Oroville Dam crisis, why 200,000 people near the US’ tallest dam are in danger

What is happening at the Oroville Dam in California, the United States’ tallest dam where structural damages caused the evacuation of 200,000 residents.

With its 230 metres (770 feet) the Oroville dam in California is the tallest in the United States, lying about 240 kilometres (150 miles) from San Francisco. On the 7th of February operators noticed damages to the main spillway, channel used to control the release of water from the basin, flowing into the Feather River. After they slowed down the flow to investigate this they realised that a large portion of concrete had been washed away. This led California Governor Jerry Brown to declare a state of emergency in the counties of Butte, Sutter and Yuba on the 12th of February, calling for the evacuation of 200,000 residents. In addition, all 23,000 soldiers of the US’ National security corps were called in to help.

What happened at the Oroville Dam

After the damage to the dam was noticed, it was decided to use the emergency spillway for the first time since it was built 50 years ago. The latter isn’t built with the same specifications as the main one, which is controlled by gates and made in concrete, leaving water to flow down the earthen hillside instead. Its use increases the risk of collapse because when the water starts to erode the ground, the dirt and water start to roll down the hill, leading to the potential creation of a 10-metre tall wall of water.

The evacuation alert

After a week of rainstorms in the area last week and snowmelt in Lake Oroville, the lake reached its full capacity and state officials had to order the state of emergency and evacuation of the three counties that lie in the dam’s proximity. President Donald Trump‘s response was to pledge to send federal aid to help in the Oroville Dam crisis. Press Secretary Sean Spicer used this occasion to underline the need to focus on the nation’s infrastructure, one of Trump’s electoral promises.

Environmental groups warned of dangers 10 years ago

Three environmental groups – Friends of the River, Sierra Club and the South Yuba River Citizens League – warned of the dangerous state of the emergency spillway over ten years ago, in 2005, asking for a renovation and modification of the project including building a concrete-armoured spillway rather than leaving it as a concrete “lip” above an unprotected hillside prone to erosion damage. These groups filed a motion to the Federal Energy Regulatory Commission, which was considering the dam’s relicensing, but the latter decided not to take actions over those concerns. Building a concrete-armoured spillway would have required water districts that rely on the State Water Project to absorb increases in the costs of water, and Ron Stork, policy director of Californian environmental group Friends of the River, said that this is what stopped action from taking place at the time.

More rain forecasted

The evacuation order was lifted late on the 14th of February as the lake returned to its normal levels and temporary repairs to the emergency spillway were promptly carried out. Though there is no longer an immediate threat, forecasts say rain will soon return. If the expected storms do fill the lake damaged infrastructure could create further dangers, so an evacuation warning remains into effect: people have returned home and businesses can operate but everyone should be ready to evacuate in case of necessity. The situation is being closely monitored and authorities need to find a way to permanently repair the main spillway as soon as possible.

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