August 9, 2007 Update
Tacoma Power is half-way through its site specific feasibility studies into
generating power by using tidal currents in the Tacoma
Narrows. The current phase of the project began in March 2007 when Tacoma Power
hired Puget Sound Tidal Power LLC (PSTP) to conduct necessary work. This update
is a summary of the project findings to date.
A trip was made into the Tacoma Narrows in early May 2007 to determine where to deploy current measuring devices known as Acoustic Doppler Current Profiler (ADCP) units. The decision abpitwhere to place the ADCP units was jointly made by PSTP members from Evans Hamilton and Coast & Harbor Engineering (see figure 1). Three locations were chosen near the Pt. Evan’s site identified in the EPRI led concept level feasibility study.
Figure 1: Dr. Vladimir Shepsis (Coast & Harbor Engineering) and Jeff Cox (Evans Hamilton) determine the best locations for deploying ADCP Units.
The locations chosen can be seen in Figure 2. Three ADCP units were first deployed on May 30, 2007. Figure 3 shows the units deployed. Each unit weighs approximately 700 lbs and contains battery packs that allow for several months of operation. Each unit emits a sonic signal capable of measuring the current's speed in a manner similar to locating naval submarines using sonar, but on a much smaller scale and at a significantly lower volume.
Figure 2: Map shows deployment and retrieval locations of the three ADCP units.
Figure 3: ADCP units are ready to for deployment.
After one month in the water, the first cruise to recover the ADCP units and download their data occurred on July 2, 2007. The blue dots in Figure 2 show the recovery locations of the ADCP units. In a demonstration of the power contained in the tidal currents, the unit placed at station 2 was moved more than 900 meters (nearly 6/10ths of a mile) along the bottom of the Narrows. In addition, station 1 moved nearly 300 feet south of the location in which it was placed. The ADCP units are capable of registering motion; this movement effectively allowed the Evans Hamilton team to gather data from more than one location with a single placement of the ADCP unit. Another item to note about station 1 is that it failed to release its retrieval buoy when commanded. It continues to collect data while the engineers make plans to retrieve it. It will require a day in which the tides are near their lowest levels and also provide the greatest window of time between tidal swings. Once recovered, its data can be downloaded. Figure 4 shows an example of the data gathered by the ADCP unit in graphical format.
Figure4: Sample of ADCP data in graphical format.
On August 2, 2007 the second retrieval trip was made into the Tacoma Narrows and station 2. The ADCP units located at station 3 were retrieved and the data downloaded. This data is now being used to update the computer model being used by Dr. Vladimir Shepsis from Coast and Harbor Engineering. This link is to a Power Point presentation which contains lots of information on the bathymetry (shape of the bottom) and tidal currents in the Narrows and how it is being used for a computer model. If you click on the slides showing the current directions and speeds, it will run a movie showing several days worth of tidal current changes. Of particular interest is the fact that the strongest currents appear in a wide band across the narrows and extend for nearly the entire length of the Narrows south of Pt. Evans. This promising indication will require additional study as the project proceeds towards a possible commercial installation.
In addition to the current studies, Tacoma Power has been working to identify the permitting and licensing issues that are likely to be associated with a tidal project in Puget Sound. To that end, Tacoma Power held a pre-permitting agency meeting on August 9, 2007. Invited to the meeting were all the local, state, federal and tribal agencies that would potentially have input into both a pilot and commercial installation. This was just the first step in the stakeholder involvement process. Future meetings are expected to include other local and state governmental agencies as well as non-governmental agencies that could be impacted by an installation in the Tacoma Narrows. In addition to the presentation by Vladimir Shepsis linked above, there were several other Power Point presentations given at the August 9th meeting. The following links are for those presentations.
Tacoma Power’s Need for Renewable Energy
The Tacoma Narrows Environment
Future work for this stage of the project
includes evaluating various available technologies for level of
development, suitability for the Tacoma Narrows and design efficiency. In
addition, the computer model being used will be updated and the
information used to establish the amount of energy available in the tidal
currents.