The Nairobi River basin consists of three main rivers: Nairobi, Ngong and Mathare. Other smaller tributaries include Gitathuru, Ruiruaka, Mbagathi, Kamiti, Kasarani, Mutuari and Riara.
Nairobi, Ngong and Mathare rivers are the main rivers draining Nairobi, the Capital City of Kenya. The city was established in 1900’s as a stop-over point and Headquarters for the Kenya Uganda Railway (KUR) workers (Obudho & Aduwo, 1992). At that time, Nairobi Rivers had clean water suitable for drinking and domestic purposes. The name “Nairobi” is derived from one of the local communities; the Maasai, which simply means a place of cool and clean water. Today, the City has tremendously expanded and hosts over 4 million people. The rapidly increasing population coupled with agglomeration of industrial, urban, commercial and settlement activities have caused serious pollution effects on the water quality of the Nairobi river sub-basin (NRSB). The NRSB is part of the upper-Athi river drainage basin in Kenya and drains the southern parts of the Aberdare ranges and flanks of the Rift valley.
The rivers in the sub basin collect wastes generated in the city and its environs and empty into the Athi River which drains into the Indian Ocean. Today the water of the three rivers is heavily polluted by solid, liquid and organic wastes. The negative impact associated with polluted water have raised a great concern from the public and scientific community regarding the toxicological effects of the rivers waters to the riparian communities as well as the aquatic organisms whose natural habitats are getting considerably degraded due to unsustainable human activities.
Phase I was implemented between October 1999 to March 2000, and constituted a situation assessment of water quality, a preliminary public awareness and education campaign, community outreach through pilot income generation projects, and capacity building amongst stakeholders. It also developed an Environmental Management Information System (EMIS)
Phase II was conducted from June 2001 to December 2003 and comprised of a pilot initiative focusing on a tributary of the Nairobi River system – the Motoine/Ngong River. It covered pollution monitoring and assessment limited to a section of the Motoine/Ngong River basin 22 km upstream of Nairobi Dam, the Dam itself, and 25 km downstream to the confluence with the Athi River. The key activities included, the assessment of pollution in Nairobi’s rivers, community education and information programmes to enable capacity building amongst key grassroots stakeholders. It enlisted the support and collaboration of a number of civil society organizations and local authority departments in designing and implementing activities aimed at restoring the ecological integrity of the Nairobi River.
Phase III was conducted from January 2005 to December 2008, incorporating the lessons learnt from phases I and II as pillars to achieve its long-term vision of a restored, rehabilitated, and managed water quality and the riverine eco-system with clean water for the capital city and a healthier urban environment for the people of Nairobi. Capacity building and increased access to vital and relevant information and methodologies have since been identified as pillar for sustainably achieving the NRBP’s vision. Community involvement and empowerment of youth and civil society organizations, the private sector, other non-governmental organizations, and relevant government agencies is key to the success of the programme geared towards achieving the Millennium Development Goal (MDG) Goal 7, and specifically the Targets 9 & 10. This involves coordinating collaboration, co-operation and partnership building efforts between different stakeholders within the Nairobi River Basin, including, UN agencies, Government of Kenya Minitries, Nairobi Dam Trust, Development partners, Private sector, Nairobi City Council, and the civil society to ensure achievement of planned NRBP outputs.
The Nairobi River Basin Program (NRBP) Phase III (Action III) revealed that no consistent monitoring had taken place in all the rivers between 1969 and 2008. The gaps identified included; variability in parameters and matrices studied, incomparable data sets, since no standard methods for sampling, analysis and interpretation was followed. In order to improve the quality of database, it is necessary to gather data that will inform policy and are consistent in measurements and methodology.
The following are conclusions emanating from the levels of physic-chemical parameters of Nairobi River Basin river waters established in the mini-monitoring exercise.
- The concentrations of BOD, COD, TDS, TSS and conductivities were higher in samples collected during the dry season compared to the wet season.
- The levels of DO, Temperature and pH were lower during the wet season compared to the dry season.
- The established monitoring Frequency will be able to capture the seasonal changes that occur in the river water quality and hence avail necessary information for formulation of appropriate policy interventions.
Regarding heavy metals, the following trends were observed:
- The concentrations of cadmium were below detection limit in all the three rivers in both dry and wet seasons.
- The contrations of lead was higher in the dry season compared to wet season implying contribution of lead pollution from anthropogenic sources.
- The levels of chromium were higher in the wet season compared to dry season implying high contribution of surface runoff to the chromium load in the rivers.
The folowing are key conclusions from the findings of the chemicals levels in Nairobi River Basin water:
- The levels of phoasphates and chlorides were generally higher during the dry season compared to the wet season impling the contribution of waste water discharges into the rivers.
- The concentrations of sulphates alternated from dry and wet season from one site to the other implying significant contribution of both waste water discharge and surface runoff.
Analysis of industrial chemicals PCBs and oil and grease showed the following conclusions:
- The levels of PCBs detected in dry season were higher than the wet season in all the three rivers water.
- The Concentration of PCBs in sediments were approximately 20 times higher that the levels detected in the water samples.
- The highest concentrations of oil and grease were measured in the dry season for all the three rivers.