Is ageing Kariba Dam Wall doomed?

Source: Is ageing Kariba Dam Wall doomed? | Herald (Opinion)

At Kariba Dam, a strict regime of monitoring and maintaining the dam has been followed since completion of the dam construction

Sifelani Tsiko The Interview

A new study by the United Nations University Institute for Water, Environment and Health warns that ageing dams pose a growing threat to public safety due to the potential for dam failures, over topping or leaks. Kariba Dam, a 128-metre-tall dam which stores 180 cubic kilometres of water straddling Zimbabwe and Zambia on the Zambezi River is cited as an example in the report. In this report, our Agriculture, Environment & Innovations Editor Sifelani Tsiko (ST) speaks to the Zambezi River Authority chief executive Engineer Munyaradzi Munodawafa (MM) on the findings of the report and how the authority is working to minimise the potential threats to human safety and the environment posed by the Kariba Dam.

ST: Large-scale dams built in the 50s and 60s on the African continent used for irrigation, power generation or flood control are coming up to a critical age, according to a new report by the UN University Institute for Water, Environment and Health. Lake Kariba Dam shared by Zimbabwe and Zambia is an example. What is your general comment about the concern around ageing dam infrastructure?

MM: There are dams in the world dating back to more than two centuries that continue to be safely operational to date. Irrespective of when the dam was built, it is a structure which requires attention to ensure its continued safe operation. The key in sustaining such structures lies in the provision of resources to address any identified safety concerns. The Zambezi River Authority just like other large dam operators around the world has progressively adopted the international guidelines set by the International Commission on Large Dams (ICOLD). At Kariba Dam, a strict regime of monitoring and maintaining the dam has been followed since completion of the dam construction.

We have in place a Dam Safety Programme that is strictly adhered to. Several instruments were installed during construction and others in response to technological advancements. Instrument readings have been collected and continue to be collected as scheduled since impoundment of the dam. The collected data is analysed to detect any early signs of abnormal behaviour. If these are detected, cause and effect are determined after which appropriate remedial measures are prescribed and corrective works instituted. This methodology keeps the dam safe.

ST: What is the current state of the Lake Kariba Dam wall? Is it of major concern in any way?

MM: The analysis of the instrumentation data collected from the end of construction shows that the dam wall is safe. There are no major concerns regarding the safety of the Kariba Dam. The current state of the dam wall has been established, through close adherence to the principles and guidelines of an effective dam safety programme, to be in a sound and safe condition. Remedial measures aimed at further enhancement of the long-term safety and reliability of the Kariba Dam are currently under implementation through the Kariba Dam Rehabilitation Project (KDRP) thus giving an added assurance of effective management of the identified dam-safety concerns. These concerns, as have been stated before, only concern the plunge pool and the spillway gates and not the wall itself as has been speculated by some media houses.

ST: What efforts and investments are being made to ensure the dam wall is secure and stable for many generations to come?

MM: The implementation of the Kariba Dam Rehabilitation Project (KDRP) is a major investment that was adopted by the two Contracting States to secure the long-term safety and reliability of the Kariba Dam and appurtenant structures. The one component relates to the Refurbishment of the Spillway Gates. The concrete supporting the movement of the maintenance gates together with the associated steel guide rails are being replaced to meet current design standards. This work is being carried out by a consortium of GE Hydro and Freyssinet International of France. The works are financed through loans and grants from the World Bank, the African Development Bank and the Swedish Government. The second component of the rehabilitation works involves reshaping the plunge pool immediately downstream of the dam to allow reduction of turbulence when spilling which will limit erosion of the riverbed in the direction of the dam foundations. The works are being carried out by Razel Bec, a French Engineering Company. The works are financed from grant aid from the European Union. An amount of US$294 million was mobilized for the project.

ST: When can a major dam be deactivated? What could be the major reasons for this?

MM: A major dam would need to be “deactivated” or decommissioned whenever it gets to a stage where the defects observed in its structural integrity and operational safety reach such magnitudes that remedial measures aimed at correcting them become no longer cost-effective. Some of the major reasons for decommissioning include: a) A dam can be decommissioned if pending failure of the dam has been identified. This normally arises from prolonged neglect of essential maintenance and remedial measures for observed safety deficiencies. b) A dam can also be decommissioned to meet legislation of the particular country that may require decommissioning to address environmental concerns or issues. c) A dam can also be decommissioned following an emergence of un-foreseen safety risks possibly linked to force majeure events such as earthquakes. In an event such an action is desirable, a programmed decommissioning is instituted in order to prevent uncontrolled release of water which may put the downstream communities at risk of flooding.

ST: The maintenance of dam wall infrastructure requires a huge amount of capital. What do you think needs to be done by responsible governments to mobilise resources and secure Lake Kariba Dam?

MM: While the Authority was strategically designed to be self-sustaining, through water-sales for power generation and capable of self-financing through these revenues to carry out routine maintenance of the Kariba Dam on an annual basis, costly ventures call for extra support from cooperating partners through either targeted national budgetary allocations or state supported borrowing from private sector or international financing institutions (IFIs). The Governments of Zambia and Zimbabwe approached the European Union, World Bank, African Development Bank and the government of Sweden through a combination of grants and loans in order to implement remedial measures required to address the identified safety concerns at KDRP.

ST: Given the ongoing rehabilitation of Lake Kariba wall, for how long will the dam continue to be safe and stable?

MM: The current rehabilitation works are not an end unto themselves. These works only address particular safety concerns mainly the ability of the dam to pass floods. Safety monitoring has to continue to allow identification of occurrence of any abnormal or unacceptable behaviour and prescription and implementation of the appropriate remedial measures. This will ensure the continued safe operation of the dam for several decades to come.

ST: What do you think needs to be done to allay fears of a dam collapse?

MM: The Authority will continue to disseminate information to the public regarding the activities that the Authority is undertaking to ensure the safety of the Kariba Dam.

 ST: Looking into the future, what will be key to the continued stability of the Lake Kariba wall?

MM: Continued monitoring of the dam and immediate implementation of corrective measures to the identified safety concerns.