Opuha Dam

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The Opuha dam at Fairlie is a dam in New Zealand, Canterbury province. The partially completed dam failed on February 6, 1997 ( a holiday) at 1:00 clock at night due to heavy water inflows result of heavy rainfall. 13 million cubic meters poured into the valley of the River Opuha. There were no deaths, but many people could be saved only by luck. There was great damage to property.

Data

The dam construction site is located 12 km north of Fairlie and 170 km from Christchurch. At the dam, only few data are known:

  • Dam Height: 47 m
  • Length of the dam: 100 m
  • Catchment area: 500 km ²

The dam break

Due to heavy rains, the inflow to the dam increased greatly. In order to prevent uncontrolled cracking, it was decided to drain the water through a breach on the rocky left abutment. There is no information whether the spillway was in operation or why it was not powerful enough. The downstream residents were warned that the outflow would increase below the dam.

Shortly before midnight, the breach was 20 m wide and 6 m deep, and began to assess the situation as serious. At this time, 13 million cubic meters of water were in the dam. Shortly before, the amount of water was not provided with 2 million cubic meters. The expected peak discharge from the dam was constantly revised upwards and now was 1500 m³ / s The area below was evacuated, and about 200 people were forced to flee. Some campers escaped only when she awakened by breaking trees, watched the waves come up.

The gap eventually grew to a width of 35 m to the left part of the dam was completely removed. The tidal wave with an estimated peak discharge from 1800 to 2000 m³ / s needed 7.5 hours to travel the 55 km long river to the sea.

Damage

In addition to the loss of approximately 1000 head of cattle, the damage to the river bed are specified with $ 500,000 added several $ 100,000 damage to farms. The damage to the dam itself is apparently not included.

The dam was completed thereafter and has been in operation since April 1999. The reservoir has 84 million cubic meters of content.

Source: see Web

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