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Temporary coffer dams were installed and a section of the canal dewatered in January to allow European specialist contractors to install a lining to solve long-standing issues with leaks, dating back to the 1970s.
The 26.5km-long canal links the Tekapo A and B powerhouses owned by Genesis Energy, and Genesis public affairs manager Richard Gordon said phase one of the $150 million repair programme was completed ''at a good pace'', thanks to a long period of good weather.
''There has only been one day affected by rain, which has been very fortunate for us.''
Exterior work would continue for the next two weeks, while the temporary dams were taken out and water waspumped back into the canal.
Both the canal and the majority of power generation facilities would be operational by the middle of this month, he said. The canal has a power station at each end - Tekapo A and Tekapo B.
Mr Gordon said Genesis Energy had been ''managing'' the level of Lake Tekapo during the repair work, and the lake was expected to have risen to its maximum operating level by the time the canal reopened.
Further work to reline a second 2km stretch of the canal at the Maryburn fill and improve the ''seismic resistance'' of the Maryburn earthen dam structure would take place over a 14-week period next January.
He said bridges crossing the canal would be strengthened as a part of repair work.
''The whole project is about future-proofing the canal so it provides good service for the next 50 years,'' he said.