Effect of Riparian Vegetation Density on Stream Flow Velocity

River restoration that can be accomplished by structural and nonstructural means is one of the most important and popular recent advances in river engineering. Stream restoration techniques generally focus on protecting or restoring aquatic, riparian, and floodplain habitat and habitat resources. This study focused on developing a methodology to systematically vegetate a straight, degraded stream corridor in order to improve habitat and habitat resources for fish and wildlife, and provide the stimuli necessary to cause stream meanders to form and equilibrate. Hence a laboratory experiment was performed in a flume with simulated alternating vegetation zones. The density of the vegetation zones was altered while all other flow characteristics were kept constant. Particle Image Velocimetry (PIV) was used to determine surface flow characteristics. PIV measurements revealed that as vegetation density increases, the following flow parameters related to potential meandering increase: average thalweg velocity, turning of the flow, flow circulation downstream of the vegetation zone, flow sinuosity, reattachment lengths, flow depth, and resistance. The average flow velocity decreased both inside and out of the vegetation zone. This study established a methodology to induce sinuosity in straight, degraded channels using vegetation and determined that placing roughness elements that simulate natural vegetation can significantly alter the flow direction.