Oroville Dam Spillway Emergency Response

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Oroville Dam Spillway Emergency Response

In early February, 2017, during widespread rainfall in California, operators at the Oroville Dam facility began making releases down the main Spillway, but soon observed an unusual flow pattern caused by damage to the middle portion of the Spillway chute. After halting the releases to assess the damage, the owner contacted Syblon Reid and asked us to serve as the prime contractor for the emergency response and stabilization work. Our management staff and crews responded swiftly, having personnel onsite within 2 hours and beginning work 24/7 to support the owner’s needs.

As the prime contractor, Syblon Reid both self-performed and orchestrated the construction response efforts, which comprised numerous subcontractors and suppliers. This involved helicopter and marine construction services, drilling, dredging operations, rock placement, and concrete pumping. The initial tasks included: establishing and maintaining control of the existing main Spillway gates; clearing trees from below the auxiliary spillway in anticipation of it overtopping for the first time since it was constructed; and implementing debris removal operations below the Spillway and at the downstream diversion dam to prevent fouling of the diversion gates and flooding of the Hyatt Power Plant. Once the flows over the auxiliary spillway ceased, the scope rapidly increased to address multiple tasks; including stabilization of the remaining spillway section and significant efforts to prevent the power plant from flooding and maintain it as an operational facility. The expanded scope also included placing large rock and concrete in the eroded areas below the auxiliary spillway and extensive dredging – both from the shore and off of barges – to remove the massive debris plug that bridged the Feather River below the main Spillway.

As a result of increased flows over the main Spillway – from 20,000 to 110,000 cubic feet per second, as well as the ensuing damage to the chute and subsequent erosion of the hillside upstream of the Spillway that transported an enormous amount of debris into the river below; the water level in the tailrace at the power plant River Outlet rose rapidly, threatening the facility. Syblon Reid provided two crews for mechanical support, operating around the clock at the power plant. This support included the following:

  • Rapid fabrication and installation of bulkheads for the turbine draft tubes to isolate the power plant and prevent flooding.
  • Providing dive services to access the River Outlet Valve Chamber bulkhead through the power plant to open a submerged marine door and allow pressure relief during the equalization of water levels in the afterbay.
  • Plumbing the six bays into headers leading to sumps in the power plant to keep the generating units dry. As we learned the tailrace water level was increasing, we fabricated a new header that ran down to a 3,000 gallon storage tank near Unit 6. Large pumps installed in the storage tank bypassed Hyatt’s existing sump system.
  • Mobilizing large pumps, both electric and air diaphragm.
  • Establishing redundant mechanical systems; including air pumps as backups in case of power loss to the electric pumps.
  • Installing cofferdams.
  • Providing design for a beam and plate bulkhead to cover the outlet to Diversion Tunnel No. 2. Syblon Reid lowered the bulkhead into the trash rack slots to prevent flooding of the tunnel from rising tailrace waters.

Syblon Reid was further requested to seal all joints and cracks within the Spillway, including the 180-foot wide chute and 20-foot tall training walls (approximately 30,000 linear feet in all), and drill 36 post-tensioned #14 bar anchors in the lower eight sections of the chute. To prevent water from going down the Spillway, the hydraulically-controlled gate seals needed to be pressurized with water. The existing water source used to pump up the seals was shut off as a result of the emergency; so Syblon Reid fabricated a hydraulic manifold, extending from the source to all six sets of gate seals, to control the main Spillway gates.

Below is a list of the equipment Syblon Reid mobilized to effectively complete the work:

  • Over 130 pieces of heavy equipment; including dozers, excavators, road graders, cranes, draglines, and articulated rock trucks.
  • Three 50+ meter boom concrete pump trucks supplied by 60 concrete trucks.
  • Four support helicopters; including 2 Utility Hawks and 2 Sikorsky Skycranes.
  • 180 rock delivery trucks importing shot rock from 7 quarries.
  • Four large barge assemblies.
  • Nine work boats; including a bathymetry boat, push boats, and support boats.
  • Nine construction support vehicles; including mobile fabrication trucks and water trucks.
  • Multiple tracked drills for installing spillway anchors.
  • Miscellaneous equipment; including grinding tubs and chippers.

Over 1.4 million cubic yards of sediment were dredged out of the Feather River to reestablish flows past the bottom of the damaged main Spillway and to maintain the Hyatt Power Plant in a dry state and support its return to service.

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