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Western Dam Engineering Technical Note August 2016 2 Dam, You’re Getting Old! – Understanding and Managing the Risks of Aging Dams Introduction Dams are a vital part of our Nation’s infrastructure, providing tremendous economic, environmental, and social benefits, including hydroelectric power, water supply for drinking and irrigation, flood control, wildlife habitat, recreation, and navigation. The benefits of dams, however, are countered by the risks they can present. In the event of a dam failure, the potential energy of the water stored behind even a small dam is capable of causing loss of life, significant property damage, and an extended period of loss of the services dams provide [1]. Historically, some of the largest disasters in the United States have resulted from dam failures. The fact that a dam has successfully served its purpose for decades, or perhaps over a century, is not itself a positive indication for future performance. Dams are long-term structures and need to withstand extreme events. Because so many of a dam’s potential detriments caused by aging are internal and difficult to directly see, understanding aging effects and ways to monitor, detect, and manage these developing deficiencies is important to maintaining adequate dam safety. How old are our dams? At a current average age of 52 years, most dams in the United States are older than the median age of the U.S. population (38.6 years). The twentieth century was a golden era of dam building in the U.S., reaching its climax in the years following World War II. Dam building began to decline in the 1970s due to the increasing cost associated with new regulations governing dam building coupled with a decreasing demand. Figure 1 presents the construction era of dams within the western states of the U.S. (AZ, CO, ID, MT, NV, NM, UT, WY). In the western U.S. alone, there are more than 1,000 dams over 100 years old. Older dams were built with minimal design using manual equipment. These dams may have been built in the middle of nowhere but in many cases are high hazard dams in the middle of a residential area now. What is their condition? In its most recent REPORT CARD FOR AMERICA’S INFRASTRUCTURE, the American Society of Civil Engineers gave the condition of America’s dams a “D” defined as “Poor: At Risk.”[2] This is due in part to the growing number of dams needing repair due to the effects of their age, the increasing size of the population protected by dams, and the limited funding available to address deficiencies. Figure 1. Construction Year (Age) of Dams in the Western U. S. as of 2013 [3] Why do we care? The age of a dam has a significant influence on both its integrity and its potential to impose adverse impacts. These impacts include costly repairs to property, financial restitution and fines, loss of intended purpose of the dam, environmental impacts, and potential loss of life. Physical aging processes influence the integrity and longevity of dam structures. Understanding these aging processes is the key to understanding why the thought that “this dam has been here forever and works fine” denotes a false sense of security. The terms “Safety” and “Risk” are a function of both the likelihood of the structure to fail, and the resulting 450 430 250 310 720 800 1830 1720 850 430 250 380