Dive Brief:

• The California Department of Water Resources (DWR) has increased its cost estimate for reconstruction work at the Oroville Dam's main and emergency spillways to $1.1 billion.
• Emergency recovery costs currently stand at $940 million and include $630 million for work — performed by Kiewit Infrastructure West — at both main and emergency spillways. The cost update accounts for additional materials and labor for extra excavation work on the emergency spillway and construction of a splashpad. Included in the costs for recovery work is $310 million for debris and sediment removal, replacement of power lines, construction of access roads and site restoration after the project is complete, as well as staff and consultant costs. A $160 million share went toward initial emergency response efforts — sediment removal, erosion mitigation, temporary transmission lines — after the spillways were damaged in February 2017.
• DWR said the initial $275 million contract awarded to Kiewit did not constitute an estimate of the project's costs but represented emergency work that needed to begin immediately after the February incident and in advance of design completion. Department officials said that as construction crews try to finish the concrete placement on the main spillway by a Nov. 1 safety deadline and aim to complete work on both spillways in 2019, cost estimates could be further adjusted. The Federal Emergency Management Agency has approved $87.4 million of the $116.5 million in reimbursement requests that DWR has submitted thus far. 

Dive Insight:

When the dam's spillways were damaged during heavy rains last year, almost 190,000 residents living downstream were evacuated, underscoring the potential for disaster if a dam should fail. Unfortunately, about a year after the Oroville event, a DWR memo obtained by local media revealed that seven other dams under the department's control had “potential geologic, structural or performance issues that could jeopardize their ability to safely pass a flood event.” 

In the most recent California DWR Division of Safety of Dams report dated September 2018, nine of the almost 1,250 dams under the state's jurisdiction were rated in "poor" condition, which includes dams that have multiple deficiencies or one major deficiency that requires "extensive" remedial work. Of those dams, according to the report: Two have the potential to cause economic loss and environmental damage should they fail; four could cause the loss of at least one human life should they fail; and two could cause considerable loss of human life upon failure. These scenarios assume a full reservoir at the time of failure.

The DWR said it is evaluating spillways of 93 dams similar to Oroville and is also conducting seismic reevaluations of dams located near active faults and in areas with dense populations. The agency noted that it could take years and hundreds of millions of dollars to address possible dam deficiencies.