HR: 17:00h
AN: H42L-05    [PDF]
TI: Quantifying Flow Resistance in Rivers and on Floodplains During Large Floods
AU: * Kean, J W
EM: jason.kean@colorado.edu
AF: University of Colorado, Campus Box 216, Boulder, CO 80309 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
AB: In an effort to improve predictions of peak discharge at ungaged sites by reducing the uncertainty in estimates of channel roughness, a series of processed-based methods have been developed over the past several years to quantify the flow resistance of common channel roughness elements using simple measurements of their geometric properties. These methods have been recently incorporated into a flow model and have been applied to predict the velocity, discharge, and boundary shear stress in a 150-m densely vegetated reach of the Rock Creek Branch of the Whitewater River, Kansas. This is done without calibration using measured stage together with detailed measurements of the channel geometry and the size, shape, and spacings of the small-scale topographic features and plant stems in the channel. Topographic features on the bed and banks of the channel are characterized by a sequence of Gaussian shaped elements, which have drag coefficients known from recent experiments. Woody vegetation is modeled as randomly distributed rigid vertical cylinders. The model explicitly calculates drag on the roughness elements and includes the effects of friction on lateral boundaries on the flow and boundary shear stress. Model predictions of discharge during a moderate flow event are in agreement with the measured discharge at a USGS gaging station at the entrance to the study reach. The model is then used to explore the effect of floodplain roughness on the flow and boundary shear stress during a hypothetical overbank event. The model shows that drag on the vegetation substantially reduces the flow velocity on the floodplain, which results in increased velocities and boundary shear stress in the main portion of the channel relative to the case with no vegetation present. When used in conjunction with information on the critical shear stress of the bed and bank material, the model can be used to determine whether or not a given event can alter the channel topography and to evaluate the geomorphic response of the channel to extreme flow events. During extreme events the topography and roughness of the channel can change with time and these changes must be calculated with bed and bank evolution models.
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting