Situated  just outside Ilorin, Kwara State capital city, Asa River Dam was constructed by Julius Berger Nigeria PLC in order to increase the supply of potable water by approximately 50,000 cubic metres per day, to the towns within the state.

Asa River Dam consists of three sections: a 400m long earth fill dam, a 150m long concrete gravity dam and a lateral earth dam with a length of 160m. The earth fill dam is 26m high above the bottom of the Asa River and has a width of 150m at the dam foot and of 5m at the crest. The concrete gravity dam is 20m high and has a width of 12m at the foot and of 3m at the crest. The lateral earth dam is 6m high and 23m wide at the foot.

Considering the size of the Asa River’s catchment area, the 60 meter wide spillway was designed for a volume of 1,300 cubic metres per second. A 65m long weir bridge was built over the spillway. During the design phase, Julius Berger Nigeria PLC proposed to raise the height of the spillway by one metre. This resulted in an increased dam capacity of up to 44 million cubic metres.

In order to obtain a better smooth and dense surface, prefabricated concrete units were used for the construction of the downward side of the spillway. These units served as formwork for the concrete of the weir. For economic reasons and to reduce hydration heat to a minimum, waterproof concrete only 1.0 metre thick was used for the construction of the gravity dam on both the upstream and downstream side.

Unreinforced concrete was used for the core. A drinking water treatment plant with a capacity of 2,300 m³ per hour was built with precast concrete units. The project also included two 40m diameter elevated water tank with a storage capacity of 10,000 m³ each and one 29m diameter elevated pre-stressed concrete tank. A total of 300,000m³ of dam material, 36,000m³ of concrete and 620 tons of steel were used for this project.

Dam Usage

The purpose of the dam includes improvement of water supply to Ilorin and other towns and settlements along the river system as well as irrigation, fisheries and livestock development and recreation.