Characteristics and Productivity of Volcanic Rock Aquifers in Kola Diba Well Field, North-central Ethiopia

Abstract

Characterization the different volcanic rock aquifers and evaluation of their respective productivity was done in Kola Diba well field (221 km2), north-central Ethiopia. Collections and analyses of pertinent secondary data were followed by detailed field investigation. Geological and structural investigations was conducted in the field paying particular attention to the different features of the overlying sediments and underlying volcanic rocks units that made them to be a water bearing formations. The structural data were analyzed using Stereonet v7.3 software. Hydrogeological logs, Semi‐log scale (specialized plot) and Log‐Log scale (diagnostic plot) were prepared to determine the different aquifer types and also to characterize the nature of each aquifer. Inventory of groundwater structures (boreholes and hand dug wells) were also conducted as part of hydrogeological investigation. Pumping test data were collected from ten deep wells and were analyzed using Theis and Neuman methods using Aquifer Test v3.5 software. Stratigraphically, the geology of the area from bottom to top is aphanitic basalt, porphyritic basalt and alluvial sediments. The rocks are affected by different degree of weathering and fractures. The geological formations of the area are categorized hydrogeologically into intergranular and fractured medium and fracture medium. The major aquifers are confined, unconfined and leaky. Hydraulic conductivity values of these different aquifers ranges from 0.0048 to 1.46 m/day with mean of 0.444 m/day, transmissivity ranges from 0.5 to 474 m2/day and specific capacity ranges from 0.026 to 0.88 l/sec/m with mean values of 86.878 m2/day and 0.325 88 l/sec/m, respectively. On the basis of their corresponding transmissivity and specific capacity value, the different aquifers of the studied area were categorized into four aquifer potentiality groups: moderate to low, low to weak, weak and very weak aquifers potentiality. Any future development of groundwater should be focused on the moderate to low potentiality aquifers.