Water first flowed through the tunnel on 24 Dec 1926. The tunnel is described in item 164.g of that year's PWD Annual Report:
South Tunnel.—This Tunnel was ‘holed’ on 4th July or about 19 months after driving was commenced, at a point 2,300 ft. from the South end and 2,350 ft. from the North end.
The rock throughout was of excellent quality and no lining has been required. It is possible however that atmospheric influence on the rock way in the future have a softening effect and that a certain amount of lining may be found necessary.
The Tunnel is of the same sectional area as the North Tunnel and has an average gradient of 1 in 2,800. The invert has been graded smooth with a minimum of 3" cement concrete.