It's not a common event. Rarely does one see a lake just drain away, spilling millions of gallons of water and leaving only about three feet or less (of its normal 16 feet) in the basin, which just hours before had offered Arizona boaters a convenient venue for practice, competition, and fun on the water.
Thankfully at night -- around 10 p.m. July 20 -- a 16-foot section of the Tempe Town Lake (TTL) dam broke and sent a wall of water gushing down the dry Salt River bed. Had the incident occurred during the day, there might have been significant damage to boats on the lake or injuries to boaters and others nearby. However, at press time, there have been no reports of injuries, and local officials say that no structures are in danger.
So, what happened? Simply, a rubberized dam burst. Or put another way, one of its 16-foot tall inflatable bladders just popped. The lake has four inflatable dams on both ends, and the sections were supposed to last for 25 to 30 years.
The Sun Takes Its Toll
However, as far back as 2007, Tempe officials worried that the fiercely harsh sun and dry climate would be tough on the rubber dams and that they might have to be replaced in a few years. (By the way, the City of Tempe checks the dams about once a month; they fixed two tears in 2002.)
A little over a year ago, Tempe officials chose to ignore a safety recommendation from the rubber dams' makers. Why? Because they were convinced that sufficient safeguards were already employed to prevent the dams from deflating.
Spokeswoman for the City of Tempe Kris Baxter-Ging reportedly said that workers were speeding up an already underway effort to replace the dam's bladders as the project had been delayed earlier by winter flooding. Officials determined that there was no criminal activity involved in the dam's failure.
Authorities said Tempe Town Lake could lose up to 75 percent of its water. Mike Reichling of the Tempe Fire Department said the man-made lake, which can hold up to 1 billion gallons of water, will likely remain at its current depth until the dam can be fixed.
Witnesses reported hearing a large "ka-boom" and felt the ground shaking. Others said the dry Salt River bed filled within seconds and they saw small animals scurrying out of the path of the flood waters.
Sirens began screaming out their warning within minutes, and first responders ran along the river bed to warn anyone there, especially any homeless persons who sometimes camp on the river bottom during summer months.
Tempe Mayor Hugh Hallman is reported to have said that water was flowing at 15,000 cubic feet per second, equivalent to the amount released during heavy storm flows.
So, what now? Hallman commented that the lake will probably be closed to the public until the fall. Repairs and replacements will be made while the lake is empty.
There had been reports of concern from the manufacturer of the dams, Bridgestone Industrial Products. The issue was that boats on TTL would get too near the dam and puncture it. Consequently the City strung a line of buoys across the lake to prevent just such an occurrence.
In 2009, Bridgestone requested that the City consider if the safety measures were enough "to prevent injury and reduce the risk of loss of life" if the dams were to rapidly deflate. At the east end (upstream) dams are submerged and have not failed. However, a plan to keep the ones on the west side wet did not work, and the rubber was exposed to the blistering sun, damaging the material.
So, whose fault is that? Tempe and Bridgestone have argued over that point, and in March 2009, the City Council okayed an agreement for the manufacturer to replace the four damaged dams on the western end of the lake. A sticking point remained, however: the question of people's safety should the dams deflate.
Bridgestone recommended that the city increase the buffer zone between safety buoys and the western dams, add warning signage, and enhance the alarm system.
To temporarily replace the dams would cost an estimated $2.5 million dollars. Earlier this year, Tempe budgeted an additional $250,000 to fund the project's contingency costs. Bridgestone was expected to reimburse Tempe up to $3 million of the costs to replace the dam.
Tempe Town Lake, containing 977 million gallons of water, had its 10th anniversary Dec. 12.
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