Laos dam construction and collapse

A dam under construction in Laos as part of a hydropower scheme has collapsed, causing flooding and damage.

At issue is the Xe-Pian Xe-Namnoy project, a 410-megawatt hydroelectric power project under development for Xe-Pian Xe-Namnoy Power Company (PNPC). PNPC is a joint venture among the government of Laos and construction and power companies from South Korea and Thailand. The project, whose construction costs are estimated at about $1 billion, involves the construction of three primary dams to form reservoirs. Construction of the system was reportedly 90% complete, with commercial operation projected for 2019, and an agreement in place agreement to export 90% of project power to Thailand. The project has been touted for the degree of international investment involved, although some have criticized the project for insufficient local benefits.

From an engineering perspective, the project's primary dams impound water in a large reservoir. The project also includes three auxiliary "saddle dams" near several heads of the reservoir, essentially to prevent the reservoir from spilling down the impoundment's back side as it fills.

A map of the project, found at http://www.pnpclaos.com/index.php/en/project/maps

Project maps posted online by PNPC show saddle dams on three of the main reservoir's western branches.

Another project map found at http://www.pnpclaos.com/index.php/en/project/maps

One of these smaller saddle dams reportedly failed on July 23, 2018, allegedly due to severe rains. Saddle Dam D -- a facility 8 meters wide, 770 meters long and 16 meters high -- was built to support water diversion around the project's reservoir. But the structure reportedly fractured, causing water to spill downstream to the Xe Pian river outside of the project's intended path of water flow. According to the prime minister of Laos, at least 26 people have died and 131 are missing from the resulting flooding, and several villages .

Response and recovery actions are ongoing. The dam collapse highlights the importance of safety in dam construction and reservoir operations, as did the February 2017 failure of the Oroville Dam's spillway in California.

FERC hydro dam safety post-Oroville

As federal hydropower regulators examine how a California dam's spillway failed, an independent forensic team has released its final report on the Oroville Dam spillway incident -- and regulators have asked all other hydropower licensees to review the report and hold internal discussions on how the findings may apply to their own facilities and overall dam safety program.

Oroville Dam is a 770-foot high earthfill embankment dam on the Feather River in Northern California. Its service spillway was severely damaged during operations on February 7, 2017; water levels continued to rise, eventually overtopping and eroding the emergency spillway, threatening the stability of the structure on February 12, 2017.  Over 180,000 people were evacuated.

Following the incident, an independent forensic team studied the incident. The independent forensic team's report was released on January 5, 2018. It found that the incident "was caused by a long-term systemic failure of the California Department of Water Resources (DWR), regulatory, and general industry practices to recognize and address inherent spillway design and construction weaknesses, poor bedrock quality, and deteriorated service spillway chute conditions."

On January 26, 2018, the Commission published a letter to licensees presenting the Oroville Dam Independent Forensic Team's final report. In that letter, the Commission asked licensees and their Chief Dam Safety Engineers/Coordinators to "read this report, share it with your senior executives as well as all your dam safety staff and discuss how the findings may apply to your own facilities and overall dam safety program.

According to the Commission, that report concludes that flaws in the Oroville Dam Spillway existed since construction that were missed by the owner, regulators, and consultants. In the Commission's words, "It is very clear that just because a project has operated successfully for a long period of time does not guarantee that it will continue to do so." Emphasizing a safety-oriented corporate culture, the Commission also highlighted the report's finding that "compliance with regulatory requirements is not sufficient to manage risk and meet dam owners' legal and ethical responsibilities." The Commission's letter to hydropower licensees and exemptees highlights the importance of communication between dam safety staff and senior executives as part of an Owner's Dam Safety Program, and stated its expectation that regulated dam owners will have internal discussions to ensure facility safety.

Guajataca Dam, spillway erosion, and repairs

As Puerto Rico continues to grapple with the aftermath of Hurricane Maria, information on damage to the Guajataca Dam remains scarce, while reports suggest spillway repairs may be ongoing.

Hurricane Maria made landfall in Puerto Rico last month, bringing 150 mph winds and 20 inches of rain.  Damage to infrastructure was widespread, and the destruction of electricity and communications networks hindered efforts to assess the damage and move toward recovery.

Early reports suggested that the Guajataca Dam had "failed".  On September 22, the National Weather Service's San Juan office tweeted an alert of a "flash flood emergency for a dam failure" at the Guajataca Dam and noted ongoing evacuations.

But as reported by Vox on September 30, an Army Corps spokesman said that the dam was not breached and "has not failed and not collapsed."  The article described damage to the dam's overflow spillway.

According to a Department of Defense posting dated October 1, 2017, the Defense Department has deployed more response capacity to Puerto Rico, while the Guajataca Dam spillway continued to erode.  The Defense Department said U.S. Transportation Command delivered 900 super sandbags for spillway stabilization to Aguadilla Airport on September 30, and that spillway sandbag installation by the Army Corps of Engineers would start on October 1 and will be complete by October 2.

An article posted by The Independent on October 4 describes the Army Corps' use of Osprey V2 rotor-tilt heavy-lift aircraft to drop concrete barriers from the dam into the spillway, in an attempt to limit further erosion of the spillway channel.  The article says the "channel has suffered serious erosion as much of its cement cladding was washed away."

Dam safety and flood control spillway damage have featured prominently in recent news.  California's Oroville Dam's spillway was damaged earlier this year, including a concrete failure on the lower chute of the gated flood control spillway, severe erosion under the gated spillway, and erosion in the areas on the hillside beneath the emergency spillway.  According to the California Department of Water Resources, repairs at Oroville Dam will remain ongoing into 2018 or beyond.