Particle saltation trajectories in supercritical open channel flows: Roughness effect

Bed load sediment transport governed by particle saltation in supercritical open channel flows causes bedrock incision high-gradient mountain streams and hydro-abrasion at hydraulic structures. Hence, a better understanding of turbulent flow characteristics dynamics is prime importance for the prediction river landscape evolution, sustainable design To this end, we experimentally investigated single-particle over fixed planar abraded beds covering smooth, transitionally rough, hydraulically rough regimes. The experiments were performed Laboratory Hydraulics, Hydrology Glaciology (VAW) ETH Zürich wide range conditions with various width-to-depth aspect ratios (b/ho) Froude numbers (F). We motions five groups differing shape, hardness, diameter. By means high-speed camera, velocities trajectory parameters—such as hop height length—were determined using tracking velocimetry. results reveal that least 120 individual particles should be used tests to determine sound statistics trajectories. In present test conditions, are dominantly transported saltation. effects properties such shape diameter on trajectories negligible, while rolling probability given condition increases increasing roughness was found key parameter having significant effect horizontal energy transfer. Hop height, length, velocities, well transfer, increase bed roughness. Based data, non-dimensional equations developed each regime enhance saltation–abrasion model Sklar Dietrich. findings contribute motion under different their mechanics three-dimensional occurring steeply sloped rivers