Aquifer Characterization and Water Quality Analysis of Sunnuta Well Field, Afar Region, Ethiopia

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Addis Ababa University


The Sunnua well field is located within Uwa catchment in arid climate of Afar rift floor, Northern part of Ethiopia. It is one of the most water-stressed areas of the country, with only a short rainy period from mid-June to mid-September. Because rainfall in this region has been consistently erratic in the last decades, both in time and space, rain-fed agriculture has become problematic. Hence, in order to supplement rain-fed agriculture with small to large scale irrigation, a detailed understanding of local and regional groundwater resources is important. However, information on the availability and distribution of groundwater resources is scarce as there has never been a systematic and detailed investigation in this region. Hence, the main objective of this thesis is to study and characterize the aquifer system, estimation of recharge by considering Uwa catchment in which the Sunnuta wellfield is located and study the water quality of the well field. An intensive field campaign has been undertaken from February 10 to 30, 2015 to collect relevant information regarding geology, hydrology, and hydrogeology throughout the study area. Water samples were collected and analyzed in the hydrochemistry laboratory of water work design and supervision enterprise and Addis Ababa University Analytical laboratory, and results were compared with WHO drinking water standards. For most of the chemical constituents, water samples are within the safety standards, except surface water samples shows high Florid content ranging from 1.5-2.66 mg/l. From the geological survey, it follows that the uwa catchment is 55% covered with flvo lacustrin deposit and the other units are dalha basalt, ashenga basalt, recernt balst ,andustic tuff, granitic intrusion and sand stone, The sand stone unit covers a very small part of the well field. Most of which have been affected by different types of geological structures due to successive episodes of geological disturbances resulting from rifting activity. The average monthly temperature and the mean annual precipitation in the study area are 26.620C and 400.9MCM, respectively. Potential evapotranspiration (PET) of the area was estimated using Penman Combination method which gives average annual PET value of stations 1298.88mm/y. Actual evapotranspiration value for the catchment estimated from Turc method gives value of 292.56MCM which is 72.9% of the total annual perception. The annual surface water out flow, estimated using runoff coefficient methods resulted 32.07MCM which is 8% the total annual precipitation. Water balance approaches were used to estimate recharge, while the annual recharge of the area is 76.27MCM/year which is 19% of the total precipitation. To characterize the aquifer system of the area pumping test data, well completion reports, well logs and geology of the area were analyzed. The study area is characterized by deep groundwater systems encountered at an average depth of 225m.The hydraulic characteristics are spatially variable, which the transmissivity of the study area ranges from 144.0 – 5533.56 m2/d and the mean is 2543.86 m2/d. the hydraulic conductivity ranges from 2 – 77 m/d and the mean is 39.9 m/d. The unconsolidated sediments and the fractured volcanic rocks are the main aquifer units in the area. These aquifers were found to be good groundwater potential zone. The general trend for groundwater flow observed from pieziometric heads is from South east to North West of the study area. Piper plots used to know the water type. Groundwater type of the area was evolved from Ca-Mg-HCO3 water type in the area closer to western escarpment in to Na-Ca- Cl--SO-24 – HCO-3 water type in the sunuta well field. The water also shows low sodium hazard and can therefore be used for irrigation without posing much risk to the compaction of soils.



Sunnuta Well Filed, Uwa Catchment, Ground Water Recharge Estimation, Hydrogeochemistry