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WESTERN DAM ENGINEERING NEWSLETTER, VOLUME 4, ISSUE 2 AUGUST 2016
RISKS OF AGING DAMS, HYDROLOGIC INADEQUACIES, INTERNAL EROSION
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Western Dam Engineering <br /> Technical Note <br /> <br /> August 2016 <br /> <br />2 <br />Dam, You’re Getting Old! – <br />Understanding and Managing the <br />Risks of Aging Dams <br />Introduction <br />Dams are a vital part of our Nation’s infrastructure, <br />providing tremendous economic, environmental, and <br />social benefits, including hydroelectric power, water <br />supply for drinking and irrigation, flood control, wildlife <br />habitat, recreation, and navigation. The benefits of <br />dams, however, are countered by the risks they can <br />present. In the event of a dam failure, the potential <br />energy of the water stored behind even a small dam is <br />capable of causing loss of life, significant property <br />damage, and an extended period of loss of the services <br />dams provide . Historically, some of the largest <br />disasters in the United States have resulted from dam <br />failures. <br />The fact that a dam has successfully served its purpose <br />for decades, or perhaps over a century, is not itself a <br />positive indication for future performance. Dams are <br />long-term structures and need to withstand extreme <br />events. Because so many of a dam’s potential <br />detriments caused by aging are internal and difficult to <br />directly see, understanding aging effects and ways to <br />monitor, detect, and manage these developing <br />deficiencies is important to maintaining adequate dam <br />safety. <br />How old are our dams? <br />At a current average age of 52 years, most dams in the <br />United States are older than the median age of the U.S. <br />population (38.6 years). The twentieth century was a <br />golden era of dam building in the U.S., reaching its <br />climax in the years following World War II. Dam <br />building began to decline in the 1970s due to the <br />increasing cost associated with new regulations <br />governing dam building coupled with a decreasing <br />demand. Figure 1 presents the construction era of <br />dams within the western states of the U.S. (AZ, CO, ID, <br />MT, NV, NM, UT, WY). In the western U.S. alone, there <br />are more than 1,000 dams over 100 years old. <br />Older dams were built with minimal design using <br />manual equipment. These dams may have been built <br />in the middle of nowhere but in many cases are high <br />hazard dams in the middle of a residential area now. <br />What is their condition? <br />In its most recent REPORT CARD FOR AMERICA’S <br />INFRASTRUCTURE, the American Society of Civil Engineers <br />gave the condition of America’s dams a “D” defined as <br />“Poor: At Risk.” This is due in part to the growing <br />number of dams needing repair due to the effects of <br />their age, the increasing size of the population <br />protected by dams, and the limited funding available <br />to address deficiencies. <br /> Figure 1. Construction Year (Age) of Dams in the Western <br />U. S. as of 2013  <br />Why do we care? <br />The age of a dam has a significant influence on both its <br />integrity and its potential to impose adverse impacts. <br />These impacts include costly repairs to property, <br />financial restitution and fines, loss of intended purpose <br />of the dam, environmental impacts, and potential loss <br />of life. Physical aging processes influence the integrity <br />and longevity of dam structures. Understanding these <br />aging processes is the key to understanding why the <br />thought that “this dam has been here forever and <br />works fine” denotes a false sense of security. <br />The terms “Safety” and “Risk” are a function of both <br />the likelihood of the structure to fail, and the resulting <br />450 <br />430 <br />250 <br />310 <br />720 <br />800 <br />1830 <br />1720 <br />850 <br />430 <br />250 <br />380
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