Dive Brief:
- California Department of Water (DWR) officials announced Wednesday that the second phase of construction work on the Oroville Dam will begin May 8, The Mercury News reported. The second phase will constitute the bulk of work at the dam.
- As part of the second phase of construction, general contractor Kiewit will demolish more than 700 feet of the main spillway's upper chute and rebuild it with steel-reinforced structural concrete; place three feet of steel-reinforced structural concrete over roller-compacted concrete (RCC) at the middle chute; remove RCC walls in the middle chute and replace them with structural concrete; hydro-blast and resurface energy dissipaters and provide new drainage systems. At the emergency spillway, crews will remove the emergency embankment of stone, or rip rap, that was put in place February 2017 – pending approval from the Federal Energy Regulatory Commission (FERC) and California Division of Safety of Dams. They will also finish work on a concrete cap at the underground secant pile wall; continue work on the RCC splashpad and build a reinforcing RCC buttress at the base of the emergency spillway.
- In a DWR update on April 18, the agency said it updated its 2018 Lake Oroville Operations Plan to reflect a spring start for Phase II so that there is time for crews to complete construction before winter arrives.
Dive Insight:
California officials and residents understandably have been paying more attention to the condition of the state's dams since the Oroville Dam's failure last year. Although no one was injured as a result, 188,000 people were evacuated in anticipation of potential additional failures that could have led to life-threatening floods.
Since the Oroville construction project got underway, the state has also undertaken a $600 million safety overhaul of the Isabella Dam in Kern County, California, with the Flatiron/Dragados/Sukut Joint Venture recently starting construction on the $204 million second phase of the project, the Army Corps of Engineers, which is overseeing the work, said in a statement last month. The work includes raising both main and auxiliary dams by 16 feet, improving the existing spillway, constructing a new, 300-foot-wide spillway and adding filters and drainage.
The Isabella project aims to reduce the risk of overtopping – the overflow of water – and address issues related to seepage and seismic resiliency, thereby reducing the likelihood that the dam will fail. The dam will remain operational throughout the construction phase, providing crews with "an interesting challenge," according to the Corps.
The state's decision to rehab the dam, according to KBAK & KBFX Eyewitness News, was driven by the media outlet's investigation of a 2006 report indicating that the dam had an "unacceptably high probability of failure combined with a very high consequence of failure," which endangered the 300,000 people living below it.
