Characterizing the mean flow field in rivers for resource and environmental impact assessments of hydrokinetic energy generation sites

The use of hydrokinetic technology in rivers for energy generation is an area of active research with potential applications in urban and rural settings. Negating the need for a physical barrier to the flow, in-stream hydrokinetic devices are viewed as having less environmental impact than conventional hydropower. The introduction of any device that alters the flow field, however, has the potential to affect both the river morphology and the ecosystem it supports. Characterizing the pre-installation flow conditions and monitoring changes following device installation are necessary to evaluate the ecological costs associated with this developing technology. This study presents techniques for quantifying the mean flow field throughout a study reach using an acoustic Doppler current profiler. Employing two survey procedures that provide flexibility in terms of the resolution and extent of measurements, quantities ranging from bulk flow features, such as discharge, to mean three-dimensional velocity profiles can be obtained. Results of the different survey procedures are demonstrated using data collected on the lower Roanoke River, USA. Recommendations are given to aid in the design of field data collection to best match the stage of the project. These measurements contribute to resource assessment at the site scale, designing turbines and planning installation, and environmental impact studies.