The rain has started to return in Northern California and will continue over the next few days, but officials aren't as concerned about the upcoming weather so much as the damage already done to the Oroville Dam's already compromised main spillway.
The risk of flooding has dropped substantially, but Butte County Sheriff Kory Honea warned residents Wednesday that they remain in "an emergency situation."
- Engineers are racing to lower the water level at Lake Oroville.
- These graphics explain what is happening at the Oroville Dam.
- Could the crisis have been prevented?
- Here is Butte County's emergency information website.
- PHOTOS: Crisis at the Oroville Dam
- VIDEOS: The Lake Oroville emergency explained | An evacuee waits to return home
Erosion near an Oroville reservoir emergency spillway was first predicted in court documents filed by environmentalists more than a decade ago.
In a technical memo on Lake Oroville’s discharge, the Yuba County Water Agency wrote in 2002 that if the Department of Water Resources used the emergency spillway, “extensive erosion would take place” and that “the spillway road and possibly high voltage transmission towers would be impacted,” according to a motion to intervene on the licensing filed by environmentalist groups in 2005.
“Because the area downstream from the emergency spillway crest is an unlined hillside, significant erosion of the hillside would occur,” the document said.
According to the California Department of Water Resources, that’s exactly what happened. After the dam’s main spillway was damaged, engineers decreased its output to save nearby power lines and prevent further damage to the spillway’s lower half.
But that allowed the lake to fill beyond capacity, which forced water to flow over the emergency spillway on Saturday. The results were as predicted more than a decade ago — PG&E; equipment was jeopardized and the hillside dramatically eroded, forcing more than 100,000 residents down river to evacuate as a precaution in case the spillway completely failed.
In the Department of Water Resources' response issued with the final environmental impact report in 2008, the agency found that the dam, its structures and the emergency spillway weir were in “good condition.”
Department of Water Resources officials said on Monday that they could not comment on the 2005 document.