Bumbuna Hydropower

The project site is located near Bumbuna Falls on the upper reaches of the Seli/Rokel river, about 200 km northeast of Freetown. The Seli River has a high flow rate in the wet season and a very much lower flow in the dry season, which is typical of the rivers of Sierra Leone.

The project was carried out by Studio Pietrangeli for the Government as part of a programme to implement electricity distribution in all urban and rural areas of the country: the exploitation of its reservoir has led to a significant improvement in the national energy situation with a generating plant of 50 MW, in a country where the electricity supply – where present – was weak and inconsistent.

Bumbuna dam is an 88 m high asphalt concrete faced rockfill structure with a crest length of 440 m and a volume of approximately 2.5 million m³ of granitic rockfill. The upstream face is covered with an asphalt concrete membrane.

Two 31.6 m diameter morning glory type spillways have been constructed upstream of the dam, one on each abutment, which will discharge into the multipurpose tunnels. The spillways consist of reinforced concrete towers approximately 36 m high which continue as shafts until meeting the tunnels.

The two 9 m diameter, concrete and steel lined, multipurpose tunnels were constructed through both the left and right dam abutments, each with a length of approximately 620 m. Both tunnels are being used for diverting the Seli River around the dam site during construction.

During plant operation, the left tunnel is utilized as the primary spillway. The right tunnel functions as an auxiliary spillway and as a power tunnel when the radial gate installed at the downstream end of the tunnel is closed.

A surface powerhouse is located at the downstream toe of the rockfill dam. Penstocks and draft tubes have been installed for two generating units. Excavation has been made to allow future expansion for two additional units.

The design and engineering process was particularly long and complex, due to the various difficulties encountered during the design, financing, tendering and execution of the works, including the aforesaid civil war.

While the BHP will help to resolve the immediate supply shortages, a clear strategy is needed for the future expansion of power generation capability: the Bumbuna project can serve as a catalyst and model for the country to introduce it to sustainable development.