Not long ago, the news was full of California’s exceptional drought conditions with nearly dry lakes and rivers. Lately, it’s been about too much rain. Going from one extreme to another is never a good thing and too much rain, after a few years of drought, is welcoming at first but can create problems later. We’re seeing these issues this winter with flooding and mudslides a now common occurrence in California. Of greatest concern is Oroville, CA and the current issues at Lake Oroville.
Lake Oroville is located just outside Oroville, CA on the western edge of the Sierra Nevada mountain range. A failing auxiliary spillway and a crumbling main spillway are creating dangerous conditions downstream of the Feather River. Crews are using the current break in the rainy weather to conduct emergency repairs to the auxiliary spillway, which was used for the first time in the dam’s history over the weekend. Officials noted that extreme erosion in the earthen auxiliary spillway along it’s concrete embankment could cause it to fail. This occurred after a sinkhole developed in the main spillway channel, sending debris downstream and creating another dangerous condition in which the concrete spillway channel could fail too, allowing for heavy erosion of the entire hillside.
A decision was made to increase the outflow of the lake into the main spillway in an effort to lower the lake level and stop using the auxiliary spillway (which is uncontrolled) so that officials could assess the damage and make emergency repairs. This process has been ongoing as large boulders and trucks full of large rocks are hauled into the area and placed in eroded parts of the emergency spillway.
Due to the impending failure of the auxiliary spillway, around 188,000 people were forced to evacuate areas downstream of the damn as a failure of the auxiliary spillway (a collapse of the concrete top) would lead to a catastrophic, uncontrolled release of massive amounts of water into the valley and farmland along the Feather River.
Video and additional pictures of Lake Oroville via the California Highway Patrol and the California Department of Water Resources:
More Rain Coming
While crews are making repairs, more water is being released from Lake Oroville to increase capacity for the impending rainfall over the next several days. Approximately 4-8 inches of rainfall is expected to fall through early next week, with nearly 11 inches of precipitation possible upstream of the lake. Officials are attempting to lower the lake level by 50 feet in order to have enough capacity for the upcoming rain. However, due to the damage along the main spillway, the lake is only able to release so much water at one time. Continued heavy rains will not help make the situation at Lake Oroville any better. Further, with spring approaching, warmer weather will begin to melt the record setting snow pack in the Sierra Nevadas, sending even more water downstream through the spring. It’s likely that this situation will not improve anytime soon.
The current issues at Oroville Dam have also brought to light previous calls to line the auxiliary spillway with concrete, as early as 2005. The Federal Energy Regulatory Commission, FERC, determined the cost to upgrade the emergency spillway was unnecessary and the concerns were “overblown.”
In 2013, a portion of the spillway cracked. It was reported that repairs were made and “everything checked out.” In July, 2015, the state division of safety of dams inspected the Oroville dam visually “from some distance.”
Oroville Dam was built in the 1960s and completed in 1967, with use starting in 1968. At 770 feet tall, it is the tallest dam in the United States. It makes up a large portion of California’s statewide water system. The dam also generates electricity. It’s important to note that the dam itself is a separate structure from the spillway and is not at risk of failing.
Just a few years ago, the lake level was down over 160 feet from it’s usual level. Check out the picture below.
Yahoo! Finance/CNBC: http://finance.yahoo.com/news/california-official-denies-oroville-dam-182825393.html
Oroville Dam on Wikipedia: https://en.wikipedia.org/wiki/Oroville_Dam
Oroville Dam on Califormia State Department of Water Resouces Website: http://www.water.ca.gov/swp/facilities/Oroville/LakeDam.cfm
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