Six sluice gates in the upper part of the concrete dam wall together form the spillway though which water is released into the plunge pool in order to manage the reservoir water levels.
Concrete exposed to water expands. This minimal expansion is natural and is expected. However, over a long period of time, the expansion could affect the smooth opening and closing of the gates and possibly cause the spillway gates to jam.
The Zambezi River Authority has monitored the performance of the dam infrastructure in accordance with the Standing Operations Procedure since its impoundment in 1958. This routine monitoring and management of the spillway system has resulted in the recommendation that the six spillway gates be refurbished to ensure their continued full operability in the long term. In addition, external consultants who undertake five-yearly inspections of the dam’s infrastructure, have also recommended that a movable back up gate be installed on the upstream side of the dam wall as an additional safeguard to be used should any of the gates jam.
Why refurbish the spillway?
The spillway refurbishment will mitigate potential risk to the operation of the spillway, will enable the Zambezi River Authority to continue to manage the water levels in the reservoir effectively and guarantee the safety of the dam for many more years.
What does the refurbishment entail?
Following the procurement and documentation phase of the spillway refurbishment, the works will include fabrication; site mobilization; preparatory works on the sluice gates; the installation of a coffer dam to allow sluice works in the dry; works in the sluice; spilling and remobilization; the installation of the gantry crane, beams and rails and commissioning.
How long will the spillway works take?
The spillway refurbishment is expected to take approximately five years. The procurement of the contractor to undertake the spillway works is underway with the appointment expected to be made towards the end of 2018 or early in 2019.
Who is funding the spillway refurbishment?
The works will be financed by the World Bank, the African Development Bank and the Swedish government through loans and grants to the Republics of Zambia and Zimbabwe.
What environmental and social impacts will the spillway refurbishment works have?
The works will take place on the dam wall and will have minimal negative impact on communities and the environment in the region of the dam. No people will be displaced or resettled as the works will be undertaken on the dam wall. The flora and fauna in the vicinity of the dam and downstream of the works will not be affected by the works. The quality and volume of water in the lake and the river downstream of the plunge pool will not be affected by the spillway refurbishment.
Will the plunge pool reshaping works affect hydropower production?
The water used to generate hydropower is diverted from the lake into the power stations upstream of the dam wall and. The volume of water available for power generation will not be affected by the spillway works.