Going with the Flow II: Using Drifters to Address Uncertainties in the Spatial Variation of Tidal Flows

Principal Investigators:

Gregory Trowse, Luna Ocean Consulting Ltd. (LOCL)

Start Date: October 2017

End Date: June 2018

Drifters are one of the oldest, simplest, and most reliable methods for measuring ocean currents. Drifters also provide a simple, low risk platform from which to gather acoustic information along flow streamlines or ‘drift tracks’.
This project will build upon previous drifter research, with the objective to reduce uncertainty in the spatial variation in flow speeds (including turbulence) within the Minas Passage (with focus on the FORCE site), Grand Passage, and Petit Passage. The project will use:

1. An ADCP drifter to evaluate flow characteristics along several drift tracks, including the vertical structure of velocity, turbulent dissipation rates, and surface vorticity; and
2. Multiple surface flow drifters to map the flow-fields throughout the flood-ebb tidal cycle.

The current standard practice for tidal energy site assessment focuses on deployment of bottom mounted ADCPs and use of vessel mounted ADCPs. Data collection using multiple drifters allows flow speeds to be measured concurrently at several locations distributed around an area of interest. Use of the ADCP drifter will include deployments upstream of a prominent bathymetric feature (e.g. a ridge) and/or a turbine, with recovery downstream of the feature. Multiple drifts, with trajectories both centered on and to the side of the feature, will be undertaken.

The project outcomes consist of site characterization information useful for advancing research and micro-siting tidal turbines for commercial developments. The information will be used by Dalhousie University’s Dr. Alex Hay to advance research on turbulence in high-energy tidal environments, and Acadia University’s Dr. Richard Karsten for further calibration and validation of the FVCOM numerical model. The surface flow measurements will be combined with existing data, and with new drift data supplied from other studies to update images of surface flow-fields that will be available on-line with public access after project completion. A preliminary example for Grand Passage, Nova Scotia is available at: www.vimeo.com/lunaocean/driftgp2