Tempe Town Lake uses eight hydraulically controlled crest gates to operate its dam structure. These gates replace the prior dam that was formed by four inflatable rubber bladders which had failed due to age and UV damage. When the gates are fully closed, the water forms Tempe Town Lake upstream of the dam, while fully open gates allow for flow in case the Salt River floods. Under normal operation the gates will be slightly lowered to allow the minor seasonal river flows to pass over their crests while maintaining a full lake level behind the dam.
One value engineering option that saved the City a substantial amount of money was the construction of the downstream scour wall. This 1000-foot-long, 25-foot-tall wall was originally proposed as a reinforced cast-in-place wall that required an extensive amount of excavation, forming, backfilling, and dewatering efforts. Working with subcontractors, the PCL project team developed a plan to install the wall using bentonite, an absorbent aluminum phyllosilicate clay, as a means to keep the excavation stable so the downstream scour wall could be placed in an excavation instead of installing it by traditional methods. Forty-foot-long panels were dug and filled with a bentonite slurry to keep the excavation stable during construction. Upon completion of the panel excavation, custom end-stop beams and the reinforcing cage were installed. Finally, a high-slump concrete mixture, used to maximize flow without sacrificing strength (as would happen if water were added at the jobsite) was pumped up from the bottom of the panel while the bentonite was displaced into a holding tank so it could be recycled and used on a future panel. This process was repeated for a total of 22 panels.
On-site use of construction technology is crucial to project success on this project because of the gate anchor bolts that need to be set perfectly in place. Crew members use Building Information Modeling (BIM) to model embeds for crest gates and hydraulic cylinders. The BIM tool allows them to model individual gate components and concrete design elements of the dam and anchor bolts to make certain that this high-precision work is installed correctly the first time.