeformed, massive base of a shield volcano, is unfavourable for groundwater occurrence and flow. Topographically high and less deformed crystalline volcanic rocks make the area unsuitable for groundwater exploration and exploitation. The eastern part of the Andasa (Abune‐Hara area) and the western part of the Andasa watershed are characterised by NE–SW radial fractures and faults, which cause springs to discharge at the points of convergence of these fractures. Moreover, structural analysis and the nature of tectonic evolution within the study area suggest a strong possibility of an N‐S trending buried dike and a multidirectional radial/feeder dike extending towards Lake Tana and the centre of the cone conduit, respectively. The collapsed surface is a potential site for groundwater occurrence. However, deep N‐S faults aligned with the Blue Nile River require careful consideration. The implications of NW‐SE‐oriented cones and buried dikes, overlaid with Quaternary basalt and sediments, mislead groundwater experts. Generally, this work clustered the set of geological structures that control groundwater flow and occurrence. Despite the need for a detailed analysis of the effects of the feeder dike, scoria cone chain, and the N‐S aligned section of Upper Blue Nile River, the highly fractured zone east and west of the Andasa plain, the lower area of the Andasa plain, and the Meshenti region (west) represent a groundwater potential zone. This study is novel in identifying, clustering, and characterising the complex cross‐cutting relationships among geological structures formed by multiple deformations in the study region to determine groundwater occurrence and barrier zones for future exploration and extraction.