Impacts of an Extreme Flood on Large Wood Recruitment and Transport Processes: Implications for System Response to Disturbance

Keywords: Extreme Floods, Large Wood, Natural Hazards, Ozarks, Geomorphology
Session Type: Virtual Paper
Day: Thursday
Session Start / End Time: 4/8/2021 04:40 PM (Pacific Time (US & Canada)) - 4/8/2021 05:55 PM (Pacific Time (US & Canada))
Room: Virtual 3

Abstract

Large wood (LW) is an important component of rivers draining forest ecosystems. The mechanisms by which LW is recruited and transported downstream are well known, however our knowledge of the impacts of extreme floods on these processes is mostly model driven, derived from limited empirical data from montane river systems, or based on floods of less than 200 year recurrence. The research presented here investigates the impacts of a >500 year flood on LW recruitment and transport in sub-basins of the North Fork River, Missouri. We implemented a rapid response data collection effort to characterize conditions before natural recovery processes could obscure flood-related impacts. The impact of the flood on recruitment was assessed by evaluating the prevalence of “new wood” in the channel, and the impact on transport was evaluated using an analog basin approach whereby we compared post-flood LW characteristics to those of un-impacted analog basins. Results showed 1) recruitment of new wood increases exponentially with flood magnitude, 2) study basins had significantly higher LW volumes than analog basins, 3) LW load in the study basins consisted of a higher proportion of individual pieces of LW compared to analog basins, and 4) transport capacity in the study basins was high compared to analog basins. Based on these findings, we present two possible post-flood disturbance response/recovery scenarios; one in which elevated post-flood transport capacity serves to speed system recovery to the pre-flood LW regime, and one in which the enhanced LW piece composition results in a new post-flood LW regime.