MIT OpenCourseWare (finance courses)

Lecture 2: Mechanics of Sediment Transport

The lecture surveys the mechanics of sediment transport in both fluvial and aeolian environments, outlining how particles move as bedload, suspended load, or wash load and describing the experimental foundations behind these concepts. It emphasizes the stages of motion—rolling, saltation, and suspension—while noting the difficulty of quantifying transport rates, especially for bedload, compared with more straightforward suspended‑load sampling. Key insights include Vito Vanoni’s microscopic flume experiments that revealed grain‑scale movements near the Shields curve, the semi‑empirical nature of transport‑rate formulas, and the pivotal role of density ratios (particle versus fluid) in setting aerodynamic thresholds. The speaker also highlights Ralph Bagnold’s pioneering wind‑tunnel work, the observable hysteresis in saltation onset and cessation, and the extreme spin rates of airborne grains. Illustrative examples range from the “magic screen” thought experiment for visualizing transport rates to real‑world wind‑tunnel strobe footage of saltating sand, and a comparison of threshold shear stresses on Earth, Mars, and Venus. The discussion of bedforms—ripples, dunes, antidunes—and their feedback on flow underscores the coupled forward and inverse problems faced by engineers and sedimentologists. Understanding these mechanisms is critical for hydraulic engineering design, river‑channel management, and predicting planetary surface processes, as accurate transport predictions inform infrastructure resilience and guide interpretations of sedimentary records.