Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Watershed Sciences

Department name when degree awarded

Watershed Science

Committee Chair(s)

Sarah Null


Sarah Null


Wayne Wurtsbaugh


David Tarboton


Utah's Great Salt Lake contributes and estimated $1.3 billion to the local and regional economy and is a vital food-source for migratory and resident birds. In 1959, the lake was fundamentally changed with construction of an earth-filled, semi-permeable railroad causeway which splits the lake into two "arms". The only flow interaction between these two arms is through the semi-permeable causeway material, and three openings in the causeway. In 2013, two of these causeway openings were closed, and a bridge was proposed to improve flow between arms. Four bridge designs were proposed. I modeled Great Salt Lake water and salt distribution with each bridge design using historical 1966-2012 measured streamflow and climate data. I then used tree-ring reconstructed hydrologic data to estimate lake elevation and salinity since 1604 to understand the effects of long-term climate variability and the long-term influence the causeway has on the water and salt balance on the lake. I find that Great Salt Lake is sensitive to changes in bridge designs, particularly in the south arm, where the largest bridge design increases mean salinity by almost 20% from the smallest bridge design over the 400-year modeled period. Additionally, if the causeway is left in its current state with few openings for interflow, salinity in the south arm may eventually approach freshwater levels, while the north would almost always be saturated. I also find that the 20th century had a lower average lake level than the three preceding centuries, and also had smaller flooding events compared to the 17th and 18th centuries. These results will aid Great Salt Lake management by quantifying elevation and salinity effects of proposed causeway changes and allow managers and stakeholders to better prepare for climate-driven Great Salt Lake elevation and salinity changes not witnessed in the historical record.