The Tempe Town Lake is contained by an inflatable dam system consisting of eight bladders, four in a row at the east end (located between Rural and McClintock roads), and four in a row at the west end (located between Mill Avenue and Hardy Drive).
The location of the Rio Salado dams was somewhat determined by the $40 million Flood Control District of Maricopa County channelization project in 1989. Grade control structures were constructed at two locations in the Tempe portion of Rio Salado: one between McClintock Drive and Rural Road, and one between Mill Avenue and Hardy Drive. The Tempe Town Lake was designed to take advantage of these structures.
The dams are made of three main elements:
- a strong, flexible, rubber coated fabric tube fixed securely to a concrete base slab by clamping bars and anchor bolts
- an operating system which controls inflation and deflation of the tube
- an automatic safety device which 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. At times, a small amount of water can be seen flowing over the top of the west dams, creating a 19-foot waterfall. This water can be recaptured by a recirculation system and pumped back into the lake.
The east dams are five feet high and sit on a two-foot cement base. The west dams are 16 feet high and sit on a three-foot base.
Each section of rubber is imbedded with a fabric mesh and ceramic chips and is designed to resist tearing. The rubber also contains a self-sealing material to re-close small holes. These dams are built to resist floodwater and debris flowing at 250,000 cubic feet per second (the highest recorded flood in Maricopa County is 200,000 cfs. in 1905. The most recent significant water release was recorded at 129,000 cfs. in 1993).
Tempe's dams are computer controlled and maintain air pressure of six pounds per square inch (an automobile tire holds about 35 psi). They can be controlled individually to within a half inch and can be lowered incrementally depending on the flood conditions.
The bladders have special ozone and ultraviolet ray protection for the southwestern climate and have been tested extensively for durability. They have a thin fin on top, which spreads water flow evenly over the surface of the dam. This patented design prevents swaying of the bladder and tearing from its structure. In some locations, these dams have been designed with airtight doors for people to enter into the bladder for dam tours. The Tempe Town Lake does not have interior bladder access.
The dams were shipped across the ocean from Japan, arriving on large spools, that were transported by truck to Tempe. These spools were stored until construction of the lake was ready for installation of the bladders. The spools were then moved by crane into the river bottom, and unrolled into place.
Soil cement was used to stabilize the channel banks and rock gabions were installed to create a second levee. The flood control levee was designed for a 100-year flood event, or 215,000 cubic feet per second, with an additional four feet of freeboard (levee space, above this water flow). With improvements to Roosevelt Dam, the capacity to contain flow within the channel is as high as 280,000 cfs. The purpose is to keep all water within the flood channel, which is why there is no construction within the levees.
One of the unique features of the inflatable dams is their ability to deflate quickly and easily to prevent upstream flooding. The dams at Tempe Town Lake can be deflated and inflated within 30 minutes, offering a high level of control and easy method of releasing and recapturing water.
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.
Inflatable dams have a multitude of uses. Among them are hydroelectricity, groundwater recharge, water supply, flood control, sewage diversion, irrigation, water diversion, water treatment, recreation and tidal barriers. The most common applications are for expanding the capacity of existing dams and replacing older dam structures.
These dams are best used in small to medium sized watercourses where width is much greater than height. The advantage of inflatable dams is that they allow for long spans of barrier with few structural piers (that might interfere with floodwater). They can easily attach to any side slope and are relatively simple to install. Inflatable dams have low maintenance requirements and high longevity. Unlike other dam designs, these dams have few moving parts which means there is less lubrication, replacement and repair costs and less corrosion.
Where in the world
Just two manufacturers in the world make this product: Japan's Bridgestone and Sumigate. The City of Tempe purchased a inflatable dam system consisting of eight bladders from Bridgestone for the Tempe Town Lake. It took a full year of the plant's capacity to produce and ship these from the plant in Japan.
Inflatable dam technology has been available for more than 30 years and more than 2,200 inflatable dams are in use around the world.
Why Replace Them?
The inflatable dams were warranteed for 30 years, however, just a few years into their lifespan, repairs were needed. In 2007, the City of Tempe negociated with Bridgestone a new set of bladders and free installation, with the understanding that a new technology would be chosen and installed by 2015.
In July, 2010, one of the bladders ruptured causing Town Lake to drain. Fortunately, construction had already been hired and were ready to start the replacement process the very next day. While it took more than a year to receive the first set of bladders needed to open Town Lake, Town Lake was able to replace all the bladders and reopen in just three months due to good planning and negotiations.
A steel-gate dam is being designed and will be in place by Dec. 31, 2015. Here is how the decision was made to choose the new dam technology. http://www.slideshare.net/tempegov/jan-5-tempe-town-lake-dam-replacement-long-version