An inflatable dam in downtown Tempe gave way just before 10pm last night, quickly filling the normally dry Salt River bed downstream with millions of gallons of water.

The dam failure was immediately reported to authorities by witnesses at the popular recreation spot in the Phoenix suburb, and emergency responders quickly went into overdrive.

"There have been no reports of injury or loss of life," says Tempe Mayor Hugh Hallman. Police were deployed to warn transients, who frequently use the dry riverbed below the dam as a camping site in the hot Arizona summers, of the approaching wall of water and a Phoenix police helicopter flew along the length of the riverbed to ensure no one was trapped.

Approximately three quarters of the 1-billion gal of water in the lake drained out overnight, with peak flows estimated by city officials at 15,000 cu ft per second.

Tempe opened the lake in 1999 within the dry riverbed, using eight rubber bladders: four downstream and four upstream to confine the water in a 2.2-mi-long space. City manager Charlie Meyer says the initial assessment is that a straight-line tear occurred along the seam of downstream bladder #2.

Over a year ago, the city inked an agreement with the dam manufacturer, Tokyo-based Bridgestone Corp., to replace the segments. "When the dams were originally installed, they were designed to have a watering system that would allow continuous flow of water over the dams," Hallman says. "That did not occur when they were first installed. In addition, during the period of time that we’ve had experience with them, the manufacturing process included ceramic chips that were intended to add to the length of life of the dams themselves, but in this desert environment with the cold of the winter and the heat of the summer and without the water system, the chips actually added to the deterioration of a piece of the dam structure."

Work was actually scheduled to begin today on staging and crane erection for the approximately $3.5-million project, led by the Tempe office of PCL Civil Constructors, to replace the downstream segments. The project has been delayed months by the region's unusually wet winter and spring. Now that the lake is emptied, work could be accelerated and construction costs reduced.

"We are evaluating the likelihood that we will go ahead with replacing several of the dam segments immediately while the lake is down, with the opportunity to perhaps bring up a fourth segment as the lake refills," Meyer says. "The original plan would have had us put up a temporary dam around each of the bladders and then replace the bladder behind that temporary dam, and it might be unnecessary for us to do that."

Follow SWContractor on Twitter