Semester

Fall

Date of Graduation

2012

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Civil and Environmental Engineering

Committee Chair

Leslie C. Hopkinson

Committee Co-Chair

Donald D. Gray

Committee Member

Nicolas P. Zegre

Abstract

Sediment is a leading cause of water quality impairment for streams and rivers. Streambank erosion is a dominant source contributing to sediment pollution and there is a growing need for adopting management practices to reduce it. Bank retreat occurs from a combination of fluvial erosion, subaerial processes, and mass failure. Fluvial entrainment, initiated by near-boundary turbulence, is one of the main drivers of streambank retreat as it leads to unstable streambank geometries. This research characterized the turbulent structure of flow near the toe of a streambank throughout a storm event, at times of high shear stress. The specific objectives included designing and building a field mount to support in-stream velocimeters during high flow events, quantifying the distribution of Reynolds stresses and turbulent kinetic energy (TKE) through a storm hydrograph, and identifying the relationship between hydraulic radius and turbulent stresses.;Three-dimensional velocity was measured using a Sontek 16-MHz ADV (Field) and two-dimensional velocity was measured using a Sontek SL3000 (ADCP) at baseflow and through a storm hydrograph at an experimental cross-section (West Run in Morgantown, WV). Velocity was measured (2 min sample time at 25 Hz) and stream stage was recorded every seven minutes with the ADV throughout a 17 hour storm event. One time-averaged velocity measurement (5 min sample time, 1 Hz) and stream stage were recorded continuously throughout an 8 hour storm event using the ADCP. Physical stability was monitored by measuring channel geometry, grain roughness, and vegetation parameters (i.e. location, size, and density) before and after each storm event. Reynolds stresses, turbulent kinetic energy, and turbulence intensities were calculated for each velocity time series, resulting in a time distribution of shear stress and turbulence characteristics.;This research resulted in the development of methods for ADV and ADCP deployment throughout storm events, including the use of two custom fabricated mounts. The study also found that TKE increased with an increase in stage height, while Reynolds stresses indicated no linear trend. Applied shear stress estimated by average boundary shear stress was found to be roughly 18 to 43 times greater than applied shear stress estimated by turbulence statistics, which may alter the ability of models to predict erosion depending on the method used. Finally, a comparison of the ADV and ADCP indicated that the ADV shows higher potential for obtaining near-bank velocity measurements and estimating local applied shear stress. Ultimately, these results will provide information on current instrumentation and methods used in the field and will provide information on the distribution of streambank erosion potential throughout storm events.

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