Dams and Public Safety, published in 1980 by the U.S. Department of the Interior (DOI), Water and Power Resources Service, did not anticipate that one of the concerns about the safety of dams in the United States would involve the possibility of terrorist attacks. In spite of that understandable oversight, a section about demolition discusses the fact that many "deliberate efforts have been made to destroy dams, including bombing sabotage and demolition." Many of us who were around during World War II remember the Royal Air Force (RAF) attacks on dams in Germany, but it is known less widely that two gravity dams—the 298-foot-high Burguillo Dam near Avila, Spain, and the 184-foot-high Ordunte Dam near Bilbao, Spain—were damaged during the Spanish Civil War in 1937. It was General Franco's Fascist forces that set off a 15-ton explosive charge in an inspection gallery at Ordunte.
But the structure, which had only been completed in 1934, was not destroyed, and its effectiveness as a civil engineering structure was impaired only slightly.
It also is a little-known fact that, in September 1941, retreating Soviet troops reportedly detonated 90 tons of explosives in a tunnel in the Dnjeprostroj Dam on the Dnieper River. The upper part of the dam, about 660 feet long, "disintegrated," and the resultant outflow of water through the breach reportedly reached a maximum rate of more than 1.2 million cubic feet per second.
Later during World War II, the RAF attacked three dams in or near the Ruhr Valley in western Germany. Two gravity dams—the 132-foot-high Mahne Dam and the 157-foot-high Eder Dam—were bombed in 1942. (Some readers may remember the 1954 movie, The Dam Busters, which is worth seeing the next time it is on TV.) Also part of the RAF trilogy of dam attacks was the 226-foot-high Sorpe Dam. The Mahne and Eder military actions released a deluge downstream that resulted in the loss of 1,200 lives.
The less-known Sorpe Dam was bombed several times during the war, but remained in service despite 11 hits. In 1945 and 1946, temporary repairs were made on the broken concrete core and the cratered embankments. In 1951, according to the DOI account, surges of water and clay suddenly occurred in the Sorpe Dam's drainlines. Grouting eliminated most of the silty leakage, but by 1956 soil loss totaled thousands of cubic meters, causing an embankment to settle almost 5 feet. Repair efforts in 1956 revealed the extent of the World War II damage. Dams and Public Safety discusses these problems and the Sorpe Dam repairs at some length. Repairs finally were completed in 1962 and included 174,000 linear feet of drilling and the placement of 4,350 tons of concrete and 1,700 tons of clay.
The Korean conflict also took its toll on dams. The 266-foothigh Hwa Cheon Dam, a concrete gravity structure on the North Han River near the 38th Parallel, was attacked and badly damaged by military forces from both sides in the war. Originally built by the Japanese during World War II, the construction was substandard because of difficult conditions at the time, including a hurried construction schedule and material shortages that resulted in design changes. When extensive repairs were undertaken after the war, the dam was found to be in very poor condition, not only from damage caused by three, 2,000-pound torpedoes launched by the South Koreans, but also by spillway scouring. The total coast of remedial work was about $13 million.
The last dam mentioned in the DOI's book is located near Vratza, Bulgaria. In 1966, sabotage was suspected as the cause of the breaching of a dike that impounded a sediment basin for a lead and zinc plant nearby. As a result, a 15-foot-high flood wave passed through two towns downstream. It was reported that as many as 600 people died, but other accounts indicated the toll was about 100.
Dams and Public Safety is prescient in its closing paragraph on the subject of demolition. The book was written long before the 9/11 terrorist attacks, but the following paragraph is of interest: "Although the consequences of hostile action against dams have been severe in some cases, the historical frequency of such events has been comparatively low. This is not necessarily reassuring, however. Looking to the future, the increasing potential for damaging attack cannot be disregarded. Both the numbers and sizes of dams have expanded rapidly in the 20th century. The record height doubled approximately in the period between the two world wars and has increased more than half again since World War II. This rapid growth has been experienced in both embankment and concrete dam construction. Even with the significant advances which have been achieved in the technology, these phenomenal statistics warrant serious analysis as parameters in the hazard equation." On a personal note, I am aware that precautions are being taken on this important subject, not only by civil engineers but also by the public. A year after 9/11, I visited a number of noted national monuments in the West. I spent a lot of time at Glen Canyon Dam and its impoundment upstream on the Colorado River, Lake Powell.
But, I could only visit a portion of most facilities. Security was tight—and properly so. Still, I would have liked to see more of this great American civil engineering wonder. Such is the price we must pay for our freedom.
Alfred R. Pagan, P.E., P.L.S., is a consulting engineer in Hackensack, N.J. He can be reached at 1-201-441-9719; or e-mail him at email@example.com.