Date of Award

Spring 2022

Document Type

Open Access Thesis


Civil and Environmental Engineering

First Advisor

Enrica Viparelli


Most research on fluvial bedforms focuses on the study of dunes (lower regime), and much less is known on upper regime bedforms. Studying upper regime bedforms, the conditions in which they form and how the geometry changes with flow and sediment properties is necessary for interpreting the stratigraphic record, estimate flow resistance and reconstruct flow characteristics from observed geometries. Here I present results of laboratory experiments designed to investigate the role of suspended bed material and sediment grain size on upper regime bedforms. Experiments were performed in open channel flow mode in a sediment-feed flume with a 0.19 m wide, 0.9 m deep, 7 m long test reach. Mean grain sizes ranged between 0.22 mm and 0.87 mm. All experiments started from a net-depositional or net-erosional (disequilibrium) condition and continued until the bed level averaged over a series of bedforms did not change in time (equilibrium). In a sediment feed flume at equilibrium, the total (bedload plus suspended load) bed material load is known because it must be equal to the sediment feed rate to guarantee mass conservation. Equilibrium water surface and bed level measurements were used to characterize average flow conditions,suspended sediment concentration was measured, and the near bed suspended sediment concentration was estimated. As expected, suspended bed material load significantly increased as the sediment grain size decreased. Our results confirm that as the ratio between the bed material load and the flow discharge increases, the bed configuration evolves from lower regime to upper regime. As the ratio between bed material load and flow discharge increases, upper regime bedforms become longer (i.e., the wavelength increases) and the flow depth becomes shallower. In experiments with relatively coarse sand transported as bedload transport, we observed the transition from upstream migrating antidunes to plane bed with bedload transport in sheet flow mode. In experiments with significant suspended bed material load, we observed the transition from downstream migrating antidunes to upstream migrating antidunes, which tend to evolve toward cyclic steps as the ratio between sediment supply and water discharge increases