Effects of Temporal Rainfall Variability on Water Quality of River Ruiru, Kiambu County, Kenya

Abstract

This paper assessed the effects of temporal rainfall variability on water quality of River Ruiru, Kiambu County. Findings from the study indicated that DO, TDS, thermal conductivity, total phosphorus and total nitrogen values were within World Health Organization (WHO) (2011) and National Environment Management Authority (NEMA) (2006) recommended values. The BOD values were found to be within NEMA (2006) limits in all sampling sites though above WHO (2011) limits both seasons except at Kwa Maiko where they were within the limit during the dry season. The pH and turbidity values were above WHO (2011)/ NEMA (2006) recommended values during dry and wet seasons except for Ruiru dam sampling site where they were within the limits during the dry season. The results for the total coliforms and E. coli indicated that River Ruiru was severely polluted. Moreover, the results indicated that pH, turbidity, DO, thermal conductivity and TDS had higher mean during wet season (M=8.40, M=79.00, M=51.20, M=87.00 and M=54.20) than in dry season (M=6.80, M=11.60, M=43.40, M=73.00, and M=45.40). The difference for these water quality parameters between dry and wet seasons was significant (P=0.003, P=0.034, P=0.005, P=0.013 and P=0.014).These findings will help in understanding the effects of temporal rainfall variability on water quality which is one component of the knowledge base required in applying the principles of integrated water resources management (IWRM) thus providing critical input to the decision making on water resources management and planning.

Keywords: River Ruiru, Temporal rainfall, Watershed, Water quality