Much like tires that wore out faster than they were supposed to, the rubber dams on Tempe Town Lake are aging faster than promised.
Instead of holding up 25 to 30 years, the dams may wear out in just 10 years, city officials said this week.
Though the city thought another generation of Tempe leaders would worry about replacing the dams, officials are preparing to set aside at least $16 million to buy new air-filled dams in the next few years.
The dam is safe despite premature wear, city officials said.
“I really doubt that it would all of a sudden burst and go,” said Roger Hallsted, who oversees Town Lake finances.
The Valley’s intense sun, heat and low humidity triggered the dams to age so quickly. That’s why the four sections on the west end — which take the brunt of the afternoon sun — are what the city is most worried about.
It’s too soon to tell exactly how much longer the dams will last. But after frequent inspections with the manufacturer, Bridgestone, the city is looking to replace a section on the west end in three or four years. Bridgestone will take it to its factory in Japan and subject it to abuse to see how much — or little — strength the material has.
At that point, the city will know if it needs to immediately replace the other three western sections.
“We may find out that we have three more, five more, seven more useful years on the ones we have left,” said Nancy Ryan, the Rio Salado Project manager.
Each western section — 240 feet long and 19 feet tall — costs about $3 million. The city is planning to bank about $16 million to cover installation and eventual replacement of the less expensive eastern dams.
Tempe installed the dams in 1999 when it created the 2-mile Tempe Town Lake. It used inflatable dams so it could lower them on the rare occasions water flows through the Salt River. Traditional dams would block too much water and lead to flooding.
The city envisioned a thin sheet of water would constantly flow over the western dam to protect it from the sun and heat. Pumps would return the water to the lake.
But when the city lowered the dams a bit, they sagged in the middle, Hallsted said. Because water flowed only over the middle, the city pumped the dams back up.
Bridgestone representatives said in 1999 that their dams could last 50 years, but that Tempe should expect 25 to 30 years because of the intense heat.
Bridgestone had no way of being certain, Ryan said, because of the dam’s size and location.
“This was the first time they had installed a dam that tall in a desert,” Ryan said.
A Bridgestone representative did not return calls Friday.
The eastern dams should hold up at least 15 years because they don’t get as much afternoon sun, Ryan said. And since last year’s wet winter, water has gathered and protected the dam from sun and heat.
The city can replace dam sections without draining the lake by dropping temporary metal sections into grooves on the concrete piers that support the dam.
City officials said they’ll explore legal action against Bridgestone. Mayor Hugh Hallman said he’s already located a video of a meeting where a Bridgestone representative assured city officials the dams would last 25 years. Councilman Hut Hutson said the high replacement cost should make the city consider false representation claims or other legal remedies.
“I’d like to look at that,” Hutson said.
Tempe Town Lake’s rubber dams
• Made in Japan by Bridgestone
• Four inflatable sections at each end of the lake
• Installed in 1999 for $4 million
• Inflated with air at seven pounds per square inch
• Originally expected to last 25-30 years
• Tear resistant and can repel a bullet
• Temporary dam can be placed to allow dam repair without draining the lake.