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Catastrophic failures at a dam in California combined with heavy winter storms have forced hundreds of thousands to flee their homes. Although the level of the dam’s lake is falling fast, more rain is forecast.

On 7 February, that carries overflow water from the Oroville dam to the Feather river.

Engineers diverted this water along an unpaved emergency spillway that hadn’t been used in almost 50 years – but this didn’t work. On 12 February, officials ordered over 188,000 residents of downstream towns to evacuate because the spillway was at risk of collapse.

Unless the erosion of the spillway is dealt with, “what we’re looking at is approximately a 30-foot wall of water”, Kevin Lawson, deputy chief of the California Department of Forestry and Fire Protection, said at a press conference that night.

To relieve pressure on the dam, more than 2800 cubic metres of water per second were being released into the main damaged spillway, nearly double its usual capacity. The target is to lower the lake’s water level by 15 metres, according to the California Department of Water Resources.

“That solution worked to reduce the threat,” Bill Croyle, the acting director of the California Department of Water Resources, told a press conference on 13 February. He said he was unaware of a that warned of just such a collapse.

Downstream of the dam, and several roads and highways have been closed by the California Department of Transportation, including at least

Now the race is on to repair both spillways before it rains again. Crews are with bags of rock and sand to avert a disastrous released of uncontrolled water from the dam.