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Calm before next storm at Oroville Dam

Oroville Dam auxillary spillway

California’s Oroville Dam should cope with impending fresh storms following a drop in water level, engineers have said.

As of last night (14 February) the water level at the dam had dropped to 270m above sea level, below the 275m capacity limit, and was dropping at eight to ten centimetres per hour. This rapid drop in water level has given California Department of Water Resources engineers confidence that the dam will cope with fresh rainfall without the need to use the auxilliary spillway.

Water continues to crash down the primary spillway – also damaged – at 2,831m³/s.

An emergency evacuation order which was issued to 180,000 residents by California governor Jerry Brown has been reduced to a warning.

More than 125 construction crews have been working round the clock to apply temporary repairs to the damage before more rain hits the region.

Damage to the emergency spillway is being plugged with more than 1,200t of material using helicopters and heavy plant.

Source: California DWR

Engineers repair Oroville Dam's damaged auxilliary spillway with large rocks and gravel using helicopters and heavy plant.

Following weeks of heavy rain erosion damage was found last Tuesday (7 February) in the middle of the primary, or main, spillway. Engineers closed the spillway before gradually reopening it for testing.

Water levels rose at the dam and the second spillway, known as the auxiliary spillway, came into use on Saturday morning (11 February) for the first time in the dam’s 48-year history.

Erosion was found at its head on Sunday (12 February), which could have undermined the concrete weir and led to flooding. An evacuation order was issued to 180,000 residents by California state governor Jerry Brown.

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