Doctoral Dissertation Research: Holocene Fluvial Response to Environmental Change in the Uinta Mountains of Northeastern Utah

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Long-term chronologies of relations between climate change and floods in North America during the Holocene (post-glacial) epoch primarily are restricted to the Upper Mississippi Valley and American Southwest. These areas provide valuable insights, but the dynamics of post-glacial physical system dynamics in other locales and for the continent as a whole remain incomplete. This doctoral dissertation research project will focus on the responses of runoff and floods to climate change recorded in relict river systems along the north slope of the Uinta Mountains in northern Utah. Low-gradient streams in this region have experienced extensive lateral migration, with former channels preserved as abandoned meanders. The magnitudes of past floods that filled these channels will be quantitatively reconstructed by applying hydraulic equations to the surveyed dimensions of relict channels. Fill sediments will be analyzed using drill cores along transects perpendicular to each relict channel. The magnitude of the modal flood for each relict channel will be compared with the magnitude of the modern modal flood at the same location and calibrated for the associated drainage basin area. Absolute ages of relict channels will be constrained directly through the use of radiocarbon dating on organic material in the channel fills. The results of these analyses will be used to reconstruct a chronology of post-glacial floods in this semi-arid region of northern Utah. The results of past flooding are expected to contribute to improved understanding of how future climate changes might influence runoff and flooding in this same region. The results also should provide evidence to test models that predict regional hydrologic responses to continental-scale changes in atmospheric circulation patterns. The Uinta study area is particularly appropriate for examination of linkages between climate change and flooding behavior because the region lies along a large-scale atmospheric circulation boundary. Variability in large-scale hemispheric circulation patterns, such as those associated with El Nino/Southern Oscillation, has been shown to influence the magnitude of the snowmelt floods. The records of past floods from these relict channels will be used to evaluate sensitivity of flood regimes to climate changes and will be compared to long-term chronologies of past floods from other regions to assess the behavior of hemispheric circulation patterns through the Holocene. The hydrologic responses recorded in the stratigraphic record also will enhance understandings of the dynamics affecting water supply in the Colorado River basin, because summer water production in this basin is sustained by runoff from the Uintas and surrounding ranges. Furthermore, the study area's transitional location between locations of similar prior studies in the arid Southwest and the humid Midwest provides a framework for understanding continental-scale linkages between climate change and hydrological responses. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.