The flood of May 2019 was a record breaker, but it was nowhere near a dam breaker.
At Keystone Dam, when the reservoir’s water hit a record height and the flow through the dam hit a level not seen in three decades, even a black cat that crossed its path turned out to be lucky.
The kitten was rescued and named Allis.
“After our turbines — they’re Allis-Chalmers turbines,” said Keystone Dam Powerplant Superintendent Tom Henry with the Army Corps of Engineers’ Tulsa District.
Henry and David Williams, the Tulsa District’s chief of hydrology and hydraulics engineering, offered a tour of the dam and power generation plant to the Tulsa World on Thursday. It was similar to many tours given during the flood to local and national dignitaries — just about everyone but the president of the United States, Henry might add with a grin.
The tours gave officials an invaluable perspective, they said. But not everyone got to visit with the jet-black kitten.
The message of the tour is that dams leak and seep, but they’re tough — really tough — and are designed to take a lot more than a river or storm system can throw at them. They are flood-control structures, not “flood prevention” structures, and the Keystone Dam during the historic May flood did what it was designed to do — prevent something even worse from happening while continuing to provide electric generation.
Although it performed well, it was not without concern or careful monitoring. Corps personnel at the dam were on 24-hour watch for 50 days straight, Henry said. That meant every person on his crew worked 12-hour shifts, daily, for almost two months.
“Every hour, you walk and inspect the whole thing,” he said. “Well, hour and a half by the time you finish walking it.”
He added there is one thing many people don’t think about when it comes to the dam, which he said is often seen as a federal government structure, something detached from the community.
“People who work here live on the lake, too, and downriver,” he said.
Designed to last
Built in the 1960s, the 50-year-old structure goes through regular maintenance, still uses much of its original equipment and is built to withstand a gigantic theoretical model of a storm, Williams said.
“If this (May) storm was a 200-year event, a probability of about .5%, the one it is designed for is something like 1 in 10,000,” he said. “We take a storm like this and, on top of it, we apply that biggest theoretical storm that could ever hit. That’s what it’s designed for.”
Every structure has a lifespan, and changes or upgrades to equipment may come, but neither Williams nor Henry could put a finger on when that will happen at Keystone. The equipment is meticulously maintained and regularly serviced, Henry said.
The lifespan of the structure itself likely is measured in centuries. Williams couldn’t guess how many.
“How many concrete structures can you think of that have stood for centuries?” he asked.
It does leak and it has cracks, but according to Thursday’s tour guides, “dams leak.” Both repeated the phrase.
Inside the structure are stairs and elevators and long tunnel-like hallways that run the length of the dam — the areas those Corps staffers patrolled 24/7.
Instead of first, second or third floors, the hallways have signs that denote the floor elevation above sea level. The lowest levels are below the lake, Henry said.
“If you tunneled out through the bottom of the dam, you would come out in dirt, under the lake,” he said.
Along those hallways are built-in troughs that collect water and route it down to holding areas where sump pumps push the water outside. The engineers even track the amount of water that collects in the pumps. There is a normal amount of seepage for any given height of water behind the dam. If suddenly there is more seepage, then that would be cause for further inspection — but not panic — because dams leak.
Henry pointed to a section of wall with a white and brown calcified substance on the surface from one side of the hall to the other, evidence of a crack where water has seeped for a long time.
“Since it was built,” he said.
The view from the catwalk access over the dam’s Tainter gates is eye-popping, as the scale of the lake on one side and the river far below on the other could tease any slight fear of heights.
“When you’re standing up here, you see it, just how much water is held up here and then looking down at the river below,” Henry said as he stood on the steel catwalk that runs about 300 yards — the length of the dam’s 18 gates, each 45 feet tall and 35 feet wide. At maximum flow, each gate was lifted to open a 13.5-foot gap for water to escape, he said. They can open a lot wider to release much more if necessary.
Keystone hit a “record pool” at 757 feet elevation during the May flood — 34 feet above normal — but the release through the dam at 275,000 cfs was far less than the 307,000 cfs that flooded Tulsa in 1986.
“The big difference was the length of time for this event,” Williams said.
At record level, the lake’s surface sloshed only about 5 feet below the catwalk on the lake side of the dam, and mist rose from the river side as water rushed through the gates.
“It shaved off roughly 100,000 cubic feet per second,” Williams said of the dam’s performance during the flood. “With this amount of rain, say if we would go back to 1935 with no dams on the river, the flow through Tulsa would have been on the order at 375,000 cfs.”
That’s the flood control, not flood prevention, part of the tour.
The dam once had an automated system to open the gates, but Henry said it wasn’t used and was later taken out. He said he believes it’s better to have an operator physically walk the roughly 300 yards of catwalk to hit the controls that operate the gates one-by-one.
“You stand up here and you look down the river and you can see what’s going on, if someone is down there in a boat, or whatever it might be,” he said.
The guided tour, around noon Thursday, was different in a big way from those held during the height of the flood event — and not just because of the cat.
The dam’s warning siren sounded just as the tour came to an end and the 18 Tainter gates closed. The flow through the dam dropped below 7,500 cubic feet per second for the first time since May 4 (save one 24-hour period June 23-24 due to flooding on the Grand River downstream).
This time, it was to accommodate salvage operations downstream, where two barges smashed into the Webbers Falls Dam (speaking of tough structures).
The lake level stood just about 11 feet over normal, also for the first time since May 4. Just one turbine was running for power generation. With 25% of the flood pool in use — compared to 103% at one point — the lake is almost back to normal.
As for Allis, the weeks-old kitten that somehow found her way to a spot near a walkway between the dam and the power plant this May, she is a full-time resident of Henry’s office and a reminder of the flood event. He said he may soon take her to his home to live.
“She is a lucky one,” he said.