1. Snohomish PUD Tidal Power Project
Mitsuhiro Kawase and Dmitri Leonov
School of Oceanography
Brian Polagye
Mechanical Engineering
November 14, 2007

2. Agenda
Tidal Currents in Puget Sound
Current Measurements in Admiralty Inlet
Numerical Modeling of Deception Pass

3. Center of Mass
Moon
Earth C C’ A A’
Centrifugal Force

4. Origin of the Semi-diurnal Tide
Earth
Moon
Moon’s Gravity
Centrifugal Force
In balance
Gravity weaker
Gravity stronger
TGF

5. Tide-Generating Force around the Earth
This is a hypothetical case exaggerated to show the direction of TGF. (Moon mass is 2/3 of earth mass and moon is at 5 earth radii away)

6. Tide in Puget Sound
Tidal height (in meters) over a four-day period in February, 2006 in Elliott Bay, downtown Seattle:
From
Tidal variation of sea surface is not regular; there are periods in which once-a-day, rather than twice-a-day, variability dominates.

7. Origin of the Diurnal Tide
Gravity stronger
In balance, no TGF
Moon
Earth’s Rotation Axis
TGF

8. Semi-diurnal, Diurnal, and Mixed Tides
From

9. The Spring-Neap Cycle Neap Tide - Lunar and Solar TGFs even out
Lunar TGF
Solar TGF
Neap Tide -
Lunar and Solar TGFs even out
Spring Tide -
Lunar and Solar TGFs combine

10. The Lunar Declination Cycle
Viewed from above the orbital plane
Pole
Rotation axis oriented to the moon - maximum diurnal tide
Rotation axis oriented 90º to the moon - minimum diurnal tide
TGF

11. Puget Sound, Washington
Southernmost fjord of Pacific North America
Deep (max. 283m)
Connected remotely to the Pacific via Strait of Juan deFuca
Stratified basins interspersed with vigorous, localized tidal mixing
Hypoxia in end basins

12. Fjords – Coastal Inlets formed by past glaciation
Occupy high-latitude coastlines of the subpolar gyres of the world ocean
Complex morphology and bathymetry, with deep basins connected through constrictions
Important habitat of marine organisms that form significant fisheries resources
Relatively unexplored except for those close to large population centers

13. Schematic of exchange circulation in a fjord (cross-section)
River Input
(Fresh, Light)
Strong Tidal Current
Outflow
Tidal Mixing
Sharp Pycnocline
Main Basin
Marine influence
(Salty, Dense)
Inflow/Reflux
Entrance Sill

14. Potential Temperature 199910 12 8
June
December
Admiralty Inlet Sills
SJDF
Dalco Passage
Main Basin
Black line: Last contiguous density surface across Admiralty Inlet

15. Tidal Energy Flux in Puget Sound
(in Megawatts)
From Lavelle et al. 1988
Most of the energy dissipation happens in the sill region:
71% of 733 MW that comes into Puget Sound is dissipated over the Admiralty Inlet sills.
59% of 133 MW that goes into the South Sound complex is dissipated over Tacoma Narrows.
Large interior basins, such as the Main Basin, Hood Canal and Whidbey Basin do relatively small part of dissipation (11% for the three basins combined)
733 30
16.5
166
133 55

16. RMS Current Speed (left) and Energy Extraction Potential (right)

17. Admiralty Inlet
Main connection between Puget Sound basins and the Pacific Ocean via Strait of Juan de Fuca
Double-silled channel
Strong tidal currents of up to 3 meters per second
Strong internal variability of the water column

18. Admiralty Inlet Skagit River Strait of Juan de Fuca
Stillaguamish River
Snohomish River
Strait of Juan de Fuca
Admiralty Inlet
Possession Sound
Whidbey Basin
Whidbey Island
Port Townsend
Kitsap Peninsula
Edmonds
Kingston

19. Slack Tide

20. Major Flood

21. Major Ebb
Headland Eddy

22. Slack Tide
Note: Tidal current reverses on the Olympic side first

23. Minor Flood

24. Slack Tide

25. Minor Ebb
Note: Headland eddy does not form during minor ebb

26. Slack Tide

27. Major Flood
Headland Eddies

28. Deception Pass
A direct, very narrow (~120m) connection between the head of Skagit Bay and Strait of Juan de Fuca
Very strong tidal currents up to 4 meters per second
Water column likely well-mixed during strong currents
An unknown fraction of Skagit River water exits through the channel to the Strait

29. Why Concerned about Tidal Energy Flux and Dissipation?
Tides are the major suppliers of mechanical energy into estuaries. This mechanical energy drives many of the processes that operate in the estuary such as:
Transport of material by tidal currents;
Generation of turbulence and mixing, which mixes the sea water and the river water, and in turn drives the circulation that flushes the estuary;
Wetting and drying of tidal flats.
Thus, tidal energy flux is one of the fundamental parameters that needs be ascertained for an estuary.

30. Agenda
Tidal Currents in Puget Sound
Current Measurements in Admiralty Inlet
Numerical Modeling of Deception Pass

31. Characterizing Tidal Currents in Admiralty Inlet
Preliminary characterization:
Historical current measurements (1940’s – 1970’s)
NOAA tidal current predictions (based on historical measurements)
Indications of locally strong currents (hot spot)
Point Wilson
Admiralty Head
Admiralty Head
Marrowstone Point
Goals of on-site measurements:
Verify NOAA current predictions
Extrapolate findings to annual basis
Point Wilson

32. Survey Plan
All surveys carried out under contract by Evans-Hamilton, Inc. using Acoustic Doppler Current Profilers (ADCP)
Two types of surveys:
Over-the-side (OTS) with ADCP mounted on boat traversing inlet (spatial series, ~ constant time)
Stationary with ADCP anchored to bottom (time series, constant spatial)
Timeline:
OTS Round 1: July 30-31
Stationary Deployment: August 18
OTS Round 2: August 27-28
Stationary Recovery: September 19
Round 1 OTS
Round 2 OTS
Stationary
Admiralty Head
Point Wilson

33. - Depth-averaged Speed -
OTS
OTS Results
- Depth-averaged Speed -
Speed (m/s)

34. - Corrected Depth-averaged Power Density -
OTS
OTS Results
- Corrected Depth-averaged Power Density -
A number of adjustments made to raw data
Convert to power density
½ x density x (velocity)3 (kW/m2)
Power density is relevant metric for kinetic power extraction
Crude correction for cycle time
Adjust measurements to cycle peak using timing of NOAA predictions
Exclude measurements more than 1.5 km from a NOAA prediction
Exclude measurements where power density estimated less than 40% of cycle peak
Power Density (kW/m2)

35. OTS Transect Flood tide, prior to peak (15:15) OTS Direction of Travel
12:44
13:14

36. OTS Transect Flood tide, near peak (14:00) OTS Direction of Travel
14:01
14:30

37. - 60m off Seabed, 85m ADCP Deployment -
Stationary
Current Ellipses
- 60m off Seabed, 85m ADCP Deployment -
Principle axis

38. Stationary
HAMELS Analysis
HAMELS (Harmonic Analysis MEthod of Least Squares) is a mathematical technique used to model underlying lunar and solar forcing
Forcing generally of the form:
ωj are frequencies of solar and lunar tidal constituents and known in advance
Rj and φj are the magnitude and phase lag of the forcing, respectively, and must satisfy:
T_TIDE package (Pawlowicz et al. 2002) used to perform analysis
Statistical analysis used to determine significant constituents (m)
Modified package to rotate ellipse onto principle axis prior to HAMELS analysis
Once magnitude and phase of forcing determined, predictions of the tidal currents can be made for past and future times

39. Sample Harmonic Prediction
Stationary
Sample Harmonic Prediction
Velocity (cm/s)
Result is for one ADCP depth “bin”. Repeat for all other bins.

40. Annual Average Power Density
Stationary
Annual Average Power Density
- 65m ADCP Deployment -

41. Annual Average Power Density
Stationary
Annual Average Power Density
- 85m ADCP Deployment -

42. Conclusions OTS ADCP surveys indicate:
Strong currents in central Admiralty Inlet
Bathymetry influences currents
Stationary ADCP surveys indicate:
Area of strong currents has a relatively high annual average power density, but there is considerable variation within the region
In combination, the ADCP surveys have:
Demonstrated that the Admiralty Inlet in-stream resource is substantial and warrants further investigation
Indicated the need for detailed numerical modeling to characterize the resource for a large array
Indicated that NOAA tidal current predictions are not uniformly accurate

43. Agenda
Tidal Currents in Puget Sound
Current Measurements in Admiralty Inlet
Numerical Modeling of Deception Pass

44. Deception Pass Model
Domain and Bathymetry

45. Deception Pass Model Grid
52000 horizontal nodes, 15 vertical levels

46. Forcing
Tidal elevation from PRISM (POM) model along each open boundaries
3 days during spring tide (Nov. 2004)

47. Sea surface height (color), current (vector)
Entire Domain
Sea surface height (color), current (vector)

48. Deception Pass Channel
Flow speed (color), velocity (vector): 10km scale

49. Deception Pass Channel
Flow speed (color), velocity (vector): 4km scale

50. Power Density
Kinetic energy flux per unit area:
1/2 |v|3

51. Modeling: Ongoing and Future Work
Improving grid (using Gambit)
Validating against recent observations by Evans Hamilton
Use Stanford’s SUNTANS code
Incorporation of simple turbine dynamics
Impact assessment, including (but not limited to):
Changes in the level of mixing in the Pass and at the head of Skagit Bay
Fate of the Skagit River outflow
Implementation of an Admiralty Inlet model, validation and impact assessment
50~100m resolution in the Inlet, ~250m resolution in the remainder of Puget Sound

52. Preliminary Grid for Admiralty Inlet
(250m resolution)

53. Summary
Power generation via tidal in-stream energy conversion is a real prospect for the Puget Sound region.
Main concern will be economic feasibility and environmental impact, the latter requiring fluid-dynamical and oceanographic knowledge for assessment.