EVALUATION OF WATER QUALITY AND MODELLING POLLUTANTS DISPERSION USING QUAL2K MODEL: CASE STUDY OF RIVER SOSIANI IN WESTERN KENYA

Abstract

River Sosiani catchment area and River Sosiani provide drinking water for the city of Eldoret. During its course, River Sosiani receives untreated point-source pollutants as it winds through different agricultural, industrial and urban zone. Additionally, in wet season, the river receives non-point (diffuse) pollutants from the catchment containing soil, fertilizer and pesticide residues. The study assessed River Sosiani water quality and modelled pollutant dispersion using Qual2K model. Water samples were collected from six (6) sampling along River Sosiani for six months. American Public Health Association guidelines for water sampling and processing procedure were applied in sample analysis. In situ water quality parameters measured were Temperature, TDS, pH and DO while NO3-N, TP and BOD5, NO3-N were determined in the laboratory. The resultant data was analysed using both the descriptive and inferential statistics. The results showed statistically significant spatial variation of all water quality parameters between the means for DO (P=1.20E-19), BOD (P=8.32E-83), Temperature (P=6.00E-13), EC (P=5.32E14), TDS (P=3.18E-13), pH (P=1.15E-28), Nitrate-N (P=1.49E-33) and TP (P=1.06E-30). Seasonally, all parameters indicated significant temporal variation between the means for DO (P=5.66E-18), BOD (P=2.38E-03), Temperature (P=3.92E-11), EC (P=3.81E-10), TDS (P=1.31E-09), pH (P=1.35E-02), NO3-N (P=1.38E-13) and TP (P=6.72E-08). The Qual2K model was calibrated using dry season data and validated using wet season data. The model performance was evaluated using R2 , RSR and NSE. The Qual2K model performance values for R 2 , RSR and NSE ranged 0.82-0.95, 0.20-0.45, and 0.75-0.95 respectively. Conclusively, the study showed that River Sosiani water quality deterioration was caused by point and non-point pollutant sources.