"GROUNDWATER QUALITY MAPPING AND CHARACTERISTICS AQUIFER: A CASE STUDY IN KOLA RIVER WATERSHED, GIDABO SUB BASIN, SIDAMA REGION ETHIOPIA

Abstract

This research assessed the groundwater quality mapping and characterized aquifers in the Kola River Watershed. Two methodologies, ArcGIS-based and the Aquifer Test 3v methodology, were employed to achieve these objectives. Data were collected from completion reports of wells, springs, shallow wells, and boreholes within the study area. Laboratory tests were conducted on water samples collected from various sources to analyze physical parameters such as pH, electrical conductivity, total dissolved solids, turbidity, hardness, calcium, magnesium, sulfate nitrate, bicarbonate, fluoride, iron, and chloride.These parameters provided insights into the quality and composition of the groundwater.The Water Quality Index (WQI) method was applied to evaluate the water samples and quantify the overall water quality and evaluate by piper digram categorize water types. Kola River Watershed is characterized by a diverse range of tertiary volcanic rocks, including ignimbrite, basalt, trachyte basalt, rhyolite, and scoria basalt. The water quality assessment in the study area found elevated iron concentrations and high turbidity levels in some boreholes, exceeding the standards set by the World Health Organization (WHO).The Water Quality Index (WQI) results, a small percentage (0.72%) of groundwater samples in the study area were classified as excellent or good quality. However, a significant proportion (4.0037%) of samples fell into the category of good quality, and an additional portion (4.77%) were classified as very poor quality. The majority of groundwater samples (90.50%) were deemed unfit for drinking purposes.three water type so were beserved: CaHCO3 with low TDS, mixed CaNaHCO3 and NaCaHCO3 with moderate TDS, and NaHCO3 with high TDS. in the aquifer system of the Kola River Watershed, there are aquifers classified as moderately productive and mixed porous and fissured aquifers of moderate productivity.In a particular part, high hydraulic conductivity (K) values of 3.47 m/d, transmissivity (T) of 207 m2/d, and specific capacity (Sr) of 1.44 were recorded. In the central part, K ranged from 0.376 to 1.81 m/d, T ranged from 15.5 to 68.2 m2/d, and Sr ranged from 0.00127 to 0.461. In the lower part of the study area, K ranged from 0.135 to 10.2 m/d, T ranged from 7.27 to 10.7 m2/d, and Sr ranged from 0.00042 to 0.0374