A piling rig was on location for piling the foundation in readiness for tunnel drilling. The mechanical tool is mainly applied to drill in homogeneous. Besides drilling in sandy soil, rock, clay or silt areas it is alsoused to cast-in-place piles, diaphragm walls, and foundation reinforcement.
Located at the upstream of Aberdare Forest, the Collector Tunnel is designed to increase water supply in Nairobi County with a capacity of 140,000 m3 of water per day. It is designed to solve water problems in the city and increase water supply in satellite towns.The KES6.8bn water project received criticisms in 2016 from local residents and politicians who said it was a secret project by the government that threatens their livelihood and environment. However, Athi Water Services Board (AWSB), the implementing state agency refutes these claims and providedus with an update and clear facts on the project.
Speaking to Kenya Engineer when we paid him a courtesy call led by the Kenya Engineer Editorial Board Vice Chairperson Eng. Francis Ngokonyo, Eng. Malaquen Milgo the Chief Executive Officer of AWSB said; “This tunnel is designed to abstract part of the flood water, when flooding occurs from three rivers Gikigie, Irati and Maragua and to quickly fill up Ndakaini dam. Once the dam is full, no more water is drawn from the three rivers until the designed dam drawdown is achieved.”
“The Collector tunnel is designed to be perfectly lined to prevent ingress of the ground water into the tunnel.The tunnel will therefore not affect ground water system in any way. The tunnel construction technology is not new and has been used widely especially in developed countries during the construction of roads, railways and inter-basin water transfer systems without any effects on ground water systems,” he stated.
Murang’a County is already a host to several tunnels. One is a 4km tunnel constructed in the 90’s to convey water from Ndakaini dam to Chania River under the Third Nairobi Water Supply project. No negative reports or impact have been recorded to date in terms of ground water ingress even though the tunnel wasn’t fully lined. The other tunnel is for hydropower generation. In this tunnel, 80 per cent of its surface is not lined but is excavated.
Inquiring on when Phase 1 will be completed, he said “By around April 2018, we hope to have completed the water intakes as the Chinese contractor, China Ghezouba Construction Company (CGCC) has now moved to Ikanju. We therefore expect sufficient water supply at Ndakaini Dam to enable us have another outlet at Kigoro where we are building a new treatment plant with a capacity of 140,000 m3 per day. This is expected to be complete by the year 2019.”
Speaking of challenges faced in carrying out the project, Eng. Milgo observed that the major issue is the misconception that the project would dry up rivers, affect underground water and existing water aquifers.“Tunnels have been used in other places and people need to be aware that water is a national asset rather than a county asset. Secondly, complains arose from the county residents and local authorities without having enough information on the project, adequate consultations hadn’t been done by then in these areas. We have invited Murang’a residents for a forum in January 2015, other engagements have also been done to get people’s opinion on the project. Therefore, as a Board we have done enough consultations and engagements on this project,” he responded.
He continued, “Another challenge is the physical impact of blasting the rocks when building the tunnel.The tunnelcan’t be compared to a quarry, it is in form of a tube therefore; if you must blast there has to be controlled blastingaffecting a very small portion of the tunnel. What the Chinese are using is the road header machine, which is simpler than a Tunnel Boring Machine (TBM).”
TBM excavates tunnels with a circular cross section through a variety of soil and rock strata. They may also be used for micro tunneling. They can bore through anything from hard rock to sand. While a road header is a piece of excavating equipment consisting of a boom-mounted cutting head, a loading device usually involving a conveyor, and a crawler travelling track to move the entire machine forward into the rock face.
According to Nairobi Water master plan study, Nairobi will require 1.2 billion litres of water daily by 2035. The overall goal is to ensure reliability and security of water supply for Nairobi and Satellite Towns.
In conclusion, the government is gearing up for construction of various water projects around the country in a bid to deliver a solution to the perennial water shortages facing different parts of Nairobi and other regions that has been attributed to population growth and climate change.
First, the Ministry of Water and Irrigation, Nairobi County and Athi Water plans to commit KES100 million each to cater for the construction of 40 boreholes to offer above 40,000 cubic meters of water per day. Secondly is the implementation of the Kenya Integrated Water Sanitation and Hygiene(KIWASH) project, a flagship project to support 9 Counties of Kitui, Makueni, Nairobi, Migori, Nyamira, Kisumu, Siaya, Busia and Kakamega at $50.9million within a five-year period. There is also an ongoing GroundwaterExploration and Assessment Projectthat isgeared toward exploring and mapping out the groundwater potential in selected regions of the country.