exploring optimal locations for underwater turbine emplacement near marine navigation passageways

Exploring Optimal Locations for Underwater Turbine Emplacement near Marine Navigation

Passageways

Steps to a “go” or “no” answer.

With Thanks to:MIT Sea Grant, the Chewonki Foundation, Mass Maritime Academy, Town of Hull, MAUSGS, Falmouth Scientific Inc.

Geoff Cowles, Dorothy Kelly, Peter Arnold, Stanley King, Tom Pham, Herman Gustafson, Jim Manning, Kurt Bornheim, Andy Stern, Neil Ganju, ….

Studies Done at Three Sites

The Three Sites

Mass. Maritime/Cape Cod Canal

The Three Sites

The Hull Gut

The Three Sites

The Sheepscot River

Site #3

The Sheepscot River

FERC Permit Area

Step 1

Hydrodynamic Modeling

The Island Tidal Node

Tidal Power Distribution

Tidal Power Distribution

Step 2

Spatial Velocity Survey

Surveyed Areas

Our sampling focused on five areas, indicated by the sampling sites (green dots) shown here. These areas were identified as high energy locations by a numerical model and by the data from a preliminary survey conducted on September 28.

The Surveying Equipment

Acoustic Doppler Current Profiler

(ADCP)R/V Seagull and Capt.

Stanley King

Surveyed Areas

The Best Area

Under the Bridge

The focus here will be on the tidal flows and tidal power near the Westport Island bridge.

Capturing the Tidal Cycle

Observations out of the Nav. Channel, but with bottom depth > 7m

The Tidal Cycle

The tidal velocity nicely follows a sinusoidal cycle, with maximum ebb (positive) and flood (negative) currents of slightly greater than 1 m/s. Velocities were somewhat higher directly underneath the bridge (by about 10 %), but this is a minor point.

Not the Strongest Tides of the Year

But wait! The timing of our survey was based on boat and personnel availability. Unfortunately, this availability did not coincide with a time of strong tides. In fact, our survey was conducted during unusually weak neap tides, as seen by highlighting the time of our survey (in red above) on a plot of tidal height at Wiscasset.

Extending the Analysis to Other Tides

With a little math, we can relate the maximum tidal velocity, Vmax, to the mean power density over the half tidal cycle. The formula is:

<F> = 2ρVmax3

3π

Assuming that Vmax is proportions to the height range, Hdiff, of a particular tide

Vmax = Hdiff*Vmax(Sept 30) 7 ft

Allows for the computation of the expected velocity and power distribution under the bridge.

For Vmax(Sept 30) = 1 m/s ; <F>year = 623 W/m2

Step 3

Evaluating the Bottom Conditions

-Side Scan Surveying

Maine DMR Side-Scan Survey April 5,2011

Refining the “Best Spot” Assessment

Step 4

Installing a Moored Velocity Profiler (e.g. ADCP) Near the Best Spot

ADCP

Conclusion

Conclusion

A four-step process:

1. Hydrodynamics modeling

2. Ship-board velocity surveying

3. Side-scan sonar surveying

4. Moored velocity profiling

Offers a cost-effective way to evaluate the tidal resource in a estuarine environment, with a “go” or

“no” assessment at each step