Matahina Dam Elver Pass Development, Installation, and Fisheries Aspects


W Gibson
J Boubee




water supply, tailrace, spillway, pipes, channel, juvenile, migration


None supplied. From summary: The pass componentry and location on the structure which had been determined prior to the 1990/91 elver season, was installed in early 1991. Between the end of this season and the 1991/92 season refinements to the pass were made to both security and function. Fluctuating lake levels, along with installation of automation equipment showed the demand for a second water supply to combat loss of water. The entry to the pass at the tailrace on the left hand side of the power house has attracted elvers. Some elvers also climb the spillway step and wall and continue on up the pass. However, elvers still gather at the transformer cooling water outlet on the right bank, and also on the draft tube stoplog platform. Elvers have no difficulty in climbing the troughs and pipes and drainage channels, and hence the pass is readily passable to these juvenile fish, and is working as intended. The success overall will be to have the pass without competition from the other collection points around the station. Several hundred climbing Galaxiid juveniles (whitebait) and at least 15,000 elvers used the pass in the summer of 1991/92. The elver migration began in mid January 1992, peaked on the full moon in January and ended soon after new moon in early March. Maximum migration occurred around midnight and was lowest during daylight hours. The number of elvers using the pass could have been several fold higher had the water supply to the pass been reliable.

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