Numerous lines of evidence have highlighted the relationship between the variability of surface hydrology and the El Niño-Southern Oscillation (ENSO) within the lower Colorado Watershed. One line of evidence, the paleoflood record, illustrates the dependence of extreme flooding on the frequency of El Niño events. Within the upper Colorado Watershed, these climatic aberrations are not positively correlated with ENSO, and in some cases, inversely correlated. There are no paleoflood studies in this region, so the hydroclimatic mechanisms responsible for driving extreme flooding is based on temporally limited, gaged records. The primary goal of this research is to address the spatial gap by developing a watershed-scale, paleoflood chronology in the Dolores Watershed to understand how extreme flooding has responded to shifts in climate. The watershed encompasses a broad region of southwestern and west-central Colorado, before draining into the Colorado River near Moab, UT. It is part of the region that correlates very weakly with ENSO, so its response to climate shifts may act as an analog to the majority of the Upper Colorado Watershed. This research places an emphasis on geochronology to create a very robust flood chronology. There are questions about the validity of using "optically stimulated luminescence" (OSL) methods for dating paleoflood hydrology. This research will provide an analytical assessment of OSL for its application to paleoflood hydrology. In addition, this study is designed to evaluate the degree of uncertainty in paleodischarge estimations by investigating the alluvial stratigraphy to assess channel stability. Peak discharge estimates will be completed with a one-dimensional hydrological model.
Results from this research will provide a more thorough understanding of flood regime responses to climate change in the upper Colorado Watershed. Hydrological responses to past climate shifts are a potentially reasonable analog for modern and future hydrologic responses to global warming. In addition, the integration of multiple age-control and field techniques will reduce uncertainty in paleoflood research. The Dolores Watershed has been selected for this study because of its unique position: in a climatic region where stream flow is very poorly correlated with El Niño events, making it a prototype for other sub-basins within the upper Colorado Watershed. The physiography of the watershed is ideal for this study because the rivers are mixed with both bedrock and alluvial channels, and the preservation potential for paleoflood evidence is high. The paleoflood record in this region indicates that numerous extreme floods have occurred, each of which greatly exceeds the maximum flood during historical times. Water managers may apply this information to mitigate the direct impacts of future flooding, especially in the context of modern and future climate change.
