Now that California is finally experiencing greater-than-normal rainfall after a prolonged drought, the state is also getting some uncomfortable reminders of the problems heavy rainfall can bring.
These two videos, for example, show a portion of Highway 35 in Los Gatos, in the northern part of the state, that completely washed away last Friday (scroll down to see the second video).
But the thing that’s making national news is the Oroville Dam, which is in danger of giving way. About 188,000 people have been evacuated from areas downstream. Lake Oroville, a manmade lake, is just north of Sacramento.Add Erosion Control Weekly to your Newsletter Preferences and keep up with the latest articles on erosion control: erosion control devices, geosynthetics, sediment control devices and soil erosion.
As of this writing, on Monday the 13th, water levels are falling and the immediate crisis appears to be past, but the situation still raises some important questions for the future of this dam and others—potentially thousands of others.
On Saturday, water from the rain-swollen Lake Oroville began overtopping the dam’s emergency spillway, causing officials to release more water through the main spillway in an effort to stop the overtopping and resulting erosion. (The main spillway was already severely eroded, with what has been described as a football-field-sized, 40-foot-deep hole.) The state’s Department of Water Resources also began dropping rocks from helicopters to plug damaged areas of the emergency spillway. At the same time, evacuation orders were issued in anticipation of the worst-case scenario—failure and release of a massive amount of water to downstream communities.
During a normal year, this part of the state receives about 31 inches of rain. However, in the last four months alone, it has received 25 inches, and the lake has received more water in the form of runoff from the Sierra Nevada mountains, which are also experiencing increased rainfall.
In 2005 when the dam was being relicensed, environmental groups claimed that the dam did not meet safety standards and urged that the emergency spillway be strengthened. According to this article, the Federal Energy Regulatory Commission rejected that request, calling the work an unnecessary expense.
The American Society of Civil Engineers periodically releases its Infrastructure Report Card—the 2017 edition is due out on March 9 at this site. The last report card in 2013 gave dams a grade of D and levees a grade of D minus; the overall grade for the nation’s infrastructure was a D plus.