PROGRESS AT KAWARAU

Otago Witness, Issue 3756, 9 March 1926, Page 80

PROGRESS AT KAWARAU

BUILDING THE BIG DAM. (See photographs “Progress of the Dam at Kawarau Falls” in this issue.) As will bo seen from our series of photographs illustrating the progress in the construction of the Kawarau dam the engineers have had to continually meet changing conditions due to the rising ot the lake level. The lowest recorded level for 1925 w r as in the middle of the month of July, when the lake level had dropped to zero on the gauge, the lowest level recorded for many years. From that date the gradual melting of the snow on the high country of the Lake Wakatipu watershed caused the lake to rise, and by December, 1925, it had reached eight feet on the gauge —a rise of eight feet in a little les.; than five months. While this difference of lake levels between winter and summer is of annual recurrence it is governed by the amount ot snow falling in the winter and the time taken for it to thaw, and run off in the spring and early summer. This year has been a particularly abnormal one, as in addition to the melting snow the summer has been an unusually wet one. the rain waters adding t the volume of water draining into the lake and keeping it at a high level even after the major portion of the snow had disappeared. In constructing the dam the present engineers had first to complete the temporary trestle bridge in order to get their concrete and material to the far.sidi and at the same time push on with the completion of the first five piers and the fitting of the first four gates and superstructure. The building of the * fourth pier was greatly delayed owing to the amount of loose material which had to be excavated in order to get a solid rock foundation. In doing this work the rising waters of the lake necessitated the construction of cofferdams, and the pumping out of the site to enable the men to work. Tjje rock bottom was reached at eight feet below the level of the sill upon which the gates rest when closed. The next step after the completion oi this work was the diverting of the water from one of the main outlet channels oi the lake. This channel ran in the site of No. 10 pier. The diverting wingdam shown in the photograph is 25'’ feet long, and when completed had a depth of 12 feet of water on its upstream face. Since its completion the work of putting in the foundation of No. 10 pier has been going ahead steadily. Divers have been employed to clean away any debris lying on the solid rock bottom, and two con crete cofferdams, one across the upstream line, and one across the downstream line of the dam, are nearing completion. • This will enable the actual site to be pumped dry, and the pier and sill built When this is completed the preseni wingdam will be removed, ; :d the water allowed to run through the three fortv-foot gate openings on the south side of the dam in addition to the four gate openings now completed on the north ride of the dam. This will then enable the work of damming the channel at present carrying water through the sites of piers six ano seven to be gone on with, and the same procedure as adopted for the building of pier ten repeated. The time taken to complete the fore going will naturally depend largely upon the level of the lake, as every difference in lake level will mean p corresponding difference in the amount of material required for the diverting of these channels,