Annex IV distributes metadata forms (questionnaires) to solicit information from researchers around the world who are exploring the environmental effects of marine renewable energy. This page provides a description and contact information related to the research. Content is updated on an annual basis.

Flow Variability in Cook Strait

Research Study Annex IV

Title: Flow Variability in Cook Strait
Researcher:
Start Date:
January 01, 2009
Research End Date:
January 01, 2012
Country:
Stressor:
Receptor:
Technology Type:
Info Updated:
August 14, 2014
Study Status: 
Completed
Princple Investigator Contact Information: 

Name: Craig Stevens

Address: NIWA

Phone: +64 4386 0476

Email: c.stevens@niaw.co.nz

Project Description: 

Determine tidal flows and variability in very large tidal stream.

Funding Source: 

NZ Goverment funding (now Ministry Business, Innovation and Employment)

Location of Research: 

Cook Strait, New Zealand

Key Findings: 

Understanding flow, transport and dynamics is a key part of defining marine habitats.  Current and turbulence measurements from the Karori Rip area of Cook Strait, the prime focal region of open-water tidal stream electricity generation in New Zealand, are measured.  A key issue is that a significant portion of the energy is contained in waters deeper than normally considered for energy extraction.  Here we compare shallow and deep sites.  Velocity data were derived from acoustic Doppler current profiler moorings, as well as spatial surveys and show flow magnitudes reaching 3.4 m s-1 in the shallow regions.  The maximum speeds in both shallow and deep sites were typically located in the upper part of the measured water column although moored acoustic Doppler current profiler (ADCP) observations showed some complexity in this regard.  Benthic boundary-layers were resolved in the bottom ~20 m of the water column.  Measured turbulent kinetic energy dissipation rates e exceeded 10-5 m2s-3 and estimated maximum e is a factor of 10 greater.  This was not distributed evenly through the water column, with stratification and velocity shear clearly persisting, especially around the turn of the tide.  The implications for tidal stream energy are that (i) there is sufficient energy resource in the region for a moderate sized array of turbines, (ii) the vertical variability in the flow speed suggests turbines that can operate near the surface would be more effective at accessing the resource, (iii) stratification may persist and influence the scales of turbulence and (iv) wave-current interaction effects will influence any near-surface structure as well as vessel operations.

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