Where’s the Water?


Why is Utah Lake so low, when the upstream reservoirs (Deer Creek and Jordanelle) seem to have lots of water? I turned to Greg Beckstrom, Division Director for Public Services, for an explanation that the rest of us could understand. Below is his response.

A complete answer to this question can be very complicated, but it ultimately comes down to balancing long established legal water rights with some practical considerations. Water is a valuable resource in a desert environment. Those who are responsible for managing this limited resource attempt to do so in a manner that economically maximizes the total amount available to all those who have rights to its beneficial use.

It is helpful to understand the relative size of the bodies of water along the Provo River. The combined storage capacity of the upstream reservoirs is only half the volume of Utah Lake at normal (full) elevations:

  • Jordanelle – 310 thousand acre feet
  • Deer Creek – 150 thousand acre feet
  • Utah Lake – 900 thousand acre feet

An acre foot is equal to an acre of ground covered by a foot of water. Most of the water stored in Deer Creek Reservoir is “imported” (transferred) from the Weber River and Duchesne River basins.

Evaporation is a major concern in managing water storage, particularly in periods of drought. While Utah Lake can hold twice the volume of the upstream reservoirs, it has almost 15 times the total surface area, due to its shallow depth. The greater surface area, combined with warmer water temperatures, result in a much higher rate of evaporation from Utah Lake, than from the upstream reservoirs. In hot summer months this can be 2000 acre feet/day of “lost” water. Total diversions from Utah Lake for irrigation and other uses are 1000 acre feet/day. As a comparison, total water consumption in Provo City on a hot summer day can be 170 acre feet.

As population growth continues along the Wasatch Front, use of Provo River water transitions from agricultural uses to municipal uses. The cost of treating water from the reservoirs to meet drinking water standards is much less expensive than treating Utah Lake water, due to its higher level of salts and silts.

These factors result in Utah Lake getting quite low during periods of drought, such as has been experienced the last five years. Most of the water stored in the upstream reservoirs can do little to help Utah Lake. It would either be lost to evaporation, or never be imported from other river basins in the first place.

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  1. Kyle W.

    So what you are saying is that we should say good bye to Utah Lake. We have depleted one of the best resources Utah County has to offer. Let’s store all the water in Wasatch County and send all the water we do have to Salt Lake County since they own the water rights. How can they Own the rights to all this water? This makes sense now. Has there been studies to prove 2,000 acre feet evaporate per day? This number does not seem accurate and I would like to see the proof of this. Seems that we should fill the natural lake first to preserve, then fill the reservoirs with the excess. What happened this summer is a result of poor management. The lake never received fresh run off water. It was then pumped lower which resulted in a higher concentrate of the elements that cause algae growth. Add heat to the mix and boom algae outbreak. They blame it on drought. We had a good winter snow pack and wet spring last year yet the lake was lower than previous years. Many questions need to be answered.

    1. Bryce

      I totally agree with this. We had great winter snow pack this year and the lake was way lower than it has been in the past. It is a shame to see Utah Lake as low as it is. It seems like a lot of bad planning going on.

    2. Joe


      From a cursory glance at the data available it looks like the 2,00 acre feet a day is pretty conservative.

      An average of evaporation pan values compiled by the Western Regional Climate Center (http://www.wrcc.dri.edu/htmlfiles/westevap.final.html) from 1928-2003 for the Utah Valley show that during the hottest summer months average daily evaporation is about 8.8 inches/day. The study does mention that the pans are placed above ground, so taking 80% of that value gives a more realistic number.

      I did some brief calculations using only 70% of the values given to be conservative.

      The Utah Lake has an surface area of 148.4 square miles. So the equation works out to:

      (8.80 in* .7) * 148.4 mi^2 = 0.01443 mi^3 (cubic miles)

      Converted to acre feet (1 cu mi = 3.379e+6 acre feet) that gives:

      48761.9286 acre feet of evaporation / day.

      But that’s if we extrapolate the evaporation of a pan of water sitting out to an entire lake. I’m sure that the good folks at the Division for Public Services are much more well versed in this than I, and can allow for cooling effects of subsurface water, mineral effects, etc. in their estimates. But 2,000 acre/feet of water a day doesn’t seem high to me at all, if anything that seems low. Utah lake is big in terms of surface area.

      Thanks for all you do, Mayor Curtis, and everyone at the Division for Public Services!

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