Oroville dam, the biggest dam in North America, is seriously damaged and can collapse any minute now. Californian authorities are hastily evacuating around 188.000 people that live in Oroville and adjacent settlements that could be flooded and leveled if the dam collapses.
Californian Department of water resources stated that it’s only a matter of time until the auxiliary spillway gives way and releases millions of cubic feet of water into a valley around Oroville, where currently evacuation is taking place. Governor Jerry Brown issued a state of emergency order for Sutter, Butte and Yuba counties. The California National guard has also been mobilized, to help in evacuation as well as in repairs of the dam.
But there are concerns that it might be too late for that now. Five days ago, a massive hole spawned on Oroville dam’s auxiliary spillway. At the time, authorities cut off the water flow and said that there is no room for concern.
Maintenance crews were sent into it to examine the damage and begin repairs, hoping to make it operational within weeks.
But instead, it just got bigger over time, eventually becoming 500 feet long and 45 feet deep. What caused the biggest concern is that the sides of the spillway started to erode, causing more damage and collapse on the hills around it.
To make things worse, Lake Oroville’s water level rose due to rains and snowfall and reached a critical point, forcing dam authorities to open the damaged spillway and let water flow directly into and over the hole. This caused a massive erosion damage, making the gap even bigger and more unstable.
Eventually, it became clear that the situation has got out of hand and that the whole spillway is in risk of collapsing. And just when things seemed like they couldn’t get any worse, water levels rose again and water started overflowing the second, emergency spillway, causing more erosion and damage to an already unstable hillside.
Authorities issued a state of emergency and started evacuating several settlements beneath the dam. Governor Brown asked the Federal Emergency Management Agency to declare the area a major disaster due to flooding and mudslides brought on by the storms.The California Office of Emergency Services main office has been staffed at levels not seen since Napa was struck by a magnitude 6.0 earthquake.
National guard has also been called into action, and will provide manpower and technical support in efforts to repair the dam. It will provide 23.000 soldiers and eight helicopters that will be used both for dam repairs and search and rescue missions, if needed.
There are some good news though. According to experts, the spillway held up longer than anyone anticipated, and the damage is not progressing as fast as originally thought. But no one knows for sure what will happen next. The newly inflicted damage is yet to be estimated. And before any repairs even begin, the whole area needs to be evacuated and secured, giving the water time to drain away and reduce pressure on the dam and its spillways.
If Oroville dam survives these unfortunate events, it will continue to be America’s biggest dam. Built in 1968, it stood proudly for almost half a century, generating 1,5 GWh per year and providing the whole region with power. It was designed to withstand the strongest possible earthquake for the region, and was fitted with hundreds of instruments that serve to measure water pressure and settlement of the earth fill used in its construction, earning it the nickname “the dam that talks back”.