Engineers building the multibillion Thwake dam have embarked on the pioneering task of diverting a stretch of Athi River from its natural course to create a dry surface for excavating the ground.
The dam builders are constructing two mega tunnels as the alternative underground route for Athi before its waters are channelled to rejoin the original course to the Indian Ocean.
The huge tunnels, which are set to be completed by next March, are 700 metres long and have a diameter of 12 metres — meaning their size can accommodate an equivalent of a four-storey building.
According to project consultant David Kimingi, the two tunnels are designed to take up to 11,480 cubic metres of flowing water per second, and, therefore, able to withstand any form of flooding.
Diverting the river, he said, would enable the builders to carry out civil engineering works, including constructing the dam walls, water treatment works and hydropower generation, without difficulties.
In terms of the technology involved and the scope of works, the river diversion is a first of its kind in Kenya and a significant step to the success of the project because it paves the way for the next phase, which involves huge volumes of excavation works.
“The dam is being built across Athi River, so we can’t carry out construction work while the river is flowing, and that’s why we’re blocking it so that we can work on the current course when its dry,” Mr Kimingi told the Sunday Nation at the dam site.
He said the tunnels would in future be used for other purposes including discharging the dam water for hydropower generation, distribution to irrigate farms and spillways for compensation flow to sustain the aquatic lives downstream.
“Once we divert the river, we’ll excavate the dam axis until we get the desired rock bottom. We’ll then undertake ground treatment by grouting the dam foundation to make sure every crack is filled and watertight to avoid leakages,” he said.
Mr Kimingi said the dam is expected to create a vast reservoir and catchment area of 10,276 square kilometres once completed.
The dam — a Vision 2030 flagship project — is being implemented in four phases, including construction of an 80-metre high dam, hydropower generation component, water supply system and a final phase of irrigation farming on 40,000 hectares in Kitui and Makueni.
“With its 80.5-metre high wall and a 10-kilometre long backflow along both Athi and Thwake rivers, it will harvest a whopping 700 million cubic metres of water — making it the biggest reservoir ever built in Kenya,” he said.
It is designed to supply 150,000 cubic metres of piped water daily for domestic use, 35,000 cubic metres for the Konza techno city while the rest would be supplied to the adjacent towns in Kitui and Makueni, and irrigate farms downstream in the two counties.
“It’s certainly a giant project that will be a game changer in economically transforming the two counties as well as generating 23 megawatts of hydropower for the national grid,” Mr Musembi Munyao, the project supervisor, said.
Unlike other dam projects, which have been dogged by corruption scandals, the progress of the undertaking has so far excited both local community and top State officials, with hopes that it will be completed on schedule.
Buoyed by a smooth project take-off that saw families living in the area fully compensated and relocated, Water Cabinet Secretary Simon Chelugui says the construction is within schedule and that already 25 per cent of the works are done.
Mr Chelugui said the national government has spent Sh3.52 billion to compensate landowners at Sh180,000 per acre excluding houses and farm developments.
“I am happy the land acquisition process was concluded successfully. Out of the 1,792 families, only 24 are yet to receive their compensation cash because there are succession cases in court, but their monies are with the National Land Commission,” he said.
The contractor, China Gezhouba Group, has been on the site since June 2018 working round the clock to deliver the project in the stipulated 56 months.
The hitch-free compensation process was attributed to a sustained public awareness by the stakeholder committee overseeing the project and close collaboration between the government, local leaders and the contractor.
When the Sunday Nation toured the dam site, it was a hive of activity with excavation works involving heavy blasting of rocks underway.
The stakeholder implementation committee chaired by Makueni county commissioner Maalim Mohammed meets at the dam site weekly to monitor the progress of the project and solve any emerging challenges.
Mr Mohammed said he had tasked chiefs to engage the families with land wrangles to find alternative dispute resolution mechanisms to ensure the land compensation process was not delayed.
“The process involved meticulous negotiations and consultations with local leadership. We are happy that this project took off without corruption scandals that rocked similar projects in other parts of the country,” he said.
According to Mr Paul Makuu, chairman of Thwake landowners committee, the local community was looking forward to tapping the social and economic benefits of the project.
“The compensated families have been able to acquire land elsewhere and even build better homes for themselves; while others have established various businesses in line with the project value chain,” Mr Makuu said.
Speaking through a translator, China Gezhouba Project Manager Chen Bi Zhan said they will continue operating in line with the Kenyan laws and cooperate with the community to ensure smooth running of the project.
China Gezhouba Group has recruited more than 942 people — 80 Chinese expatriates while the rest are drawn from Makueni (500), Kitui (150), Machakos (100) as well as other parts of the country.
The Kenyan government and the African Development Bank are jointly funding the project: the government is financing two thirds and donors the remaining amount.