CHARACTERISTICS OF NEAR-BOUNDARY FLOW THROUGH Two RIPARIAN VEGETATION TYPES: A FLUME STUDY

摘要

Stream restoration designs frequently involve establishing vegetation on the bank face and floodplain, resulting in mixed patterns of riparian vegetation. This study examined the effects of varied patterns of simulated vegetation on time-averaged velocity and turbulence statistics. A flume experiment was conducted with eight submerged vegetation treatments composed of three characteristics: flexible grass height (0.7 and 3.9 cm), percent grass cover (100% and 50%), and the presence of herbaceous tubelings (with and without). Turbulence statistics (e.g., turbulence intensities, turbulent kinetic energy, and Reynolds stresses) were examined using near-bed velocity measurements. The 50% grass cover treatments introduced additional boundaries located at the vegetation edges that were not present in the 100% cover treatments. These additional edges resulted in complex flow patterns and velocity gradients, as well as heterogeneous distribution of turbulence statistics. Elevated Reynolds stresses located at the vegetation patch edges indicated potential for localized particle entrainment, consistent with previous observations of erosion. The presence of dowels also contributed to flow complexity while not significantly elevating overall turbulence. Results indicate that combining dense vegetation with varying lengths and sparsely positioned herbaceous tubelings will promote flow complexity.