Holladay declares a state of emergency; Big Cottonwood Creek is to be created

Minor flooding is expected near Big Cottonwood Creek on Monday.

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Holladay officials declared a state of emergency Tuesday, citing the “imminent threat” of local flooding as warmer temperatures accelerate snowmelt in Big Cottonwood Canyon.

The local declaration of emergency gives the city access to state and other outside resources should spring runoff water cause flooding along Big Cottonwood Creek.

It was reading about 340 cubic feet per second as of 6 a.m. Tuesday, according to the National Weather Service. That’s the equivalent of about 340 beach balls flying by every second.

The creek is expected to reach 650 cfs on Sunday, exceeding its “action stage” of around 600 cfs. An “Action Phase” is a threshold that the weather service uses to determine when it should take action to prepare for potential flooding.

Areas adjacent to the creek are expected to experience minor flooding beginning about 1 a.m. Monday, with daily peak discharges reaching about 800 cfs Monday through Friday, May 26.

“It’s because of the heat we’re in there — I think we’re about five to 10 degrees above average,” said Brian McInerney, a hydrologist who advises Salt Lake City on flooding. “We’ll be hovering in the low 80s by the weekend, and that coupled with clear skies… will fuel that surge.”

As of Tuesday afternoon, the highest forecast creek flow is 819 cfs, which is forecast for May 25 at 6 a.m

Conversely, should the creek reach 861 cfs, moderate flooding would likely occur in Murray Park and downstream areas.

Should the level reach 893 cfs, there could be major flooding along the entire creek, from the Big Cottonwood Canyon outlet to the Jordan River.

There are a few “eventful” weeks ahead of us

“While we cannot control current temperatures and the rate of snowmelt due to this natural phenomenon,” Holladay Mayor Rob Dahle said in a statement Tuesday, “Holladay has invested significant time and resources in preparing for the spring runoff. “

“I’m especially grateful for all the volunteers who selflessly filled sandbags and helped their neighbors fortify their properties,” Dahle said. “This is an extraordinary situation and the declaration of a state of emergency will allow us to receive more assistance if needed.”

The city has a portion of Knudsen Park at 6290 S. Holladay Blvd. closed because Big Cottonwood Creek runs through its western boundary. Individuals should avoid the river bank because the creek’s fast water is cold and has strong currents, officials said.

McInerney said about 38 inches of snow-water equivalent remains in the Mill D North portion of Big Cottonwood Canyon, which is currently melting at about 1.7 inches per day.

“If we go an inch a day until we melt 38 inches, we’ll be here by mid-June,” McInerney said, noting that the snowpack further up the gorge in Brighton has about 26 inches of snow-water equivalent left and melting with it about 1.2 inches per day.

“The northern part of Big Cottonwood is still frozen. The south side and the west side — to some extent to the west — produce the meltwater we’re seeing now,” he said.

Air temperature doesn’t affect snowmelt as much as sunlight does, McInerney said, because snowmelt relies on the sun’s energy melting snow. As a result, the northern part of the canyon — which doesn’t get as much sun — still remains frozen.

“As the sun gets higher in the sky, the closer we get to the summer solstice…then the water starts to melt through the snowpack and into the ground,” McInerney said. “We expect quite high inflows in both Big and Little by the middle of next week [Cottonwood].”

McInerney said the biggest thing people can do right now is stay away from the canyons and creeks of Big and Little Cottonwood.

“It’s not known at this point,” McInerney said of when the streams will peak. “And that’s because we can’t predict the weather for more than five days. So if we pick up the heat again sometime in June, and that’s a good possibility, then we’ll hit another peak. But at the moment we have to wait and see.”

At a Salt Lake County Council meeting Tuesday, Mayor Jenny Wilson said she expects the next six to eight weeks to be “quite eventful.”

Kade Moncur, Salt Lake County director of flood protection engineering, said the county’s flood protection crews were working “normal and extended” hours but would rotate 12-hour shifts if necessary. Emergency contractors working on debris clearance and risk assessment teams are also on standby.

– Blake Apgar, Contributor to the Tribune, contributed to this report.