Work to redesign and replace the heavily damaged main spillway at Oroville Dam is underway, with officials saying that design work is about 60 percent complete on this rush job, which could begin construction as early as April 17. This week, as the Associated Press reports, Governor Jerry Brown waived some permitting and review requirements that could slow that work, and signed an executive order making repairs on the dam a priority for all state agencies.
William Croyle, acting director at the Department of Water Resources, tells the Chronicle that this is going to mad dash to get a working spillway complete by the time November and the next rainy season begins. "This is the kind of project that would [typically] take two or three years to design and two or three years to build," Croyle says.
Instead, they have seven months, and work is already going out to bid but the DWR clarifies that the plan now is to get the spillway only partially rebuilt, able to release 100,000 cubic feet of water per second by November, and work during the summer of 2018 will then make the spillway's capacity 270,000 cubic feet per second. Prior to the erosion damage and collapse the spillway suffered in February, it had a capacity of 160,000 cubic feet per second, but caution on the part of officials after water began rushing down and eroding the adjacent hillside led to a crisis on February 12 after the reservoir's emergency spillway was put into use for the first time in its nearly 50-year life.
The emergency spillway, which is essentially just a 30-foot-high, 1,700-foot-wide concrete lip over a bare hillside, appeared in danger of failure after one full day of water spilling over it, when a chunk of the hill beneath one side of it was heavily eroded. Officials called for the evacuation of some 200,000 residents downstream of Lake Oroville in a story that made national headlines and served as a prime example of the dangers of our nation's aging infrastructure.
Part of this year's repairs, the Chronicle reports, will be a "massive concrete slab" being added to buttress the emergency spillway just in case it ever needs to be used again.
If the main spillway is only being partially repaired this year, questions likely linger about how well the spillway will function in the event of another very wet winter. A comprehensive assessment of Oroville Dam itself is underway, which may influence the design of the reconstructed spillway. Per the AP, "the state expects to finish laying new concrete, or bolting down stretches of existing concrete, on the key, upper stretch of the main spillway by the Nov. 1 target date," but the lower portion of the spillway, which is much more heavily damaged, could require more time.
Meanwhile, the main spillway was expected to put into use again today to lower lake levels following Thursday's storm.