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Frequently Asked
Questions
Where is the Water to Refill Town Lake
Coming From?
Water to fill Tempe Town Lake will
come from Tempe’s New Conservation Storage (NCS) at Roosevelt Lake, part
of the Salt River system that Tempe Town Lake resides within.
The cost of refilling the lake will be less than $50,000.
This amount is based on Salt River Project’s water transportation charge
of $16.77 per acre-foot. There is no charge for the actual water. It
will take between 2,500 – 3,000 acre-feet to replenish Town Lake.
The water will come to Tempe
from Roosevelt Lake down through the SRP chain of lakes on the Salt
River, be diverted from the Salt River at Granite Reef Dam into the SRP
Arizona Canal, then to the SRP Crosscut Canal and into SRP lateral 2-4.6
off of the Crosscut Canal forebay. The SRP lateral 2-4.6 goes under Mill
Avenue/Van Buren and is diverted to Tempe Town Lake via a storm drain.
Click
here to watch the video.
View Water Path in a larger map
How Do
the Dams Work?
The Tempe Town Lake inflatable dams are made of three
main elements:
·
- a flexible, rubber coated fabric
tube fixed securely to a concrete base slab by clamping bars and anchor
bolts;
·
- an operating system that controls inflation and deflation of
the tube; and
-
an automatic safety device that ensures tube
deflation in flood situations.
Each section of dam, or bladder, is about 240 feet long,
weighs 40 tons and is more than one inch thick.
The west dams are 16 feet high and sit on a three-foot
base. The east dams are five feet high and sit on a two-foot cement
base.
When water flows from upstream dams, such as the
Roosevelt Dam, notification is made to clear downstream users of the
Tempe Town Lake and the Salt River bed. The downstream dams are then
lowered, releasing water from the lake and westward down the Salt River
channel. Floodwater is then allowed to flow through the lake. The dams
are inflated once the flood nears its end, capturing the tail waters of
the flood and refilling the lake.
Why
Inflatable Dams?
Inflatable dams are best used in small to medium sized
watercourses where width is much greater than height, such as rivers.
The advantage of inflatable dams is that they allow for long spans of
barrier with few structural piers to interfere with passing debris. They
can easily attach to any side slope.
Tempe Town Lake is part of the Salt River. As such, when
floods happen, Town Lake has to be ready to be lowered and act like a
river, allowing water to pass through in a controlled manner.
One of the features of the inflatable dams is their
ability to deflate quickly and easily to prevent upstream flooding. The
dams at Town Lake can be deflated and inflated within 30 minutes,
offering control and a method of releasing and recapturing water.
Because Town Lake receives water from several sources,
including the Salt River, the Verde River, the Indian Bend Wash
Greenbelt and smaller sources such as the Mesa Water Reclamation
facility and sand and gravel operations, during floods, debris comes
through the lake. In the past, entire trees, refrigerators and other
large pieces of trash have gone over the top of the dams, carried by the
water from far upstream. The inflatable dam system allows this debris to
pass through easily because of the very large spaces between the four
bladders. Traditional concrete dams with their smaller spillways do not
offer the same level of response.
What
Happened to Make the Lake Drain?
There are four rubber bladders that hold back the waters
of Tempe Town Lake. Bladder No. 2 at the west end of Town Lake, near the
Tempe Center for the Arts, burst. A rip in the seam of the bladder was
found near the top of the bladder. No criminal activity was involved.
When the bladder tore, the air pressure was released and
the dam deflated very quickly. Water rushed out of Tempe Town Lake into
the empty river bottom, in exactly the manner that would be expected.
Tempe had a response plan for this that had been practiced, and it was
implemented instantly.
Was Town
Lake Safe Before the Dam Rupture?
Tempe worked to ensure the safety of residents and
visitors to Tempe Town Lake. Staff placed a buoy line 1,000 feet from
the western dams for the specific purpose of ensuring the safety of any
boats or swimmers in Tempe Town Lake in the event of an emergency. Also,
we have signs around the lake to keep people out the river bottom west
of the western dam.
The dams are monitored for safety, which is why we were
able to respond as quickly as we did when Bladder No. 2 burst. Tempe had
an emergency action plan and it was activated immediately. Tempe
emergency personnel had practiced this plan just months before Bladder
No. 2 burst.
No one was hurt and no buildings were damaged when the
deflation of the bladder occurred. Police and fire crews from Tempe and
adjacent cities went into action instantly to ensure no one was in the
river bottom.
Bridgestone told Tempe that the bladders would last 25-30
years. In 2002, two bladders had to be patched. Before the warranty
expired, Tempe proactively negotiated replacement bladders. Bridgestone
would pay to manufacture the bladders and cover the cost of their
installation.
Bridgestone determined the order in which the bladders
would be replaced, and determined to start with Bladder No. 3, followed
by Bladder No. 1. Bladder No. 2 was scheduled third for replacement.
The original construction schedule was to have started in
January 2010, however, flows from winter rain and snowmelt delayed
construction.
Will the
Next Dam Be Safe?
Tempe is taking even more precautions to ensure that
residents and visitors to Tempe Town Lake are safe. The replacement
bladders will not have embedded ceramic chips.
The bladders will also be cooled by a watering system and
shaded by a pedestrian bridge. This bridge will span Town Lake from the
south bank at Tempe Center for the Arts to the north shore. People will
then be able to travel easily back and forth between the two sides of
the lake.
Tempe will use these bladders for the next five years,
and a new, still to be determined dam system will be implemented at that
time.
What is
the Process for Repairing Town Lake?
As construction on the dam replacement project had
already begun, we are ready to move quickly. Bladders No. 3 and No. 1
have been delivered to Tempe. PCL Construction, the company that had
been contracted to do this work, was already working on this project.
Bridgestone set the construction schedule and had
manufactured the replacement bladders accordingly. Bladders No. 3 and
No. 1 had already been patched in 2002, and Bridgestone determined that
these would be replaced first. These bladders will be installed very
soon. It will take about six weeks to secure them in place.
Bladder No. 2 will arrive in mid-August and that will be
replaced next.
A coffer dam will then be installed in front of Bladder
No. 4 and we will begin filling Town Lake with water.
Once Town Lake is full, expected near Nov. 1, the lake
will open for recreation once again.
When Bladder No. 4 arrives in mid-October, it will be
installed as soon as possible and the coffer dam will be removed.
This project was originally scheduled to take a year.
Because the water has drained from the lake, the cofferdam will not need
to be installed and taken down three times, saving nine months of work.
A cofferdam is a type of
watertight barrier designed to facilitate construction projects in areas
which are normally submerged, such as bridges, dams and piers. A
cofferdam is installed in the
work area and water is pumped out to expose the bed of the body of water
so that workers can construct structural supports, enact repairs, or
perform other types of work in a dry
environment.
What is Grading?
Grading is the use of a bulldozer to level the land,
moving large rocks and filling in holes. The bottom of Town Lake had
been scoured by past floods. Staff had been considering dredging the
bottom of the lake while it was full of water to accomplish the same
thing. Dredging is more expensive and brings up silt, which is not as
environmentally friendly. While the lake is empty of most water, staff
is taking the opportunity to do this routine maintenance.
What Are
These Repairs Costing?
Tempe was already in the process of replacing the dam
when this incident occurred. Bridgestone is paying to manufacture and
install the replacement bladders, with the understanding that in five
years, Tempe would find a new system for holding back the waters of Town
Lake.
Construction had started when the No. 2 Bladder burst.
There may be some savings as a result of this, both in
terms of time and money. Without water in Town Lake, there is no need to
install cofferdams in front of each bladder. The process of replacing
all four bladders was to take about a year. Now it should take about 90
days. Only one bladder will need a coffer dam in front of it, Bladder
No. 4. The reason for that is it is being manufactured at this time and
will not be delivered until mid-October. We hope to be filling Town Lake
with water by that time.
What
About Boating?
Without water in Tempe Town Lake, all boating classes and
club meetings will be unable to use the lake. Some classes are still
meeting off site to practice so crews can stay in shape.
What
about Ironman Arizona?
Ironman Arizona happens on Nov. 21. Town Lake should be
open well before then. We do not expect anything to interfere with this
event.
What
about Triathlons and Other Lake Events?
We are working with those events that were planning to
use the water to either reschedule them or to restructure them.
Triathlons might become duathlons – instead of swim, bike, run, they may
become run, bike, run. Each event is being looked at individually and we
are meeting with each organizer.
What
About Events that Don’t Use the Water?
Those events are still scheduled to occur. The parks and
pathways surrounding Tempe Town Lake are still open for public use. We
encourage you to visit and see the progress we are making.
What is
the Economic Impact to Tempe?
We don’t know yet. Summer is Tempe’s slowest season, as
it is for much of Arizona. As a result, the impact could be minimal. We
have also experienced an increase of people visiting Town Lake recently
to see what has happened.
What’s
Being Done with the Fish?
The fish are being collected by Aquatic Consulting,
bagged and donated. The Phoenix Herpetological Society is feeding their
hundreds of animals with the fish. Also, we are composting
the remaining fish and will use them as fertilizer in our city parks and
landscaping.
What
About Mosquitoes?
We are treating the standing pools of water remaining in
the lake with short-lasting and environmentally friendly chemicals. We
are aware that some mosquitoes can carry West Nile virus and are
proactively doing everything we can to mitigate that possibility to
protect your health.
Can
People Walk Around the Lake Bottom?
No. We know there is the temptation to explore and go
treasure hunting, but Tempe is telling people not to do this. It is not
legal and might not be safe.
The mud could have sharp debris beneath its surface from
years of the lake being there. Anyone who gets cut would need Tetanus shots to
protect them from possible disease.
Soon, there will be workers out there replacing the dam,
removing debris and smoothing the bottom of the lake. Graders and other
heavy machinery will be working in the lake and river bottoms. People
need to stay out of the bottom of the lake and river.
I Have
Other Questions. What Do I Do?
Please send an email to
townlake@tempe.gov. We will answer your questions as soon as we can. |
