Tragedy struck on The Agua Fria River Monday, December 18, 1978, when both I-17's north and southbound spans collapsed into the raging desert torrent at Black Canyon City, Arizona. Five people died when two vehicles plunged into the swift, chocolate waters.
We've decided to dig deep back into one of I-17's worst natural disasters. More questions remain than have been answered. Over 39 years later, available details are few and far between.
We found this partial account from The December 20th edition of "The Arizona Republic":
"Highway patrolman Chuck Torrey was in Black Canyon City Monday night when he heard a citizens band radio report that the bridge was shifting. "I went to the southbound side of the bridge and the bridge was falling apart by the time I got to it. There were several cars on the southbound side and two cars on the northbound side," he said. "About that time the bridge dropped down about six feet." he said. The 34-year-old patrolman attempted to throw a tow strap to a trapped occupant in one of the cars. "But the bridge started to come down and I jumped in my car, threw it in reverse and got out because the road beneath me was crumbling," the officer said. Torrey said the bridge made "a deep groaning sound and metal was twisting." He said after he backed up, another patrolman had arrived on the opposite side of the collapsed bridge and the two officers blocked it off. When the bridge finally collapsed, he said, the missing woman was out of her car and both she and the vehicle were plunged into the river. The car, a late model El Camino pickup, was located about a quarter-mile from the bridge. The top of the pickup had been sheared off. State engineers said the river washed away cobbles and boulders that supported the $2-million twin span. The flood "scoured out" the material beneath the south abutments, dropping it down and pushing it sideways. Sam Lanford, an engineer with the state Department of Transportation, said "there was certainly nothing wrong with the bridge's structure. It just gave way to nature." When the south end of the bridge dropped shortly before midnight Monday, the force of the stream came to bear on the rest of the superstructure, pushing it off its supports. The south and northbound portions of the 450-foot bridge fell apart as the river purged its banks."
"Tuesday were searching for up to five persons believed to have been swept down the rampaging Agua Fria River after the bridge on Interstate 17 collapsed. One car driven by 40-year-old Jeri Lee E. Griffith of Sedona was found submerged in the river about 9 a.m. Tuesday. Efforts to find the woman were unsuccessful by nightfall. Authorities also said a late-model Pontiac station wagon may have fallen into the river with four members of a Phoenix family inside. Authorities would not identify the four immediately. "All I can say is that a party of four is overdue on their arrival in Phoenix," said Department of Public Safety Lt. F.J. Avars. "They were expected by certain people who arrived in Phoenix late Monday night." "Our next step is to wait for the water to drop." Ayars said. "If it clears up we can get into a ground search maybe within a couple of days." Ayars said the Griffith woman was traveling to Phoenix to pick up her husband, Paul, at Sky Harbor International Airport. The missing Phoenix family had attended a church revival Monday night in Sedona and was to have returned to Phoenix on 1-17."
I-17's twin 422-foot spans over The Agua Fria River were constructed in 1960. Documentation is yet to be found of the engineering of those bridges 57 years ago. In any event, Arizona entered a protracted "wet cycle" in late 1978. The United States Geological Survey produced a 150 page report on the storm events from November 1978 to March 1979 with particular emphasis on the December 16-18 episode.
Although the term "atmospheric river" did not come into weather lexicon until the 1990's, all evidence points to a prolonged, highly-amplified series of atmospheric rivers that washed into Arizona during that time period.
The atmospheric river that hit Arizona the week before Christmas 1978 was particularly intense, producing historic flooding on many of Arizona's creeks, streams and rivers. Although a figure of 60,000 cfs has been bandied about with regard to the failure of the Agua Fria Bridges, the flow was probably more in the 30,000-32,000 range.
Confusion about the flow stems from the fact that the Agua Fria Rock Springs gage is widely cited for "the" flow for the event. The Agua Fria Rock Springs gage is located quite some distance downriver from I-17. This gage logged a max flow of 52,800 on December 18, 1978. However, Black Canyon Creek logged a peak flow of 22,300 on December 18. Black Canyon Creek joins the Agua Fria well downriver from the I-17 bridge site. Moreover, the Bradshaw Mtns. were hit heavily by the storm while the mainstem area of the Agua Fria was not.
It appears that the engineering decision to anchor bridge pier footing on relatively unstable conglomerate was the primary cause of the ultimate failure of the twin spans.
We are going to be digging into this story for the foreseeable future. We have many objectives for this story.
First and foremost, we would like to Memorialize the victims of this highway disaster. They all deserve at least that much. We've always wondered why there isn't a plaque of some sort located beside that bridge to memorialize those innocent victims.
Second, we intend to delve into ADOT archives and see what we can dredge up on this topic. We have NO idea whether we will be able to find anything in ADOT archives but we're going to give it the good old college try.
Third, we'd like to find the Highway Patrolman who responded and made such a gallant effort to save one of the victims. He's undoubtedly retired by now and we hope he is still with us and willing to talk.
Fourth, we will take a look at how the current spans are faring with the bridge safety index.
Fifth, we'd like to find one or more weather experts to discuss if and how such a repeat incident might happen once again.
Sixth, we'd like to obtain some possible validation of our theory that atmopsheric rivers were responsible for Arizona's devastating weather pattern in that epic, historical November 1978-March 1979 time period.
Finally, we plan to visit the site and walk around and take photos and reflect on this tragedy. People take highways for granted. Highways are to a large degree considered a haven of safety. You expect that you keep driving and you will get to your destination. When the pavement (and your world) falls out from beneath you, it is one of life's truly rudest of shocks...and often very fatal.
As a footnote, here is how the storm pattern was described for the December 16-18, 1978 event:
(From Page 13 of the USGS Report cited above)
"The heaviest and most extensive rainfall of the study period occurred during December 17-20. Total precipitation during this period ranged from less than 1 inch in northeastern and southwestern Arizona to about 10 inches in the Mazatzal Mountains northeast of Phoenix.
The U S Environmental Data and Information Service (1979h) described the storm as follows:
"Several days before the onset of this storm on the night of December 16, an upper low was meandering over the eastern Pacific near 27 °N [latitude] and 133 °W [longitude] This cutoff low developed several days previously from an eastern Pacific trough. The north portion of the trough moved eastward and a strong zonal flow was established across the northeastern Pacific, much of the United States, and southern Canada. The air in these westerlies [winds moving from the west] was quite dry Arizona, likewise was dry. As the upper low continued to meander, moisture began to increase over the southwestern United States. Satellite imagery from December 14 through 17 showed a large mass of cloudiness stretching from Baja [Mexico], southwestward. The flow across the Baja Peninsula and southern California was still anticyclonic, and all cloudiness streaming into Arizona from the southwest was cirriform [high thin clouds]
By Friday, December 15, 1t was evident that a short-wave trough was intensifying near 170 °W. Within 24 hours this developed into a moderately strong trough in the Gulf of Alaska near 140 °W. By OOZ Sunday, December 17 [1400 hours December 16 MST], the trough had deepened, moved to 133 °W, and absorbed the low-latitude low, [thus] forming a large amplitude quasi-stationary trough. The trough continued to deepen while remaining nearly stationary. As the upper portion of the trough moved eastward, the lower portion remained between
120°-130°W, from Sunday morning, December 17, to Tuesday morning, December 19. At the same time, a short wave rotated out of the long-wave trough, resulting m a steady flow of nearly saturated air from the southwest into Arizona. Cloudiness over Arizona thickened rapidly Saturday night as the flow backed from west-southwest of southwest. Rain began over most of Arizona before dawn Sunday and gradually increased in intensity The most intense rains were Sunday night and Monday morning, decreasing slowly until they were virtually over by Wednesday morning [December 20]. As the heavy flow of moist tropical air encountered mountain ranges, such as the Bradshaw, Mazatzal, and Sierra Ancha Mountains and the Mogollon Rim, large amounts of precipitation occurred because of the orographic uplift. Rainfall intensities were moderate to high but in themselves were not responsible for the high runoff. Few, if any, extreme intensities of short duration occurred during this storm, but rates of 0 .25 to 0.5 inch./hr were common throughout the foothills and mountainous areas of central Arizona on December 17 and 18, 1978."
Sources:
The USGS Report: https://pubs.usgs.gov/wsp/2241/report.pdf
Note that the page numbering is weird. We're using your PDF Reader's page number. It may or may not agree with "actual" page numbering.
Source of the photos: http://azsce.org/downloads/The%20High%20and%20Low%20of%20Engineering%20Options.pdf
Source of the newspaper quotes:
https://www.newspapers.com/newspage/119609355/
Acknowledgements: Many Thanks to the Phoenix National Weather Service Office Staff for their gracious assistance in sourcing the USGS report. Thanks also to Salt River Project Staff for their valuable insights.
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