Date of Award


Document Type

Campus Access Thesis



First Advisor

Jean Ellis


This study presents field-based observations demonstrating the relationships between vegetation density, shear stress and sediment transport surrounding hummocks, a type of small dune. While qualitative observations and holistic, large-scale experiments regarding vegetation density and sediment transport have confirmed a negative correlation, fewer papers have quantitatively described the nature of that relationship. Moreover, virtually no studies have specifically focused on hummocks. Field-based data collection recorded wind velocities using a sonic anemometer upwind of the hummock, grain impacts from four miniphones deployed on and to the side of the hummock (MICs), trap-derived sand transport, and hummock vegetation density. These data sets provide the parameters for model-estimated transport rates from Bagnold, Zingg, Kawamura, and Lettau and Lettau, as well as a slope correction coefficient from Bagnold. Observations were made in an uncontrolled natural setting so that heterogeneities in vegetation density and slope were included in the data; this study highlights the variability inherent from these conditions. Average wind velocity at z = 1.0 m was 7.8 m/s with an average shear velocity of 0.39 m/s. The average trap-based transport rate was 25.0 g/m2/s, while the unobstructed MIC transport was 89.8 g/m2/s. Trap and MIC-derived sand transport rates had an R2 of 0.39 (p0.05). These findings suggest that steering and projection of grains around and over the hummock play an important role in hummock morphology and processes.