DOC
EPA
United States
Department of
Commerce
National Oceanic and
Atmospheric Administration
Seattle WA 98115
United States
Environmental Protection
Agency
Office of Environmental
Engineering and Technology
Washington DC 20460
EPA-600/7-81-089
June 1981
Research and Development
Circulation and
Trajectory
Calculations in the
Eastern Strait of
Juan de Fuca Using a
CODAR System
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RESEARCH REPORTING SERIES
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This document is available to the public through the National Technical Informa-
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CIRCULATION AND TRAJECTORY CALCULATIONS
IN THE EASTERN STRAIT OF JUAN DE FUCA
USING A CODAR SYSTEM
by
A. S. Frisch and B. L. Weber
Wave Propagation Laboratory
National Oceanic and Atmospheric Administration
Boulder, Colorado 80303
Prepared for the MESA (Marine Ecosystem Analysis) Puget Sound
Project, Seattle, Washington in partial fulfillment of
EPA Interagency Agreement No. D6-E693-EN
Program Element No. EHE625-A
This study was conducted
as part of the Federal
Interagency Energy/Environment
Research and Development Program
Prepared for
OFFICE OF ENVIRONMENTAL ENGINEERING AND TECHNOLOGY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
June 1981
w.^Hw.rv.-.-.nt-a Protection Agency
V.-r' " -V- '•• -- C'/'&i-t,, Room 1670
Chicago, II. 6GC,;4
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Completion Report Submitted to
PUGET SOUND ENERGY-RELATED RESEARCH PROJECT
MARINE ECOSYSTEMS ANALYSIS PROGRAM
OFFICE OF MARINE POLLUTION ASSESSMENT
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION
by
Wave Propagation Laboratory
National Oceanic and Atmospheric Administration
Boulder, Colorado 80303
DISCLAIMER
This work is the result of research sponsored by the Environmental
Protection Agency and administered by the National Oceanic and
Atmospheric Administration.
The National Oceanic and Atmospheric Administration (NOAA) does not
approve, recommend, or endorse any proprietary product or proprietary
material mentioned in this publication. No reference shall be made to
NOAA or to this publication furnished by NOAA in any advertising or sales
promotion which endorses any proprietary product or proprietary material
mentioned herein, or which has as its purpose an intent to cause directly
or indirectly the advertised product to be used or purchased because of
this publication.
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FOREWORD
In this report we present CODAR (Coastal Applications Dynamics Radar)
measurements in the Eastern Strait of Juan de Fuca. These measurements were
taken over a 4-day interval in 1978 and another 5-day interval in 1979. We
have estimated the mean surface flow and the semi-diurnal and diurnal compo-
nents of tidal flow. The semi-diurnal components from the two years were
combined to give a representation of the semi-diurnal flow over the areas
covered in both years. The current velocity components were included
across the radar baseline using a special interpolation technique. Finally,
we have tried to estimate areas of shoreline that would be impacted by an
oil leak from a proposed pipeline.
These measurements and calculations demonstrate the ability of CODAR to
measure the extreme complexity of the surface circulations and help in
understanding the physical oceanography of this complicated, ecologically
sensitive region.
Donald E. Barrick
Chief, Sea State Studies
Wave Propagation Laboratory
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ABSTRACT
During the summers of 1978 and 1979, the surface currents of the Eastern
Strait of Juan de Fuca were mapped with a high frequency (HF) radar system
(CODAR). This system measures surface currents over several hundred square
kilometers. During 1978, we measured currents in the vicinity of New
Dungeness Spit and Point Wilson for three days, and then moved one of the
sites to measure currents near New Dungeness Spit and Ediz Hook. In 1979, we
measured surface currents in the vicinity of New Dungeness Spit and Partridge
Point, concentrating on an area around Protection Island, a site near a pro-
posed oil pipeline.
In this study, we have used data from both years to make a composite
picture of the tidal flow over an area covered by the radar in all the
experiments. Because the area across the radar baseline in our 1979 study
is important, we have used an interpolation technique to fill in this data.
In addition, because of the potential impact from an oil leak along the path
of a proposed oil pipeline, we have simulated a continuous release of a
material and computed a trajectory for a no-wind condition.
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ACKNOWLEDGMENTS
The authors acknowledge the indispensable support ot the following
people without whom this study would not have been possible. We thank Don
Barrick for his leadership and direction before and during the experiment.
The operation and maintenance of the radar were largely due to Mike Evans,
Dan Law, Alan Carr, Karl Sutterfield, and John Forberg. These same people
designed, built, and operated the radar system that will permit oceanog-
raphers to view the sea through new "eyes."
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CONTENTS
Foreword iii
Abstract iv
Acknowledgments v
Introduction 1
Conclusions 3
Recommendations 4
Radar Operation 5
Radar Analysis 6
Results 9
Tidal Flow 9
Trajectory Calculations 9
Accuracy 10
Bibliography 11
Figures
1. Locations of radars for 1978 12
2. CODAR operating times for 1978 13
3. Radar locations for 1979 14
4. Composite tidal ellipses for 1978 and 1979 15
5a, 5b, 5c. Drifter trajectory computed from CODAR-derived
tidal and ocean surface currents 16-18
6. Impacted shore areas 19
VI
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INTRODUCTION
During the summers of 1978 and 1979, the Sea State Studies Area provided
surface current measurements, in order to understand the circulation in the
Eastern Strait of Juan de Fuca and its impact on a possible oil spill. The
need for this information has increased in the last few years because of
expanded oil tanker traffic and a proposed oil pipeline in the region. In a
report on the tidal hydrodynamics of this region, Parker (1977) points out
that the damage due to oil spills on the marine environment could be detri-
mental to the large salmon and shellfish industries, as well as to the
larger commercial fishing and recreation industries.
To predict where spilled oil will go, one needs to know the spatial and
temporal distribution of currents. The acquisition of such a data base with
conventional techniques, such as use of moored current meters or tracking
floating objects, is a formidable task that would still fall short of provid-
ing an adequate understanding in certain situations.
The CODAR system has the capability of measuring the surface current in
great detail. In addition, when these currents are separated into their
tidal, wind, and mean circulations, we gain some knowledge of the subsurface
circulation, since the tidal components are fairly constant with water depth
under many conditions. The tidal and mean flows give the background condi-
tion, upon which we can add wind effects for a more general approach to any
trajectory predictions.
During 1978, the NOAA/WPL CODAR Group was joined by other investigators
from NCAA's Pacific Marine Environmental Laboratory, Evans-Hamilton, Inc.,
and the Canadian Institute of Ocean Sciences (IDS). During this particular
experiment, both oceanographic and meteorological data were gathered for
various lengths of time. Current meter and meteorological data were col-
lected over several months; the surface current data from CODAR were col-
lected over a 4-day period. During the summer of 1979, the CODAR Group
operated independently, with no coordinated observations made by other
institutes in the radar coverage area. Most of the information obtained
during these two summers has been published (Frisch and Hoi brook, 1980;
Frisch, 1980) and will not be repeated here. This report gives details of
some further analysis of the data which:
1. Gives a composite picture of the semi-diurnal tidal flow over the
areas covered in both years, referenced to 7 July 1979.
2. Fills in some of the spatial gaps previously appearing in the tidal
flow across the radar baseline.
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3. Shows trajectory estimates and shoreline impact areas that one might
expect from an oil line leak in the vicinity of Protection Island.
In our previous reports (Frisch and Hoi brook, 1980; Frisch, 1980), we
harmonically decomposed the observed flow into mean, 12-hour, and 24-hour
tidal components. The data were taken at the Port Angeles site over only a
24-hour period, so the 24-hour component was not accurate, and we did not
include it. The 1979 data set is limited in that we had no two-dimensional
currents in part of the area of interest near the proposed pipeline, because
of the radar locations. This happens whenever the velocity measurements are
along a line between the two radars; only the component along that line from
each radar can be resolved. Since we do not have the component normal to the
line, we cannot compute the two-dimensional Cartesian velocity components in
this region directly.
Because there is a proposal to place an oil pipeline in the vicinity of
Protection Island, we computed surface trajectories with the radar data that
start at various locations along the proposed pipeline. These calculations
assume that floating material would move with the surface current, and have
no corrections for direct wind force on the object; they should be helpful
in showing how and where an oil leak might drift in the absence of wind.
These calculations illustrate that the trajectory is not only very sensitive
to the initial location of the leak, but also to the time when the trajectory
starts relative to the tidal components.
Since the radar has a fixed range, it cannot always cover the whole area
that might be affected by an oil leak; and, therefore, some trajectories must
be terminated when they reach the coverage boundary. As a result, we may be
losing some of our "hits" on the shore, since the floating material that
drifted out may have been returned into the radar coverage area by the tides
or mean flow.
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CONCLUSIONS
We used the results of two summers' observations (1978, 1979) to put
together a composite picture of the M2 tidal flow in the Eastern Strait of
Juan de Fuca and interpolated this flow across the radar baseline. In
addition, we have simulated trajectories from sources along a proposed oil
pipeline using CODAR-derived tidal and mean flow coefficients. These re-
sults show that for the three-sample source locations (1) the floating
material would hit the shore in several locations, and (2) the trajectory
is very sensitive not only to the location of the source, but also to the
time it was started relative to the tidal cycle.
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RECOMMENDATIONS
We believe that this technique is the best way to measure the spatial
distribution of surface currents. We must develop a more reliable way to
interpolate across the radar baseline where we have only one component of
velocity. In addition, higher operating frequencies and shorter range gates
should be developed to permit higher spatial resolution for the study of
small water bodies.
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RADAR OPERATION
During 1978 two CODAR units were deployed at the Eastern Strait of Juan
de Fuca. One unit operated continuously from New Dungeness Spit for 115
hours. The other unit operated first from Point Wilson for 73 hours and
then Ediz Hook for 28 hours. The locations of these radar sites and the
principal regions mapped during this year are shown in Figure 1, and the
dates and times when the data were collected are shown in Figure 2 (Frisch
and Hoi brook, 1980).
During 1979 the CODAR group deployed two units at the end of New
Dungeness Spit and at Fort Ebey on Whidbey Island (Figure 3). This set of
data were obtained 3 hours for most of the 5-day interval starting at 0130
Pacific Daylight Time on 5 July until 1200 on 10 July. Occasionally, one
hour sampling was undertaken for immediate needs.
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RADAR ANALYSIS
The radar measures the phase velocity of a six-meter ocean wave, which
is shifted by currents (Barrick et al . , 1977). This phase velocity is also
affected by dynamic wave action relative to the surface current, limiting
the accuracy of the radar-measured currents to a few centimeters per second
(Barrick and Weber, 1977; Weber and Barrick, 1977).
One of the measurement problems is the inability of the CODAR system to
measure total current velocity in the area along and adjacent to a line
between the two radars. There is no velocity data perpendicular to this
line. There are two possible ways to fill in the data between the baseline.
One is an interpolation technique developed by Leise (personal communication)
and the other is to integrate the continuity equation in polar coordinates
ignoring the vertical velocity at the ocean surface (Frisch and Leise, 1981).
One can see that if V.U = 0
expressed as
F
+ uz =
where r is the radial coordinate, 0 the azimuthal coordinate, z the vertical
coordinate and the subscripted U's are the velocity components in the direc-
tion of the subscript. If we ignore the vertical velocity, then the equation
reduces to
By placing the origin of this coordinate system at one of the radar
locations, then the U corresponds to the radial velocity component
measured by that radar", and IL is the velocity perpendicular to that radial
velocity. Thus we can integrate the equation of continuity (2) with respect
to 0 and obtain
UQ(0,r) = UQ(00,r) -
(r
(3)
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In the area outside of the baseline, we can compute UQ(9 ,r) from measurements
by both radars. We can use (3) to solve for UQ(0,r) in the area between
the baseline.
One significant potential error in this estimate results from ignoring
9U
the - — term (Eq. 1). Since the bathymetry effect of strong tidal flow on
oZ
au
could not easily be evaluated, we felt that Leise's interpolation tech-
oZ
nique could be applied with as much accuracy and was available.
Since the 1978 experiment had some data taken west of New Dungeness Spit
and we had a longer data set in 1979 for the area east of New Dungeness Spit
(and, therefore, statistically more accurate), we made a composite picture of
the M2 tidal flow by adjusting the size of the 1978 tidal ellipses based on
comparisons of the ellipses for both years in the common overlap area which
was just north of New Dungeness Spit. (The 1978 ellipses were about a factor
of two smaller than the ones for 1979 at the same location.) We then adjusted
the ellipses from 1978 to correspond to the 1979 ellipses by multiplying them
all by a constant factor of about 2.0. (It should be noted that this picture
is very qualitative because of the short sample length in 1978.)
The trajectory calculations were made using the semi-diurnal, diurnal,
and mean flow computed from our 1979 data set. We used this set because it
was the longest, had the best spatial resolution, and was taken around an
area where a proposed oil pipeline may be placed.
The position of a particle can be computed if one knows the velocity
field over the area of interest and for the time of interest. The location
is given by
x(t) = xn + /* U(x,y,t)dt
o t x
y(t) = y + / U (x,y,t)dt
where t is the time after the particle has been released (t is the release
time), and U (x,y,t) and U (x,y,t) are the two surface velocity components.
If one is interested in computing the trajectory of a particle for the mean
tidal components, these Ux(x,y,t) and U (x,y,t) would be those tidal compo-
nents.
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In our case, we used the semi-diurnal and diurnal components along with
the mean flow derived from the 1979 data for the trajectory calculations.
Data were collected from 0130 Pacific Daylight Time (PDT) on 5 July
until 1200 on 10 July. Further details of the experiment can be found in
Frisch (1980).
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RESULTS
Tidal Flow
The results presented here illustrate surface circulation patterns in
the Eastern Strait of Juan de Fuca derived from HF radar observations. Of
particular use is the calculation of the surface trajectory, based only on
tidal components and the mean flow. This type of trajectory calculation
gives the surface drift with no wind, on which we can later superimpose the
wind-driven circulation. This technique will become increasingly useful
for planning and cleanup as tanker traffic increases in the Strait of Juan
de Fuca area. The data sets were tidally analyzed by least squares fitting
the data to two dominant tidal components, namely the Kl and M2 (Holbrook
and Frisch, 1980). We display these tidal components"as ellipses, since
most people are familiar with this kind of display. The ellipses have the
advantage that a large quantity of data can be displayed in a very compact
form.
We put together a tidal model for the 12-hour component based upon
results from 1978 and 1979 (Figure 4). This model is very crude, since we
had data from only one day for the calculations of the M2 components (semi-
diurnal) west of New Dungeness Spit, and the data contained a surge event
(Frisch, Holbrook, and Ages, 1981). We did not compute a composite for the
24-hour component (Lyons and Frisch, 1980) because of the short sample and
this surge event.
Trajectory Calculations
We computed the trajectory of a surface particle at three locations in
the southern region between New Dungeness Spit and Admiralty Inlet. We
used the tidal coefficients alone, along with the mean current, to compute
these trajectories over a three-day interval to illustrate no-wind condi-
tions. The trajectories that we calculated depended not only on the initial
position, but also on when we started it.
We show an example of three trajectory calculations in Figures 5a, 5b,
and 5c having the same starting location but slightly different starting
times. The trajectory at 1100 (Figure 5a) goes west of the island. Start-
ing just one-half hour later (5b), the trajectory loops to the east of
Protection Island, and makes two loops about 2 km to the east of the pre-
vious trajectory. In the third example (Figure 5c) at 1200 we see that
initially the trajectory is similar to the trajectory at 1100, but instead
of making several complicated loops, it travels south and is displaced
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enough west that it intersects the shore. This trajectory information can
be used to show where a floating contaminant will be carried on
If we compute these trajectories over a longer time interval, we can
see the possible extent of shore contamination from a continuous source of
floating pollutants. As an example, we have taken three different locations
along a proposed pipeline route, computed trajectories in 10-minute incre-
ments from each location, and marked the area of the shore where the con-
taminants will hit. In Figure 6 we indicate three sources along the
proposed pipeline path; the shoreline areas that will be affected by a
continuous leak from each location are depicted by different degrees of
shading. The time of arrival between the release of a particle and its
arrival on shore varied between two hours and two days. If the trajectory
intersected a region near the baseline between the two radars, we stopped
the calculation because we had no two-dimensional surface current velocity
in this area, and the tentative baseline interpolation technique used here
needs more verification. Because calculation for this area stopped, we can-
not say whether the trajectory would continue away from the southern coast
or be carried back onto the southern shore.
Accuracy
The type of tidal analysis done herein has been done by Frisch and
Weber (1980), and the radar-derived tidal components have been compared with
current metered data by Hoi brook and Frisch (1980). In this comparison,
they found that current-meter-derived tidal coefficients and the HF radar
coefficients were within 10 cm/sec of each other at the Kl and M2 tidal fre-
quencies. Part of the errors in the computation of these components will be
due to the sampling (both the interval and the length), as well as to the
errors in the radar measurement.
Simulations of tidal coefficient recovery with noise present indicates
that when we take measurements for five days, the Kl and M2 components will
have only a few percent error in the amplitude and phase. Therefore, the
average magnitude of the current fluctuation errors in the coverage area is
±10 cm/sec (Lyons and Frisch, 1980).
10
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BIBLIOGRAPHY
Barrick, D. E., M. W. Evans, and B. L. Weber (1977), Ocean surface currents
mapped by radar. Science, vol. 198, pp. 138-144.
Barrick, D. E., and B. L. Weber (1977), On the nonlinear theory for gravity
waves on the ocean's surface. Part II: Interpretation and Applica-
tions. J_. Phys. Ocean., vol. 7, no. 1, pp. 11-21.
Frisch, A. Shelby (1980), HF radar measurements of circulation in the
Eastern Strait of Juan de Fuca near Protection Island (July, 1979).
NOAA/EPA Report EPA-600/7-80-129, June, 1980.
Frisch, A. Shelby, and J. Hoi brook (1980), HF radar measurements of
circulation in the Eastern Strait of Juan de Fuca (August, 1978).
NOAA/EPA Report EPA-600/7-80-096, April, 1980.
Frisch, A. S., J. Holbrook, and A. B. Ages (1981), Observations of a
summertime reversal in circulation in the Strait of Juan de Fuca.
J_. Geophys. Res., vol. 86, no. C3, pp. 2044-2048.
Frisch, A. S., and J. A. Leise (1981), A note on using the two dimensional
continuity equation for extending dual H-F radar coverage. (Submitted
to J_. Geophys. Res.)
Frisch, A. S., and B. L. Weber (1980), Tidal and mean currents and applica-
tions in the Eastern Strait of Juan de Fuca from HF radar measurements.
(To be submitted to J_. Remote Sens.)
Holbrook, J., and A. S. Frisch (1980), A comparison of HF surface current
observations with current meter measurements. (In draft)
Lyons, R. S., and A. S. Frisch (1980), Simulations of surface tidal current
calculations for HF radar applications, NOAA Technical Memorandum
ERL-WPL-61.
Parker, B. B. (1977), Tidal hydrodynamics in the Strait of Juan de Fuca -
Strait of Georgia, NOAA Technical Report NOS 69, U.S. Dept. of Commerce.
Weber, B. L., and D. E. Barrick (1977), On the nonlinear theory for gravity
waves on the ocean's surface. Part I: Derivations. J_. Phys. Ocean.,
vol. 7, no. 1, pp. 3-10.
11
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V
Vancouver Island
WASHINGTON SOUND
I -.______ >-^
REGION II
I
Strait of Juan de Fuca
\
\
\ __-
L --""
Ediz Hook 48°8' 26" N
~~<^* 123°24' 2" W
•;
i'
l\
l\
REGION I
Dungeness Spit - _ /
48° 11' 6" N ~~ •—-J
Point Wilson1
48° 8' 39" N
122° 45' 18" W
"S.
Olympic Peninsula
Figure 1. Locations of radars for 1978. The two radar units were operated from the
three indicated sites at Dungeness Spit, Point Wilson, and Ediz Hook.
Region I is the main area mapped with the Dungeness Spit/Point Wilson
site combination, and Region II is the principal area mapped with the
Dungeness Spit/Ediz Hook site combination. The latitude and longitude
of each of the sites is given next to each of the site symbols.
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Dungeness Spit
Point Wilson
Ediz Hook
200
\z.
200C
D
////// A
200C
)
L£. ( t t
1200
1500
/ ' / /)
1500
22
23
24 25
August 1978
26
27
Figure 2. CODAR operating times for 1978. Two HF Doppler radar units were
operated between 22 and 27 August 1978. One unit operated at the
Dungeness Spit site uninterrupted throughout the period. The other
unit operated successively from the Point Wilson and Ediz Hook sites,
All data collection commenced on the hour (PDT), every hour and
continued for 36 minutes.
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Eastern Strait of Juan"*"de Fuca
New Dungeness Spit
\
Protection
Island
Admiralty
Inlet
Sequim
Discovery
Bay
Figure 3. Radar locations for 1979. The location of radars for the 1979 experiment
were at New Dungeness Spit and Fort Ebey. The rectangular area indicates
the approximate coverage area for surface current measurements. The
dashed-dot line depicts the proposed oil route.
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6.0 km, 300.0 cm/s i-
New Dungeness Spit
Figure 4. Composite tidal ellipses for 1978 and 1979. This model was made by adjusting
the amplitudes of the ellipses at the common boundary, i.e., New Dungeness
Spit. This is only schematic; to do a more accurate model, data should be
taken for several days in each area of interest.
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05-JUL-79 11:00:00 Q
6 JUL 79 11: -0:00
4.00 KM |_
0.50 HR
TRUE NORTH
Dungeness Spit
Figure 5a. Drifter trajectory computed from CODAR-derived tidal and
ocean surface currents. The trajectory calculation starts
at 1100 using radar-derived tidal and mean flows. The
upper left corner indicates the times used for the calcu-
lation. Each tick mark along the trajectory is one half
hour. The small square box at the end of the trajectory
indicates the starting point. The solid line depicts the
. proposed oil pipelines.
16
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05-JUL-79
7 JUL 79
11:30:00 Q
11:30:00
14.00 KM ,
0.50 HR
TRUE NORTH t
Dungeness Spit
Figure 5b. Drifter trajectory computed from CODAR-derived tidal and ocean
surface currents. The trajectory calculation starts at 1130
using radar-derived tidal and mean flows. The upper left corner
indicates the times used for the calculation. Each tick mark
along the trajectory is one half hour. The small square box at
the end of the trajectory indicates the starting point. The
solid line depicts the proposed oil pipelines.
17
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Ob-JUL-79 12:00:00 Q
6 jUL 79 19; Q:OQ
4.00 KM
0.50 HR
TRUE NORTH
Dungeness Spit
Figure 5c. Drifter trajectory computed from CODAR-derived tidal and ocean
surface currents. The trajectory calculation starts at 1200
using radar-derived tidal and mean flows. The upper left
corner indicates the times used for the calculation. Each
tick mark along the trajectory is one half hour. The small
square box at the end of the trajectory indicates the start-
ing point. The solid line depicts the proposed oil pipelines.
18
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Dungeness Spit
4.0km
Figure 6. Impacted shore areas. Shore areas affected by trajectories
starting at A, B, and C. Solid line depicts the proposed
oil pipeline location and the various shadings the shore
area affected by each leak.
19
•d U S Government Priming Office 1981—798-455/236
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