Fall velocities of natural sediment particles: a simple mathematical presentation of the fall velocity law

The fall velocities of large natural sediment particles (shingle) and of commonly used model sediments (anthracites) have been measured using a video imaging technique. The study covers a Reynolds number ranging from 35 to 23,000, a significant extension to the existing database for natural sand particles (up to 1500). Making use of the extended database, a simple empirical equation has been derived giving the relationship between the particle fall velocity and sieve diameter. Additional analysis of the drag coefficient has led to a revised formula based on that of Fredsoe and Deigaard (Mechanics of Coastal Sediment Transport. Advanced Series on Ocean Engineering, World Scientific, Singapore), providing a better fit for the data obtained at high Reynolds numbers.