Evaluating the efficacy of particle image velocimetry to estimate surface flow velocity in vegetated rivers

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Aquatic plants are prevalent in lowland rivers and they exert a dominant influence on river hydraulics. Flow resistance (via Manning's Roughness Coefficient) has been shown to change seasonally in response to macrophyte growth, were higher values for Manning's n tend to be recorded during periods when there is a greater abundance of aquatic plants in the water column (Naden et al 2006). The increase in flow resistance caused by an abundance of aquatic vegetation growing in the channel has the effect of decreasing the flow velocity of water, which in turn can increase the water's depth and enhance the chance of flooding. Particle Image Velocimetry (PIV) is a well-established technique for measuring velocity fields in macroscopic fluid systems and this image-based approach is considered a suitable method for estimating surface flow velocities (Sun et al 2010). However, very few attempts have been made to estimate surface flow velocities using PIV technology for heavily vegetated rivers. Given that aquatic plants have a significant influence on river hydraulics, it is necessary for flood control and water supply to measure surface flow velocities in vegetated rivers. This project aims to evaluate the efficacy of PIV to estimate surface flow velocities in vegetated rivers. The PIV results will be compared with those measured by an (in-situ) Acoustic Doppler Velocimeter (ADV), which is one of the most popular instruments for measuring flow velocities, to evaluate their accuracy