Physical Monitoring of Flow Into and Within Great Salt Lake, Utah

Great Salt Lake (GSL) is the hydrologic terminus for the eastern part of the Great Basin. As the largest inland waterbody in the Western United States, GSL plays a critical ecologic role for many migratory bird species. In terms of harvest quantity and quality, the brine shrimp (Artemia) fishery of GSL is among the strongest in the world. The characteristic of GSL as a hydrologic sink amplifies anthropogenic activities throughout the basin, most specifically activities that occur along its eastern and southern shores, the urban corridor of the Wasatch Front. In 1959 GSL was divided into north and south parts by a rock-fill railroad causeway. Since then, an extreme density gradient between the north and south part exists as a result of limited conveyance of water from the south part where more than 95 percent of the total freshwater input occurs (Loving, and others, 2000). To date, little is known about the loading and cycling of various chemical constituents associated with human activities including nutrients, selenium, and mercury. Hydroacoustic technology, specifically acoustic Doppler technology, is currently being used to obtain a better physical understanding of GSL. Since 1999, stratified bi-directional discharge has been measured at the causeway breach with an acoustic Doppler current profiler. From these measurements, net flow components to the north and south have been used to assess the movement of water and salt through the causeway. Low hydraulic gradients and variable backwater conditions at the two largest inflows to GSL required the deployment of in-situ acoustic Doppler velocity meters to accurately compute continuous discharge, critical for constituent loading analyses. These discharge records, computed using the index velocity method, show sensitivity to large wind events that can lead to a complete reversal of flow. Velocity profiles acquired during two multi-day water-quality synoptic sampling runs with acoustic Doppler current profilers have identified surface currents related to both freshwater inflow and wind throughout main body GSL. Velocity profiles have also determined the flow direction and magnitude of a persistent anoxic layer at depth in the south part of GSL. Movement of this layer between the two main basins of the south along a topographically high divide has also been documented (5 to 31 centimeters per second). References Cited Loving, B.L., Waddell, K.M., and Miller, C.W., 2000, Water and salt balance of Great Salt Lake, Utah, and simulation of water and salt movement through the causeway, 1987-98, U.S. Geological Survey Water-Resources Investigations Report 00-4221, 31 p.