2026 CSDMS meeting-018

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Measurement of turbulent pressure fluctuations to inform plucking and entrainment thresholds

Nicholas Colaianne, (he/him),University of Idaho Center for Ecohydraulics Research Boise Idaho, United States. cola8842@vandals.uidaho.edu

Elowyn Yager, University of Idaho Center for Ecohydraulics Research Boise Idaho, United States. eyager@uidaho.edu

Aaron Hurst, University of Colorado Boulder Boulder Colorado, United States. Aaron.a.hurst@gmail.com

The entrainment of bedrock blocks by flow hydraulics (“plucking”) is a key mechanism driving erosion in both natural and man-made channels. Despite its role in knickpoint migration and bedrock incision, the physical processes controlling block motion remain poorly constrained. In particular, we lack an understanding of how the instantaneous turbulent pressure field around the block contributes to its motion. Turbulent fluctuations may act to initiate motion even when time-averaged fluid forces are below block resisting forces. To quantify the forces contributing to fluvial plucking, we measure turbulent pressure fluctuations acting on a simulated bedrock block at a downstream-facing step in a laboratory flume for subcritical, critical, and supercritical flows. The block is instrumented with 66 pressure transducers and two accelerometers, enabling simultaneous measurement of instantaneous pressures and block motion. Block protrusion (−20 to +20 mm) and fracture (joint) width (0–100 mm) are systematically varied to quantify their effects on instantaneous lift and drag forces. We also use planar particle image velocimetry (PIV) to resolve the near-bed velocity field and shear stress acting on the block top. The resulting dataset will provide new mechanistic insights into how flow turbulence and fracture geometry control block entrainment, which may be applied to existing erosional frameworks and models of bedrock plucking.