Thursday, August 13, 2015

Is the Great Salt Lake Approaching a Record Low Stand?

Modis Image of the Great Salt Lake taken 9 August 2015.
Based on historical levels, the Great Salt Lake is going through an especially low period.  Is it, however, a record?  It turns out this is a surprisingly difficult question to answer.  What could be so hard about measuring the elevation of a lake?  

The Great Salt Lake is a terminal lake (i.e., it has no outlet) and thus the surface elevation and area of the lake fluctuate with variations in inflow and evaporation.  The former plays a primary role with long-term wet periods leading to high stands and long-term dry periods leading to low stands.  High stands occurred in the 1870s and 1980s, with a record minimum of 4,191.3 feet in 1963.
Source: USGS
We are currently in a long-term dry period and the Great Salt Lake levels are relatively low (note that the graph above ends in 2006, so don't use it for the recent past).  As shown below, the USGS guage at Saline is presently sitting at only 4191.4 feet, just a shade above the record low.  Thus, a record should be imminent right?  
Source: USGS
Not so fast.  If we examine the gauge at Saltair, we find that the lake level is sitting at about 4193.3 feet, nearly 2 feet higher than the record low from 1963 (note the shift in range of the y-axis compared to the plot above).  

How can the lake level vary by almost 2 feet between these two gauges?  In 1956 the Southern Pacific railroad began construction of a rock-fill causeway across the center of the Great Salt Lake, which was completed in 1959.  You can see the location of the causeway in the MODIS image at the top of this post as there is a clear contrast in the color of the two halves of the lake that it separates.  Breaches have subsequently been added to the causeway to allow some flow between the two halves, but ultimately the Great Salt Lake remains a lake divided.  Much of the freshwater inflow enters the southern half of the Great Salt Lake.  As a result, the southern half of the lake is usually higher than the northern half, as is the case at present, leading to a higher reading at Saltair (southern half) compared to Saline (northern half).  

Now let's talk about the record.  It is fairly clear that the historical low stand of the Great Salt Lake occurred in 1963.  That was shortly after the completion of the causeway.  At that time, measurements were only collected at Saltair in the southern half.  Saline wasn't added until 1966.  The record of 4191.3 feet was based on a measurement at Saltair.

Thus, it appears that water levels in the northern half of the Great Salt Lake may be nearing an all-time low, although we don't have measurements from Saline in 1963 to confirm this.  It is possible, given the existence of the causeway that water levels in the north half in 1963 were even lower than they were in the south half.  Water levels at Saltair are presently above those measured in 1963, although the current low stand probably qualifies for the 2nd lowest in the historical record.  

It is possible that there are some manual observations of water levels or photographs that might shed a bit more light on this issue.  It would be an interesting project to explore.  Too bad we didn't have high-resolution satellite images in 1963!


  1. does a change in the weight of the water in the lake, not influence the ground below it?

  2. It is time you and I joined forces to explain Utah's most beautiful Force of Nature. You have the science, and Keith Vaught (mostly) and I have the Pictures.
    We can tackle GREAT SALT LAKE SUNSETS: How to Predict Them, Grab Them By The Throat and Ride Them Into The Sunset.

    We can match up your weather data going back 10 years to our weather pictures.

    Do the mountains funnel storms through the Tooele valley to GSL?
    Why do some sunsets crap out, while others magically appear in your rear-view mirror?
    Is there a combination of weather events that causes the ace of hearts, the crepuscular rays, and the ace of spades, the anti-crepuscular rays?
    Name the clouds, their colors, and explain how they got here.
    What is the price of gas per sunset, when the lake is on average, 100 miles away?

    http://Greatsaltlake.Photography Me Keith

    We can write a book!

  3. Pem H here Jim. Love your book BTW. I recall travelling to Salt Lake in the late 80's and all the talk then was when would the lake overtake the north end of the Airport (not exactly that but it was getting close). I remember flying in and seeing quite a few roads flooded. All that said, hard to believe that in the warmer world that we will see that in a cycle again soon.

    1. Yeah, I wonder that too, but we could still go big for perhaps a couple of decades. There's always hope.

      Post up a review for me on Amazon!

  4. Another important aspect of the current difference in lake elevation between the north and south arms is the fact that the culverts (2) in the UPRR causeway are currently closed. This prevents the lake from adjusting between the two halves, and the north arm has essentially no freshwater inputs. UPRR will be replacing the culverts with a bridge located more towards the west side of the lake (on more stable geological footing) that will (in theory) replace the bi-directional flow through the causeway that supports the beneficial uses of multiple stakeholders (the top three are mineral companies, brine shrimp harvesters and avian populations).

  5. Thanks for the information. That will hopefully be a helpful upgrade.