Theodore Roosevelt Dam spillway test
In the early-morning hours of Aug. 29, SRP crews opened up two of the four north spillway gates at Theodore Roosevelt Dam. More than just a mesmerizing sight, the test helped ensure that the gates will work properly in the event of a flood.
Roosevelt Dam’s gates were opened incrementally until they reached 3 feet open. Water roared through the gates and out onto the spillway, creating a powerful flow of water for about an hour until the test was complete. Most tests in the last eight years were “dry,” as lake water levels were too low to reach the spill gates.
Although monsoon storms have been nearly nonexistent in the Valley this summer, the 2019 runoff season produced more than 1.1 million acre-feet of water between January and May. During the test’s peak flow, 22,440 gallons of water per second was released.
That water will be stored in Apache Lake, where it’ll eventually be released downstream into the canals that deliver water to the Valley. We asked one of our in-house water experts, Charlie Ester, to share more information on Roosevelt Dam and the use of its spillway gates through the years.
Q&A with an SRP water expert
Question: Has water ever “spilled” from Roosevelt Dam since it was modified (and storage capacity was increased) in 1996?
Answer: Modified Roosevelt Dam has never made an operational spillway release. Every release from the spillway has been for testing and compliance purposes only. In 2008 and 2010, the reservoir did enter into flood control space, but generator releases were sufficient to manage the level. The lake would have to reach an elevation of 2,162 (11 feet into flood control) before a spillway release of approximately 27,000 cubic feet per second (cfs) would be required.
Q: What was the total volume of water spilled during this test?
A: Despite how impressive the release looked, less than 150 acre-feet (af) of water was released. This is far less than the typical 2,000 af or so passed through the system in a normal summer day.
Q: What is normally released through the hydrogenation unit during normal operations?
A: The generator at Roosevelt moves about 2,200 cfs of water, while the spillway test was 3,000 cfs.
Q: Can you tell us some history about these tests, dating back prior to when dam expansion began in 1993?
A: Most years since Roosevelt was modified have been drought years; therefore, most annual spillway tests have been dry tests, when the gates are raised but there is no reservoir water behind them to spill. This year’s test is more significant, as the test was done with water behind the gates creating a much more realistic situation.
Q: How were tests conducted before modification was completed in 1996?
A: Prior to modification completion in 1996, the original dam’s spill gates were also tested but almost always in the dry. If there was water behind the gates, the gates were often just raised fractionally, enough to verify that they would operate but not enough to spill water.