Construction of twin trunk Sewer Lines
The Trunk Sewer Project is a flagship infrastructure intervention being implemented under the Nairobi River Regeneration Programme (NRRP), with the Nairobi Rivers Commission (NRC) playing a central coordinating role among national and county government agencies, implementing institutions and development partners. The project is designed to address longstanding wastewater management challenges that have significantly contributed to pollution of the Nairobi River system.
Background and Rationale
For decades, rapid urbanisation, population growth and unplanned settlements along the river corridor have placed immense pressure on Nairobi’s sewerage infrastructure. The existing trunk sewer, originally designed for much smaller urban loads, became overstretched and prone to frequent overflows, leading to direct discharge of untreated wastewater into the river. This situation undermined environmental health, public safety and the overall objectives of river restoration.
In response, the Government initiated the construction of a new reinforced concrete box culvert trunk sewer as part of the broader river regeneration agenda. This intervention aligns with the NRRP’s goal of restoring the ecological integrity of the river while improving urban sanitation and resilience.
Scope of Works
The Trunk Sewer Project involves the construction of a high-capacity trunk sewer to replace the old, overloaded system and significantly enhance wastewater conveyance. The new trunk sewer is seamlessly integrated with existing transverse sewers to ensure efficient collection and transportation of wastewater to treatment facilities.
The trunk sewer runs along the Nairobi River riparian reserve, covering a cumulative distance of over 27 kilometres across three main sections:
Nairobi River – Naivasha Road to Museum Hill: approximately 10.7 km
Kirichwa Kubwa River – Dagoretti to Chiromo, at the confluence with the Nairobi River: approximately 9 km
Nairobi River – Museum Hill to Dandora Waterfall: approximately 16.7 km
As part of the works, the sewer crosses key transport corridors, including Outer Ring Road, Murang’a Road, Uhuru Highway and Naivasha Road. All road sections affected by construction will be reinstated to their original condition, with traffic management measures applied to minimise inconvenience to road users.
Complementary Infrastructure
Beyond the sewer works, the project incorporates complementary infrastructure aimed at improving accessibility and safety along the river corridor. These include the construction of footbridges and motorized bridges, which enhance connectivity for communities while supporting orderly movement across the river in line with urban planning and environmental standards.
NRC’s Coordinating Role
As the coordinating institution for the Nairobi River Regeneration Programme, NRC provides strategic oversight, facilitates inter-agency collaboration, and ensures alignment of the Trunk Sewer Project with broader environmental, social and urban renewal objectives. Through this coordination, the project contributes not only to improved sanitation but also to cleaner rivers, healthier communities and a revitalized Nairobi River ecosystem.
The Trunk Sewer Project represents a critical step in transforming the Nairobi River from a pollution channel into a restored urban river that supports sustainable development and improved quality of life for residents.
