United States
Department of
National Oceanic and
Atmospheric Administration
Seattle WA 98115
United States
Environmental Protection
Office of Environmental
Engineering and Technology
Washington DC 20460
June 1981
              Research and Development
             Circulation and
             Calculations in  the
             Eastern  Strait of
             Juan de Fuca Using a
             CODAR  System


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                     USING A CODAR SYSTEM


                 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
                    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

                       Completion Report Submitted to


                         Wave Propagation Laboratory
               National Oceanic and Atmospheric Administration
                           Boulder, Colorado  80303
     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.

     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

     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.

     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."

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


   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

     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.

     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.

     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.

     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.

                              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.

                               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
                                +    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)  -


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

the  -   term (Eq. 1).  Since the bathymetry effect of strong tidal flow on
     could not easily be evaluated, we felt that Leise's  interpolation tech-

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-

     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).


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

     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

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.


     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).

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

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.

  Vancouver Island

                              WASHINGTON SOUND
                                          I	-.______   >-^
                      REGION II
   Strait of Juan de Fuca
    \          __-
    L	--""
 Ediz Hook 488' 26" N
	~~<^* 12324' 2" W
                                      REGION I
                                         Dungeness Spit - _          /
                                         48 11' 6" N      ~~   -J
                                                                 Point Wilson1
                                                                 48 8' 39" N
                                                                 122 45' 18" W
                         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.

Dungeness Spit
Point Wilson
Ediz Hook





////// A


L. ( t t


/ ' / /)
24          25

  August 1978
     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.

         Eastern  Strait of Juan"*"de  Fuca
               New Dungeness Spit
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.

                                                              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.

 05-JUL-79  11:00:00  Q
  6 JUL 79  11: -0:00
  4.00 KM |_
  0.50   HR
             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.


      7 JUL 79
11:30:00   Q
  14.00 KM ,	
  0.50   HR
                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.

        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.

             Dungeness Spit
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.
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