Characteristics and Productivity of the Sediments and Volcanic Rocks Aquifers in Sunuta Sub-Basin, Northeast Ethiopia

Abstract

Sunuta sub-basin is found within the lower Awash basin, Northeast Ethiopia, having an area of 1490.5km2. The objective of the research was to characterize the different sediments and volcanic rocks aquifers and evaluate their respective productivity. To achieve these objectives, primary and secondary data were collected. Primary data such as geological, geological structures, and 82 water levels were collected during field investigation. 35 constant pumping test and 33 borehole log data were collected as secondary data from water offices in the area. With the exception of specific capacity, all other hydraulic properties were determined from recovery test data using Theis and Neuman analysis methods. Specific capacity was determined from constant discharge test data. The Mesozoic sandstone, Tertiary and Quaternary volcanic rocks and recent sediments are the main geological formations of the sub-basin. The aquifer types around the escarpments are unconfined whereas in the rift floor the aquifers are confined and semi-confined. In the rift floor the sediment thickness varies from 166-200m and also found interlayered with volcanic rock of rhyolite and basalt, forming multilayer confined and semi-confined aquifer. The general groundwater flow direction is from west to east. The different geological formations that are found constituting the area are categorized hydrogeologically into aquifer with intergranular weathered and fracture porosity and permeability, extensive aquifer with intergranular porosity and permeability and aquifer with fracture porosity and permeability. Analysis of pumping test data revealed that hydraulic conductivity ranges from 0.268 to 31.1 m/day and transmissivity ranges from 9.6 to 2420 m²/day with mean values of 9.55 m/day and 632.79 m²/day, respectively. Specific capacity ranges from 0.07 to 65.31 l/sec/m with mean values of 5.45 l/sec/m. On the basis of their corresponding transmissivity and specific capacity value, the different aquifers of the studied area were categorized into three aquifer potentiality groups: low, moderate and high potentiality aquifer. Any future development of groundwater should be focused on the moderate and high potentiality aquifers.