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.

Abstract

Stream restoration is estimated to be a multi-billion dollar industry and includes techniques such as planting vegetation, modifying channel form, and installing in-stream structures. These techniques potentially alter the velocity field and flow complexity. The specific objective of this research was to characterize near-boundary flow within the three restored reaches of varying intensities located in the Stream Research, Education, and Management (StREAM) Laboratory at Virginia Tech. Three restoration techniques were applied in 2009-10 to consecutive reaches of Stroubles Creek: 1) cattle restriction only (0.5 km); 2) cattle restriction, banks reshaped to 3:1 slope and re-vegetated (0.6 km); and, 3) designed and installed a two-stage channel with inset floodplains and re-vegetated (0.3 km). Results were compared to an upstream reference reach (∼0.35 km) where cattle have been excluded for approximately 17 years. Two experimental sample locations, positioned in riffles, were identified within each section of restoration treatment and the reference reach. Velocity measurements, pebble counts, and topographic surveys were completed twice at each location. Three-dimensional velocities were measured with a 16-MHz acoustic Doppler velocimeter (MicroADV) at 49 points within a 30 cm x 30 cm grid within each experimental sample location. Velocity was measured at a vertical distance of 7 cm from the streambed, and the MicroADV recorded velocity for 2 min at 50 Hz at each of the 49 points. All measurements were completed at baseflow. Stage and turbidity were measured continuously during velocity measurements utilizing existing monitoring equipment. Turbulent kinetic energy (TKE) and Reynolds shear stresses (tauxy and tauxz) were calculated for each velocity measurement. At baseflow the differences among restoration treatments did not directly result in differences in turbulence statistics. Overall velocity vector magnitudes were influenced by the flow depth and the channel width of the stream cross section at the location and time of the sample. With few exceptions, TKE and tauxz varied by sample date likely due to redistribution of bed sediment following storm events. TKE and tauxz were statistically different between the two sample locations within a common reach. A correlation can be seen between turbulence characteristics and the variation of flow depth within the measurement area. This correlation indicates that the streambeds with greater depth variability cause greater TKE and tauxz. TKE and tauxz had similar spatial distributions.

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