D.—l.

To enable repairs to be made, a coffer-dam was built of timber cribs, loaded with sand-bags, and sealed with canvas. When dewatered it enabled repairs to be carried out to the area of floor and side lining that had suSered damage, and when this work was complete, the tunnel-gates were closed, to allow the normal lake-level to be restored, the lake having been maintained 10 ft. below normal during the repairs. Normal lake-level was reached by the 11th September. On the 20th September further leakage developed. Investigation disclosed that this was coming from the floor of the headrace from a point outside the area that had been covered by the coffer-dam, and had been due to the previous leakage disturbing the drainage-pipe system and undermining the floor lining, allowing it to subside and crack. This leak was temporarily staunched with tarpaulins and eventually sealed by grouting the porous layers round the damaged section. All these repairs were completed by the end of January, 1933. To prevent a" recurrence of this trouble, side drains have been cut on both sides of the headrace behind the lined banks. These drains will carry off any heavy flow of water during rainstorms, so that the system of 9 in. drains cannot be overtaxed. Diversion Tunnel. —Work in the diversion tunnel in connection with the gate installation was resumed after January of this year. The plate work on the down-stream face of the existing gates was strengthened by the addition of heavier angles, extra anchor bolts, and welding. All construction joints in the concrete tunnel lining up to the springing of the arch have been sandblasted and cementgrouted with the guniting machine. The installation of the emergency gate as part of the works recommended in the Hornell report was commenced in March, 1933. The work involved breaking out 226 cubic yards of old concrete, and the placing of 800 cubic yards of new concrete, in addition to the erection of gate and frame. The frame, the lining downstream of the gate, and the lifting-gear at the head of the shaft were all in place by the end of June, and a start had been made with the erection of the gate itself. The total weight of steel involved is 300 tons, of which 200 tons had been erected by that date. Relief Work. During the year relief work with funds provided by the Unemployment Board was undertaken to give employment to sixty men. Some 20,000 cubic yards of batter trimming, adjoining the headrace, was'done, as well as the formation of 2 miles of 6-ft.-wide walking-roads. In addition, 100,000 trees have been planted on an area of 250 acres of the Government land at Arapuni. Horahora Power Scheme. —The work of protecting the old river-channel below the spillway weirs and gates was resumed in January last. The work, which involved 2,270 cubic yards of excavation and the placing of 1,530 cubic yards of concrete, was completed during the rest of the year. Waitaki River Power Development. D am . The most important work now in connection with the completion of the dam is the building of that portion in the river on the Otago bank. To enable this to be done a coffer-dam similar to that erected on the Canterbury bank has to be built. It would have been of considerable benefit to the progress of the whole scheme if this coffer-dam could have been built during the winter of 1932, but the necessary restriction of financial appropriation made this impossible. In March of this year, however, a start was made upon this coffer-dam. A succession of small floods has somewhat delayed the work, making the driving of the sheet piling in the deep swiftly-running water a matter of considerable difficulty. By the middle of June, however, the coffer-dam was closed and pumping out was commenced. Excavation of the foundation is now in full swing. The coffer-dam on the Canterbury side was entirely dismantled to increase the available waterway and minimize the risk of flood damage. The capacity of the temporary sluices in the Canterbury section of the dam is insufficient, however, to pass the usual floods anticipated in the autumn without overtopping the Otao-o coffer-dam, and therefore every effort will be made to complete the latter section of the dam before the season of peak flood. At the same time, all the remaining work in the dam and powerhouse that is liable to be submerged by high floods will be pushed on to completion before the Otago coffer-dam is dismantled. As mentioned in my last annual report, the cut-off wall in the river on the Otago side was commenced by tunnelling methods under the river. Working from a shaft near the Otago river-bank tunnels were driven, one above the other, to meet similarly excavated tunnels from the Canterbury side. The concreting was done in successive " lifts " of about 6 ft., and the last lift was built to a level as close to the bottom of the river as was deemed expedient and consistent with safety. Now that the coffer-dam is built, the concreting of the cut-off wall should be completed by the end of August to the floor of the inspection gallery. The lowest levels of the cut-off wall in the river section are 80 ft. below the ordinary river-level. By a combination of tunnelling and open-trench methods the cut-off wall along the powerhouse and Otago end of the dam has been completed to the gallery-floor level, with the exception of a length of about 30 ft., which should be finished by the end of August. The walls and roof of the inspection gallery have been constructed for a length of 235 ft., and a further 280 ft. is expected to be finished by the end of September. The 260 ft. length that lies in the Otago coffer-dam will be concreted in conjunction with the concreting of the dam. The total excavation for cut-off wall to date amounts to 17,760 cubic yards, of which 8,000 were taken out during the year. The total concrete in the cut-off wall placed to date is 7,300 cubic yards, and of this 4,900 were placed this year. All the concrete placed in the dam proper this year has been in the spillway section between the Otago riverbank and the power-house. A length of 400 ft. has been concreted to within 20 ft. of the crest. By October it should be finished to crest-level. The concreting programme on the dam for the year had to be limited to suit the financial provision, but owing to a reduction in unit cost it was possible to place more concrete than had been anticipated. The amount placed for the year was 39,740 cubic yards. A total quantity of 104,300 cubic yards has now been put into the dam.

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