Informing a Tidal Turbine Strike Probably Model Through Characterization of Fish Behavioral Response Using Multibeam Sonar Beam

The Informing a Tidal Turbine Strike Probably Model Through Characterization of Fish Behavioral Response Using Multibeam Sonar Beam project closed in FY2016.

Project Background - One of the most important biological questions facing the marine and hydrokinetic (MHK) energy industry is whether fish and marine mammals that encounter MHK devices are likely to be struck by moving components. For hydrokinetic devices, i.e., those that generate energy from flowing water, this concern is greatest for large organisms because their increased length increases the probability that they will be struck as they pass through the area of blade sweep and because their increased mass means that the force absorbed if struck is greater and potentially more damaging. Key to answering this question is understanding whether aquatic organisms change their swimming behavior as they encounter a device in a way that decreases their likelihood of being struck and possibly injured by the device. Whether near-field or far-field behavior results in general avoidance of or attraction to HK devices is a significant factor in the possible risk of physical contact with rotating turbine blades. In 2012 while testing a new generation of the Kinetic Hydropower System (KHPS) turbine at their Roosevelt Island Tidal Energy (RITE) site, Verdant Power deployed a dual-frequency identification sonar (a.k.a a DIDSON acoustic camera), to collect continuous data on fish interactions with the turbine over three weeks in August–September. Until this study, the only analysis of these data was a visual assessment of the DIDSON videos.

Scientists take advantage of the latest sonar technology to assess the interactions between passing fish and tidal turbines.

Project Details - In this study, researchers used state-of-the-art software to conduct a systematic analysis of behavior and fate of individual fish and schools as they passed through the acoustic beam relative to turbine presence and operation. Researchers also evaluated data collected during previous Verdant monitoring using a more traditional split-beam sonar system that collected data at a greater distance from several deployed turbines but with lower resolution.

Scientists took advantage of the latest sonar technology to assess the interactions between passing fish and tidal turbines. The first overall objective of this project was to use the previously collected sonar data to quantify near-field and far-field fish behavior (i.e., changes in water-column position and swimming direction) because of encounters with an operating full-scale hydrokinetic turbine. The second overall objective was to use the fish behavior results to update parameterization of an existing fish interaction model and use the model to assess what approaches (i.e., field observation, experimentation, models) were most effective for predicting or monitoring the effects of turbine arrays on fish interactions and impacts. The specific objectives were to:

  • Quantify near-field (i.e., within 12 m) behavioral response response and swimming trajectories of fish encountering an operating HK turbine using 373 hours of video from a deployed DIDSON multibeam hydroacoustics system. Evaluate fish trajectories, avoidance behavior, and general distribution relative to near-field hydraulics (i.e., water velocity and tide direction) with and without the influence of a turbine.
  • Quantify the far-field response (normal swimming trajectories and distribution) of fish near the deployment site using previously collected data from a splitbeam hydroacoustics system during the same seasonal period. Evaluate vertical and horizontal distributions and trajectories of fish relative to water velocity and tide stage (ebb, flood and slack tide) with and without the influence of a turbine.
  • Update parameterization of existing fish interaction model developed for the East River and the RITE Project.
  • Assess relative effectiveness of approaches (i.e., field observation, experimentation, models) for application to monitoring the effects of turbine arrays.

Project Benefits - Accomplishing the project objectives directly benefitted the MHK industry as the study provided a complete analysis of fish interaction data at a full-sized turbine that developers and regulators can use to estimate the likelihood of encounter and injury at tidal and riverine sites. The methods refined in this study are widely applicable to other sites and conditions and can be used to improve estimates of potential impacts and develop monitoring protocol. For Verdant Power at its RITE site in the East River (NY), the work was built on the understanding of fish behavior at the pilot project and provided additional understanding used in the adaptive management of ongoing compliance activities associated with RITE monitoring plans and the FERC license. As part of the project, the analytical results have been incorporated into a revised fish interaction model which will be used by Verdant Power in future discussions with regulators.