Kariba Dam rehabilitation progressing well

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THE Zambezi River Authority (ZRA) is progressing work at the Kariba Dam Rehabilitation Project (KDRP).

In a January 19 update, the authority said that ongoing KDRP works comprise two components, namely reshaping of the plunge pool and the refurbishment of the spillway gates.

The project aims to enhance the structural integrity of the Kariba dam wall for efficient power generation for the benefit of Zambia and Zimbabwe and the Southern African region as a whole.

The reshaping of the plunge pool, which started in May 2017 and is now 60% complete, involves excavation of the rock in the pool in order to increase the pool volume and minimise erosion which can undercut the dam foundations.

These works, which are being undertaken by French civil engineering construction company Razel Bec, are expected to be completed before the end of 2024.

The work comprises the construction of a downstream cofferdam to enable the blasting and the excavation of an estimated 300 000 m3 of rock from the downstream end and north and south bank sides of the pool in the dry, the ZRA said.

“This will create a new pool profile that will dissipate the energy of the water jets from the flood gates to non-erosive levels, as well as reduce turbulence by guiding the spilling water in the downstream direction, thereby avoid any backward erosion towards the dam foundations in the process.”

Meanwhile, the spillway refurbishment works, which a consortium comprising GE Hydro and Freyssinet International started in September 2019, aim to ensure free movement of the gates used to shut the upstream opening of the flood gates during maintenance of the flood gates.

An emergency gate, to be used in emergency situations such as where a gate fails to close after spilling, together with a lifting crane will be fabricated and installed. The hoisting equipment for the spilling gates will also be renewed.

The activities are expected to be completed in 2024.

“The spillway refurbishment contractor is currently working on the establishment of construction site facilities as well as the fabrication of the electro-mechanical equipment required for execution of the works through specialist sub-contractors,” the ZRA commented.

“The manufacturing progress details are two-fold. Firstly, the manufacturing of stop logs is being done in China by the subcontractor Sinohydro Bureau 8. The works are progressing well and delivery of the first components is expected by mid-February 2021. Secondly, the manufacturing of the needle cofferdam, which is required to isolate the works, is being undertaken in Poland, by the subcontractor APC Presmet.”

The ZRA will maintain the 30-billion cubic metres of water allocated for power generation operations at Kariba for 2021, shared equally between Kariba North Bank Power Station and Kariba South Bank Power Station.

The allocation is based on the Meteorological Authorities’ projections of normal to above normal rains for the ongoing 2020/21 rainfall season.

“In line with the seasonal forecast released by the twenty-fourth annual Southern Africa Regional Climate Outlook Forum in August 2020, the bulk of the Southern African Development Community region in general and the Kariba catchment in particular, is poised to receive normal to above-normal rainfall for the first quarter of 2021,” the ZRA pointed out.

Between December 22 and January 18, the lake levels increased by 0.40 m, or 0.08%, which brought the overall lake levels to 3.21 m above the minimum operating level (MOL) of 475.50 m.

“This 3.21 m above the MOL translates to 14.55-billion cubic metres of usable water storage currently in the lake.”

“It is very encouraging to note that the lake levels, which should generally be in a decreasing trend at this time of the year, have continued to record a steady rise owing to increased rainfall activity on and around the lake, leading to a lake level of 478.71 m, with 22.45% live/usable storage on January 18.

“Last year on the same date, the lake level was lower at 476.71 m with 8.36% usable storage.”