RAPID: Characterizing Sediment Mobilization and Landscape Response to the Combined Effects of Wildfire and Extreme Flooding along Fourmile Canyon, Front Range Colorado

University Of Connecticut, Storrs CT

Investigators

Abstract

This RAPID project focuses on the impacts of flooding and erosion on Fourmile Canyon in the Colorado Front Range following the exceptional September 2013 rainfall event. The catchment is still responding to a 25 km2 wildfire in 2010 and the team will test the hypothesis that the 2013 flood reworked and deposited sediments initially mobilized by the earlier fires. The team will study the 2013 flood deposits, eroded hillslopes, side-tributary and gully deposits, and deposits freshly exposed beneath terraces along the canyon. They will revisit locations that have been part of an ongoing post-fire study, and will use short-lived fallout radionuclides (7Be, 137Cs, and 210Pb) in these deposits to help identify remobilized fire sediments. In addition, they will analyze the geochemistry and stratigraphy of valley deposits and compare measures of short-term wildfire and flooding-related erosion with ongoing studies documenting erosion rates and hillslope processes over the past 10,000-30,000 years. Sediment deposits and exposures that formed during the September 2013 flooding must be sampled and studied soon, before they degrade and disappear as road rebuilding, channel manipulation, and landscape recovery proceeds. These new exposures greatly increase the ability to analyze and date Holocene slope and valley stratigraphy using 14C. The work will enhance understanding of consequences of increased incidence of wildfires and large-magnitude floods on the landscape and those who live there. As such, the project outcomes will inform hazard mitigation and resilience. The team will leverage existing collaborations with USGS scientists and the Boulder Creek Critical Zone Observatory, and will directly involve undergraduates and a graduate student.