Abstract:
The Nyabugogo River, located in the Nyabugogo watershed in central area of Rwanda, is
an important water resource for people living in this area. Agriculture dominates land use
in the basin, while the river receives waste water effluent from the town of Kigali capital
city.
The purpose of this study was threefold. First, to evaluate the water quality of the
Nyabugogo River and compare water quality parameters at different sites. Then, to study
selected parameters by using water quality index (WQI) and evaluate its suitability for
livestock and drinking use. Lastly to discuss the statistical results based on WHO surface
water quality Standards for dinking purpose. WQI was calculated on the basis of Weighted
Arithmetic Index by analyzing 12 physico-chemical parameters at Rwesero, Rusine, and
Giticyinyoni sites. The overall WQI results showed high pollution values at two sites for
rainy and dry season, except at Rwesero. On other side, the water quality parameters that
were examined statistically include physical, chemical, and microbiological parameters
where thirteen sampling sites were chosen along the Nyabugogo River. Turbidity and Lead
levels were high in all sites monitored, the highest average concentration of turbidity was
(3675.3NTU) at Rusine while Lead was (0.08g/L) at Nyacyonga site. These concentrations
exceeded water quality guidelines. The average concentration of DO was highest
(7.0mg/L) at Mwange. The conductivity was above the WHO limit at Rwesero, bridge1
and wetland sites, with the highest average concentration (408.3 s/cm) at wetland site. It
was found that the concentrations of faecal coliform and E.coli were higher to the WHO
limit especially downstream of the city indicates the untreated wastewater disposal from
the Kigali city. Moreover, nitrate showed a higher pollution with a highest average value
of (37.1 mg/L).
This thesis revealed that both urbanized and rural area have serious but different types of
pollution. Based on the parameters concentrations and the land uses impacts, it was
concluded that domestic and agricultural waste strongly influenced the variation and the
quality of the Nyabugogo River.
