Fluctuations in Lake Level Introduce New Challenges

South-arm brine pouring into the north arm through the newly created breach in the Southern Pacific causeway during the opening ceremonies on August 1, 1984.

From the time of the causeway’s construction in 1959 until 1987, Great Salt Lake experienced its greatest recorded changes in surface elevation, from its low of 4,191.35 feet in 1963 to its high of 4,211.85 feet in 1987. Within this range of over 20 feet, the lake rose above and fell below its “normal” surface elevation of about 4,200 feet. Beginning in 1982-83, the lake began to rise from its “normal” elevation of 4,200 feet.

The south arm rose five feet in 1983, over four feet more in 1984, and nearly three feet more by 1987 to its historical high of 4,211.85 feet. With this rise came extensive flooding, especially around the southern arm of the lake. Roads, farms, wildlife management areas, and other facilities were inundated.

State officials reviewed a number of options, and decided that breaching the causeway would bring the most immediate relief from the flooding. The breach would be constructed as a bridged opening 300 feet long, with a design bottom elevation of about 4,195 feet. Unfortunately, during construction the bottom elevation of the breach was not built at the design elevation of 4,195 feet, but was completed somewhat higher at about 4,200 feet. The breach was quickly completed, and on August 1, 1984, south-arm water flooded into the north arm. Within two months, the head differential between the south and north arms had decreased to less than one foot.

As the whole lake continued to rise, however, the hydrostatic conditions within the breach opening became favorable for bi-directional flow to occur. During the period from 1984-88, large volumes of south-arm water flowed through the upper portion of the breach opening into the north arm. By 1987, the salinity of the north arm had dropped from its 1981 level of about 27 percent salt to about 18 percent. At the same time, large volumes of north arm brine were flowing into the south arm as return flow, adding to the south arm’s intermediate density brine layer.

Between mid-1984 and mid-1986, the elevation of the south-arm interface had risen about 12 feet due to the large influx of dense northarm brine. Even as the State opened the breach in 1984, the lake continued to rise, and the State decided to pump water from the lake westward into the Great Salt Lake desert (informally known as the West Desert) to provide additional evaporation area. This project became known as the West Desert Pumping Project.

Three large pumps were installed near Hogup, about 13 miles west of Lakeside, that lifted brine from the north arm of the lake into a 4.1- mile canal, where it flowed westward into a shallow depression called the West Pond, located west of the Newfoundland Mountains. Pumping started on April 1, 1987, and continued through June 30, 1989. During this time, about 2.2 million acre-feet (153 billion gallons) of brine was pumped from the north arm of the lake into the West Pond. Concentrated brines were returned to the lake through the East Pond.

Pumping contributed about 26 inches to the total lake-level decline of 5 feet during that period of time. From 1989 through the mid-1990s, the lake level continued to drop. From 1993-94 through 1997-98 there was some south-to-north flow through the breach opening, but no north-to south return flow. Then, as the lake started to rise again in 1998, large volumes of south-to-north flow moved through the breach opening, but still no northto- south flow occurred.

As a result, the salinity of the south arm of the lake experienced a steady decline from 1994 through 1999. During this time, the south-arm salinity dropped from about 14 weight-percent salt in 1994 to only about 7 weight-percent in 1999. The north-arm salinity, on the other hand, remained near 25 weight percent salt.