TY - JOUR
T1 - Field measurements of three-dimensional hydraulics in a step-pool channel
AU - Wilcox, Andrew C.
AU - Wohl, Ellen E.
N1 - Funding Information:
This work was funded by the National Science Foundation grant EAR-9902440 to support the primary author's PhD research, NSF equipment grant EAR-9907048, an NSF grant (EAR-0097560) to Colorado State University to support the Research Experiences for Undergraduates program, and a Geological Society of America Graduate Research Grant. Thanks to Julie Kray and Glen Vallance for field assistance, Tracy Phelps for assistance with data processing, Laurie Porth and Manuel Martinez (U.S. Forest Service) for discharge data and field support, and Craig Huhta (SonTek) for providing insights on the FlowTracker ADV. We also thank Anne Chin, Lee Harrison, Jonathan Nelson, and Greg Pasternack for comments that greatly improved the manuscript.
PY - 2007/1/30
Y1 - 2007/1/30
N2 - We investigated the effects of morphologic position and discharge on flow structure in a steep (0.10 m/m) mountain channel by collecting three-dimensional measurements of time-averaged and turbulent velocity components with a SonTek FlowTracker Handheld ADV (acoustic Doppler velocimeter) on a 30-m reach of a step-pool channel in the Colorado Rockies. Velocity profiles were measured at morphologic positions characteristic of steep channels (above steps, step lips, base of steps, pools, cascades, runs), and at five different discharges. A marked three-dimensionality of flow structure was documented in East St. Louis Creek. Velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes; cross-stream and vertical components contributed averages of 20% and 15%, respectively, to overall vector magnitudes. Turbulence intensities were especially multi-dimensional, however, with large contributions to turbulent kinetic energy from the vertical component of velocity. Analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities, with substantially higher velocities upstream from steps than in pools. Discharge and morphology effects on cross-stream and vertical velocity components, however, were not significant. Discharge and morphologic position also significantly affected turbulence intensities for all flow components, with the greatest turbulence intensities occurring in pools and at high discharges. These results illustrate the strong discharge-dependence of hydraulics in step-pool channels, where relative submergence of bedforms changes rapidly with discharge, and the substantial spatial variation in hydraulics created by step-pool sequences.
AB - We investigated the effects of morphologic position and discharge on flow structure in a steep (0.10 m/m) mountain channel by collecting three-dimensional measurements of time-averaged and turbulent velocity components with a SonTek FlowTracker Handheld ADV (acoustic Doppler velocimeter) on a 30-m reach of a step-pool channel in the Colorado Rockies. Velocity profiles were measured at morphologic positions characteristic of steep channels (above steps, step lips, base of steps, pools, cascades, runs), and at five different discharges. A marked three-dimensionality of flow structure was documented in East St. Louis Creek. Velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes; cross-stream and vertical components contributed averages of 20% and 15%, respectively, to overall vector magnitudes. Turbulence intensities were especially multi-dimensional, however, with large contributions to turbulent kinetic energy from the vertical component of velocity. Analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities, with substantially higher velocities upstream from steps than in pools. Discharge and morphology effects on cross-stream and vertical velocity components, however, were not significant. Discharge and morphologic position also significantly affected turbulence intensities for all flow components, with the greatest turbulence intensities occurring in pools and at high discharges. These results illustrate the strong discharge-dependence of hydraulics in step-pool channels, where relative submergence of bedforms changes rapidly with discharge, and the substantial spatial variation in hydraulics created by step-pool sequences.
KW - Acoustic Doppler velocimeter
KW - FlowTracker
KW - Step-pool channel
KW - Turbulence intensity
KW - Velocity
UR - http://www.scopus.com/inward/record.url?scp=33846029161&partnerID=8YFLogxK
U2 - 10.1016/j.geomorph.2006.02.017
DO - 10.1016/j.geomorph.2006.02.017
M3 - Article
AN - SCOPUS:33846029161
SN - 0169-555X
VL - 83
SP - 215
EP - 231
JO - Geomorphology
JF - Geomorphology
IS - 3-4
ER -