Paleoflood hydrology on the lower Green River, upper Colorado River, Utah

Tao Liu1 and Noam Greenbaum2, Victor R. Baker1, Lin Ji1, Tammy Rittenour3

1Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, AZ

2Department of Geography and Environmental Studies, University of Haifa, Haifa, Israel;

3Department of Geology, Utah State University, Logan, Utah

Through a comprehensive paleoflood investigation, employing the abductive mode of inference, we document natural evidence of 70 paleofloods at six sites on the Lower Green River, Utah. Hydraulic analysis, using the Sedimentation and River Hydraulic-2D model (SRH-2D), shows that the responsible peak paleoflood discharges ranged between 507 and 7499 m3/s. At least 14 of these paleoflood discharge peaks exceed a level twice that of the maximum systematic gauged flow of 1929 m3/s. Geochronological analysis, employing optically stimulated luminescence (OSL) and radiocarbon dating techniques, demonstrates that these 14 paleoflood peaks occurred in the past 700 years. Integrated of these paleoflood data into flood frequency analyses (FFA) showed higher values for the upper tails of the flood distribution than did an FFA based only on the systematic record, showing that extreme floods are more frequent than indicated by the relatively short gauged records. Through philosophical examination the three approaches to extreme flood estimation, FFA, probable maximum flood estimation, paleoflood hydrology, we show the significance of the natural evidence for advancing the scientific understanding of extreme floods.