Source: PCL Construction, Inc.
Arizona is home to the largest hydraulically controlled crest-gate dam in the country. Comprising eight fabricated steel gates, each weighing more than 130 tons and standing 17 feet high, Tempe Town Lake Dam regulates water from the Salt River, which forms Tempe Town Lake.
The dam’s eight gates are mounted onto a 21-foot-thick concrete foundation and supported by seven concrete piers and two abutment walls. Hydraulic cylinders support the gates at a 70° angle, which helps maintain the water level of the lake.
Unlike the original rubber-bladder dam structure, which does not allow for incremental adjustment of flow, hydraulically operated gates provide the city with the opportunity to lower or raise the gates in response to water flow. Each of the eight steel gates can be opened independently to control the flow from the Salt River into Tempe Town Lake, meaning the lake can transition to a river during major flow events.
In August 2014, approximately four months into constructing the new dam, record flooding hit the city of Tempe, erasing two months’ worth of construction progress. PCL worked feverishly to make up these two months of work and ultimately completed the project on schedule, but the challenges weren’t over. One of the team’s first priorities was to construct a scour wall to protect the dam’s foundation from water during release.
The groundwater conditions in the drained lake and riverbed were less than ideal, so the team decided upon a diaphragm wall construction. This method enabled crews to build the 1,000-foot scour wall in wet conditions, without the need for a mass excavation. Crews combated the sheer size of the scour wall, which contributed to the more than 47,000 cubic yards of concrete used on the project, by installing the wall in 40-foot sections.
Upon completion of the dam in April, more than 900 million gallons of water began flowing back into the Lake.