Water budget and water-surface fluctuations, Great Salt Lake, Utah

The water-budget equation for Great Salt Lakes is: Inflow = Outflow + or - Storage change. The average annual inflow for the period 1931-76 was about 2.9 million acre-feet; 1.9 million acre-feet from surface sources, about 900,000 acre-feet from direct precipitation, and about 75,000 acre-feet from ground water. The average annual outflow for the same period, all be evaportion, also was about 2.9 million acre-feet. Storage changes are computed on the basis of changes in the surface level of the lake. During the period of historic record, 1847-1978, the lake surface has fluctuated within a range of about 20 feet but has shown little overall change. The lake surface would have been about 5 feet higher in 1978 than it was in 1947 had there been no consumptive use of water caused by man 's activities in the lake basin. Since 1959 the lake has been divided into two parts by a railroad causeway, which has restricted the natural circulation. This has resulted in a difference of salinity and of surface level across the causeway. The difference in surface level between the two parts of the lake varies seasonally and annually and has been as much as 2.35 feet. (USGS)