Here’s still another reason why Emergency Action Plans (EAPs) for High-Hazard Potential (HHP) dams are important: Warmer average temperatures can shorten the life of concrete. While earthen dams are by far the dominant structural type, many of them also have concrete spillways and other features. The National Inventory of Dams reports there are 1,979 concrete dams around the nation, 543 masonry dams, and many others with concrete components.
Engineers have extensive knowledge of the long-term corrosion and decay of concrete composition and rebar as environmental elements work on even the best built dams. But two Northeastern University researchers, civil engineer Matthew Eckelman and graduate student Mithun Saha, studied the impact of new projections of rising temperatures and global warming on the lifespan of concrete.
As reported in the Boston Globe, the study focused on two processes that slowly eat away at concrete: carbonation (in which carbon dioxide diffuses into concrete) and chlorination (in which chloride ions, dissolved in water, are absorbed into concrete). Eventually the carbon dioxide or chlorides reach the rebar inside, causing it to corrode and expand. The process is largely invisible until potions of a dam show cracks or chunks of concrete fall away.
Dams typically have a design-life of 50 years. Urban building codes specify that concrete should be formulated and built to last 75 years. Eckelman and Saha realized that those building practices didn’t take global warming into account, and how the climate will change over the life of a structure when considering both the temperature and the rising levels of carbon dioxide, which is part of the carbonation reaction. So a 75-year design life could be in trouble within 50 to 60 years, as much as 25 years sooner than if temperatures remained steady.
HHP Concrete dams that are federally built and/or regulated will have EAPs and regular inspections. State-regulated concrete dams may not be required to have EAPs, and dam safety inspectors may not have access to the sophisticated inspection technologies available to federal agencies. Dams in coastal states such as Georgia, North Carolina, Texas and California already experience more onshore storms that brings additional oceanic chemistry onto the dams. And deterioration may be faster in regions such as the Southwest and West where temperatures may become even more extreme.
The Northeastern study was focused on the Boston area’s buildings, bridges and infrastructure, where the impact will be largely financial for repairs needed sooner and more costly building practices to avoid corrosion in the future. Eckelman and Saha expect the first wave of advanced deterioration to begin around 2025. They note that concrete used in the 1950s and 1960s was often weaker.
With an urban building or a highway, warning signs of concrete deterioration can be more readily spotted and acted upon. With a dam, particularly one privately owned and not accessible to many visitors, those symptoms may not be as easy to see or, worse, may be ignored for years.
Once discovered, problems with concrete dams and elements can be repaired and maintained, but the public at risk from HHP dams would be better protected with EAPs on any HHP dam.