Oroville >> Construction work began just after midnight Tuesday morning on phase 2 of the repairs to the Oroville Dam main spillway.
The Department of Water Resources had been granted permission by federal and state regulators to start work May 8, and contractor Kiewit Infrastructure West didn’t waste any time.
The main work is planned to be done by Nov. 1, reporters were told during a media call Tuesday with Kiewit and DWR officials. Some finishing work like sealing joints and connecting drainage systems will continue after that date.
This is the second year of work to correct design, construction and maintenance deficiencies that led to the spillway’s breakup in February 2017, according to an independent review ordered by the Federal Energy Regulatory Commission.
The breakup resulted in use of the emergency spillway, but the bare hillside below the concrete weir eroded rapidly, resulting in evacuation orders for more than 180,000 people.
The main spillway
The plan for this year on the main spillway includes three main tasks and a couple of smaller ones.
The big jobs are replacing the top 730 feet of the upper chute, putting a structural concrete cap on the center section that was filled in with roller compacted concrete last year, and replacing the RCC walls of that part of the chute with structural concrete.
Work has begun to remove the upper chute section. Jeff Petersen, executive project director for Kiewit, said the ends of that part of the spillway will be destroyed mechanically to avoid damaging the adjacent section and the spillway gates. The center will be destroyed with controlled blasting.
After that, the site will be cleaned, and a layer of leveling concrete, slab anchors and a new drainage system will be installed, starting in June.
Pouring of the new structural concrete surface slabs and walls should begin in July.
The roller compacted concrete center section has already been ground down to accept a new three-foot-deep layer of structural concrete.
Destruction of the RCC walls of that stretch of the spillway is the next step, with Kiewit having 16 excavators at work to remove those now, according to Petersen.
Then starting in June, a new drainage system will be built and slab anchors placed. Starting in July, a new surface and new walls of structural concrete will be constructed.
The RCC floor of the chute had a two-foot drop from the layer above it when work was concluded last year. Erin Mellon, DWR’s deputy director for public information, said the new floor will be flush to the one above it.
Workers will also repair three slabs poured last year that didn’t meet quality control standards.
Work should begin on one of those next week, according to Ted Craddock, assistant deputy director of the State Water Project.
The energy-dissipating blocks at the bottom of the spillway are also being resurfaced. The process involved removing the outer 16 inches of concrete, adding reinforcing steel, and resurfacing with erosion-resistant concrete.
The lake surface is currently at 824 feet above sea level, which puts it above the bottom of the spillway gates. Mellon said some leaking is expected, but a system is in place to control that and it should not interfere with construction. The lake is considered full at 900 feet of elevation.
The emergency spillway
Work on the emergency spillway never really ended last winter, but it was divided into two parts.
On the northern part, the underground wall of poured concrete pilings was topped. It is designed to prevent uphill erosion to the weir like what prompted the evacuation.
Work on the RCC “splash pad” that will protect the area between the wall and the weir is about 65 percent complete, according to Petersen.
Federal and state regulators recently approved removal of the concrete that was dumped after the emergency on the southern part of the spillway, which will allow splash pad construction to begin there.
Workers are topping the underground wall on that section now, which will tie the pillars together and link them to the splash pad. Pouring of the splash pad should begin in July.
Buttressing for the emergency spillway weir is also on the agenda for this year.
An injury
Petersen said the first reportable injury happened last week, when an excavator driver fell and broke his leg. Meetings with the entire work crew followed to analyze what happened and how it could be avoided.
The safety record is pretty good though. Petersen said Kiewit workers have put in 980,000 hours of work thus far. There are 430 Kiewit employees on the job now, and 80 contract workers.
Craddock said 500 DWR workers have put in 480,00 hours on the spillway project.
Reach City Editor Steve Schoonover at 896-7750.
