California's Oroville Dam Cracks: Counties Evacuate Thousands

California's Oroville Dam Cracks: Counties Evacuate Thousands

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OROVILLE, CA – As parched California celebrates it wettest winter in years, the state’s reservoir structures are now being put to the test with the sudden onslaught of extra precipitation. Authorities are releasing mass amounts of water from the Oroville Dam in order to relieve pressure from an overflowing and damaged emergency spillway, preventing further damage to the structure, and a potential overflow that could threaten the areas below Lake Oroville.

The Oroville Dam protects the state’s second-largest reservoir, and is also the country’s tallest dam. Due to heavy amounts of rain and snow in the region, coupled with water accumulated from the Sierra Nevada mountain range, has seen the lake fuller than it has been in years and in need of its spillways. However, both spillways are currently damaged.

Map of Oroville Dam highlighting the affected spillway. Image via Google Earth.

Authorities issued evacuation orders for up to 188,000 people in three counties, after realizing the damage to the emergency spillway that was in use. As the spillway overflowed with water on Sunday, authorities released around 100,000-cubic-feet per second from the main spillway in order to reduce the water flowing down the emergency. Authorities noted that normal flows down that spillway are generally around 55,000-cubic-feet per second.

Doug Carlson, Spokesman, DWR"We want to drop that water level before the next storm hits Wednesday," the DWR's Carlson told CNN. "It's supposed to be a colder storm, which is good. Last week the rain storm was warmer. So we had both the rain runoff and the warmer rain melting the snow and that snow melt also flowed into the lake." 

Workers inspect a hole that developed in the main spillway on Wednesday, Feb 8th. Image via CNN.

The Oroville Dam has two spillways to assist in flood control for the region, allowing authorities to release water out of the lake to prevent overflow. The main spillway currently hosts a large and deep hole in part of its channel. The emergency, once brought into use, also began to erode under the pressure of the water. 

CNN reported that annual rainfall in Oroville is around 31 inches, but as of this weekend, Lake Oroville has already seen 25 inches of rain with another week’s worth of wet weather predicted to begin on Wednesday. 

Dan Brekke, Reporter, KQED"So the lake rose 50 feet in just a few days," said Dan Brekke of radio station KQED, according to NPR, "and got up to this emergency spillway which had never been used since the dam went into service in 1968. And on Saturday morning, it began pouring over there."

As of last evening, officials reported that the amount of water coming down the emergency spillway had significantly lessened after releasing pressure down the main. Authorities are using this brief respite in California rain to attempt to drop the Lake’s water level, and attempt to increase the integrity of the spillways’ structures.

What will the next few days bring for the Oroville Dam and its spillways, and will more massive amounts of needed water need to be released from the strucuture? AndNowUKnow will report as the new unfolds.