Large wood hydraulics: Using structure from motion to estimate flood depths

Year: 2023
Presenter/s: Michal Tutka
Symposium Session: 2023 - 09 - An Open Toolbox: Tools and Assessments to Tackle Complex Questions
Topics covered: hydraulics, modeling, and wood


The design of large wood (LW) is limited by a lack of mechanistic tools for predicting how LW features (e.g. porosity, orientation, frontal area, flow area, wetted perimeter) will affect flow depths and velocities. This project aims to understand how submerged LW features impact flow depths and velocities as well as which LW features have the greatest effect on hydraulic resistance (represented as roughness coefficients, Manning’s n and Darcy f). Analysis involves integrating data derived from structure from motion (SfM) meshes of eight log jams in the Coastal Range, Oregon, USA, with varying channel span, log placement, and orientation with a topographic survey over a range of depth and discharge observations. Analysis is underway – greater drag and higher roughness coefficients are expected at jams with logs oriented orthogonal to the flow, spanning the channel, and/or at low relative submergence due to increased form resistance. Except in cases where channel-spanning logs are encountered with stage, the relative influence of log jams on hydraulic resistance is expected to decay exponentially with degree of submergence. This study aims to provide (1) a more accurate approach to quantifying jam features, (2) insight on the relative importance of physical features on flood depths in natural settings, and (3) practical value for better designing, prioritizing, permitting, and implementing LW projects.