A primary and emergency spillway at Lake Oroville, California, have eroded to the point where repair is immediately required. Water levels have risen to historic levels resulting in worried authorities evacuating more than 190,000 people from the valleys below; they fear that the dam won’t hold.
The reservoir is California’s second-largest provider of water. The dam’s capacity is 4.363537 km3, which equates to 1.75 million Olympic swimming pools.
The dam recently reached capacity due to winter rains and snow melt. Worryingly, the main spillway has eroded - chunks of cement have recently given way. The deluge of new water is spilling into a 200-foot-long, 30-foot-deep hole, creating even more erosion.
Engineers now have to utilize the dam’s emergency spillway, unused since its construction in 1968. The concern is the erosion on this spillway too; it has not been adequately reinforced.
The dam safety engineers are anxious about keeping water away from the emergency spillway. Once water spills over into it the erosion there means that they have little control. This was what motivated them to hand down the evacuation order.
Auxiliary Spillway at Lake Oroville
Credit: Mike Anderson/ Twitter: @abros805
If the emergency spillway does indeed founder, the dam will begin draining. The officials are now concerned that the situation could lead to catastrophic failure.
To counteract further erosion on the main spillway, engineers are dropping bags of rocks into the hole. This will help mitigate the damage from the energy the dam is releasing and will slow the erosion.
The full repair of the damage to the spillways will cost, it is estimated by officials, between $100 and $200 million. The engineers believe they have the situation under control, but they describe it as a “dynamic”. Residents will not be allowed back into the county until they are sure it is safe.
The fact that more rain is forecast will be a setback, water levels will rise further and the emergency slipway could dump large amounts of water into the Feather River, which runs through downtown Oroville.
What went wrong?
The state of California has been sternly criticized for wilful ignorance. There is a claim that, at least a decade ago, documents were filed, warning the government that they could be facing the probable catastrophe they are facing today.
According to Mercury News, state officials had warned the federal government that the emergency slipway was eroding. The state officials, purportedly, continued to warn them for a decade. Head of the Californian Department of Water Resources, Mark Cowin, said he was unaware of any such documents.
Nonetheless, engineers have been clear in saying that they are not sure what caused the erosion on both the main and emergency spillways.
According to the LA Times, the spillway is checked annually and was repaired in 2013. Water Resources engineer, Kevin Dossey, told them: “We made repairs and everything checked out. Obviously, something has happened that we didn’t expect.”
Los Angeles Times. Los Angeles Times. Web. 13 Feb. 2017.
Rogers, Paul. "Oroville Dam: Feds and State Officials Ignored Warnings 12 Years Ago." The Mercury News. The Mercury News, 13 Feb. 2017. Web. 13 Feb. 2017.