By 1955, approximately three-quarters of the work on the construction of the Inniscarra dam had been carried out. The power station foundations had been poured and work was in progress in the erection of the superstructure. The excavation of the tailrace was nearing completion. The temporary culvert or river diversion was sealed with concrete. A gate was lowered to close the upstream opening. The reservoir was filled in November 1956. The filling was regulated by a temporary sluice gate.

In case it would be necessary to lower the reservoir below the lowest level at which the turbines can operate, a 7-foot (2.1 m)-diameter circular culvert was built at present bed level in one block of the dam. The downstream end of the culvert was fitted with a conical dispersing valve, which can jet the water through it in a com¬paratively thin sheet over a large area of the stilling basin and so reduce the risk of erosion at the foot of the dam.

The tailrace, which is 60 feet (18 m) wide at invert, ex¬tends to a point approximately one mile downstream of the dam. To increase the available head on the turbine, the river downstream was deepened by about 10 feet (3 m). The excavation was done by 33 RB and 19 RB draglines working from both banks and dumpers disposed of the material. The soft material excavated was generally gravel and sand and the total quantity of this material was approximately 224,000 cubic yards (171,260 cb. m). The total quantity of rock excavated was approximately 4000 cubic yards (3060 cb. m).

The route of the tailrace was chosen to minimize rock excavation and for this purpose the ground along and adjoining the river was thoroughly explored by probing during site investigations. The probing indicated that rock was at or close to the surface of the riverbed over more than half the total length of the proposed tailrace. But, by departing from the course of the river, rock would not be met except at the upper end where it was unavoidable. By 1957, the construction of the superstructure of the Inniscarra power station was well advanced. At Inniscarra, the 4000 kW set was commissioned on 24 May and the 15,000 kW set on 21 August 1957. Early in 1958, finishing work and site restoration were substantially completed.

Economic benefit

The construction of the dams, roads and bridges necessitated by the Lee scheme, was of great benefit financially to the mid-Cork region and beyond. More than six hundred men were employed on the scheme. While some of the workers were recruited locally, men from all over Ireland flocked to the dam sites seeking employment. Some stayed to see the contract com¬pleted, while others left after a short time. They were not suitable or they found conditions too difficult. Carpenters were in great demand as much shuttering was needed during construction.