Theses and Dissertations Collection

Vegetation is a vital component of river systems because it impacts habitat and flow and changes sediment transport regimes and local bed topography. Specifically, rigid emergent vegetation changes turbulence intensities, velocities, and shear stress near the bed, which contributes to erosion and deposition in vegetation patches. However, the effects of vegetation density on spatial distributions of near-bed flow parameters are not well understood. Furthermore, no studies have investigated the relative effects of vegetation and vegetation induced topography on near-bed flow. We conducted three laboratory flume experiments with a single stalk and flat bed, a single stalk with a scour hole, and a scour hole with no stalk to investigate the individual effects of a vegetation stalk and a scour hole on the distributions of near-bed velocities, Reynolds stresses, and turbulent kinetic energies (TKE). We also used experiments from another study to test the accuracy of previously published equations for mean channel velocity (U) and spatially averaged TKE (〈???〉) in flat beds with data from a bed with vegetation and natural bed topography. Lastly, we fit a gamma distribution to the TKE distributions from the single stalk experiments and from experiments from another study. Our goal was to find a relation between fit parameters of the gamma distribution and mean channel velocity to predict the shape and scale parameters of a TKE distribution from mean channel velocity. We found that equations designed for flat beds predict mean channel velocity and mean near-bed turbulent kinetic energy fairly well for low measured U and 〈???〉 in beds with natural topography and vegetation. Not all experimental TKE data fit a gamma distribution well, however a relation may exist between vegetation density and the shape parameter of a two-parameter gamma distribution.