HR: 09:15h
AN: H51H-06    [Abstracts]
TI: Riparian Vegetation Effects on Near-Bank Turbulence During Overbank Flows: A Flume Experiment
AU: * McBride, M
EM: mmcbride@cems.uvm.edu
AF: Dept. of Civil and Environmental Engineering, University of Vermont, 213 Votey Building, Burlington, VT 05405
AU: Thompson, D M
EM: dmtho@conncoll.edu
AF: Dept. of Physics, Astronomy and Geophysics, Connecticut College, Box 5585 270 Mohegan Avenue, New London, CT 06320
AU: Owen, T E
EM: teowen@uvm.edu
AF: Dept. of Civil and Environmental Engineering, University of Vermont, 213 Votey Building, Burlington, VT 05405
AU: Pearce, A R
EM: apearce@cems.uvm.edu
AF: Dept. of Civil and Environmental Engineering, University of Vermont, 213 Votey Building, Burlington, VT 05405
AU: Hession, W C
EM: chession@vt.edu
AF: Biological Systems Engineering, Virginia Tech, 315 Seitz Hall, Blacksburg, VA 24061
AU: Rizzo, D
EM: drizzo@cems.uvm.edu
AF: Dept. of Civil and Environmental Engineering, University of Vermont, 213 Votey Building, Burlington, VT 05405
AB: Measurements from a fixed-bed, Froude-scaled hydraulic model of a stream in northeastern Vermont demonstrated the importance of riparian vegetation effects on near-bank turbulence during overbank flood events. The prototype stream, a tributary to Sleepers River, increased in channel width within the last 40 years in response to passive reforestation of its riparian zone. Previous research has found that reaches of small streams with forested riparian zones are commonly wider that adjacent reaches with non-forested, or meadow, vegetation; however, the driving mechanisms for this morphologic difference are not fully explained. Flume experiments were performed to investigate near-bank turbulence as a mechanism for channel widening in response to reforestation. A 1:5 scale, simplified model of half a channel and its adjacent floodplain was constructed within a 6 m long recirculating flume. The test region was 3.7 m long and 0.9 m wide and oriented with the channel centerline at the flume wall. The channel bed slope was fixed at 0.03, and experiments were run at three discharges: 30, 33, and 36 l/s. Two types of riparian vegetation scenarios were simulated: forested, with rigid, randomly-distributed, wooden dowels, and non-forested, with synthetic grass carpeting. Three-dimensional velocities were measured with a Nortek Vectrino acoustic Doppler velocimeter at 41 different locations within the channel and floodplain at near-bed and 0.6-depth elevations. Observations of three-dimensional velocities and calculations of turbulent kinetic energy (TKE) showed significant differences between forested and non-forested runs. Results indicated that turbulence intensity, as quantified by TKE, roughly doubled throughout the channel and floodplain when forested vegetation was introduced. Given that sediment entrainment and transport can be amplified in flows with high turbulence intensity, our results demonstrated the potential for increased erosion during overbank flood events in stream reaches with recently reforested riparian zones. The concentration of high TKE values and vertical upwelling at the channel-floodplain interface in forested runs indicated a probable erosion hot spot that could promote channel widening.
DE: 1825 Geomorphology: fluvial (1625)
DE: 1856 River channels (0483, 0744)
SC: Hydrology [H]
MN: Fall Meeting 2005