Assessment of Groundwater Variability in Mbagathi River Catchment

Groundwater is increasingly an important source of water. Assessment of its variability spatially and temporally besides quality and quantity is not easy. Groundwater contains multiple range of chemical parameters. This contribution proposes a water quality index (WQI) to synthesize various groundwater quality parameters (Na+, F-, Cl‑, SO42-, Ca2+, Mg2+, K+ and NO3-) in Geographic Information Systems (GIS) based environment. The parameters are analyzed relative to the Kenya Standard (KS) East Africa Standard (EAS) 12:2018 standard in the Mbagathi river catchment, a metropolitan area, Southwest of Nairobi, Kenya. Prediction maps for three seasons (wet, moderate and dry) and a combination all three seasons were produced. Based on WQI classification, results showed 36% - 28% good, 58% - 61% fair, and 6%-11% poor. A noticeable declining groundwater quality trend from wet to dry seasons was observed. Groundwater quality deterioration was observed to be greater in areas with higher yield and water rest level. Groundwater is safe for drinking, barring the elevated fluoride content in some areas. Application of GIS was a valuable tool in exploration of groundwater characteristics. Maps generated can serve as first-hand information for groundwater development. Keywords: groundwater, quality, kriging, semivariogram, variability DOI: 10.7176/JEES/12-4-03 Publication date: April 30th 2022