CHARACTERIZING EROSIONAL “WOOD GOUGES” ON NEAR-CHANNEL RIVER FLOODPLAINS WITH UAS AND LIDAR

High-resolution topography often reveals fine details within landscapes, which can lead to a more complete understanding of geomorphological processes. The recent advancement and proliferation of remotely sensed high-resolution topographical measurement techniques, such as LIDAR and photogrammetry obtained from Unmanned Aerial Systems (UAS), has vast potential to characterize these fine details and advance knowledge of fluvial landscapes. This presentation details the presence of persistent, elongated erosional gouges on the floodplain near the outer bank of an actively eroding meander bend and within an evolving chute cutoff channel on large meandering rivers in Indiana, USA. Through the combined use of LIDAR, structure-from-motion photogrammetry, and field observation, we characterize these erosional gouges and discuss both their formation and potential impacts on channel and floodplain geomorphology. The features appear to be formed by large wood dislodging sediment as the wood is transported over the floodplain via overbank flows, as many of the gouges were found to terminate at the base of a piece of wood. Thus, we term these features “wood gouges”. Wood gouges are generally less than 10 cm in width and depth, but can extend many meters in the direction of mean flow. Wood gouges might weaken channel banks locally or form preferential pathways for overbank flow back into the channel, resulting in locally altered bank erosion rates and patterns. In addition, wood gouges might form initial floodplain defects or knickpoints, from which the initiation or extension of chute channel erosion occurs. Although the importance of large wood in fluvial environments has been recognized, the particular processes which lead to the formation of wood gouges as well the impact of wood gouges on channel and floodplain morphology requires further research.