Almost 200,000 Residents Near The Tallest U.S. Dam Are Under Evacuation As A Spillway Failure Threat Remains

This Sunday evening video followed evacuation orders for residents near the Oroville Dam, the tallest such structure in the nation. Over the weekend, the situation grew ever more precarious due to heavy rainfalls. The State of California’s Department of Water Resources began evacuating low-lowing areas near the dam, and the order has grown from Oroville’s 16,000 residents to a much larger area. Currently, 180,000 residents remain evacuated.

The State of California stresses that the dam itself was never under danger of collapse. However, increased flow caused the main spillway to erode to the point where a massive hole (200 feet long and 30 feet deep) developed. For the first time ever, the dam’s auxiliary spillway was put into use on Saturday, which led to almost immediate erosion. As such, the Butte County Sheriff’s Office warned that uncontrollable flooding from Lake Oroville could occur, should the auxiliary spillway fail. The numbers remain grim:

The California Department of Water Resources said it is releasing as much as 100,000 cubic feet per second from the main, heavily damaged spillway to try to drain the lake.

Department engineer and spokesman Kevin Dossey told the Sacramento Bee the emergency spillway was rated to handle 250,000 cubic feet per second, but it began to show weakness Sunday at a small fraction of that. Flows through the spillway peaked at 12,600 cubic feet per second at 1 a.m. Sunday and were down to 8,000 cubic feet per second by midday.

According to NBC Bay Area, water stopped flowing over the auxiliary spillway early Monday, but the structure still remains vulnerable due to the erosion that has occurred. At around 4:00am local time, crews began placing bags filled with rocks near the eroding spillway to ward off flood waters.

However, Bill Croyle, acting director of California’s Department of Water Resources, told the Washington Post, “Once we have damage to a structure like that, it’s catastrophic … You don’t just throw a little bit of rock in it.”

The local NBC affiliate, KCRA, says concerns remain high despite Lake Oroville finally falling under 100 percent capacity (from 901 feet to 898 feet). This will ease pressure on the auxiliary spillway, although outflow continues to remain dangerously high at almost 100,000 cubic feet per second.

(Via Bloomberg, NBC Bay Area, KCRA & Washington Post)