Impacts of an extreme flood on large wood recruitment and transport processes

ABSTRACT This research investigates impacts of an extreme flood on recruitment and transport of large wood (LW) in sub-basins of the North Fork River, Missouri. Data collection took place two months after a >500 year flood to characterize LW conditions before natural recovery processes could obscure impacts. We used sites from previous LW studies in the region as reference to help identify flood impacts. Results showed 1) LW load volumes were no different than reference sites, but individual LW pieces comprised a greater percentage of the total load, 2) a high proportion of pieces at flood-impacted sites contained root wads, 3) transport capacity of the flood-impacted sites was high compared to reference sites, and 4) LW recruitment increased exponentially with flood magnitude. These results suggest that extreme floods have a significant impact on the composition of the LW load, and that geomorphic impacts of such floods may result in enhanced transport capacities. Based on these findings, we present two possible post-flood LW response/recovery scenarios; one in which elevated 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 with an enhanced load.