HR: 17:15h
AN: H54B-06    [Abstracts]
TI: Channel Flow Modeling Incorporating Effects of Bank Friction and Woody Bank Vegetation in an 81-km Reach of the Rio Puerco, New Mexico
AU: * Griffin, E R
EM: egriffin@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St., Suite E-127, Boulder, CO 80303 United States
AU: Kean, J W
EM: jwkean@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St., Suite E-127, Boulder, CO 80303 United States
AU: Vincent, K R
EM: kvincent@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St., Suite E-127, Boulder, CO 80303 United States
AU: Smith, J D
EM: jdsmith@usgs.gov
AF: U.S. Geological Survey, 3215 Marine St., Suite E-127, Boulder, CO 80303 United States
AU: Friedman, J M
EM: Jonathan_Friedman@usgs.gov
AF: U.S. Geological Survey, 2150 Centre Avenue, Bldg C, Fort Collins, CO 80526-8118 United States
AB: Over the past four decades, the lower Rio Puerco in New Mexico has undergone substantial channel narrowing and about 2 m of sediment deposition on the channel and floodplain. The first step in understanding the cause of the widespread deposition and channel narrowing is to apply a process-based hydraulic model to in-channel flow. We applied a physically based model for steady, horizontally uniform flow to calculate velocity and boundary shear stress distributions in a natural stream with woody vegetation on the channel banks. The model calculates explicitly the form drag on woody plant stems and includes the effects of vegetation on turbulence. The model solves the equations of motion using a ray-isovel turbulence closure, which accommodates lateral boundaries, to determine the velocity and boundary shear stress fields. Average channel shapes, bed gradients, and shrub characteristics were determined from field surveys in April 2002 within an 81-km reach of the lower Rio Puerco. Channel bed and banks are composed of fine sand, silt and clay. Effects of friction on lateral boundaries and reduction of shear stress due to form drag on bank shrubs were quantified for three flow events associated with nearly continuous silt lines. Records from a streamflow-gaging station at the downstream end of the study segment provided discharges used to constrain model calculations and check results. Close agreement between the model-calculated discharge and discharge determined from streamflow measurements demonstrates that flow in this ephemeral stream can be modeled using a relatively modest set of field measurements. Model results indicate that friction on the lateral boundaries reduced the boundary shear stress in the center of the channel from 7 to 20 percent, depending on the channel width and flow depth. Form drag due to flow through stems on the banks further reduced the maximum boundary shear stresses by 5 percent during near-bankfull flows. In the two reaches with vegetated banks, bank shrubs reduced the mean boundary shear stress by almost 40 percent during the near-bankfull flows. Field data and model results indicate water losses to infiltration over the 81-km reach were about 40 percent of the discharge at the upstream end. Now that we have determined the surface roughness, form drag due to bank shrubs, and water loss due to infiltration, we can proceed with the addition of sediment transport to the in-channel flow model.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting