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<br />47 <br /> <br />Resulted in <br /> <br />Graham <br /> <br />Table 2. Failure of Older U.S. Dams That <br />Loss of Life <br /> <br />Percentage of failures <br />during decade of dams <br />more <br /> <br />than 50 years <br />old <br /> <br />Percentage of dams in <br />U. S. inventory over <br />50 years old: <br /> <br />Decade during <br />which dam fail- <br /> <br />ure took place <br /> <br />50 <br /> <br />14 <br /> <br />1960s <br /> <br /> <br />. <br /> <br />33 <br /> <br />15 <br /> <br />1970s <br /> <br />50 <br /> <br />20 <br /> <br />1980s <br /> <br />33 <br /> <br />27 <br /> <br />1990s <br /> <br />42 <br /> <br />conditions <br />All of the other dams a the <br />reservoir to rise to higher than normal levels or overtopping. It can be <br />concluded that older dams have a higher rate of failure than newer dams that <br />have passed the initial test of being able to hold water. However, it can not <br />be concluded with the data available that the aging of the U.S. dam inventory <br />is adding to our risk. Most of the over-50-years-old dams that failed did so <br />during a major flood event. These older dams, built using less demanding <br />design floods, would be expected to have a higher failure rate than newer <br />dams that generally have been designed using more demanding standards. <br />Data is also available for the failure of dams in the United States (Hatem, <br />1985). This analysis indicated that during the period 1971 to 1980 there were <br />100 dam failures for which the age at the time of failure could be determined. <br />The failure of dams more than 50 years old accounted for 32 % of all dam <br />failures during this time. The number of dams in the U.S. during this time <br />that were more than 50 years old was about 15 % of the total number of dams. <br />Thus, dams that were more than 50 years old failed at a rate about double the <br />expected rate if failures were evenly distributed based on age. <br /> <br />23 <br /> <br />an indication that the dam had deteriorated to a point of failure <br />failed either as result of rainfall that caused <br /> <br />Average <br /> <br /> <br />[ <br /> <br />Conclusion <br /> <br />suggests that older dams are more prone to failure than <br />that have passed the initial test of being able to hold water. The <br /> <br />The evidence <br />newer dams <br />