A yearlong project to replace Tempe Town Lake’s aging dams was set to begin today, just hours after it ruptured and drained the lake.
Had the dam failed just a few hours later, a torrent of water would have flushed away equipment and the people working on the project.
“I’ll be the first to tell you that sometimes it’s better to be lucky than to be good,” Mayor Hugh Hallman said at the side of the drained lake this morning.
Sections of the new dam are waiting to be installed, and Tempe expects it will refill the lake by Nov. 1. Some small events will be displaced but the lake should be restored in time for the Arizona Ironman competition, one of the lake’s main events.
The city tried to find a silver lining in the overnight loss of a lake that’s a centerpiece luring tourism and economic development to the once-blighted riverbed.
No injuries were reported, and an emergency alarm system on the lake was triggered within minutes of the rupture at 9:46 p.m. Tuesday.
“The system worked exactly as it was supposed to,” Hallman said.
Anybody who would have been on the lake would have noticed the water level dropping, but city officials said barriers by the dams keep boaters far enough away to prevent a current from sweeping them away.
Video surveillance on the dam showed the rupture was quick and there no warning signs or indication of intentional damage, City Manager Charlie Meyer said. The dam appeared to come apart at one of its seams.
With the lake’s billion gallons of water mostly gone, crews can replace the dams much faster and at a lower cost.
Tempe had planned to replace each of the four rubber bladders without emptying the lake, as a metal structure can be placed next to the dam to prevent water loss while a segment is removed.
It takes about six weeks to replace each segment. Once the dams are back up, it takes two weeks to fill the lake.
Three of the structures will be in place when the city starts filling the lake, while the temporary dam will be in place as the final one is being installed.
In the meantime, Hallman said visitors will notice a smell coming from the riverbed. Puddles up to 3 feet deep will accumulate in parts of the former lake.
Work still began on Monday, as two dam segments have been delivered by manufacturer Bridgestone Industrial Products. The last of the Japanese-made rubber bladders is set to arrive in October.
The dam’s integrity has been a known issue since 2006, when Tempe learned the rubber was aging much faster than expected. A manufacturing problem was to blame, Meyer said.
When the dams were installed in 1999, water was supposed to flow over the west dam to cool the rubber and reduce sunlight. But one of the segments sagged too much in the middle, making it impossible to have water flowing.
The city will install a sprinkler system so the new dams are kept wet. Also, a pedestrian bridge will be built over the dam after the repairs are made, and that structure will offer some shade.
The dams were supposed to last 25-30 years, but a 10-year warranty expired in 2009.
Tempe will lease the replacements for five years, after extensive negotiations with Bridgestone to have it cover some costs because the dams were not as durable as expected.
The transaction was complicated in part because Bridgestone exited the rubber dam business in 2008. These structures are the last ones the company plans to make, spokesman Don Darden said.
Bridgestone has about 200 rubber dams throughout North America, but none in a place as hot as Arizona, he said. The company said heat was to blame for the short lifespan.
“To our knowledge, this is not something that’s happened before,” Darden said.
Tempe expects Bridgestone to pay expenses related to the rupture, including the roughly $250,000 worth of water to refill it. Hallman noted the city has been frustrated with Bridgestone in the past but said he expects the company will fulfill its obligations now.
Tempe has studied dam replacements since learning about the problems with the existing ones. Options include other brands of rubber dams or other types of mechanical systems that allow for adjustable height. A solid dam is not an option: The river has had flows of 200,000 cubic feet of water per second in flood events, and any structures have to be lowered during those times to prevent Tempe from flooding.
Preliminary studies suggest a new system could cost $25 million, said Jeff Kulaga, an assistant city manager. But he cautioned that more research is needed to select the new system and determine its cost.
The city does not plan to replace the four rubber bladders on the lake’s east end because they are usually covered with water and haven’t suffered significant damage.
Until the lake is restored, Tempe will work to accommodate groups that planned events there. Hallman said it’s in everybody’s best interest to have the lake back as quickly as possible, but he said the work is complicated.
“This is not an Erector Set and this is not LEGOs,” Hallman said.
People gathered all day to gawk and snap pictures of the busted dam section near the Tempe Center for the Arts. Shiloh Murillo of Tempe visits the lake about once a week and returned this morning with her three daughters, ages 5 to 9. Murillo said she’ll probably keep going to Tempe Beach Park even if the lake is empty, in part out of fascination over how the repairs will be made.
She recalled watching the city build the 220-acre lake and following the debate over whether Tempe should have built the $45 million lake.
“This whole concept was pretty controversial,” Murillo said. “Not to me. I thought it was a great idea.”