Kashimbila Hydropower Station, Nigeria

In order to meet the country’s power generation needs the Nigerian government embarked on a policy to increase the hydropower generation capacity of the country.  

Aurecon was first appointed to carry out a technical feasibility study of the spillway at the Kashimbila Dam. This was followed by appointments to carry out the detailed design of the dam, a technical feasibility study of the hydropower station and eventually the detailed design of the hydropower station.

The scope of Aurecon’s services included the design of all engineering disciplines, such as civil, structural, hydrological, geotechnical and mechanical for the detailed design of the dam, outlet works and hydropower station. Aurecon also provided project management services and advice for the appointment of the hydro-mechanical and electro-mechanical suppliers. 

The preliminary design was done for a dam with a storage capacity of 200 million m3. A 500 metre wide chute spillway with a long return channel to the river was incorporated on the southern side of the dam. The storage capacity was subsequently increased to 500 million m3. This pushed the spillway into the foothills of the surrounding mountains, which increased the excavation volume too far beyond that required for the embankment. Aurecon modified the overall dam design to a composite dam with the spillway located close to the river channel thus minimising on the excavation for both the approach and discharge channels.

Aurecon also reviewed the flood hydrology and flood attenuation within the dam basin which reduced the design flood, thus once again leading to a more economical solution. 

The cost of the river diversion works were also substantially reduced by replacing the 136 metre long diversion conduits of the original design by 25 metre long diversion culverts through the bottom of the spillway weir.

The main challengers were related to the lack of data in the hydrological and geological studies as well as the project location in the extreme south-eastern part on Nigeria, which required long travel times on very poor roads. 

The hydropower station was initially designed with an installed capacity of 18 MW, however, following the detailed hydrological modelling and yield analysis carried out by Aurecon, a 40 MW installed capacity was recommended, which was accepted and implemented.

Aurecon’s input on this project led to a more economical design of the dam and an increased installed capacity for the hydropower station.