Settlement Canyon and Grantsville reservoirs both reached capacity last week and started to send water over their spillways.
The Settlement Canyon Irrigation Company reported at about 7:50 a.m. on Friday, June 2, that the Settlement Canyon Reservoir had reached capacity and was starting to run over the spillway into the dry creek bed below.
“It’s over the spillway! As it gets into the creekbed below the dam, the ground seems to be absorbing a lot of the water along the way,” read the post on the irrigation company’s Facebook page.
The Settlement Reservoir made a steep climb in May 2023. It rose from 38% capacity on May 1, 2023 to over 97% on June 1, 2023.
Grantsville Reservoir is also full, according to the Division of Water Resources, which reported on June 1, 2023, that the reservoir reached 100.1% of its capacity. The Grantsville Reservoir jumped from 76% at the beginning of May 2023 to over 100% by June 1, 2023.
While reservoirs are full, data shows that most of the snow in the mountains above the valley has already melted. The National Resource Conservation Service reported no snow was left at their remote sensor SNOTEL sites at Dry Fork on top of the Oquirrh Mountains east of Erda, up Mining Fork Canyon in South Willow west of Grantsville, and near Vernon Creek above the Vernon Reservoir as of June 6, 2023.
However, the Rocky Basin-Settlement Canyon SNOTEL site reported a snow water equivalent of 6.2 inches as of the morning of June 6. The Rocky Basin-Settlement Canyon SNOTEL site peaked at 46.3 inches of SWE on April 6, 2023, which was 94.5% above the 30-year average SWE peak of 23.8 inches.
The 30-year median for snow water equivalent at the Rocky Basin-Settlement Canyon monitoring site on June 6 was zero inches. In 2019, the last year that the Settlement Canyon Reservoir overflowed, the NRCS reported approximately 15 inches of SWE at the Rocky Basin-Settlement Canyon site.
Although the reservoirs are spilling over, that doesn’t mean there will be flooding, according to the managers of the reservoirs and government officials .
When Settlement Canyon Reservoir reaches capacity and overflows, the water runs into a deep ravine and flows towards state Route 36 where it enters a large pipe that carries the water under state Route 36 and 700 South and eventually towards the Tooele Army Depot where it comes back to the surface south of state Route 112 near the Deseret Peak Complex.
Usually flood waters are contained under the road, but if it does overflow, water may run down the street [700 South], according to Bucky Whitehouse, Tooele County Emergency Management director.
A lot of proactive work was completed in and along the drainage to clear debris, trash and deadfall in an effort to prevent any unnecessary flooding, according to Tooele City Emergency Management.
Tooele City said they will monitor the Settlement Canyon drainage daily so that any issues can be found and mitigated promptly.
“All water that is spilling over will be directed down the Settlement Canyon Irrigation pipe, and at this time we anticipate that no water should have to be sent down 700 South,” said Tooele City Emergency Management officials.
In May 2017, the Transcript Bulletin wrote about the impending overflowing of the Grantsville Reservoir. The watermaster for the Grantsville Irrigation Company at the time reported that when the reservoir overflows, the water can be turned out through a ditch onto the Tooele Army Depot into a pond.
The water that was detoured through Grantsville City towards the Clark Historic Farm in May 2023 was not from the Grantsville Reservoir. That water was from Magpie and Baker Canyons that are north of the Grantsville Reservoir and cannot flow into the reservoir.
The Settlement Canyon Reservoir, with a capacity of 1.0 KAF — kilo acre feet — of water, holds enough water to fill 493.7 Olympic size swimming pools or approximately 325,851,429 gallons.
The Grantsville Reservoir holds 3.3 KAF of water when it is at capacity
One KAF would fill 493.7 standard Olympic size swimming pools, with one standard Olympic size swimming pool holding approximately 660,000 gallons.