Tokwe-Mukosi Dam, Zimbabwe

Zimbabwe, a South African country characterised by limited water resources and frequent droughts, experienced a significant improvement with the construction of the Tokwe Dam, Mukosi. The dam has created the country's largest artificial lake, with a capacity of 1.8 billion m³ of water, extending over 40 km in length. The main purpose of the dam is to irrigate around 25,000 hectares of farmland, promoting agricultural and agribusiness development in one of the country's most disadvantaged areas.

The construction is a reef dam with an upstream reinforced concrete waterproofing membrane. More than 90m high from the foundation, the dam has created a large basin thanks to its weir. The intake structure includes a 35m high tower with grates, which conveys water to a tunnel; the water is then released into the riverbed. Finally, there are two goblet spillways with discharge tunnels.

Ancillary works include an 8-kilometre access road, a stone and concrete earthfill cofferdam and five saddle dams with a clay core. In addition, a Plunge Pool was added to protect and safeguard the safety of the foot of the dam.

The project benefited from significant technological innovation improvements. These innovations can be summarised as the improved distribution of rockfill with three zones of differentiated grain size and the addition of an additional berm to ensure greater stability; the introduction of a plastic sheath in the diversion tunnel to reduce the risk of 'Hydrocracking'; the revision of the joints in the concrete membrane of the upstream face; and, as mentioned above, the creation of a Plunge Pool to protect the foot of the dam during operations.

The project faced several challenges, such as numerous interruptions due to the political situation in Zimbabwe. After work resumed in April 2011, it was necessary to train local workers and implement a strict work plan to meet deadlines, to the extent that the peak workforce exceeded 1,200 per month.

A widely recognised effort: in February 2014, during a period of exceptional rainfall, the dam proved its effectiveness thanks to the commitment and readiness of the staff, so much so that it received an award from the Institution of Engineers of Zimbabwe for the engineering innovations implemented in the project.