Hydrodynamic effects of surface piercing plants

Under a variety of circumstances creeks and rivers overtop their banks and inundate the surrounding land and flora. The inundated flora become arrays of flow obstructions, dramatically changing the characteristics of the local flow. This thesis describes a laboratory study of the effects of flow obstructions on the velocity and turbulence profiles within the obstructions. The flow in three plant densities was modeled with a pump driven current and wooden dowels in a laboratory flume. It was found that the major effect of increasing plant density was to significantly increase the horizontal and vertical turbulence. This is due predominantly to wake interaction, and the overall increase in the number of wakes producing strong lateral shears. In addition, pressure forced vertical velocities were measured just upstream and downstream of individual array elements, and these vertical velocities are swept into the main flow as the turbulence levels increase. The increased turbulence mixes momentum downward, and compresses the boundary layer to approximately 0.5 cm, which is 1/16 of the boundary layer thickness in the approaching free-stream. Thesis Supervisor: Dr. Heidi M. Nepf Title: Assistant Professor of Civil and Environmental Engineering