Thwake Dam: AfDB Backs Final Works as First Phase Reaches 94.2% CompletionThwake Dam: AfDB Backs Final Works as First Phase Reaches 94.2% Completion

The African Development Bank (AfDB) has backed the remaining works at Thwake Dam, on the Makueni-Kitui border, with new financing, following an additional KSh 10.6B ($81.58M) package that closed the gap which had slowed construction. The size of the latest commitment was not given, but the dam stood at 94.2% complete on Thursday, with water impoundment targeted for the end of January 2027 and commissioning for April 2027.

What is still to be built

The first phase is the dam itself: an 80.5-metre structure at the confluence of the Thwake and Athi rivers, designed to hold 688 million cubic metres of water across a reservoir of about 9,217 acres. Two jobs remain, the concrete face slab and a bridge linking Makueni and Kitui counties.

Water Secretary Samuel Alima of the Ministry of Water Sanitation and Irrigation has confirmed that the contractor has resumed work on the concrete face panels and has started the bridge. Both target dates depend on those works finishing on schedule.

The bank's director for water and sanitation, Mtchera Chirwa, said the lender would see the project through. "As a Bank, we will ensure the project reaches completion and achieves the benefits," he said, adding that the AfDB is also discussing financing for downstream infrastructure.

Who pays, and what is not yet known

The first phase is estimated at KSh 42.4B ($326.31M), shared between the AfDB and the Kenyan government. In June 2026 the bank approved €68.4M (KSh 10B or $76.96M) for the phase, alongside €15M (KSh 2.2B or $16.93M) in counterpart funding from Nairobi.

The original design priced the full four-phase programme at 487 million units of account, an AfDB accounting unit that moves with currencies. No original budget in shillings was published alongside the latest announcement, so Mwenendo cannot yet compare the final cost with the plan. That comparison will matter once the dam is filled and phase one is closed out.

Why the later phases matter to households

A full reservoir does not by itself put water in taps. The wider programme has four phases: the dam, hydropower, water supply and sanitation, and irrigation. Only after the later phases are financed and built would the project deliver up to 150,000 cubic metres of treated water a day to about 1.3 million people in Makueni and Kitui and to Konza Technopolis in Machakos County.

The power component is a 20-megawatt hydropower plant. As Mwenendo earlier reported, peak electricity demand rose from 2,241MW in September 2024 to 2,549MW in July 2026, so 20MW would add only about 0.78% of the current peak. The irrigation scheme, planned to cover up to 40,000 hectares, and flood control on the Athi River are the larger prizes for farmers.

Mwenendo earlier reported on how electricity and water grew 7.7% in the second quarter of 2026, which shows the demand that new supply would meet.

The test between now and January

The next marker is impoundment at the end of January 2027. If the face slab and bridge are finished by then, commissioning in April 2027 stays within reach; if they slip, the dates move with them. The financing for phases two to four is the gap to watch, because the bank says talks on downstream works are only under way.