HR: 0800h
AN: H51E-0800    [Abstracts]
TI: Quantifying and Partitioning Roughness in Mountain Streams, Fraser Experimental Forest, Colorado USA
AU: * David, G C
EM: gcldavid@lamar.colostate.edu
AF: Colorado State University, Department of Geosciences, Fort Collins, CO 80521, United States
AU: Wohl, E
EM: ellenw@warnercnr.colostate.edu
AF: Colorado State University, Department of Geosciences, Fort Collins, CO 80521, United States
AB: Flow resistance is recognized as an important component of hydraulics in mountain streams, yet researchers are unable to accurately quantify values for mountain channels. Manning and Darcy-Weisbach equations used for indirect flow estimates are based on the assumption of steady, uniform flow, and the quantification of flow resistance in a channel. Steep channels are characterized by unsteady, rapidly varied flow in which grain size is comparable to flow depth. To improve predictions of resistance and subsequently discharge approximations in mountain channels, we need to obtain a better understanding of resistance and the parameters that control variations in total resistance. This study investigates the interactions of bed, bank, and form resistance in cascade, step-pool, and plane bed channels of headwater streams. We hypothesize that magnitude and variability of individual components of resistance vary systematically by channel type. Detailed surveys were conducted on 15 stream reaches on East St. Louis and Fool Creek in Fraser Experimental Forest, Colorado. Both streams have long term discharge records from US Forest Service gages placed just downstream of the study sites between 1941 and 1943. Each reach was measured under at least three different discharges: low flow, intermediate flow, and peak flow. The detailed surveys included directly measuring all variables needed to calculate discharge, Froude number, total flow resistance, and grain resistance. A total station and LIDAR (Light Detection and Ranging) unit were used to survey channel geometry. These data are used to determine planform geometry, bankfull width, depth, bed gradient, bedform geometry where present, relative submergence and wood size and orientation where present. Flourometers were attached to rebar at 0.6 flow depth, and a rhodamine tracer was used to determine reach-averaged mean velocity at the three stages at which measurements were made. The total flow resistance varied significantly over the three measured flows and between channel types. The most significant factor for variations in flow resistance is gradient.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1824 Geomorphology: general (1625)
SC: Hydrology [H]
MN: 2007 Fall Meeting