TRANSPORT PATHWAYS

IN THE LOWER REACHES OF

HOOD CANAL

By

Marlene A. Noble, Anne L. Gartner, Anthony J. Paulson, 

 Jingping Xu, Edward G. Josberger, and Christopher Curran

 2006

U.S. Department of Interior

Open-File Report 2006-1001

U.S. Geological Survey
Transport Pathways in the

Lower Reaches of Hood Canal

By

Marlene A. Noble1, Anne L. Gartner1, Anthony J. Paulson2,

Jingping Xu1

, Edward G. Josberger2, and Christopher Curran2

Open-File Report 2006-1001

1

U.S. Geological Survey, Menlo Park, California

2

U.S. Geological Survey, Tacoma, Washington

Any use of trade, product, or firm names is for descriptive purposes only and does not imply

endorsement by the U.S. Government.
INTRODUCTION

In 2003, studies revealed that the waters in the lower reaches of Hood Canal in Washington

State have had very low dissolved-oxygen concentrations, low enough to cause some fish kills

between June and October of that year.

http://www.hoodcanal.washington.edu/aboutHC/scienceprimer.jsp

Although available data suggests that dissolved-oxygen concentrations have been low in

previous years, even as far back as 1950 (Collias et al, 1974), recent measurements have shown

that the low dissolved-oxygen conditions have not only become more frequent, but also more

persistent.

http://www.hoodcanal.washington.edu/observations/historicalcomparison.jsp

The U.S. Geological Survey's (USGS) Water Resources Discipline (WRD) office in Tacoma,

Washington, was asked by Congress to become actively involved in a study of this problem. A

meeting between the USGS, local groups and governments, agencies, tribes, and the University

of Washington was held on January 8, 2004. It was agreed that the USGS could make a

significant contribution to the overall effort to determine the causes and solutions of the low

dissolved-oxygen concentrations by assessing the sources and quantifying the amounts of

nitrogen compounds discharged by those sources into Hood Canal.

The objectives of assessing nitrogen inputs into Hood Canal will be accomplished in three

phases: 1) use available information and data to make initial estimates of the amounts and spatial

distribution of nitrogen entering Hood Canal from all sources, 2) use the initial estimates to

select, design, and conduct focused studies to better quantify nitrogen loading from major

sources to Hood Canal, and 3) use the results of the focused studies to improve the overall

estimates of nitrogen loading to Hood Canal.

During phase 1 of the project, one major information gap was identified–the lack of

understanding of the transport of nitrogen compounds into Lynch Cove from the rest of the

canal, as nitrogen can boost primary production and thus reduce dissolved oxygen. Lynch Cove

is at the most landward reach of Hood Canal and is most susceptible to low dissolved-oxygen

conditions. In the fall of 2004, the USGS WRD and the USGS Coastal and Marine Geology

Team (CMGT) in Menlo Park, California, designed a small, focused research program to assess

the currents, density, and oxygen levels in the lower reaches of Hood Canal. This project was

designed to provide an initial assessment of the transport of nutrient compounds to Lynch Cove.

The data will also be used to model transport processes and oxygen patterns in the canal. This

program is part of a larger effort by CMGT to monitor coastal change and coastal ocean

processes in the Pacific Northwest. All information collected by this program will be shared with

cooperators in the academic and federal communities. In particular, the desired information will

be passed to WRD in Tacoma and to the numerical modeling group at the University of

Washington. This report describes the data collected in this program and presents an initial

analysis of that data.
MOORED ARRAY

A two-month study to obtain information on the circulation patterns and water properties in

the lower reaches of Hood Canal was initiated at the end of August 2004 and completed in

October 2004 (Figures 1, 2). In order to determine exactly where the moorings should be

deployed, a short preliminary cruise was conducted in the lower reaches of the canal to

determine the amplitude of the currents and the spatial structures of the current, temperature, and

salinity fields. Currents were measured with a shipboard-mounted Acoustic Doppler Current

Profiler (ADCP) during a spring tide (Figure 3). A short hydrographic survey determined water

properties and oxygen levels in the lower reaches of the canal. ADCPs determine water velocity

and channel depth by measuring the return characteristics of acoustic signals using the Doppler

shift principle (RD Instruments, 1996). A total of five ADCP transects were measured across

Hood Canal at different locations, with start and end points determined using a hand-held GPS

receiver. The maximum currents near the surface were about 50 cm/s. Currents near the bed

seemed to be much less than 40 cm/s. These current speeds were well within the design limits of

the instruments scheduled to be deployed in the canal. There was no marked horizontal shear in

the currents along transects near the proposed mooring sites, suggesting that currents measured at

the mooring sites would be representative of the regional current field.

After a small bathymetric survey of each proposed deployment location to confirm the

suitability of the proposed deployment site, Tripod A (Figure 4) was deployed in the natural

constriction at Sister Point and Tripod B was deployed at a nearby location to the west along the

canal from the first tripod (Figure 1). Each tripod contained an upward-looking ADCP to collect

continuous current data in 1-m bins over the entire water column. Instruments on the tripods also

monitored near-bed salinity, temperature, and water clarity (Table 1). In addition, near-bed

oxygen was measured at Site B. Each tripod weighed about 1100 pounds. The tripods were

deployed for eight weeks to cover at least two lunar cycles. Most instruments sampled the water

properties every five minutes.

Mooring A

The tripod at Site A was deployed in 54 m of water. The first bin in the upward-looking

ADCP at Site A was centered in water depth of 47.3 m, about 7 m above bed (mab). The last

surface bin that contained high-quality data was centered around 3.3 m below the surface. A

Microcat was attached at 59 cm above bed (cmab) to measure conductivity and temperature.

Two Brancker loggers were attached with transmissometers to measure temperature and nearbottom water clarity (Figure 5a).

Mooring B

The tripod at Site B was deployed in 44 m of water. The first bin in the upward-looking

ADCP at Site B was centered in water depth of 37.9 m, about 6 mab. The top bin measured

currents centered around 3.9 m from the surface. A Microcat was attached at 53 cmab to measure

conductivity and temperature. Two Brancker loggers were attached with transmissometers to

measure temperature and near-bottom water clarity. A Seacat measured near-bottom oxygen

concentrations at 90 cmab, as well as temperature and salinity at 64 cmab (Figure 5b).
-123.19137 -122.986946

47.4259647.30434

Map

Extent

H H

B A

Figure 1. Location of mooring sites in Hood Canal and index map. Black lines (1-5) 

show approximate locations of transect lines from Figure 3.

S kokomish

Hamma Hamma R iver

The Great Bend

Tahuya R iver

Dosewalips R iver

Duckabush R iver

GR AY WOLF R

Union R iver

B ig B eef C reek Hood C anal

Lynch

Cove

Dabob B ay

R iver

Hoodsport

Bremerton

Bangor

SUBBASE

Washington State

Location

of study

area

Hood Canal

Floating Bridge

A B

Study area 

1,2,5

3

4
2004

Aug Sept Oct

54 m 

ADCP 

Bottom C,S,T

Hood Canal 2004 Moorings

 

2004

Aug Sept Oct

Site B (773)

ADCP 

Bottom C,S,T,O

KEY:

 C - Light Attenuation 

 S - Salinity/Conductivity

 T - Temperature

 

44 m

Site A (772) 

O - Oxygen sensor

Figure 2. Timelines showing dates when valid data from current meters and data 

for temperature, water clarity, oxygen, and salinity exist for Hood Canal sites.
Transect #1

Start time: 0916 PDT Location: N 47 21’ 20” W 123 01’ 07”

End time: 0929 End loc. N 47 21’ 39” W 123 01’ 28”

Transect #2

Start time: 1004 PDT Location: N 47 21’ 39” W 123 01’ 28”

End time: 1017 End loc. N 47 21’ 20” W 123 01’ 07”

Figure 3. Transects taken in short preliminary cruise with ACDP to measure currents.

See Figure 1 for location of transect lines.
Transect #3

Start time: 1037 PDT Location: N 47 20’ 59” W 123 03’ 36”

End time: 1108 End loc. N 47 22’ 16” W 123 03’ 59”

Transect #4

Start time: 1116 PDT Location: due SW of Transect#3 end point

End time: 1136 End loc. N 47 21’ 26” W 123 05’ 20”

Figure 3, cont.
Transect #5

Start time: 1227 PDT Location: N 47 21’ 39” W 123 01’ 28”

End time: 1237 End loc. N 47 21’ 20” W 123 01’ 07”

Figure 3, cont.
y for Sites A and B tripods.

Longitude

Deployment

date

Recovery

date

Water

depth

(m) Instrument Type

Manufacturer and 

Model # 

Instrument

depth 

(cmab)

Variables

Measured

Sampling

Rate

Serial 

Number

23°01.14 W 8/28/04 10/28/04 54 300kHz ADCP RDI Instruments 

Workhorse Sentinel 122 V 5 min 587

Microcat SBE 37-5M 59 T,S 5 min 2538

Brancker XR-420 104 L 5 min 10750

Transmissometer Seatech TR2025 104 Clarity 5 min 21

Brancker XR-420 49 L 5 min 10752

Transmissometer Seatech TR2025 49 Clarity 5 min 515

23°04.81 W 8/26/04 10/26/04 44 300kHz ADCP RDI Instruments 

Workhorse Sentinel 122 V 5 min 411

Seacat SBE 16+ 64 T,S 5 min 4250

Oxygen sensor Seabird 43 64 Oxygen 5 min 430253

Microcat SBE 16+ 53 T,S 1 min 283

Brancker XR-420 103 L 5 min 10754

Transmissometer Seatech TR2025 103 Clarity 5 min 516

Brancker XR-420 48.5 L 5 min 10755

Transmissometer Seatech TR2025 48.5 Clarity 5 min 618
Figure 4. Recovery of Tripod A in October 2004.

While the moorings were in the water, several casts with a conductivity-temperature-depth

(CTD) sensor that measured the temperature and salinity of the water column were taken near

the instrument sites (Figures 6a-d). In addition, nutrients and other ancillary constituents within

Lynch Cove were discretely sampled several times during the deployment period in order to

collect the chemical data needed to calculate the transport of nutrients into Lynch Cove from the

seaward reaches of Hood Canal.

DATA QUALITY AND PROCESSING PROCEDURES

The data sets from individual instruments were downloaded, transcribed into scientific units,

and then passed through several quality-control steps. The data were checked for errors caused

by instrument failures. Obvious spikes and gaps were removed from the data. Greenwich mean

time (GMT) is the common timebase for all data records.

There were short temporal gaps in many of the data records. Most gaps were less than 10

minutes long. Gaps of less than 20 minutes were linearly interpolated. Gaps of a few hours were

filled with a spectral method that uses the frequency properties of the data adjacent to the gap to

generate the interpolated data. Longer gaps were not filled.

The very-near surface currents measured by the ADCPs were removed from the currentmeter files due to obvious measurement errors. Hence, the shallowest currents measured at Sites

A and B were 3.3 and 3.9 m below the surface at the lowest portion of the tidal cycle. The
Brancker/transmissometer 

Figure 5a. Schematic diagram of tripod mooring at 54 m at Site A.

300 kHz ADCP

Edgetech release

Microcat
300 kHz ADCP

Edgetech release

Microcat

Figure 5b. Schematic diagram of tripod mooring at 44 m at Site B.

Seacat/oxygen sensor

Brancker/transmissometer 
Figure 6a. Water column temperature and salinity profiles recorded by CTD casts taken near Site A.

Site A
Site B

Figure 6b. Water column temperature and salinity profiles recorded by CTD casts taken near Site B.
Site A

Water Depth: 55 m

Figure 6c. Water column temperature and salinity profiles recorded by CTD casts taken near Site A.
Figure 6d. Water column temperature and salinity profiles recorded by CTD casts taken near Site B.

Site B

Water Depth: 45 m
deepest currents measured at these sites were in water depths of 47.3 and 37.9 m, which was

about 6-7 mab.

The currents at Sites A and B were rotated into a coordinate system aligned roughly parallel

and perpendicular to the local axis of the canal. At Site A, positive along-canal currents flow

toward the mouth (seaward), aligned toward 225 degrees true. Positive cross-canal currents flow

toward the northwest shore, aligned toward 315 degrees. The positive along-canal currents at

Site B are aligned toward 295 degrees. They also flow toward the mouth (seaward) of the canal.

Positive cross-canal currents are aligned along 25 degrees, flowing toward the northern shore.

Several statistical quantities are discussed in this report. The mean, standard deviation, and

minimum and maximum amplitude of many measured water properties are included in Appendix

A (Tables A-1a, A-1b). The error bars around the mean values indicate the stability of that mean

value. In order for a mean current direction to be reliable, the mean values must be greater than

the error bar. Otherwise, the mean directions are not significantly different from zero.

The formula for the error bar around the mean is

tn; / 2

n +1 (1)

where  is the standard deviation of the subtidal data, t is the student t statistic at the 100(1-

) percent confidence limit, and (n+1) is the degrees of freedom in that data. The degrees of

freedom is the record length divided by the auto-correlation scale of the subtidal data set. For

currents, there were 19 degrees of freedom.

The tidal analysis is the result of performing a least-squares fit of the observed series to

amplitudes and phases of specific frequencies that are derived from the motions of the sun and

moon. The methods are given in Godin (1972), and the implementation for the pressure and

current records uses the programs written by Foreman (1977; 1978). The major constituents of

interest are grouped into two frequency bands, the semidiurnal (M2, S2) and diurnal (K1, O1).

Tidal current amplitudes were computed for currents measured each meter for water depths 6-7

m above the seabed and 3-4 m below the estuary’s surface. A barotropic, or surface, tide was

calculated from currents averaged over the entire water column.

The current records were also low-pass filtered to remove the diurnal and semidiurnal tidal

constituents from the records. These records are designated subtidal currents.

MOORED CURRENT OBSERVATIONS

Mean currents

All current components–mean, tidal, and subtidal currents–are generally aligned with the axis

of the canal. The mean currents for the two-month measurement period were generally weak. At

Site B, the mean along-canal flow was not significantly different from zero (Appendix A; Table

A-1b). At Site A, the mean along-canal current was slightly stronger at depths deeper than 34 m.

At these depths, average currents flowed about -1.94 + 1.44 cm/s landward, toward the head of

the canal (Appendix A; Table A-1a).
Tidal current and sea-level fluctuations

Tidal currents are a major portion of the current field in Hood Canal. The semidiurnal tidal

currents (primarily M2 and S2) flow up and down the canal roughly twice per day. The diurnal

tidal currents (primarily O1 and K1) flow up and down the canal once a day. The depth-averaged

(or barotropic) tidal current is aligned with the axis of Hood Canal (Appendix A; Table A-2).

The principal lunar component of the barotropic tide (M2) is the dominant tidal current.

Maximum along-canal M2 current amplitudes were 8 and 14 cm/s at Sites B and A respectively.

The along-canal currents associated with the other three barotropic tidal components were

generally weak, 5 cm/s or smaller at both sites. Usually, the along-canal tidal currents at Site A

were twice the size of tidal currents measured at Site B. This is consistent with canal topography.

The cross-sectional area of the canal at Site A is only half that measured at Site B; hence currents

must flow faster through this relatively narrow portion of the canal. The phase change in tidal

currents between the two sites was minimal. The cross-canal tidal currents, as represented by the

amplitude of the minor axis of the tidal current ellipse, were at least an order of magnitude

smaller than the along-canal currents.

The detailed measurements of velocity with depth in Hood Canal showed that, although the

depth-averaged tidal currents accounted for most of the tidal flow, there was some vertical

structure in the amplitude and the phase of tidal currents at both sites (Appendix A; Tables A-3ad, A-4a-d). At each depth level, the measured along-canal tidal currents were usually only 20

percent larger or smaller than the depth-averaged tidal current. The phases of each tidal

constituent were fairly steady over the water column and close to the phases of their respective

barotropic constituent.

The sea-level fluctuations associated with the diurnal and semidiurnal tides were 0.5 to 1

decibar (approximately 0.5-1 m) (Appendix A; Table A-2). The amplitude of the sea-level (or

pressure) fluctuation for each tidal constituent was nearly identical at both sites. There was no

significant change in the tidal phase between Sites A and B.

Within the diurnal and semidiurnal tidal bands, the barotropic tidal currents and sea-level

fluctuations have similar ratios for their relative amplitudes. The ratio of K1 to O1 amplitudes is

approximately 1.5 for both currents and sea level. The ratio for M2 to S2 is 3. The diurnal ratio is

what one would expect from simple astronomical tidal forcing. The ratio of the semidiurnal

components is somewhat larger, indicating M2 is slightly larger (or S2 is slightly smaller) than

one would expect from astronomical forcing. The phase shift between the barotropic tidal

currents and sea level is around 110° for the diurnal constituents and 125° for the semidiurnal

constituents. The phase properties suggest that the tidal currents are nearly, but not quite, a

standing wave, as the phase is slightly larger than 90°.

Subtidal current patterns

The vertically averaged subtidal currents at Sites A and B flow primarily up and down the

canal (Figure 7). Most of the energy in the fluctuating flow showed periods between 3 and 6

days. There is a slight tendency for the flow at Site A to be towards Lynch Cove, at the head of

the canal, with speeds of 1 cm/s (Table 2). It is clear that the amplitude of the fluctuations in the

along-canal flow at Site A is twice that measured at Site B, consistent with the changes in the

cross-sectional area of Hood Canal at these two sites. It is also obvious that the flow up and
-8

-6

-4

-2

0

2

4

6

8

29

Aug

2004

5

Sep

12 19 26 3

Oct

10 17 24

-8

-6

-4

-2

0

2

4

6

8

Figure 7. Subtidal currents summed over the water column. The length of each line in the plot indicates the speed of the 

subtidal flow. The angle of each line represents the direction of flow. Hence a positive vertical line indicates currents are 

flowing parallel to the canal axis toward the mouth of Hood Canal.

Site A

Site B

cm/s cm/s
Table 2. Statistics for vertically averaged along-canal currents. The currents are averaged

over the entire water column (VA) or over the surface (SF) and lower layer (LL) of the

water column as defined by the first mode in the current field for Sites A and B. Mean

currents are significant at the 95 percent confidence level.

Site Mean

(cm/s)

Standard

Deviation

VA_A -1.0 1.9

VA_B 0 0.9

SF_A 0 3.8

LL_A 0 2.7

SF_B 0 2.7

Ll_B 0 1.7

Table 3. Coherence for various pairs of subtidal currents in the 3-6-day frequency band.

The currents are averaged over the entire water column (VA) or over the surface (SF) and

lower layer (LL) of the water column as defined by the first mode in the current field for

Sites A and B. Reported coherences are significant at the 95 percent confidence level. A

transfer function (Tr) larger than 1 means that the coherent portion of the energy in the

second pair is larger that that in the first. Phases of 0 and 180 are reported if the measured

phase is not significantly different from those values. The lowest resolvable period was

444 hours.

Current 1 Current 2 Coherence Phase Tr

VA_B VA_A 0.89 0 2.2

VA_A LL_A 0.97 0 1.4

VA_B LL_B 0.80 0 2.0

SF_B SF_A 0.95 0 1.3

LL_B LL_A 0.92 0 1.3

SF_A LL_A 0.78 180 0.6

SF_B LL_B 0.80 180 0.6

Mode_2 B Mode_2 A 0.64 0 1.0
down the canal is highly correlated between sites. The coherent (or similar) portion of the

fluctuating flow field in the 3-6-day band accounts for 79 percent of the energy (Table 3).

However, if one examines only vertically averaged current records, one misses the fact that

there is a persistent vertical structure in the subtidal current field. Currents near the surface

tended to flow in opposite directions to currents near the bed (Figure 8). The change in flow

direction occurred below the relatively shallow thermocline at a depth of 10 m (Figures 6a-d).

Because the flows in each layer (surface and bottom) were highly correlated both within and

between layers, Empirical Orthogonal Functions (EOF) (Joreskog et al, 1976) were used to

represent this vertically sheared current field. The first mode of an EOF represents the most

energetic spatial pattern associated with the correlated portion of a fluctuating current field. The

first mode represents both the amplitude variation and the temporal fluctuations in a set of

currents in a particular region if that mode contains a large percentage of the variance, or energy,

in the regional current field. The second mode represents the next most energetic correlated

structure in that current field.

The vertical structure of subtidal currents in the first mode confirms the initial observation

that the majority of currents above the thermocline flow in a direction opposite to currents below

the thermocline (Figure 9).

At Site A, the first mode accounts for 75 percent of the subtidal along-canal flow (Table 4a).

The surface layer is quite shallow, extending to only 6 m of water depth. The lower layer is much

thicker, extending from about 13 m below the surface to the bed. There is a similar sheared flow

pattern at Site B, where the first mode accounts for 63 percent of the flow field. The surface layer

at Site B is 5 m deeper than that found at Site A. This may relate to the changing depth of the

thermocline at the two sites, as there is a slight tendency for the thermocline to be deeper in

September and October at Site B (Figure 6b).

In order to examine the sheared flow pattern more closely, subtidal along-canal currents in

the surface and lower layer at each site were averaged over the bins defined by the mode (Table

4a). The currents in the two layers clearly flow in opposite directions (Figure 10). Not

surprisingly, the coherence between the surface and lower layers is 0.8, with a phase of 180

degrees (Table 3; Figure 10).

Fluctuations in the averaged along-canal currents ranged from 5-10 cm/s (Figure 10). These

current oscillations can transport suspended material more than 15 km in a few days. Currents in

the lower layer are not quite as strong as those in the surface layer, but because the lower layer is

much thicker, they dominate the net transport. Hence, the currents averaged over the entire water

column not only flow in the same direction as in the lower layer, but also are highly coherent

with the lower layer currents at both sites (Table 3). Eighty to ninety percent of the vertically

averaged fluctuating flow field at Site A is represented by flow below the thermocline.

When currents in the surface layer at Site A are flowing toward the mouth (seaward) of the

canal, surface currents at Site B are slower, but flowing in the same direction (Figure 11).

Currents in the lower layer at both sites are flowing toward the head of the estuary. Flows in both

the surface and lower layers are highly coherent between measurement sites; coherence

amplitudes are above 0.9 (Table 3; Figure 11). There was no measurable phase lag between the

two sites.

The high correlations in modal currents between Sites A and B suggest that the vertically

sheared fluctuating flow field has a length scale much larger than the 5-km separation of the two

measurement sites. A simple calculation using Merian’s formula (Pond and Pickard, 1983) for

the length-scale of an internal seiche with periods of 3-6 days suggests that the seiche could
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5

10

29

Aug

2004

5

Sep

12 19 26 3

Oct

10 17 24

 tempud

-15

-10

-5

0

5

10

 tempud

Figure 8. Subtidal currents nearly 6 m below the surface (blue) and 9 m above the bed (red) at Sites A and B.

Site B

Site A

cm/s cm/s
Mode 1 54 m Mode 2 54 m

44 m

0 m 

0 

0 m 0 m

Site A Site B Site A 

Figure 9. Vertical structure of subtidal alongcanal currents in Modes 1 and 2. The horizontal lines show the current velocity with depth. If currents at a particular depth are not associated with the mode, no horizontal l
-10

-5

0

5

29

Aug

2004

3

Sep

8 13 18 23 28 3

Oct

8 13 18 23

-10

-5

0

5

10

Site B

Site A

cm/s cm/s

Figure 10. Subtidal currents averaged over the surface (blue) and bottom layers (red) of Mode 1 at Sites A and B.
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-5

0

5

10

29

Aug

2004

3

Sep

8 13 18 23 28 3

Oct

8 13 18 23

-10

-5

0

5

surface

bottom

cm/s cm/s

Figure 11. Subtidal currents averaged over the surface and bottom layers of Mode 1 at Site B (blue) and A (red).
occupy 50 to 100 percent of the length of Hood Canal. It is not clear what forces this internal

seiche, but it is probable that the seiche is persistent. Our measurements suggest that it was

present during the entire two-month deployment.

In order to determine whether winds could be partially responsible for forcing the seiche,

wind measurements were obtained from Shelton, Washington, a town about 10 miles south of the

canal. Given the prevalent mountains and hills around Hood Canal, the direction of winds at

Shelton may not represent the wind direction over the canal, but the wind strength could be

correlated between the two regions. If it is windy at Shelton, it should be windy at Hood Canal.

Winds at Shelton were converted to wind stress using a formula by Wu (1980), then low-pass

filtered to produce records with fluctuations at periods similar to those found in the baroclinic

seiche. Wind stress was then rotated into a component aligned with the direction of maximum

wind stress amplitude using the principal axes (prominent direction) of the subtidal wind stress

velocity. Positive winds aligned along the principal axes flowed toward Hood Canal and were

highly correlated with winds at Shelton blowing toward the north, roughly aligned with the axis

of Hood Canal.

Fluctuations in the principal-axis wind stress seem correlated with currents in the baroclinic

seiche (Figure 12). At the beginning and end of the measurement program, relatively strong

wind-stress fluctuations with periods of a few days were followed by similar fluctuations in

current about one day later. A statistical analysis shows that 22 percent (34 percent) of the

surface (lower-layer) currents at Site A (Table 5) were correlated with wind stress. The

correlations were slightly weaker at Site B, where only correlations in the lower layer were

significant at the 95 percent confidence level. A coherence analysis between wind stress and

modal currents at Sites A and B indicates that wind stresses with periods of 2-3 days had the

strongest correlations with seiche currents, consistent with the pattern shown in Figure 12.

Roughly 50 percent of the current energy in these periods is associated with wind forcing.

It is interesting to note that the daily flow from the Cushman Powerhouse on the western side

of the Great Bend has fluctuations with periods similar to those found in the seiche (Figure 13).

For the first third of the measurement period, an increase in flow from the Powerhouse was

associated with surface currents in Hood Canal flowing seaward toward the mouth of the canal.

This flow pattern tended to reverse in the latter portion of the record, with surface currents

flowing toward Lynch Cove when the flow from the Powerhouse increased. Given that the flow

from the Powerhouse enters Hood Canal at Potlatch, in the middle of the Great Bend, it may not

be surprising that, at times, surface currents bend toward the mouth (seaward) of the canal, and at

other times bend toward Lynch Cove. On average, surface flows in the 3-4 day frequency band

were coherent and flowing toward Lynch Cove when flow from the powerhouse increased. Only

a small percentage of the total variance in surface currents was associated with flow from the

Powerhouse; values were generally less than 15 percent. Wind-stress forcing appeared to be the

more dominant process. However, this was a very short measurement period; the relative

importance of the various forcing processes may not be robust. Clearly, many processes could

contribute to the internal seiche in Hood Canal, and more measurements must be collected before

these connections between the several flow patterns can be confirmed.

The second mode for subtidal currents accounted for most of the remaining subtidal current

variability in Hood Canal (Table 4b; Figures 9, 14). It was present only near the thermocline,

where the first mode was weakest (Figure 9) and was not coherent with the first mode. Again,

currents at the two sites tended to flow in the same direction (Figure 15), though the coherence

was not as strong as for mode 1. Coherence amplitude was 0.6, suggesting that only 36 percent
Table 4a. Mode 1 subtidal current statistics. Only currents significantly correlated with

the mode are included in the modal structure. The zero level for the squared coherence is

0.21. Lower layer currents are assumed to reach the bed.

Site Percentage

variance

Width of

surface layer

Top of lower

layer

Width of

lower layer

A 75 6 m 13 m 41 m

B 63 11 m 18 m 26 m

Table 4b. Mode 2 subtidal current statistics. Only currents significantly correlated with

the mode are included in the modal structure. The zero level for the squared coherence is

0.21.

Site Percentage variance Shallowest layer for

Mode 2 current

Deepest layer for

Mode 2 current

A 18 4 m 18 m

B 22 9 m 21 m

Table 5. The correlation between wind stress and currents in the internal seiche in Hood

Canal. The wind stress is aligned with the principal axis of wind measured at Shelton

WA, a city 10 miles south of Hood Canal. A positive wind blows toward the north,

toward the mouth of the canal. A positive lag means the first record leads the second. The

95% confidence for zero coherence is 0.45.

Record 1 Record 2 Correlation Lag (Days)

Wind stress Surf A 0.47 1

Wind stress Bottom A -0.58 1

Wind stress Surf B - -

Wind stress Bottom B -0.45 1
-4

-2

0

2

4

6

29

Aug

2004

5

Sep

12 19 26 3

Oct

10 17 24

 wind_curr.nc , dam_A_B_sd.cdf 

-2

0

2

4

6

 wind_curr.nc , dam_A_B_sd.cdf 

Surface-layer current

� � � � � ��� � � � �� � � � � � �

Figure 12. The principal axis of wind stress at Shelton, WA (blue), and surface and lower-layer currents in the 

internal seiche at site A (red). For clarity, wind-stress amplitudes have been multiplied by 100. cm/s cm/s
-4

-2

0

2

4

29

Aug

2004

5

Sep

12 19 26 3

Oct

10 17 24

 dmflow.cdf

-4

-2

0

2

4

 dmflow.cdf

Figure 13. Subtidal currents averaged over the surface and bottom layers for Mode 1 at Site A (red) and flow into 

Hood Canal from the Cushman Powerplant at Potlatch (blue). For clarity, currents in the surface (bottom) layer have 

been divided by 2.8 (1.7).

face current 

(cm/s)

ar-bed current 

(cm/s)

 Powerplant

 flow

(m /s)

Powerplant

 flow

(m /s)

3

3

0

24

48

 0

24

48
-10

-5

0

5

10

29

Aug

2004

3

Sep

8 13 18 23 28 3

Oct

8 13 18 23

-10

-5

0

5

10

Figure 14. Vertically averaged subtidal along-canal currents of Mode 2 at Sites A (red) and B (blue).

Sites A & B

Site B

cm/s cm/s
of the energy was coherent between the two sites (Table 3). Despite the change in canal width,

the amplitudes of the coherent fluctuations were similar at both sites.

WATER PROPERTY OBSERVATIONS

Subtidal fluctuation patterns

The temperature, salinity, and oxygen content of the water near the bed increased markedly

about halfway through the measurement period (Figure 15). A pool of warmer, saltier, and more

oxygenated water near the bed passed over Site B, then Site A in mid-September. A rough

estimate of the frontal passage between the two sites suggests the warmer water traveled toward

the head (landward) of the canal at about 1 cm/s, roughly at the mean current speed at Site A.

The warmer, more oxygenated water remained in the region at least until the end of October, at

the end of our measurement program.

CTD casts show that the changes in water properties measured near the bed by the moorings

in September and October actually represent changes in the water properties from the bed to

within 15-20 m of the surface (Figures 6a-d). During these periods, temperatures below 15 m

varied by less than a degree and salinities varied by less than 1 PSU. The changes in the CTD

profiles show that the entire portion of the water column below the thermocline was warmer,

saltier, and more oxygenated in October than in September, consistent with the moored timeseries measurements made near the bed. It is of interest to note that this portion of the water

column occupied the same depth range, represented by the lower layer of the first subtidal

current mode (Table 4a). Hence, the water column from 15 m to the bed not only had similar

water properties, but it moved uniformly up and down the canal over the two-month deployment

period.

This change in near-bed water properties was not associated with a similar change in the

current patterns in Hood Canal. The mean and subtidal flow patterns did not show any systematic

change between the first and second half of the measurement period.

Fluctuation patterns at tidal frequencies

The tidal currents are the largest current component in Hood Canal. A close examination of

the relationship between tidal current flow and frontal passage confirms that the warmer, saltier,

and more oxygenated water was moving slowly toward Lynch Cove, at the landward end of

Hood Canal. When tidal currents flowed seaward toward the mouth of the canal in midSeptember, the water at each site became fresher, cooler, and less oxygenated (Figure 16). The

amplitude of the fluctuations in water properties at Site B was stronger than at Site A, despite the

fact that the tidal excursions at Site B were weaker than at Site A. This suggests that the front in

water properties became more diffuse as it moved up the canal. It may have mixed with the

surrounding water as it was being advected toward Lynch Cove.

The phases in the diurnal and semidiurnal tidal bands between currents and water properties

support the advection of a front toward the Lynch Cove end of the canal (Tables 6, 7). The near90-degree phase shift and the fact that water properties lead the currents suggest that warmer,

saltier, and more oxygenated water tends to be found toward the mouth (seaward) of Hood Canal

for the entire measurement period. At Site B, most of the tidal-band fluctuations in higher

oxygen were associated with warmer, saltier water (Tables 6, 7). Coherence levels were above
-10

0

10

26

Aug

2004

2

Sep

9 16 23 30 7

Oct

14 21 28

0.5

1

1.5

30

30.2

30.4

30.6

10

10.5

11

11.5

Figure 15. Subtidal along-canal currents, hourly recorded oxygen, salinity, and temperature near the bed at Site A 

(red) and Site B (blue). 

Temperature

Salinity

Oxygen

Alongcanal currents 

cm/s degrees (C) ppt ml/L
-20

0

20

13

Sep

2004

15 17 19 21 23 25 27 29 1

Oct

0.5

1

1.5

30

30.2

30.4

10

10.5

11

Figure 16. Tidal currents advect warmer, saltier, more oxygenated water from Site B (blue) toward Site A (red).

Temperature

Salinity

Oxygen

Alongcanal current

ppt cm/s degrees (C) mg/L
Table 6. Coherence among the vertically averaged current and other water properties in

the diurnal tidal band. A positive phase indicates the second member of the pair led the

first. The longest resolvable period is 192 hours. The coherence calculation used a

hanning window with a 50 percent overlap.

Site Site Coherence Phase

A_current A_Temp 0.66 69 ± 27

A_Salt 0.82 56 ±16

ATEMP A_Salinity 0.92 0

B_current B_Temp 0.69 101 ±25

B_Salt 0.83 98 ±16

B_Oxygen 0.78 103 ±19

B_Temp B_Salt 0.96 0

B_Oxygen 0.98 0

B_Salt B_Oxygen 0.99 5 ±3

Current_B Curr_A 0.99 5 ±3

Temp_B Temp_A 0.64 -32 ±29

Salt_B Salt_A 0.72 -39 ±23

Table 7. Coherence among the vertically averaged current and other water properties in

the semidiurnal diurnal tidal band. A positive phase indicates the second member of the

pair led the first. The longest resolvable period is 186 hours. The coherence calculation

used a hanning window with a 50 percent overlap.

Site Site Coherence Phase

A current A_Temp 0.58 88 ±34

A_salt 0.81 83 ±17

A temp A_salt 0.87 0

B_current B_Temp 0.71 86 ±23

B_Salt 0.87 86 ±14

B_Oxygen 0.83 83 ±16

B_Temp B_salt 0.95 0

B_Temp B_oxygen 0.98 0

B_Salt B_Oxygen 0.99 0

Curr_b Curr_A 1.0 4

Temp_B Temp_A 0.82 0

Salt_B Salt_A 0.83 0
0.95. Tidal current amplitudes suggest that water-property fronts are moved back and forth at 1-3

km per day. Given that the fluctuations in temperature and salinity were highly coherent between

sites that are 5 km apart, this suggests that fronts in water properties have length scales at least

that large.

CONCLUSIONS

Measurements collected in the fall of 2004 at two locations near the head of Hood Canal

show that tidal currents are the dominant current component in the canal. The tidal currents are

aligned primarily along the axis of the canal, with the semidiurnal M2 tidal current the largest;

current amplitudes are 8 to 14 cm/s. Site A, which is located in a relatively narrow portion of the

canal, has the strongest tidal currents. The increase in amplitude is roughly proportional to the

decrease in cross-sectional area between Sites B and A.

The subtidal currents also flow primarily up and down the canal. The mean flow is weak, or

nonexistent, in the canal except in the seabed at Site A. Here, currents flow toward the head of

the canal with speeds usually less than 2.3 cm/s.

An internal seiche dominates the fluctuating portion of the subtidal flow field in Hood

Canal. Subtidal currents above the shallow thermocline flow primarily along the canal, but in a

direction opposite to the subtidal currents beneath the thermocline. The amplitudes of the current

fluctuations are generally less than 8 cm/s, and the phase between the upper and lower layer

currents is about 180°. The high correlations and small phase lags in the subtidal currents

between sites suggest that this subtidal seiche has a length scale much longer than the 5-km

separation between the two measurement sites. It is probable that at least a portion of the energy

in the seiche is driven by the local winds that blow up and down the canal.

During the measurement program, a pool of warmer, saltier, and more oxygenated water

moved past the measurement sites. A rough estimate of the speed of the frontal passage

suggested this water moved toward the head of the canal with a speed of 1 cm/s. This speed is

consistent with that of the mean currents measured near the bed at Site A. CTD measurements

taken near the two measurement sites during the deployment indicate that this more oxygenated

layer of water extended from the bed to the thermocline. Oxygen data from the tripods showed

that this water remained in the region until at least the end of October 2004, when the tripods

were recovered.

The spatial and temporal patterns seen in the data collected in this program are interesting,

but are clearly limited. The tidal current amplitudes measured in the canal probably represent

tidal current amplitudes in this region over the year. However, the data sets are too short and

cover too limited a region to allow one to infer that the patterns seen in the subtidal and mean

flows are either persistent or represent a large region of the canal. More data taken at different

sites and over much longer time periods is needed before one can characterize the transport

patterns in Hood Canal.

Data files used for this report can be obtained from Anne L. Gartner (agartner@usgs.gov),

Marlene Noble (mnoble@usgs.gov), or the Coastal and Marine Geology Team Chief Scientist,

U.S. Geological Survey, 345 Middlefield Road, MS 999, Menlo Park, California 94025.
REFERENCES

Collias, C.E., McGary, N., and Barnes, C.A., 1974. Atlas of physical and chemical properties of

Puget Sound and its approaches. University of Washington Sea Grant Publication WSG 74-1,

285 p.

Foreman, M.G.G., 1977. Manual for tidal heights analysis and prediction. Pacific Marine

Science, Institute of Ocean Sciences, Patricia Bay, Sydney, B.C., Report 77-10, 97 p.

–– 1978. Manual for tidal currents analysis and prediction. Pacific Marine Science, Institute of

Ocean Sciences, Patricia Bay, Sydney, B.C., Report 78-6, 70 p.

Godin, G., 1972. The analysis of tides. University of Toronto Press, Toronto, 264 p.

Joreskog, K.G., Klovan, J.E., and Reyment, R.A., 1976. Geological factor analysis. Elsevier,

New York, 178 p.

Lipscomb, S.W., 1995. Quality assurance plan for discharge measurements using broad band

acoustic Doppler current profilers. U.S. Geological Survey Open-File Report 95-701, 7 p.

Norris, J.M., 2001. Policy and technical guidance on discharge measurements using acoustic

Doppler current profilers. Office of Surface Water Technical Memorandum No. 2002.02, 4 p.

Pond, S., and Pickard, G.L., 1983. Introduction to dynamical oceanography, 2nd edition.

Butterworth-Heinemann, Oxford, 329 p.

R.D. Instruments, Inc., 1996. Principals of operation. A practical primer for broad-band acoustic

Doppler current profilers (2nd ed.). R.D. Instruments, Inc., San Diego, CA, 51 p.

Simpson, M.R., 2001. Discharge measurements using a broad-band acoustic Doppler current

profiler. U.S. Geological Survey Open-File Report 01-1, 123 p.

Wu, J., 1980. Wind-stress coefficients over the sea surface near neutral conditions. Journal of

Physical Oceanography, 10, 727-740.
Appendix A: Mean and Tidal Current Statistics
Table A-1a. Statistics for the hour-averaged current readings at Site A. The standard deviation of the subtidal

current field is used to compute the error bars around the mean flow. Studies were carried out from August toOctober 2004; table includes statistics for whole record. Means in bold type are significantly different from zeroat the 95% confidence level. Depths are calculated using pressure sensors on the Microcat instruments.

Alongcanal (cm/s) Crosscanal (cm/s)

Instrument

Depth (m)

Mean Error

Bar

Standard

Deviation

Max Min Mean Error

Bar

Standard

Deviation

Max Min

3.3 -0.7 2.2 13.0 31.7 -36. 4 -0.1 0.3 2.6 14.9 -15.04.3 -0.7 2.0 13.0 31.7 -42.7 -0.2 0.3 2.3 13.9 -9.35.3 -0.9 1.7 12.5 28.3 -36.4 -0.1 0.2 2.2 7.6 -9.96.3 -0.9 1.5 12.2 28.1 -32.8 -0.0 0.2 2.1 7.7 -9.27.3 -0.8 1.4 11.9 27.9 -30.4 0.1 0.2 1.9 7.7 -7.58.3 -0.7 1.3 11.8 27.0 -29.0 0.2 0.2 1.9 7.1 -7.49.3 -0.6 1.2 11.7 27.0 -29.1 0.2 0.2 1.8 7.3 -8.0

10.3 -0.5 1.1 11.6 28.7 -27.6 0.2 0.2 1.8 7.1 -9.011.3 -0.4 1.1 11.6 30.7 -26.8 0.3 0.2 1.8 6.1 -7.912.3 -0.3 1.0 11.5 32.6 -26.0 0.3 0.2 1.7 6.6 -7.013.3 -0.3 1.1 11.6 33.5 -26.3 0.3 0.2 1.7 6.3 -7.114.3 -0.2 1.1 11.6 33.4 -28.3 0.3 0.2 1.6 6.3 -6.415.3 -0.2 1.1 11.6 33.8 -29.6 0.3 0.2 1.6 5.9 -5.916.3 -0.1 1.1 11.7 34.1 -28.9 0.4 0.2 1.6 5.6 -4.917.3 -0.1 1.2 11.7 34.0 -28.9 0.4 0.2 1.6 5.7 -4.918.3 -0.1 1.2 11.8 34.1 -28.9 0.4 0.2 1.5 5.3 -5.519.3 -0.1 1.2 11.8 35.0 -29.0 0.4 0.2 1.5 5.4 -5.620.3 -0.1 1.2 11.9 34.9 -28.7 0.4 0.1 1.5 5.0 -5.221.3 -0. 2 1.2 11.9 35.5 -28.5 0.4 0.1 1.5 5.0 -4.722.3 -0.2 1.2 12.0 35.2 -28.4 0.4 0.1 1.4 4.8 -4.523.3 -0.2 1.3 12.1 34.9 -28.9 0.4 0.1 1.4 4.6 -4.724.3 -0.3 1.3 12.2 34.5 -28.9 0.4 0.1 1.4 4.7 -5.025.3 -0.4 1.32 12.2 34.3 -29.5 0.4 0.1 1.4 4.5 -4.9
Table A-1a, cont.

Alongcanal (cm/s) Crosscanal (cm/s)

Instrument

Depth (m)

Mean Error

Bar

Standard

Deviation

Max Min Mean Error

Bar

Standard

Deviation

Max Min

26.3 -0.5 1.3 12.3 33.8 -29.6 0.4 0.1 1.3 4.8 -4.927.3 -0.6 1.3 12.3 33.6 -29.7 0.4 0.1 1.3 5.0 -4.628.3 -0.7 1.3 12.3 33.5 -30.2 0.3 0.1 1.3 5.7 -3.829.3 -0.9 1.4 12. 4 33.5 -30.7 0.3 0.1 1.2 5.9 -3.830.3 -1.0 1.4 12.4 33.7 -31.5 0.3 0.1 1.2 5.2 -4.331.3 -1.1 1.4 12.5 33.5 -31.0 0.3 0.1 1.2 5.3 -4.632.3 -1.2 1.4 12.5 33.3 -31.5 0.3 0.1 1.2 5.4 -4.433.3 -1.4 1.4 12.5 33.0 -31.1 0.2 0.1 1.2 5.1 -3. 934.3 -1.5 1.4 12.6 32.1 -31.1 0.2 0.1 1.2 4.4 -3.835.3 -1.6 1.4 12.6 31.9 -31.3 0.2 0.1 1.2 4.8 -3.736.3 -1.7 1.4 12.6 31.9 -31.6 0.2 0.1 1.1 4.6 -3.637.3 -1.8 1.4 12.6 32.1 -32.0 0.2 0.1 1.1 4.8 -4.038.3 -1.9 1.4 12.7 31.9 -32. 2 0.2 0.1 1.1 4.9 -3.839.3 -1.9 1.4 12.7 31.7 -33.0 0.2 0.1 1.1 4.8 -4.140.3 -2.0 1.4 12.7 31.6 -32.5 0.2 0.1 1.2 5.6 -3.841.3 -2.1 1.4 12.6 31.5 -32.4 0.2 0.1 1.2 5.5 -4.142.3 -2.1 1.4 12.6 31.9 -32.9 0.2 0.1 1.3 5.9 -4.943.3 -2.2 1.4 12.5 31.0 -32. 6 0.2 0.1 1.4 6.4 -4.844.3 -2.2 1.4 12.4 31.1 -31. 9 0.2 0.1 1.5 6.7 -5.645.3 -2.2 1.4 12.3 30.2 -32.3 0.2 0.1 1.6 7.3 -5.446.3 -2.3 1.3 12.1 29.5 -32.4 0.3 0.2 1.8 8.1 -5.747.3 -2.3 1.3 11.8 29.0 -32.0 0.4 0.2 1.9 8. 2 -5.5
Table A-1b. Statistics for the hour-averaged currents at Site B. The standard deviation of the subtidal current fie

is used to compute the error bars around the mean flow. Studies were carried out from August to October 2004;table includes statistics for whole record. Means in bold type are significantly different from zero at the 95%confidence level. Depths are calculated using pressure sensors on the Microcat instruments.

Alongcanal (cm/s) Crosscanal (cm/s)

Instrument

Depth (m)

Mean Error

Bar

Standard

Deviation

Max Min Mean Error

Bar

Standard

Deviation

Max Mi

3.9 0.2 1.9 9.1 30.8 -40.7 0.5 0.5 3.4 33.2 -224.9 -0.1 1.8 9.2 40.6 -26. 6 0.5 0.5 3.2 10.8 -235.9 -0.6 1.6 8.7 38.1 -27.2 0.6 0.4 2.9 13.2 -96.9 -0.8 1.4 8.3 31.4 -26.5 0.6 0.4 2.8 10.5 -87.9 -0.8 1.3 8.0 26.0 -25.3 0.5 0.4 2.7 9.3 -88.9 -0.7 1.2 7.7 19.5 -26.6 0.4 0.5 2.7 9.3 -89.9 -0.5 1.1 7.3 19.8 -26.9 0.3 0.4 2.6 8.8 -8

10.9 -0.3 1.0 7.0 20.3 -25.9 0.3 0.3 2.5 8.1 -811.9 -0.0 1.0 6.8 20.3 -23.8 0.2 0.3 2.4 7.3 -812.9 0.2 0.9 6.7 20.9 -21.9 0. 3 0.3 2.4 9.3 -713.9 0.4 0.9 6.6 22.1 -19.8 0.2 0.3 2.2 9.6 -714.9 0.6 0.9 6.6 24.9 -19.2 0.2 0.2 2.1 9.9 -615.9 0.7 0.9 6.6 26.7 -17.7 0.2 0.2 1.9 9.9 -616.9 0. 8 0.9 6.7 28.7 -15.8 0.2 0.2 1.8 10.2 -717.9 0.8 0.9 6.8 29.6 -14.7 0.1 0.3 1.8 9.3 -518.9 0.9 0.9 6.9 29.2 -14.2 0.2 0.2 1.8 10.1 -419.9 0.8 1.0 7.0 28.8 -14.7 0.2 0.3 1.8 10.4 -620.9 0.8 1.0 7.1 28.5 -15.3 0.2 0.3 1.8 10.5 -521.9 0.7 1.0 7.2 29.3 -16.1 0.3 0.3 1.8 9.8 -522.9 0.5 1.0 7.3 28.6 -15.9 0.2 0.3 1.9 9.5 -623.9 0.3 1.0 7.3 28. 3 -15.5 0.2 0.3 1.9 9.6 -624.9 0.2 1.1 7.4 28.3 -17.1 0.2 0.3 1.9 9.3 -525.9 0.0 1.1 7.4 28.0 -17.1 0.1 0.3 2.0 8.8 -5
Table A-1b, cont.

Alongcanal (cm/s) Crosscanal (cm/s)

Instrument

Depth (m)

Mean Error

Bar

Standard

Deviation

Max Min Mean Error

Bar

Standard

Deviation

Max Mi

26.9 -0.1 1.1 7.4 27.5 -17.2 0.1 0.3 2.0 7.8 -627.9 -0.2 1.0 7.4 27.0 -17.9 0.1 0.3 2.1 6.8 -528.9 -0.3 1.0 7.3 26.8 -17.8 0.1 0.3 2.1 6.7 -529.9 -0.4 1.0 7.3 27.4 -18.5 0.0 0.3 2.1 6.5 -630.9 -0.4 1.0 7.2 27.0 -18.0 0.0 0.3 2.1 6.2 -731.9 -0.4 0.9 7.1 25.8 -18.9 -0.0 0.3 2.0 5.8 -732.9 -0.4 0.8 6.9 23.8 -18.0 -0.1 0.3 2.0 6.1 -833.9 -0.4 0.8 6.8 23.3 -17.3 -0.1 0.3 1.9 5.2 -734.9 -0.3 0.7 6.6 21.4 -16.9 -0.2 0.3 1.8 4.9 -835.9 -0.2 0. 7 6.5 20.4 -16.5 -0.2 0.3 1.7 5.1 -736.9 -0.1 0.6 6.2 19.4 -16.5 -0.2 0.3 1.6 4.6 -637.9 0.0 0.6 6.0 17.8 -15.5 -0.3 0.3 1.6 4.7 -6
Table A-2. Barotropic tides, summed over 45 bins for Site A and over

35 bins for Site B. Studies were carried out from August to October

2004; table includes statistics for whole record. A 90-degree inclination

indicates the major axis of the tide is aligned parallel to the local axis of

the canal. Sea-level fluctuations are measured by a pressure sensor. A 1-

decibar pressure measurement represents a 1-m change in sea level. A

positive minor axis indicates the tidal currents rotate anticlockwise.

Depths are calculated using pressure sensors on the Microcat

instruments.

Site A

Current Pressure

Major

axis

(cm/s)

Minor

axis

(cm/s)

Inclination

(degrees)

Phase

(degrees)

Amplitude

(dbar/s)

Phase

(degrees)

Tide

O1 3.1 -0.1 90 349 0.5 239

K1 5.0 -0.1 90 3 0.6 259

M2 13.7 0.1 91 86 1.1 337

S2 4.7 0.0 90 108 0.4 358

Site B

Current Pressure

Major

axis

(cm/s)

Minor

axis

(cm/s)

Inclination

(degrees)

Phase

(degrees)

Amplitude

(dbar/s)

Phase

(degrees)

Tide

O1 1.6 -0.3 92 360 0.5 238

K1 2.6 -0.3 91 16 0.6 259

M2 7.8 -0.5 95 104 1. 1 337

S2 2.6 -0.2 99 127 0.4 358
Table A-3a. Characteristics of diurnal O1 tidal currents with depth at Site A. Current

characteristics were calculated between August and October 2004. A 90-degree inclination is the

major axis of the tide aligned parallel to the local axis of the canal. Phase is defined so that the

major axis of the tidal ellipse has a positive crosscanal component. A positive minor axis indicates

the tidal currents rotate anticlockwise. Depths are calculated using pressure sensors on the

Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.3 4.5 -0.3 90 322

4.3 4.9 -0.1 88 331

5.3 4.7 -0.0 89 336

6.3 4.5 0.0 90 342

7.3 4.3 -0.0 90 347

8.3 4.2 -0.0 90 349

9.3 4.1 -0.0 90 351

10.3 4.0 0.0 90 352

11.3 3.9 0.0 90 353

12.3 3.8 -0.0 89 354

13.3 3.7 -0.0 90 355

14.3 3.6 -0.0 90 355

15.3 3.6 -0.0 91 356

16.3 3.4 -0.0 91 356

17.3 3.3 -0.1 92 356

18.3 3.3 -0.0 92 357

19.3 3.2 -0.0 93 356

20.3 3.1 0.0 92 356

21.3 3.1 0.0 92 356

22.3 3.0 0.1 91 355

23.3 2.9 0.1 91 354

24.3 2.9 0.1 90 353

25.3 2.8 0.0 91 352

26.3 2.8 0.0 90 352

27.3 2.8 0.0 90 352

28.3 2.7 0.0 90 351

29.3 2.7 -0.0 89 352

30.3 2.7 -0.0 90 352

31.3 2.7 -0.0 90 352

32.3 2.7 -0.1 90 352

33.3 2.7 -0.1 90 351

34.3 2.7 -0.1 90 350

35.3 2.6 -0.1 90 349

36.3 2.6 -0.1 90 349
Table A-3a, cont.

Depth

(m)

Major Amplitude

(cm/s)

Minor Amplitude

(cm/s)

Inclination

(degrees)

Phase

(degrees)

37.3 2.6 -0.1 90 348

38.3 2.6 -0.1 90 348

39.3 2.5 -0.1 91 347

40.3 2.5 -0.2 91 346

41.3 2.4 -0.2 91 345

42.3 2.4 -0.2 92 344

43.3 2.3 -0.2 93 343

44.3 2.3 -0.2 93 342

45.3 2.2 -0.2 94 341

46.3 2.1 -0.2 95 340

47.3 2.1 -0.2 95 339
Table A-3b. Characteristics of diurnal K1 tidal currents with depth at Site A. Current

characteristics were calculated between August and October 2004. A 90-degree inclination is the

major axis of the tide aligned parallel to the local axis of the canal. Phase is defined so that the

major axis of the tidal ellipse has a positive crosscanal component. A positive minor axis indicates

the tidal currents rotate anticlockwise. Depths are calculated using pressure sensors on the

Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.3 4.7 -0.2 87 3

4.3 5.0 0.1 88 7

5.3 5.0 0.1 89 10

6.3 5.2 0.1 90 11

7.3 5.3 -0.0 90 11

8.3 5.3 -0.0 90 11

9.3 5.2 0.0 90 11

10.3 5.2 0.1 90 10

11.3 5.1 -0.0 90 10

12.3 5.1 -0.1 90 10

13.3 5.0 -0.1 90 9

14.3 5.0 -0.1 90 9

15.3 5.0 -0.1 91 9

16.3 5.0 -0.2 91 9

17.3 5.0 -0.2 91 8

18.3 5.0 -0.1 91 7

19.3 5.0 -0.1 91 7

20.3 5.0 -0.1 91 6

21.3 5.0 -0.1 90 6

22.3 5.0 -0.1 90 5

23.3 5.0 -0.0 90 4

24.3 5.1 -0.0 90 4

25.3 5.1 -0.0 89 3

26.3 5.1 -0.0 89 3

27.3 5.1 -0.0 89 2

28.3 5.1 -0.0 89 2

29.3 5.1 -0.0 89 1

30.3 5.1 -0.0 89 1

31.3 5.1 -0.0 89 1

32.3 5.1 -0.06 88 1

33.3 5.2 -0.0 88 0

34.3 5.1 -0.1 88 360

35.3 5.1 -0.1 88 359

36.3 5.1 -0.1 88 359
Table A-3b, cont.

Depth

(m)

Major Amplitude

(cm/s)

Minor Amplitude

(cm/s)

Inclination

(degrees)

Phase

(degrees)

38.3 5.1 -0.1 89 358

39.3 5.0 -0.1 89 358

40.3 5.0 -0.1 90 357

41.3 5.0 -0.1 90 356

42.3 4.9 -0.1 91 356

43.3 4.9 -0.1 92 356

44.3 4.8 -0.2 92 355

45.3 4.7 -0.2 93 355

46.3 4.7 -0.1 94 355

47.3 4.5 -0.2 95 354
Table A-3c. Characteristics of semidiurnal M2 tidal currents with depth at Site A. Current

characteristics were calculated between August and October 2004. A 90-degree inclination is the

major axis of the tide aligned parallel to the local axis of the canal. Phase is defined so that the

major axis of the tidal ellipse has a positive crosscanal component. A positive minor axis indicates

the tidal currents rotate anticlockwise. Depths are calculated using pressure sensors on the

Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.3 12.6 -0.9 87 88

4.3 13.4 -0.5 88 89

5.3 13.3 -0.3 89 89

6.3 13.2 -0.1 90 90

7.3 13.1 -0.0 91 90

8.3 13.0 0.1 91 90

9.3 12.9 0.2 91 90

10.3 12.9 0.3 92 90

11.3 12.9 0.3 92 90

12.3 12.9 0.3 92 89

13.3 12.9 0.3 92 89

14.3 13.0 0.3 92 88

15.3 13.0 0.3 92 88

16.3 13.0 0.3 92 88

17.3 13.1 0.4 92 87

18.3 13.1 0.4 91 87

19.3 13.2 0.4 91 87

20.3 13.2 0.4 91 86

21.3 13.3 0.4 90 86

22.3 13.5 0.4 90 86

23.3 13.6 0.3 89 86

24.3 13.7 0.3 89 86

25.3 13.8 0.2 89 86

26.3 13.8 0.2 89 86

27.3 13.9 0.2 89 86

28.3 14.0 0.1 89 86

29.3 14.0 0.1 88 85

30.3 14.1 0.1 88 85

31.3 14.1 0.0 88 85

32.3 14.2 0.0 89 85

33.3 14.3 0.0 89 85

34.3 14.3 0.0 89 85

35.3 14.4 -0.0 89 85

36.3 14.4 0.0 89 85
Table A-3c, cont.

Depth

(m)

Major Amplitude

(cm/s)

Minor Amplitude

(cm/s)

Inclination

(degrees)

Phase

(degrees)

37.3 14.5 0.0 89 85

38.3 14.5 0.1 90 85

39.3 14.6 0.1 90 85

40.3 14.6 0.1 91 84.

41.3 14.6 0.2 91 84

42.3 14.6 0.2 92 84

43.3 14.5 0.2 92 84

44.3 14.4 0.3 93 83

45.3 14.3 0.3 94 83

46.3 14.1 0.3 95 82

47.3 13.8 0.3 96 82
Table A-3d. Characteristics of semidiurnal S2 tidal currents with depth at Site A. Current

characteristics were calculated between August and October 2004. A 90-degree inclination is the

major axis of the tide aligned parallel to the local axis of the canal. Phase is defined so that the

major axis of the tidal ellipse has a positive crosscanal component. A positive minor axis indicates

the tidal currents rotate anticlockwise. Depths are calculated using pressure sensors on the

Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.3 4.5 -0.3 90 113

4.3 4.7 -0.3 87 117

5.3 4. 6 -0.2 86 117

6.3 4.5 -0.1 87 116

7.3 4.4 -0. 1 89 114

8.3 4.3 0.0 90 113

9.3 4.3 0.1 91 113

10.3 4.3 0.1 92 110

11.3 4.3 0.1 92 110

12.3 4.3 0.1 92 110

13.3 4.4 0.1 91 110

14.3 4.4 0.1 90 109

15.3 4.5 0.1 90 109

16.3 4.6 0.1 90 110

17.3 4.7 0.1 90 109

18.3 4.8 0.0 90 109

19.3 4.9 0.0 89 109

20.3 4.9 0.0 89 109

21.3 5.0 0.1 88 108

22.3 5.0 0. 1 88 108

23.3 5.0 0.1 88 108

24.3 5.0 0.1 88 108

25.3 5.0 0.2 87 107

26.3 5.0 0.2 88 107

27.3 5.0 0.2 88 106

28.3 5.0 0.2 88 106

29.3 5.0 0.1 88 106

30.3 4.9 0.1 88 105

31.3 4.9 0.1 88 106

32.3 4.9 0.0 88 106

33.3 4.9 0.0 88 107

34.3 4.9 -0.0 88 107

35.3 4.9 -0.0 88 107

36.3 4.9 -0.0 89 107
Table A-3d, cont.

Depth

(m)

Major Amplitude

(cm/s)

Minor Amplitude

(cm/s)

Inclination

(degrees)

Phase

(degrees)

37.3 4.9 -0.0 88 107

38.3 4.9 -0.0 89 106

39.3 4.9 -0.0 90 106

40.3 4.9 -0.0 90 106

41.3 4.9 -0.0 91 105

42.3 4.9 0.0 92 105

43.3 4.9 0.0 93 104

44.3 4.8 0.0 93 104

45.3 4.8 0.0 94 103

46.3 4.7 0.0 95 102

47.3 4.6 0.0 96 102
Table A-4a. Characteristics of diurnal O1 tidal currents with depth at Site B. Current

characteristics were calculated between August and October 2004. 90 degree inclination is the

major axis of the tide aligned parallel to the canal. Phase is defined so that the major axis of the

tidal ellipse has a positive crosscanal component. A positive minor axis indicates the tidal currents

rotate anticlockwise. Depths are calculated using pressure sensors on the Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.9 1.6 0.0 91 347

4.9 2.1 0.1 96 7

5.9 1.9 -0.1 97 6

6.9 1.7 -0.2 98 5

7.9 1.6 -0.3 96 2

8.9 1.5 -0.2 97 359

9.9 1.5 -0.2 101 356

10.9 1.5 -0.2 105 354

11.9 1.4 -0.1 107 354

12.9 1.3 -0.0 110 353

13.9 1.3 0.0 111 355

14.9 1.3 -0.0 111 356

15.9 1.3 -0.1 109 357

16.9 1.4 -0.1 105 358

17.9 1.4 -0.2 103 359

18.9 1.4 -0.2 100 1

19.9 1.4 -0.3 96 2

20.9 1.5 -0.3 93 5

21.9 1.6 -0.3 91 5

22.9 1.6 -0.3 89 6

23.9 1.7 -0.3 88 6

24.9 1.8 -0.3 86 6

25.9 1.8 -0.3 85 6

26.9 1.9 -0.4 82 7

27.9 1.9 -0.4 80 8

28.9 1.9 -0.4 80 7

29.9 2.0 -0.4 80 7

30.9 1.9 -0.4 80 6

31.9 1.9 -0.4 80 3

32.9 1.9 -0.5 82 1

33.9 1.9 -0.4 83 357

34.9 1.9 -0.4 84 354

35.9 1.9 -0.4 85 351

36.9 1.9 -0.3 86 349

37.9 1.8 -0.3 86 346
Table A-4b. Characteristics of diurnal K1 tidal currents with depth at Site B. Current

characteristics were calculated between August and October 2004. A 90-degree inclination is the

major axis of the tide aligned parallel to the local axis of the canal. Phase is defined so that the

major axis of the tidal ellipse has a positive crosscanal component. A positive minor axis indicates

the tidal currents rotate anticlockwise. Depths are calculated using pressure sensors on the

Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.9 1.9 -0.1 100 24

4.9 2.1 -0.1 104 32

5.9 2.3 -0.2 103 23

6.9 2.3 -0.1 102 17

7.9 2.3 -0.0 101 13

8.9 2.4 -0.0 102 10

9.9 2.4 0.0 101 8

10.9 2.4 0 100 6

11.9 2.4 -0.0 100 7

12.9 2.4 -0.1 99 8

13.9 2.4 -0.0 96 9

14.9 2.5 0.0 95 12

15.9 2.5 0.0 94 14

16.9 2.6 -0.0 94 16

17.9 2.6 -0.1 93 17

18.9 2.6 -0.2 92 19

19.9 2.7 -0.3 91 20

20.9 2.8 -0.4 91 22

21.9 2.8 -0.4 90 22

22.9 2.9 -0.4 89 24

23.9 2.9 -0.4 88 25

24.9 2.9 -0.4 86 25

25.9 3.0 -0.4 86 25

26.9 3.0 -0.4 85 25

27.9 3.0 -0.4 84 24

28.9 3.1 -0.4 83 22

29.9 3.1 -0.4 82 9

30.9 3.0 -0.4 82 6

31.9 3.0 -0.5 81 4

32.9 3.1 -0.5 82 2

33.9 3.1 -0.5 83 9

34.9 3.0 -0.5 83 7

35.9 2.9 -0.5 84 5

36.9 2.8 -0.4 86 3

37.9 2.6 -0.3 87 1
Table A-4c. Characteristics of semidiurnal M2 tidal currents with depth at Site B. Current

characteristics were calculated between August and October 2004. A 90-degree inclination is the

major axis of the tide aligned parallel to the local axis of the canal. Phase is defined so that the

major axis of the tidal ellipse has a positive crosscanal component. A positive minor axis indicates

the tidal currents rotate anticlockwise. Depths are calculated using pressure sensors on the

Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.9 8.3 -0.3 98 95

4.9 9.1 -0.1 101 99

5.9 9.0 -0.1 102 96

6.9 8.8 0.1 103 95

7.9 8.6 0.2 103 96

8.9 8.4 0.4 103 97

9.9 8.2 0.6 103 99

10.9 7.9 0.8 102 100

11.9 7.7 0.9 101 101

12.9 7.6 0.9 100 102

13.9 7.5 0.9 99 103

14.9 7.4 0.7 98 104

15.9 7.4 0.6 96 105

16.9 7.5 0.3 95 106

17.9 7.5 0.1 93 107

18.9 7.6 -0.2 92 107

19.9 7.7 -0.4 90 108

20.9 7.9 -0.7 89 109

21.9 8.0 -0.9 89 110

22.9 8.0 -1.1 88 110

23.9 8.1 -1.3 88 111

24.9 8.1 -1.4 88 111

25.9 8.1 -1.5 89 111

26.9 8.1 -1.6 89 111

27.9 8.0 -1.6 90 111

28.9 7.9 -1.6 91 111

29.9 7.9 1.6 92 110

30.9 7.8 1.5 92 110

31.9 7.7 1.4 93 109

32.9 7.5 1.2 93 108

33.9 7.4 0.9 93 107

34.9 7. 2 0.7 94 105

35.9 6.9 0.5 94 103

36.9 6.7 0.4 94 101

37.9 6.4 0.1 93 98
Table A-4d. Characteristics of semidiurnal S2 tidal currents with depth at Site B. Current

characteristics were calculated between August and October 2004. A 90-degree inclination is the

major axis of the tide aligned parallel to the local axis of the canal. Phase is defined so that the

major axis of the tidal ellipse has a positive crosscanal component. A positive minor axis indicates

the tidal currents rotate anticlockwise. Depths are calculated using pressure sensors on the

Microcat instruments.

Depth Major Amplitude Minor Amplitude Inclination Phase

(m) (cm/s) (cm/s) (degrees) (degrees)

3.9 2. 7 0.0 103 116

4.9 3.0 0.1 104 119

5.9 3.2 0.1 105 113

6.9 3.3 0.1 105 113

7.9 3.2 0.2 105 116

8.9 3.1 0.2 104 118

9.9 2.9 0.3 103 121

10.9 2.7 0.4 103 123

11.9 2.6 0.4 102 125

12.9 2.6 0.4 100 126

13.9 2.5 0.3 97 126

14.9 2.5 0.2 95 126

15.9 2.5 0.1 93 128

16.9 2.5 -0.0 92 129

17.9 2.6 -0.1 92 131

18.9 2.6 -0.2 92 134

19.9 2.7 -0.3 93 135

20.9 2.7 -0.4 93 137

21.9 2.7 -0.4 93 138

22.9 2.8 -0.4 94 150

23.9 2.8 -0.4 95 139

24.9 2.7 -0.4 96 139

25.9 2.6 -0.5 98 138

26.9 2.5 -0.5 100 137

27.9 2.5 -0.5 101 135

28.9 2.4 -0.5 101 134

29.9 2.4 -0.5 101 133

30.9 2.4 -0.5 102 132

31.9 2.4 -0.5 102 130

32.9 2.4 -0.4 102 128

33.9 2.3 -0.4 100 126

34.9 2.3 -0.3 98 123

35.9 2.2 -0.2 95 121

36.9 2.1 -0.1 91 117

37.9 2.0 -0.1 89 113