Aging U.S. Dam Risks

Project to replace decades-old structure near San Francisco Bay has seen delays and unexpected construction issues.

The coastal mountains that frame this working-class city next to San Francisco Bay harbor a hidden menace: a reservoir 10 miles away that sits next to an active earthquake fault, which experts say could cause a dam break and flood thousands of homes.

The potential threat is so severe, the owner of the Calaveras Reservoir decided to build a replacement dam. But seven years after that work began, the dam is unfinished and isn’t expected to be complete until 2019—four years behind schedule.

The myriad issues hampering the Calaveras Reservoir project show how difficult it can be to repair or replace an old dam, which is of growing concern nationally.

An estimated 27,380 or 30% of the 90,580 dams listed in the latest 2016 National Inventory of Dams are rated as posing a high or significant hazard. Of those, more than 2,170 are considered deficient and in need of upgrading, according to a report by the American Society of Civil Engineers. The inventory by the U.S. Army Corps of Engineers doesn’t break out which ones are deficient.

But both funding and inspection staffing to deal with the problem are considered inadequate, the civil engineers’ report said. An estimated $64 billion is needed to upgrade those dams, including $22 billion for the ones posing the highest hazard, according to the Association of State Dam Safety Officials, a nonprofit safety group in Lexington, Ky.

“It’s a huge problem with limited resources,” said Ivan Wong, a consulting seismologist from Walnut Creek, Calif., who works on dam projects nationally. “We can barely pay for our schoolteachers, but if a dam fails and there’s a population downstream, we’re talking about a disaster. We have to fix our dams, there’s no doubt about it.”

While no dam collapses have claimed lives in the U.S. in recent years, historically they have represented some of the nation’s biggest disasters. The failure of a dam above Johnstown, Pa., in 1899 sent a wall of water into the town, killing 2,209. The near failure of an emergency spillway at California’s Lake Oroville in February, following heavy rains, prompted the evacuation of nearly 200,000 people downstream.

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