Understanding Piping and Seepage Failures - The No. 1 Dam Safety Problem in the West

No, it is not earthquakes! No, it is not overtopping as a result of floods! It turns out that for dams greater than 50 feet high piping is the predominant failure mode in the Western United States.
An awareness of the relative criticality of the various threats to the safety of a dam is important in the conduct of dam safety programs. Thus, in the early 1980 1 s, as part of Reclamation's dam safety program development, the author attempted to gain a general understanding of the relative risk of failure of dams in the United States. This was done by examining failure rates according to height, date of construction, type, region of the country (Eastern or Western United States) and mode of failure [1, 2). Some of the results of that study, relevant to Western U.S. earthfill dams are summarized in tables 1, 2, and 3. Table 1 illustrates the distribution of dams by type, height, age and location. Table 2 illustrates failure rates for earth dams by these categories, and Table 3 provides a breakdown of the percent of failures by type.
The key statistic, relative to the subject of this paper, is that the study showed that 60 percent of the dam failures in the Western United States for earth dams greater than 50 feet high were classified as piping failures.