From Okie Connor (Boating Coordinator for Tempe Town Lake) about the repairs:
The letter that follows was prepared by one of our City of Tempe Engineers:
“Regarding the construction schedule, originally replacement of the four bladders was scheduled to take approximately one year by moving from one bladder to the next, utilizing a cofferdam for each installation. Each individual bladder installation would take about three months to install.
Without having to manage lake waters, there is no need for a cofferdam to be installed for replacement of three of four of the bladders, and this allows for a significant time savings. As such, the installation schedule will be compressed from an estimated one year to three months. We anticipate completing the replacement of all four bladders by mid-November and having the lake refilled and operating by November 1, 2010.
Bladders will be replaced in this order: bladder 3, bladder 1, bladder 2, and then bladder 4 (Bladders are numbered from the south shore). Again, Regarding the construction phasing, original replacement called for bladders to be without lake waters to manage, bladders 1 and 3 will be replaced concurrently, followed by bladder 2, then bladder 4. As we discussed, bladders 1, 2, and 3 will be replaced without the use of a cofferdam. Generally, we anticipate replacing bladders 1 and 3 in August and bladder 2 in September. We will begin replacing bladder 4 in October and completing it in mid-November. As such, to meet our schedule, we will install the cofferdam to replace bladder 4. Our intention is to begin refilling lake waters once bladders 1, 2 and 3 are installed and the cofferdam is in place. Not only does this approach allow us to meet our schedule, it also ensures that none of the existing bladders will be used. Once bladder 4 is replaced, the coffer dam will be removed.
While the replacement of the four new bladders is underway, we will also be analyzing the ruptured bladder 2. Rubber experts have already begun examining sections of the ruptured dam to determine the cause of the rupture, if possible. This examination will continue through September, once bladder 2 is removed from the lake. The City of Tempe acknowledges that replacement of the bladders will occur prior to the conclusion of the examination. We understand that we are proceeding without full knowledge of what caused the rupture.
Nonetheless, we are confident that the new replacement bladders will be effective. It is important to note that new features will help protect the bladders from the elements. First, a new pedestrian bridge will be constructed over these bladders to provide shade, while the original bladders were fully exposed to the sun. Second, a watering / sprinkling system will be mounted under the bridge to keep the new bladders cool. These two changes will certainly reduce the weather-related deterioration of the bladders. Additionally, the new bladders will be operating at pressure 20% less than the existing bladders, where the rubber will be subjected to less stress. Lastly, it is equally important to note that the original bladders functioned for approximately eleven years and that the new bladders will be in place for only five years, at which time a new dam using a different technology will be installed.”
