The new American Society of Civil Engineers 2017 Infrastructure Report Card (ASCE) has identified 15,498 high-hazard dams, whose failure could risk loss of life.

ASCE is appropriately holding this year’s Environmental & Water Resources Institute (EWRI) in Sacramento, California from May 21 to 25. The meeting is an opportunity for its members and infrastructure regulators to share ideas and strategies to address the growing risk of life-threatening catastrophes, exposed this winter by the failure and near-collapse of Oroville Dam’s spillway due to the dangerous combination of age and lack funding to address known infrastructure risks.

The average age of America’s 90,580 dams is 56 years, the same age as the Oroville Dam, which the California Department of Water Resources began constructing in 1961. As America’s tallest dam, Oroville was built with what was considered at the time to be the best engineering and construction safety standards to withstand floods and earthquakes.

Over the next almost six decades, the U.S. population grew by 57 percent to 321 million, and California’s population has grown by 136 percent to 39.2 million. But despite the improved collection of scientific and engineering data, there has been little new infrastructure built, and greater pressure is being put on aging dam systems.

The ASCE annual report notes that the Association of State Dam Safety Officials estimates that the cost to rehabilitate the nation’s federal and non-federal dams would now exceed $64 billion.

The number of high-hazard dams — those whose failure would be anticipated to cause loss of life — climbed by 52 percent in the last 12 years, from 10,213 to 15,498 dams. Another 11,882 dams are currently labeled as significant hazard potential, meaning that they are expected to soon join the watch list for high-hazard dams. The cost to rehabilitate just the most critical dams is estimated to cost $22 billion.

The U.S. Army Corps of Engineers estimates that more than $25 billion will be required to address federally-owned dam deficiencies. But at the current congressionally-authorized rate of investment, those repairs would take over 50 years.

Frank Blackett, a regional engineer at the Federal Energy Regulatory Commission’s Division of Dam Safety and Inspections, told the EWRI attendees that federal regulators, who have authority over licensing of about 16 percent of America’s dams, are re-evaluating how they conduct dam inspections following the Oroville Dam spillway crisis, according to the Sacramento Bee.

He added that none of the federal and state safety inspectors that visited Oroville Dam over the last decade recognized the now obvious signs that a giant sink-hole could form in the spillway, causing the crisis evacuation of 188,000 people.

Blackett stressed that FERC has stepped up on-site inspections and is re-evaluating its construction and design models to anticipate scenarios that could lead to infrastructure failures. FERC has also hired outside consultants to perform an internal audit of how federal regulators can improve their inspections and dam oversight.