Early warning

Ruapehu Bulletin, Volume 10, Issue 485, 11 May 1993, Page 9 (Supplement)

Early warning

Early warning systems to detect volcanic activity play a vital role in protecting the Taupo catchment from acidic water and slurry from Mount Ruapehu. Two lahar early warning systems are operated by ECNZ as part of the Tongariro Power Scheme. Lahar is acidic water and slurry associated with volcanic activity. The early warning systems operated by ECNZ ensure such material doesn't end up in the important Taupo catchment. "There are two lahar systems on the Tongariro Power Scheme," said Denis Drinkrow, production manager at the ECNZ Tokaanu Hydro Group. "One on the eastern slopes and the other on the north-western slopes of Ruapehu. They indicate discharges from the crater lake or any volcanic activity from around the range, particularly on the sides of Ruapehu." The early warning devices include probes in rivers that check for acid build-up and floats that detect sudden increases in river-flows. Should the equipment find something out of the ordinary, they send signals to various intake structures causing them to close. This ensures water containing lahars is not diverted into the Taupo catchment. On the western slopes of Ruapehu, two detectors are located in the upper Whakapapa river. River water takes between 10 and 20 minutes to travel from this site

to the Whakapapa intake. This is enough time to allow the gates of the intake to close if lahars are detected. On the eastern side of Ruapehu, detectors trip gates to prevent lahars from entering Lake Moawhango. Instead, the lahars will travel down the Whangaehu river, which is acidic anyway. Should the early warning system be activated, ECNZ personnel contact other agencies such as the Whakapapa visitor centre and forest rangers

to see if they are detecting anything similar. "While that's happening, we'll send someone to investigate. They can check out the water by its smell or taste," said Mr Drinkrow. As an extra precaution, some personnel use vehicles that can remotely close intake gates if they suspect something is wrong. "We'd rather have the gates closing on a false alarm than not trripping at all," said Mr Drinkrow.