Determining the 2-D Surface Velocity Field around Hydraulic Structures with the Use of a Large Scale Particle Image Velocimetry (LSPIV) Technique

Abstract

The objective of this investigation is to employ the state-of-the-art large scale particle image velocimetry (LSPIV) technique for free surface flow measurements around and within the vicinity of hydraulic structures (e.g. weirs, ladders) used for fish passage in the loess region of Western Iowa, USA. Knowledge of the 2-D free surface velocity allows engineers and biologists to determine the hydraulic performance of the above structures as it relates to fish passage. The magnitude of the velocity will provide unique information about the level of turbulence around and within the vicinity of the structures, the approach velocity magnitude, the dissipation rate and the forces acting on juvenile and adult fish passing through the structures. The LSPIV technique is founded on similar principles with those of the particle image velocimetry (PIV). LSPIV is a powerful and efficient technique for measuring river surface velocities especially in natural -large scale- systems which are of the primary interest of this research. It is a cheap method as it needs, basically, an inexpensive video equipment (camera) and a geodetic survey to describe the region of interest (ROI). The water velocity vector magnitude and direction are calculated by dividing the estimated displacement of the particles with the time interval between two sequential images. The LSPIV technique does not require calibration and it is well-suited for measuring in very shallow flows quickly and accurately; also can be used to estimate the discharge in conjunction with bathymetry information and assumed velocity distribution over the depth. Validation of the LSPIV measurements will be attained with the use of a SonTek flow tracker.