Surface Water Hydrology Within the Great Salt Lake Basin

The Great Salt Lake (GSL) and its tributaries are ecologically and economically important resources for Utah. It is a highly saline lake, with salinity that is several times saltier than the ocean. Lake uses are heavily influenced by its salinity and lake level and, similarly, river uses by its streamflow quantity. Currently, the GSL Basin is experiencing changes that affect tributary inflows, lake level, and salinity. For my dissertation and in support of better lake management, I addressed important gaps in our understanding of the lake and the changes it is undergoing. Chapter 2 is an examination of the distribution of salinity and salt mass within the lake. Existing measurements from multiple agencies were aggregated to quantify the variability in salinity and the intermittent presence of a deep brine layer, which occurs only with causeway flow from the north to the south arms. I found that the overall mass of salt in the lake is declining and quantified this in terms of mineral extraction records and historical density measurements. Chapter 3 estimates the historical magnitude of human consumptive water use within the basin. Lake volume changes and evaporation estimates were used to quantify inflows to the lake corresponding to changes in lake level. The trends in these inflow estimates were used to quantify basin wide human consumptive water use to be upwards of 2.3 km3 /yr and the current lake level decline associated with this estimate to be as much as 4.5 meters. Chapter 4 presents a learning module targeting undergraduate hydrology students that was developed to advance innovative approaches in hydrologic education. While this project does not directly relate to the GSL, it enhances student learning of hydrologic processes within the GSL Basin. The newly developed content is centered on case-based, data- and simulation-driven learning of the fundamentals of hydrology, rainfall-runoff processes, and engineering design for an online module focused on a detention basin at the mouth of a canyon in the GSL Basin. Overall, this dissertation has contributed knowledge on the salinity, deep brine layer and declining salt mass in GSL due to mineral extraction. It has also provided a lake volume based water balance estimate of consumptive water use extending back prior to the period when streamflow was measured. These contributions provide important scientific information about the lake that can inform decision making on water management and efforts to restore the lake to healthy levels

Variability of Water Storage and Instream Temperature in Beaded Arctic Streams

The purpose of this study is to investigate variation in water export and instream temperatures throughout the open water season in a beaded Arctic stream, consisting of small pools connected by shallow chutes. The goals are to better understand heat and mass movement through these systems, how this may impact chemical and biological processes, and the resulting shifts with changes in climate. This is accomplished by first examining the extent and variability of water storage and export through qualitative analysis of observational data. Further, heat fate and transport is examined through development of an instream temperature model. The model formulation, a simple approach to model calibration and validation, and information regarding residence and characteristic times of different pool layers are presented. Using temperatures measured at high spatial resolution within the pools and surrounding bed sediments as well as other supporting data (e.g., instream flow, specific conductivity, weather data, and bathymetry), various types of storage within the pools, banks, and marshy areas within the riparian zone, including subsurface flow paths that connect the pools, were found. Additionally, data illustrated that some pools will stay stratified during higher flow periods under certain weather conditions. Through modeling efforts, the dominant heat sources were found to vary between stratified layers. It was also found that potential increases in thaw depths surrounding these pools can shift stratification and mixing patterns. These shifts can further influence mass export dynamics and instream water quality. Given the amount and different types of storage within these systems and the influence of stratification patterns on the residence times in the pools, Imnavait Basin and similar beaded Arctic watersheds will likely experience delayed export of nutrients that are limiting in most Arctic systems

Engineering Students’ Perceptions of Mathematical Modeling in a Learning Module Centered on a Hydrologic Design Case Study

Engineering students need to spend time engaging in mathematical modeling tasks to reinforce their learning of mathematics through its application to authentic problems and real world design situations. Technological tools and resources can support this kind of learning engagement. We produced an online module that develops students’ mathematical modeling skills while developing knowledge of the fundamentals of rainfall-runoff processes and engineering design. This study examined how 251 students at two United States universities perceived mathematical modeling as implemented through the online module over a 5-year period. We found, subject to the limitation that these are perceptions from not all students, that: (a) the module allowed students to be a part of the modeling process; (b) using technology, such as modeling software and online databases, in the module helped students to understand what they were doing in mathematical modeling; (c) using the technology in the module helped students to develop their skill set; and (d) difficulties with the technology and/or the modeling decisions they had to make in the module activities were in some cases barriers that interfered with students’ ability to learn. We advocate for instructors to create modules that: (a) are situated within a real-world context, requiring students to model mathematically to solve an authentic problem; (b) take advantage of digital tools used by engineers to support students’ development of the mathematical and engineering skills needed in the workforce; and (c) use student feedback to guide module revisions

The Salinity of the Great Salt Lake and Its Deep Brine Layer

The Great Salt Lake is a highly saline terminal lake with considerable fluctuations in water surface elevation and salinity. The lake is divided into two arms by a railroad causeway. River inflows enter the larger south arm, while the north arm only receives minimal surface runoff. Evaporation from both arms and limited exchange of water and salt through causeway openings result in complex water and salinity processes in the lake. The north arm is typically homogeneous and close to saturation. The south arm is typically stratified with periodic occurrences of a deep brine layer. This paper analyzes the lake’s long-term historical salinity and water surface elevation data record. Its purpose is to better document the movement of salt and changes to salinity in time and space within the lake and the occurrence and extent of its deep brine layer. This work is important because of the lake’s salinity-dependent ecosystem and industries as well as the role played by the deep brine layer in the concentration of salt and contaminants. We documented that the deep brine layer in the south arm is intermittent, occurring only when causeway exchange supports flow from the north to the south arms. We found that the overall mass of salt in the lake is declining and quantified this in terms of mineral extraction records and historical density measurements