Records dating back more than 10 years show the state and federal government were warned about problems at the Oroville spillway, and the latest dam inspection report filed last September raises similar issues.
The NBC Bay Area Investigative Unit uncovered the inspection reports, which show the government's own inspectors were concerned about erosion. The report says a plan for "surface monitoring" downstream of the spillway "remains oustanding," meaning no plan was in place when the inspection took place last fall.
The report also concluded that, "Adequate and reliable reservoir drawdown capacity is important for dam safety." Inspectors suggested that too much water and not enough capacity to geit it over the spillway safely could jeopardize the dam itself.
The government engineer who performed the inspection last fall said the dam and facilities were safe, but he also said the issues raised in the report needed to be addressed. The potential erosion issues appeared in inspection reports dating back years.
Meantime, 12 years ago the Sierra Club, South Yuba Citizens' League and Friends of the River filed a legal motion with the Federal Energy Regulatory Commission, or FERC, saying the spillways at Oroville did not meet federal engineering guidelines. The motion said that areas below the emergency spillway at Oroville were not armored and that extensive erosion could take place. The groups also raised concerns that diverted flow over the ungated spillway could, "mobilize the hillside."
That is exactly what began to occur over the last 48 hours at the Oroville spillway. Back then, both the federal government and the state dismissed the concerns raised by the environmental groups in their legal motion, and apparently nothing was done to change the design of the emergency spillway.
The Oroville Dam is about 100 miles northeast of the Bay Area, but among the big concerns raised by this week's incidents is the safety of local dams. One hundred dams in the Bay Area have been labeled "high hazard" by the Army Corps of Engineers.
The National Inventory of Dams maintains records for all 1,585 dams in California. According to the latest data from 2013, 833 dams -- more than half of all dams in California -- carry a high hazard potential. That doesn't necessarily mean they are at risk of failing, but if they do the feds say it could mean the loss of human life.
Of those dams, 296 have no emergency action plan. It's worth mentioning that Oroville Dam did have a such a plan in place.
And 1,186 or 75 percent of all dams in the state are earthen dams, including Oroville, which means they can be at risk for erosion.
Finally, 80 percent of all dams in the state were build before 1970, including Oroville Dam, which was built in 1968. This means many of the components of these dams are nearing the end of past their designed lifespans.