Submitted to: International Conference on Hydroinformatics
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2000
Publication Date: N/A
Interpretive Summary: Woody vegetation is often used to restore and rehabilitate stream channels impacted by erosion and degradation. Such channels provide little aquatic habitat and habitat resources and aesthetics. A laboratory experiment was designed to assess the effect of adding woody vegetation to the channel in order to transform a straight, eroded channel into a vegetated, meandering channel. This study used an experimental flume with zones vegetated with dowels simulating woody vegetation. In order to alter the vegetation density, vegetation elements were added in a staggered arrangement, and five vegetation densities were examined. The flow pattern within the channel was measured using a video technique that can accurately determine the velocity of the water. This paper provides important guidelines for the successful application of this video technique. Researchers and practitioners interested in using video for data collection can use these guidelines.
Technical Abstract: Using an experimental recirculating flume, hemispherical point bars spaced at an equilibrium meander wavelength were progressively vegetated with emergent wooden dowels. In order to alter the vegetation density, alternate dowels were added in a staggered, geometric pattern, and five vegetation densities were examined. The turbulent structure of the water surface was characterized with Particle Image Velocimetry (PIV), which can determine very accurately the displacement of particles within recorded images. Tracer particles floating on top of the water surface were recorded by a video camera suspended orthogonally above the flume. Pairs of successive video images separated by a known time length were digitally acquired using a video tape player and frame grabber. Commercially-available software applied cross-correlation to discrete areas of interrogation in pixel space and determined the displacement of particles. Provided accurate time and space resolutions for each image were obtained, scaled velocity vectors were derived for the entire flow field. Vector fields from paired images at the same location were also time-averaged. This paper provides guidelines for image recording and analysis, interrogation area size, sampling frequency, data mining and reduction, and time averaging.