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Flow Resistance of Emergent Vegetation
River restoration and bioengineering programs commonly use vegetation to stabilize banks. For this, it is important to know the forces that the flowing river water exerts on the vegetation. To this end, a laboratory study was performed at the USDA-ARS National Sedimentation Laboratory. Dowels were used to simulate emergent rigid vegetation. Dowels were systematically placed in the laboratory flume, beginning with a single dowel connected to a load cell to measure the drag force and then placing dowels around the single dowel to determine any shielding effect. It was found that the drag coefficient of a single dowel ranged from 4.5 to 6.5, which is higher than that published for a 2-D cylinder of infinite length. A momentum balance analysis shows that (1) for the single dowel case, the momentum balance approach determines CD>>1 contrary to the low values for a cylinder and (2) the CD for the measured dowel is about two times higher than the momentum formulation. This difference is attributed to the presence of large standing waves upstream of the dowel and the breaking of these waves. When additional vegetation elements were added to form a matrix, it was found that as vegetation elements were added, the drag forced increased initially due to the vegetation concentrating the flow towards the instrumented dowel, and then decreased due to dowels being directly upstream of the instrumented dowel and thereby blocking the flow. These results have implications for managed planting arrangements in stream corridor rehabilitation programs.
Flow Resistance of Emergent Vegetation
River restoration and bioengineering programs commonly use vegetation to stabilize banks. For this, it is important to know the forces that the flowing river water exerts on the vegetation. To this end, a laboratory study was performed at the USDA-ARS National Sedimentation Laboratory. Dowels were used to simulate emergent rigid vegetation. Dowels were systematically placed in the laboratory flume, beginning with a single dowel connected to a load cell to measure the drag force and then placing dowels around the single dowel to determine any shielding effect. It was found that the drag coefficient of a single dowel ranged from 4.5 to 6.5, which is higher than that published for a 2-D cylinder of infinite length. A momentum balance analysis shows that (1) for the single dowel case, the momentum balance approach determines CD>>1 contrary to the low values for a cylinder and (2) the CD for the measured dowel is about two times higher than the momentum formulation. This difference is attributed to the presence of large standing waves upstream of the dowel and the breaking of these waves. When additional vegetation elements were added to form a matrix, it was found that as vegetation elements were added, the drag forced increased initially due to the vegetation concentrating the flow towards the instrumented dowel, and then decreased due to dowels being directly upstream of the instrumented dowel and thereby blocking the flow. These results have implications for managed planting arrangements in stream corridor rehabilitation programs.
Flow Resistance of Emergent Vegetation
Barkdoll, Brian D. (author) / Vittilam, Sandeep (author) / Bennett, Sean J. (author) / Alonso, Carlos V. (author)
World Water and Environmental Resources Congress 2004 ; 2004 ; Salt Lake City, Utah, United States
2004-06-25
Conference paper
Electronic Resource
English
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