Investigation of the Impact of Informal Settlements of Ngong River

Nairobi city has seen a rapid growth of its population leading to rise of informal settlements such
as Kibera and Mukuru slums which are located along Ngong River. Both Kibera and Mukuru
slums lack social services such as sewers, waste disposal and clean water supply services.
Therefore, Ngong River is used for sewage and domestic waste disposal, resulting in pollution of
Ngong River. Consequently, Ngong River waters are heavily polluted and rendered unsuitable
for human use or consumption.
In this study, samples collected from Ngong River were tested for ten water parameters namely:
turbidity, temperature solids, pH, alkalinity, iron and chloride ions concentrations, dissolved
oxygen, BOD and COD. Four sample points were selected before and after each of Kibera and
Mukuru slums. Samples were then tested for wet and dry seasons.
As Ngong River leaves Ngong Forest, its water parameters are well within the set limits. As it
passes through Kibera slums, water parameters, such as chloride ion concentration (69-166 mg/l
during dry season and 84-169 mg/l during wet season) and BOD (25-44 mg/l for dry season; 1853
mg/l for wet season) were found to exceed set limit of 50 and 10 mg/l respectively for natural
surface waters. The river then undergoes self purification between Kibera and Mukuru slums.
This is because Ngong River passes through South C estate which is well provided with sewage
and domestic waste collection services. The self purification process is however not completed
before Ngong River enters Mukuru slums. Through Mukuru informal settlement, Ngong River is
again polluted by slum residents before the process of self purification is complete. Parameters
such as chloride (98-99 mg/l for dry season; 99-110 mg/l for wet season) and BOD (67-71 mg/l
for dry season; 49-62 mg/l for wet season) were found to be excessive of set limits for natural
surface waters.
Pollution of Ngong River was established to be due to human activities such as use of detergents,
vehicle repairs, agricultural activities, and organic waste disposal. Further pollution could only
be stopped by proper planning.