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Show PAGE 18 THE ZEPHYRJANFEB 1992 the collapse of glen canyon dam a futuristic government report by Thomas Budlong Juristic "government report came remarkably close to reality in May of 1883. A cold wet sudden heat wave, resulted in rapid mountain runoffs at unprecedented levels. The Bureau fated a spring fotewedby Tom Budtong's to draw down tfi'e lake during spillway (at 3700 feet above a few more feet the previous winter, and thus had no place to put the water. As tie lake approached die level), BuRec actually placed plywood across the spitiways to increase tie lake level sea Finally forced to open its spillways, water cascaded from the lake at a rate of 1 16,000 cubic feet per second Later, engineers discovered massive damage to one of the near vertical spiBway tunnels. The power of the water had cut through tie concrete been breached lining and ripped into the sandstone. Another few days, and the canyon waB might well have Due to the depth of the lake bottom at this point the behavior of the two leading waves from the two collapses was similar to deep water ocean tidal waves. A tidal wave In deep water causes a small, placid, vertical displacement of the water surface. When the wave reaches shallow water, the shore water Is sucked outward, followed by Inundation as the wave crest reaches the shore. After Inundation, the water returns to normal level. The depth of Lake Powell simulates ocean geometry. The dam, however, presents a vertical boundary, exactly the opposite of the sloping boundary of an ocean shore. Simulating ocean mechanics, the first wave caused a drawdown against the upstream side of the dam. The drawdown depth is unknown. This was followed by inundation which undoubtedly spilled over the dam. Unlike shallow, sloping shores In ocean wall of the dam would cause a series of drawdownlnundatlon conditions, the cycles at the dam. The first Inundation was therefore followed by another drawdown. The second wave, caused by the collapse of the east wall, arrived approximately coincident with the second Inundation of the first wave. The effect of the combination was an even larger breach of the dam. The top section of the dam was destroyed, releasing a massive wall of water and dam debris, a flood vastly larger than any known to recorded history. near-vertic- al L& July 4, 1994 FINAL SUMMARY REPORT Lake Powell Disaster Congressional Commission The Lake Powell Disaster Congressional Commission was authorized by Congress on November 15, 1992 to investigate the causes and effects of the Lake Powell disaster of July 4, 1992. Approximately 200,000 investigative man hours have been expended, Involving different government agencies, thirteen independent contractors, and testimony from over 500 witnesses and experts. It is the opinion of the commission that all currently available data relevant to the event has been recorded. This is a summary of the investigation. All material collected, in formal reports and raw data, is in the custody of the Library of Congress. The Commission members wish to thank all those who have worked on this massive undertaking, with special thanks to the individual members of Congress who have been instrumental In providing avenues for collection of information and testimony. This report is dedicated to the estimated 1300 people who lost their lives in the disaster. twenty-thre- e . Background Glen Canyon is located in northern Arizona and southern Utah. At its southern end the canyon is approximately 700 feet deep and 1400 feet wide. It terminates at Lees Ferry, Arizona, where it abruptly exits the Navajo Sandstone geologic formation into a relatively level area. Through the years, numerous dam site suggestions near the end of Glen Canyon have been made; the first was by Major Powell during his historic 1871 voyage down the length of the Colorado River. After decades of study and negotiation the Glen Canyon dam was authorized by Congress in 1957. Sited approximately four and one half miles below the UtahArizona border and sixteen river miles upstream from Lees Ferry, it was completed in 1964. The original constructed height was approximately 710 feet, with a width across the top of the dam of 1560 feet The closest town is Page, Arizona, two miles east, which was created to support the dam. In 1963 the gates of Glen Canyon Dam were closed, restricting flow on the Colorado River to begin forming Lake Powell. In subsequent years the lake filled, creating million acre-fee- t a reservoir of twenty-seve- n by 1980. Lake Powell represented one of the major water control features of the Colorado River Storage Project. Turbine generators at of electricity annually. The lake was Glen Canyon Dam created four billion kilowatt-hour- s used as a major recreational facility by over one million visitors as recently as 1991. On July 4, 1992 a partial collapse of the upper part of the dam released more than one third of the water in the reservoir in a little over three hours. The resultant flood was unprecedented In historic times and is classed as the worst peacetime disaster ever billion dollars worth recorded. It took over 1300 lives and caused approximately twenty-rigflood of damage to capital facilities downstream. control, electric power Irrigation, were all affected western for states recreational facilities and permanently. generation ht The Trigger Event This description Is reconstructed from witness reports and is believed to represent the most probable sequence of events. The actual facts, if different, would not be sufficiently different to be of consequence. The vicinity of Lake Powell experiences occasional violent thunderstorms and flash flooding In mid summer. Thunderstorms during the three or four days preceding the disaster were exceptionally frequent and violent, probably a result of the extra moisture from the previous winter, which was unusually wet and resulted in filling Lake Powell to its historic high level of 3708.4 feet. It is almost certain that the sandstone formations bordering Lake Powell had been saturated with this unusual amount of moisture and therefore weakened. The afternoon of July 4, 1992 experienced continuous thunderstorms and associated heavy Actual drawdown depths and breach volumes cannot be determined with any precision. The effects, however, are known. After the waters had calmed, between ten and eighty feet of the top of the dam had been tom loose and carried downstream. The turbine bays and machine shop below the dam were washed away. The highway bridge Immediately below the dam remained intact but was battered by debris. One single concrete boulder weighing eighteen tons with rough measurements of right by four by five feet was deposited on the bridge roadway. Approximately eleven million acre feet of water were released during the three hours immediately following the event. This brought the lake to the 3619 foot level, the lowest point of the break in the dam. Upstream Effects - Lake Powell The lake level lowered approximately eighty feet In three hours, the majority of the the afternoon of July 4, 1992 a massive piece of the western sandstone perimeter of Lake Powell, weakened by subsurface Immersion during the twenty-fou- r year life of the lake, the Immediately previous wet winters, the continuous rain during the preceding days, and immediate flash flooding, collapsed into the lake. The displaced volume of material has been estimated to be 17.6 million cubic yards. This created a "tidal wave" radiating upstream, across the lake, and downstream from the collapse point. The upstream wave caused no major damage. wave arrived The lake width was about 0.5 miles at this point. When the cross-lak- e at the opposite side it caused collapse of that wall, which had been weakened by the same forces responsible for the initial collapse. This slump Is estimated at eight million cubic yards. This caused a second radiating tidal wave, closely following the first elevation change and water discharge taking place the first thirty minutes. Approximately 200 boats, mostly rented houseboats, containing over 700 people, were swept over the dam In the rush of water. A much larger number were stranded on newly formed shore or remained floating on the lowered lake. Since the current during the initial drainage varied from extremely fast near the dam to mild 200 miles upstream, survival depended on distance from the dam and proximity to shore. Those some distance from the dam were able to motor upstream faster than the current caused by the draining. Those near shallow, sloping shores were able to ground themselves as the water receded. Boats moored at shallow slopes were quickly beached. Boats moored to vertical walls broke their mooring lines as the water level fell. Most occupants were able to scramble to safety In the few minutes available as the water level rapidly dropped. The most tragic were those near the dam who could not reach shore or motor against the current snd were swept Into the flood almost immediately. Approximately one half the floating facilities at the Wahweap Marina were lost Six were lost; all others on the floating marina facilities, warned by the initial wave swell people toward the dam from the slump, had sufficient time to get to shore. travelling Due to their distance from the dam, Dangling Rope Marina (forty miles upstream), and other facilities further from the dam saw no loss of life. Effects of the Event Downstream Effects - Marble Canyon Effect on Glen Canyon Dam Glen Canyon Dam is 7.4 miles downstream from the wall collapse point It took approximately ten minutes for the downstream wave from the Initial collapse to reach the narrow gorge of Glen Canyon continues sixteen river miles below the site of the dam, ending abruptly at Lees Ferry and the Paris River. This gorge continues the typical convoluted, twisted path of original river bed above the dam site. Average depth Is 600 feet downpours. At approximately 4:32 of In The |