Nature-Directed Approach to Hydrology and Hydraulics of Extreme Floods and Megafloods

Abstract

Both paleoflood hydrology and megaflood studies emphasize the identification of various signs or traces that can be interpreted by the experienced geological and/or hydrological investigator as evidence of past flood processes. This is a nature-directed approach to advancing scientific understanding of flooding phenomena. This dissertation includes three of the author’s research studies demonstrating the naturedirected approach to making scientific discoveries about extreme flooding. The first study focuses on improving extreme flood risk estimation by deciphering natural evidence of the past floods on the lower Green River, Upper Colorado River Basin. Integration of the paleoflood data into various flood frequency analysis (FFA) procedures reveals considerably higher values for the upper tails of a flood distribution than does an FFA based solely on the systematic gauged record, indicating that extreme floods are larger and more frequent than implied by relatively short gauge records. The second study identifies the temporal clustering of extreme floods in the upper Colorado River Basin by employing a meta-analysis of paleoflood data extending through the past ten thousand years. The results show that maximum extreme flood clusters in time can be linked to long-term climatic change. The third study associates late Pleistocene megaflood processes with landforms in northwestern U.S. using hydraulic modeling simulations. The simulations indicate the necessity of employing an iterative simulation modeling approach, involving both geological and hydraulic analyses, to enhance the understanding of cataclysmic hydrological events in planetary history. The dissertation also includes several other studies involving the author that introduce or extend work done for the three primary research papers.