USA – Tens of Thousands Evacuate in Northern California as Authorities Warn of Dam Spillway Failure

Tens of thousands of residents in Northern California were ordered to immediately evacuate their homes on Sunday 12 February after erosion at the emergency spillway at Lake Oroville threatened to flood towns and communities downstream, including Oroville and other towns in Yuba, Sutter and Butte counties.

Lake Oroville Dam is located about 75 miles north of Sacramento. The dam itself is not damaged and is a separate structure from the auxiliary spillway.

During January and February of 2017, three atmospheric river storm systems struck California, bringing massive amounts of rainfall. The rainfall inundated lakes, rivers, and streams throughout the state, causing them to reach capacity, resulting in widespread flooding. Lake Oroville in Butte County reached capacity, causing officials to utilize the spillway to reduce the lake’s water levels.

On 07 February 2017, the spillway at Lake Oroville Dam began to erode, causing officials to begin utilizing the auxiliary emergency spillway on 11 February. However officials have determined that the auxiliary emergency spillway at Lake Oroville Dam is in danger of failing, which if it fails, may cause widespread and severe flooding.

Local media reports that as many as 188,000 people are under an evacuation order. A statement by the Governor of California stressed that all citizens should heed the advice of emergency officials with regard to this emergency in order to protect their safety.

In a press statement yesterday, California Department of Water Resources said:

“Based on information received from the California Department of Water Resources (DWR) and the incident command team managing Lake Oroville, counties and cities near Lake Oroville and the surrounding area issued evacuation orders for residents. The concern is that erosion at the head of the auxiliary spillway threatens to undermine the concrete weir and allow large, uncontrolled releases of water from Lake Oroville. Those potential flows could exceed the capacity of downstream channels.”

To avert more erosion at the top of the auxiliary spillway, DWR doubled the flow down its main spillway from 55,000 cubic feet per second (cfs) to 100,000 cfs on 12 February.

DWR said “The next several hours will be crucial in determining whether the concrete structure at the head of the auxiliary spillway remains intact and prevents larger, uncontrolled flows.”

Governor Issues Emergency Order

California Governor Jerry Brown issued an emergency order to assist in dealing with Oroville Dam crisis and support subsequent local evacuations.

“I’ve been in close contact with emergency personnel managing the situation in Oroville throughout the weekend and it’s clear the circumstances are complex and rapidly changing,” said Governor Brown.

“I want to thank local and state law enforcement for leading evacuation efforts and doing their part to keep residents safe. The state is directing all necessary personnel and resources to deal with this very serious situation.”

The Governor’s Office of Emergency Services has activated the State Operations Center in Mather, California to its highest level and is coordinating with personnel at the Incident Command Post in Oroville, California and with other local, state and federal emergency response officials to address all emergency management, evacuation and mutual aid needs.

Oroville spillway, 12 February 2017. Photo: DWR Acting Director William Croyle
Oroville spillway, 12 February 2017. Photo: DWR Acting Director William Croyle