Why are some Utah reservoirs almost empty while others are above capacity?

SALT LAKE CITY — Piute Reservoir in southwest Utah is now virtually empty, as its last remaining water dries up in the July heat.

The reservoir's demise can easily be blamed on the poor snowpack over the past few years, making it impossible for the reservoir to recharge in winter. After a few poor cycles, the Utah Division of Water Resources listed it as just 0.23% full as of noon Wednesday.

"All of those reservoirs in the center of the state, almost, are struggling," said Laura Haskell, the drought coordinator for the Utah Division of Water Resources.

But it's a completely different story at Stateline Reservoir, more than 350 miles to the northeast. The reservoir in the Uinta Mountains is actually spewing over its listed capacity — one of two in the area still above 100% capacity even midway through meteorological summer.

Utah's reservoir system is collectively at 57% of its capacity, but why is it that some of Utah's reservoirs are bordering on empty while others are flourishing?

There are a few factors, Haskell says.

What helps and hurts Utah reservoirs

Utah's reservoirs all thrive on snowpack, which is the water found in the snow that falls in Utah's mountain ranges. It melts in the spring, flowing into rivers, streams and creeks — many of which flow into reservoirs built over the past century.

That hasn't always been the case, though. Last year's runoff was thwarted by dry conditions to close out 2020 mixed with a below-average snowpack collection between fall 2020 and spring 2021. Experts found that most of the runoff wound up going into recharging groundwater levels.

Though 2021 closed out strong in terms of precipitation, the state's below-average snowpack meant there wasn't a lot of water to flow into reservoirs that had been depleted through drought conditions over the past two years. The two-decades-long megadrought has also depleted reservoir levels across the state.

But there are a few differences that allow for vast ranges within Utah reservoir levels.

First, there's size. Lake Powell, the country's second-largest reservoir, is a monster compared with most of the state's other reservoirs. It's about 48 times the size of Piute Reservoir in land acreage alone. That means it takes much longer for Lake Powell to empty than Piute Reservoir, but it also takes much longer to refill.

Then there's consumption. Many Utah conservancy districts made a point before the irrigation season to cut back on water usage this year, Haskell said. This allowed for some reservoirs to build up levels without losing water to farms or communities.

The late-season wintry storms that slammed into northern Utah also had an impact. Consumption reduction and last-season storms are likely why Stateline and Smith and Morehouse reservoirs are listed above 100% capacity in July, and others in northeastern Utah are well above the statewide average.

"It just dumped right in that area," Haskell said. "It really helped because it was snowpack (and) it was right in that runoff time. It was good timing."

One noticeable example of this is Rockport Reservoir in Summit County. The reservoir made global headlines last year when water levels fell to a point where parts of the ghost town that once existed on the land resurfaced. Those low levels were the result of the reservoir's inability to refill in 2021.

Rockport is now over 90% full because it had a much more normal snowpack runoff this spring, and it's small enough that one year can make a big difference.

Unfortunately, the spring snowstorms didn't hit every part of the state, leaving southern and south-central Utah especially dry. It's why most of the lowest reservoir levels are in these parts of the state, though low reservoir levels can be found anywhere in the state.

Many of the reservoirs in southern and central Utah are typically bodies of water that can refill in one to two years, according to Haskell. Since so much water was used last year, there was a below-average snowpack, and some of the wetter spring weather escaped the region, these reservoirs didn't really refill this spring.

"It really has dried those out," she said.

What does it mean for residents who use those reservoirs? Haskell explains that most people do have different sources of water to go to after a reservoir dries, such as springs, streams and groundwater reservoirs. These are the type of sources that communities with low reservoirs will likely have to rely on before some of the reservoirs have water again.

Utah's water supply outlook

Utah Gov. Spencer Cox and Utah's water experts feared the statewide reservoir system could drop to as low as 40% last year. It dropped below 50% for some time, but it never went lower. The governor said that billions of gallons of water were saved through conservation efforts to make a difference.

A year later and the state's reservoirs are almost exactly where they were this time last year, despite the worse starting point this year. Water levels are expected to continue to decline over the next few months before stabilizing in the fall and winter months.

Given that there is no answer to how long the state's drought will last, Haskell said she hopes that similar cutbacks in water use happen over the next few months so that statewide levels don't drop too low.

"We had hoped for a great winter this past year — a good snowpack — and it was kind of disappointing," she said. "Every drop that we save now is just going to help us in the future because we don't know how long we will be in drought."

Tips on how to help reduce water consumption can be found online through Utah's Slow The Flow program.

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