Leaving Tempe high and dry
City will begin draining lake to make way for dam construction
Tempe will begin emptying Town Lake on Wednesday to complete work on a new dam, a process that will close the popular attraction to all activities until at least late April.
The closure, which begins the same day, will affect recreational boaters and anglers, as well as groups that use the 16year-old lake for competitions or training.
“No boating, no fishing, no water,” said Nikki Ripley, a city spokeswoman, summing up the situation over the next few months.
The process of moving water out of the lake and later refilling it will take up to three weeks each time. The city ex- pects that about 2,700 acre-feet of water, or about 880 million gallons, will fill the lake once the new dam is completed. About 800 million gallons has occupied the lake while a temporary rubber dam has been in place.
Work on the new steel and concrete dam at the west end of the lake has been ongoing since June 2014. It will replace an inflatable rubber-dam system that was installed in1999 to create the lake by holding back water that otherwise would flow through the Salt River bed. The original rubber dam on the west end failed in 2010, causing an estimated 1 billion gallons of water to rush downstream, the amount the lake held at its peak. The temporary rubber replace-
ment dam has been in place since then.
The new dam construction will cost about $46 million. Of that, $33 million is coming from voterapproved bonds, while the rest is from the city’s general fund, Tempe officials said. The new dam, which will span a distance of about 950 feet across the river, is projected to last at least 50 years. PCL Construction, which is headquartered in Edmonton, Alberta, is the general contractor.
Once the lake is emptied, work can begin on removing the rubber dam on both the west and east ends of the lake. Work also will be completed on the new west-end dam, just west of the rubber structure that rests beneath a pedestrian walkway. Eight of the new dam’s seven hydraulic gates are completed, with the remaining gate left open to allow workers access between the new and old dam.
The east side won’t need a replacement dam, since water naturally flows to the west, forming the lake against the western dam, Ripley said. A concrete wall that is in place at the east end of the lake will remain after the rubber bladder is removed there, allowing the lake to maintain its form, but pressure from the flowing water only impacts the west end.
Moving all that water out of Town Lake
The city will remove the water using a series of pumps on the north side of the lake and east of the Mill Avenue bridges. The pumps will send the lake’s water flowing through two pipes that run under Loop 202, at a rate of about 25 cubic feet per second, 24 hours a day, said Jim Duncan, an engineering analyst for Salt River Project’s Water Engineering Group.
From there, the water will flow through an irrigation ditch and into the head of SRP’s Grand Canal, located north of the lake and west of Mill Avenue, Duncan said. At that point, it will become part of the SRP water-delivery system, continuing westward in the canal through central Phoenix to its terminus in Glendale, near 99th Avenue and the Loop 101 freeway, not far from University of Phoenix Stadium, Duncan said.
Ripley said while most of the water will go into the canal, some will be allowed to trickle through the Salt River bed downstream.
The city already has taken steps to prepare for life with an emptied lake, she said.
The city hired an aquatics consultant to help collect fish from the lake bed and the pools of water that will remain. In addition, state Game and Fish officials in late 2015 lifted limits on fish caught from the lake and the city did not restock it with trout this winter, as it regularly does, Ripley said.
The aquatics consultant also will monitor mosquito problems that result from standing water pools and take steps to keep them in check, she said.
An empty lake means regular lake users will have to wait for the water’s return or go elsewhere for boating or fishing. Boat rentals are a lake fixture, along with kayaking and group training. Ripley said the city has notified groups about the pending closure and posted signs around the lake informing users.
“This has a huge impact on our club for both our current members’ training and for recruiting new members,” said Larissa Gaias, co-president of Team Arizona Outrigger Canoe Club, which trains regularly on Tempe Town Lake for competitions. The group has about 30 full-time members and 20 recreational paddlers who participate in training.
“We will go to Saguaro Lake to practice, but we obviously won’t be able to get on the water as frequently as we can in Tempe,” Gaias said. “Our first major race of the season is in early May in San Diego, and we expect that we won’t have as many (members) ready to compete by that point this season as we do typically.”
Saguaro Lake is about 30 miles northeast of Town Lake.
All water is not considered the same
Refilling the lake is a fairly simple process, but legally allowing water to again be used for that purpose is somewhat complicated, Duncan said.
SRP-delivered water can only be used on lands that are entitled to its rights. That includes Valley municipalities. However, Town Lake, which is formed on the Salt River bed, is not included as part of Tempe’s water rights, he said.
Two things will allow the city to overcome that:
Tempe will receive water credits for the water it empties into the Grand Canal. The credits will entitle the city to receive water back to refill the lake.
The city also will receive water from the New Conservation Storage program at Roosevelt Lake. As part of that project, which strengthened Roosevelt Dam, several Valley cities agreed to contribute money to raise the dam 77 feet. That increased the lake’s storage capacity and participating cities can tap nearly 300,000 acre-feet of that additional water.
Gravity will be the main force to refill the lake, Duncan said.
Water from SRP’s Crosscut Canal, located near Papago Park, will feed into a small reservoir near Tempe Rolling Hills golf course. From there, the water will be released into an irrigation ditch that flows from Papago Park into Tempe’s Moer Park south of Curry Road and into a storm drain near the Mill Avenue Bridge. The water then will be diverted into the lake’s north side, between Mill Avenue and a railroad bridge.
The dam itself will hold water up to about 18 inches below the height of the closed flow-control gates. The hydraulic operation of gates will allow water to be released as needed, Duncan said.
“No boating, no fishing, no water.”
NIKKI RIPLEY
TEMPE SPOKESWOMAN, ON THE CLOSURE OF TEMPE TOWN LAKE AS A NEW $46 MILLION STEEL AND CONCRETE DAM IS FINISHED