Oroville Dam: repaired in record time | The Feather River suspension bridge over Lake Oroville
In the aftermath of Hurricane Maria’s sweep through the Caribbean, the United States was reminded of the urgent need to address the risk posed by its ageing dams as one of them – the Guajataca - threatened to fail in Puerto Rico, putting 70,000 lives at risk.
As if the damage wreaked by the hurricane on their two towns in the island’s northwest was not enough, survivors emerged from the rubble of their homes to an urgent call to flee.
Water was overflowing the spillway of the nearby Puerto Rico Guajataca Dam and risked sweeping away everything in its path – including what was left of their homes in the towns of Isabela and Central Quebradillas.
Damaged by the hurricane, the Guajataca dam was under enormous strain after the subsequent heavy rainfall had swollen its reservoir.
Guajataca Dam is failing: Stay away or be swept away
«Stay away or be swept away», warned the National Weather Service in a post on its website on September 26. «The risk of failure of the Guajataca Dam (continues), which would potentially cause life-threatening flash flooding downstream on Rio Guajataca», it added, referring to the river of the same name as the dam.
«River banks and culverts can become unstable and unsafe», it said. «Stay away from evacuated areas until told by emergency officials it is safe to return».
Speaking to U.S. television network NBC a few days earlier, Puerto Rico Governor Ricardo Rossello said 70,000 people in the river valley downstream from the dam could be in danger if the structure were to fail.
Television images of the waters rushing down from the dam joined those of the devastation brought about by the hurricane, which left many parts of the island without power or water.
Puerto Rico Dam Recalls Oroville Dam
The images, which were also posted on social media, recalled those from Oroville in northern California. The tallest dam in the United States saw its spillway suffer severe damage following heavy rainstorms in February, forcing the evacuation of more than 100,000 people who lived downstream.
Both cases are similar: old dams in need of inspection and repair overwhelmed by bad weather.
An interim status memorandum published on September 5 by an independent forensic team inspecting Oroville identified a number of design and construction weaknesses that might have facilitated the damage, such as a “deficient” drainage system and shallow rock anchorage.
Work is already underway to repair and reinforce the structure.
Puerto Rico Dam Reservoir Levels
Built in 1929, the Guajataca Dam is one of 38 dams in Puerto Rico, according to the National Inventory of Dams managed by the Army Corps of Engineers.
It is 120 feet (37 metres) high and nearly 1,000 feet (305 metres) long, lying across the Guajataca River to form a reservoir for drinking, irrigation and power generation.
The reservoir’s water storage capacity of 39,286 acre-feet (48.5 million cubic meters), but by 1999 it was reduced by sediment infilling to 34,276 acre-feet (42.3 million cubic meters), according to the U.S. Geological Survey.
According to the inventory of the Army Corps of Engineers, the Guajataca Dam in Puerto Rico was last inspected in 2013 and rated as having a “high hazard potential”.
