OCS Study

MMS 2000-025

Environmental Studies Program

Mapping Cook Inlet Rip Tides Using Local

Knowledge and Remote Sensing

Prepared for Minerals Management Service

Contract No. 01-98-CT-30906

Prepared by

LGL Alaska Research Associates, Inc.

4175 Tudor Centre Drive, Suite 202

Anchorage, Alaska 99508

U.S. Department of the Interior

Minerals Management Service MMS Alaska OCS Region
OCS Study

MMS 2000-025

Environmental Studies Program

Mapping Cook Inlet Rip Tides Using Local

Knowledge and Remote Sensing

Contract No. 01-98-CT-30906

Prepared by:

Beth Haley1

Geoff Tomlins, Ph.D2

Orson Smith, Ph.D3

William Wilson1

Michael Link1

1LGL Alaska Research Associates, Inc.

 4175 Tudor Centre Dr., Suite 202

 Anchorage, AK 99508

2Pacific Geomatics, Ltd.

 2817-144 Street

Surrey, B.C. Canada V4P 1R4

3University of Alaska Anchorage

 School of Engineering

 3211 Providence Dr.

 Anchorage, AK 99508

Prepared for:

U.S. Department of the Interior

Minerals Management Service

Alaska Outer Continental Shelf Region

949 E. 36th Avenue, Suite 308

Anchorage, AK 99508-4363

This study was funded by the U.S. Department of the Interior, Minerals Management Service (MMS),

Alaska Outer Continental Shelf Region, Anchorage, Alaska, under Contract Number 01-98-CT-30906,

as part of the MMS Alaska Environmental Studies Program.

U.S. Department of Interior

Minerals Management Service September 2000
This report has been reviewed by the Minerals Management Service and approved for

publication. Approval does not signify that the contents necessarily reflect the views and policies of the

Service, nor does mention of trade names or commercial products constitute endorsement or

recommendation for use.
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TABLE OF CONTENTS

TABLE OF CONTENTS............................................................................................................... i

LIST OF FIGURES ..................................................................................................................... iii

LIST OF TABLES ....................................................................................................................... iv

ABSTRACT................................................................................................................................... v

1.0 INTRODUCTION................................................................................................................ 1

1.1 Objectives...................................................................................................................... 1

2.0 BACKGROUND: OCEANOGRAPHY OF COOK INLET RIPTIDES ....................... 4

2.1 Cook Inlet Water Depth................................................................................................ 4

2.2 Cook Inlet Circulation................................................................................................... 4

2.3 Cook Inlet Tides............................................................................................................ 4

2.4 Bottom Friction Effects On Cook Inlet Currents.......................................................... 8

2.5 Cook Inlet Roll Cells..................................................................................................... 8

3.0 METHODS ......................................................................................................................... 11

3.1 Local Knowledge ........................................................................................................ 11

3.1.1 Interviews........................................................................................................ 11

3.1.2 Mailings........................................................................................................... 11

3.1.3 Meetings and Publicity.................................................................................... 11

3.1.4 Workshops....................................................................................................... 12

3.2 Satellite Imagery......................................................................................................... 12

3.2.1 RADARSAT Data Collection......................................................................... 13

3.2.2 Analysis of Historical Satellite SAR Images of Cook Inlet............................ 13

3.3 Test Fishery................................................................................................................. 18

3.4 Aerial Surveys............................................................................................................. 18

3.5 Literature ..................................................................................................................... 19

4.0 RESULTS AND DISCUSSION ........................................................................................ 20

4.1 Location and Dynamics of Rip Tides......................................................................... 20

4.1.1 Qualitative Local Knowledge About Cook Inlet Rip Tide Location

and Dynamics................................................................................................... 20

4.1.2 Quantitative Information About Cook Inlet Rip Tide Location

and Dynamics................................................................................................... 23

4.2 Fishermen’s Use Of Cook Inlet Rip Tides.................................................................. 26

4.2.1 Qualitative Information About Fishermen’s Use of Cook Inlet Rip Tides..... 26

4.2.2 Quantification of Fishermen’s Use of Cook Inlet Rip Tides.......................... 27

4.3 Remote Sensing........................................................................................................... 29

4.3.1 RADARSAT Imagery..................................................................................... 29

4.3.2 Historic ERS Imagery..................................................................................... 34

4.4 Potential Conflicts Between Fishermen And Offshore Industry Development .......... 36

4.4.1 Obstacles......................................................................................................... 36

4.4.2 Discharges/Spills............................................................................................. 40
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Table of Contents Continued

5.0 COMMENT........................................................................................................................ 41

6.0 SUMMARY........................................................................................................................ 42

6.1 Rip Tide Location........................................................................................................ 42

6.2 Fishermen’s Use of Rip Tides..................................................................................... 42

6.3 Potential Conflicts with Oil and Gas Industry Development...................................... 42

7.0 ACKNOWLEDEMENTS.................................................................................................. 43

8.0 REFERENCES................................................................................................................... 44

LIST OF APPENDICES............................................................................................................. 45
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LIST OF FIGURES

Figure 1 NOAA Chart #16013 showing Cook Inlet driftnet fishery boundaries in

Cook Inlet, Alaska....................................................................................................2

Figure 2 Major rip tides (frontal zones) in lower Cook Inlet, Alaska ....................................3

Figure 3 Water depths in fathoms in Cook Inlet, Alaska .......................................................5

Figure 4 Water circulation patterns in Cook Inlet, Alaska .....................................................6

Figure 5 Cotidal lines in Cook Inlet, Alaska and surrounding areas......................................7

Figure 6 Corange lines for Cook Inlet, Alaska and vicinity...................................................7

Figure 7 Graphic depiction of the properties of a possible “rip tide” in Cook Inlet...............9

Figure 8 Driftnet fishery area with highlighted 10-fathom contours and 50-fathom

hole, Cook Inlet, Alaska.........................................................................................22

Figure 9 Synthetic aperture radar (ERS-1) image of Kalgin Island in central

Cook Inlet, Alaska on 22 July 1994.......................................................................24

Figure 10 Synthetic aperture radar (ERS-2) image of Kalgin Island in central

Cook Inlet, Alaska on 30 August 1998..................................................................25

Figure 11 RADARSAT images of lower Cook Inlet collected between 28 June and

26 July 1999...........................................................................................................31

Figure 12 Synthetic aperture radar (RADARSAT EH-3) image of central Cook Inlet,

Alaska between Chisik Island and Anchor Point on 28 June 1999........................32

Figure 13 Boat positions and RADARSAT imagery, 28 June 1999 fishery opener,

Cook Inlet, Alaska..................................................................................................33

Figure 14 West rip tide during mid-flood tide off Kalgin Island July 1997 and

August 1999 Cook Inlet, Alaska ............................................................................35

Figure 15 Maximum east and west boundaries of interpreted west rip lines at all tide

stages from ERS synthetic aperture radar images of Cook Inlet, Alaska from

1992–1999..............................................................................................................37

Figure 16 Maximum east and west boundaries of interpreted middle and east rip tide

lines at all tide stages from ERS synthetic aperture radar images of

Cook Inlet, Alaska from 1992–1999......................................................................38

Figure 17 ERS synthetic aperture radar image lines of rip tides interpreted as other than

the west, middle, or east rip tides Cook Inlet, Alaska from 1992–1999................39
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LIST OF TABLES

Table 1 Operating parameters, RADARSAT and ERS.......................................................12

Table 2 RADARSAT acquisitions from satellite overflights of Cook Inlet, Alaska,

Summer 1999 .........................................................................................................14

Table 3 ERS scenes and tide conditions..............................................................................16

Table 4 Test fishery observations of velocity difference within Cook Inlet rip tides.........21

Table 5 Percent of fishermen recording observations of Cook Inlet rip tides per

total fish delivery during satellite overpasses........................................................23

Table 6 Weather conditions reported by fishermen on the grounds during aerial

surveys, Cook Inlet, Alaska....................................................................................26

Table 7 On-ground observations of Cook Inlet rip tides from data forms on

28 June 1999 during the commercial fishery.........................................................28

Table 8 Percent of time fishermen spent fishing in or adjacent to rip tides in Cook

Inlet, Alaska during six, 12-hour fishery openers in June and July 1999..............28

Table 9 ERS images used to map rip lines..........................................................................30
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ABSTRACT

Rip tides are strong tidal currents that occur where marine water masses converge or

diverge. Commercial drift gillnet salmon fishermen in Cook Inlet, Alaska, often focus their

fishing effort on rip tides, because salmon are known to concentrate in these areas. Offshore oil

development in Cook Inlet poses potential conflicts with the salmon driftnet fishery because

drilling rigs could create obstacles and spilled contaminants may converge and submerge along

rip tides. Because of this, Cook Inlet fishing groups have asked the Minerals Management

Service (MMS) to exclude Cook Inlet rip tide areas from upcoming oil and gas leases.

The objectives of this study were to map rip tides in Cook Inlet, provide statistics on the

consistency of rip tide locations, and develop an information base on fishermen’s use of rip tides

that could help the MMS avoid conflicts between local fishermen and future offshore oil industry

activities. Local knowledge was obtained from fishermen on the location and use of rip tides

within Cook Inlet. The locations of rip tides also were interpreted and mapped using satelliteborne Synthetic Aperture Radar (SAR) imagery. During the summer of 1999, the Canadian

Space Agency’s RADARSAT 1 satellite was programmed to image the study area during

commercial gillnet openers in Cook Inlet. These image data were simultaneously ground-truthed

with the help of local fishermen and aerial surveys to document both the fishermen’s use of rip

tides and the ability of satellite radar imagers to map rip tide locations. Historic radar imagery

collected by the European Radar Satellites (ERS-1 and ERS-2) between 1992 and 1999 were also

examined to determine the consistency of Cook Inlet rip tide locations at different tide stages

among years.

The results of this work were entered into a database, interpreted, summarized, and

presented to scientific and local stakeholder audiences. Several rip tides consistently appear

along the longitudinal axis of lower Cook Inlet. A west rip tide and a combined middle and east

rip tide were noticeable on the SAR images analyzed. Fishermen verified the persistent presence

of these rip tides, and reported that they often fish along rip tides where salmon may concentrate.

Thus, any future offshore oil and gas development in Cook Inlet should consider these rip tide

locations and their use by fishermen.
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1.0 INTRODUCTION

Cook Inlet, Alaska is an approximately 340-kilometer (km) extension of the Gulf of Alaska

that contains an important commercial driftnet salmon fishing industry (Figure 1). Because of

Cook Inlet’s importance to the Alaska economy, the U.S. Department of Interior, Minerals

Management Service (MMS) contracted with LGL Alaska Research Associates, Inc. to map the

location and variability of rip tides in Cook Inlet, Alaska (Figure 2). The particular emphasis of

the study was to use both local knowledge and remote sensing to examine rip tides in the portion

of Cook Inlet used by the driftnet salmon fishery.

Rip tides are strong tidal currents that occur where water masses converge or diverge. Cook

Inlet is characterized by extreme tidal fluctuations of up to 12.2 meters (m) (National Oceanic

and Atmospheric Administration—NOAA 1999) that produce strong currents in excess of 8

knots (Tarbox and Thorne 1996). The convergence and divergence of different water masses

(generally, southward-flowing low-salinity water and westward-intruding sea water) create

robust rip tides in Cook Inlet. A map of approximate locations of Cook Inlet rip tides was

generated in 1977 based on interviews with local fishermen, pilots, and other people with

experience in the Inlet (Burbank 1977). This map was produced before geographical information

systems (GIS) or global positioning systems (GPS) were available (Figure 2). This map was part

of the historic database available prior to initiating the present study.

The Cook Inlet salmon driftnet fishery is of great importance to the local and state economy.

The annual catch of salmon by the driftnet fleet between 1990 and 1997 averaged $23.3 million

(Commercial Fisheries Entry Commission web site), and deliveries during the 1998 and 1999

seasons were estimated to be worth $5.3 and $13.2 million, respectively (Jeff Fox, Alaska

Department of Fish and Game, Cook Inlet Commercial Fishery Management Biologist, pers.

comm., 13 January 2000). Cook Inlet drift gillnet fishermen often focus their effort at rip tides

because salmon are known to concentrate in these areas.

The three nautical-mile boundary that separates state from federal waters delineates the

areas of State of Alaska jurisdiction (within three nautical miles of shore) from MMS jurisdiction

(three or more nautical miles offshore) (Figure 1). The MMS is responsible for permitting oil

and gas exploration and development beyond the three nautical-mile boundary.

The possibility of offshore oil and gas industry development in Cook Inlet poses potential

conflicts with the salmon driftnet fishery. Construction of stationary drilling rigs could create

obstacles where fishermen typically fish. Oil and gas exploration and development and

production facilities would add possible sources of contaminants to existing sources, i.e.,

commercial vessels and other boats. There is a possibility that spilled contaminants may

concentrate along rip tides. Because some Cook Inlet fishermen fish predominantly along rip

tides, they have requested that the MMS consider excluding rip tide locations from future lease

sales to avoid interference with the fishery.

1.1 Objectives

The objectives of this study were to: (1) quantify the spatial and temporal variability of rip

tide locations; (2) determine the locations of rip tides used by the fishing fleet; and (3) collate

information on fishery use of rip tides and identify potential conflicts between fishermen and the

oil and gas industry.
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Figure 1. NOAA Chart #16013 driftnet fishery boundaries (water depths in fathoms) in Cook Inlet,

Alaska. One fathom equals 1.8 meters. The three nautical-mile boundary within the

commercial salmon fishery zone indicating the separation of State and Federal waters is

shown. Note: the boundary of the Territorial Sea extends near Ninilchik through southern

Kalgin Island to Harriet Point.
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Figure 2. Historic map of major rip tides (frontal zones) in lower Cook Inlet, Alaska (Burbank

1977). The dashed lines indicate where the rips are weak or obscure. The bathymetry

shows only the 10-fathom (20 m) contour. One fathom equals 1.8 meters.
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2.0 BACKGROUND: OCEANOGRAPHY OF COOK INLET RIPTIDES

According to drift gillnet fishermen, rip tides are bands of strong currents delineated by

chaotic surface roughness, slicks, or lines of flotsam. Three oceanographic processes are

probably associated with the presence and behavior of rip tides, or currents, in Cook Inlet. These

include tides, wind-induced surface motion, and variations in seawater density. Any or all of

these processes may influence generation of the rip tides and their surface signatures.

2.1 Cook Inlet Water Depth

All three oceanographic processes are affected by average water depth, which generally

increases from north to south in Cook Inlet (Figure 3). Upper Cook Inlet, between Fire Island

and the Forelands, has an average depth of approximately 18.3 m. Central Cook Inlet, from the

Forelands to Kachemak Bay, has an average depth of about 27.4 m. The average depth from

Kachemak Bay to the Barren Islands (inlet mouth) is approximately 36.6 m. Also notable are the

constrictions caused by islands and prominences at the Barren Islands, Augustine Island, Homer

Spit (mouth Kachemak Bay), Kalgin Island, the East and West Forelands, Middle Ground Shoal

(just north of the Forelands), and Fire Island at the confluence of Knik and Turnagain Arms.

2.2 Cook Inlet Circulation

The general circulation pattern of lower and middle Cook Inlet is that denser, saltier water

flows northward along the east shore and fresher, silty outflowing water flows southward along

the west shore (Burbank 1977; Wapora Inc. 1979; Figure 4). The lower Inlet, including outer

Kachemak Bay, has a “salt wedge” system characterized by incoming salty Gulf of Alaska water

that lies below buoyant outgoing water freshened by runoff from tributaries. These patterns

overlay tidal currents that reverse in the upper Inlet and become increasingly elliptical (rotating

in direction) in the middle and lower Inlet. The average location of the east, west, and middle rip

tides are noted in Figure 4.

2.3 Cook Inlet Tides

Cook Inlet rip tides are primarily driven by tides, since they follow the reverse direction

pattern of rising and falling water levels. The speed with which rip tides move along the surface

is proportional to the range of tide heights. Daily changes in tidal ranges, termed diurnal

inequality, are due to the moon’s declination from the plane of the equator during its orbit around

the earth. Complex interactions between the earth-moon and sun-earth astronomical systems are

magnified in Cook Inlet, making it extremely difficult to predict tide levels.

Tides wash in and out of the Cook Inlet basin like a very long wave. Fluid motion on this

large scale is affected by the rotation of the earth, causing incoming currents in Cook Inlet to

veer toward the east coast and outgoing currents to veer to the west coast. Because incoming

currents have more energy, tidal ranges on the east shore are generally larger than those on the

opposite shore. In the deeper, broader areas of the lower Inlet, the tidal current changes

directions in an elliptical pattern, known as rotary tides.

Cotidal lines are lines along which the phase of the tide is equal (i.e., high tide occurs at the

same time). Cook Inlet cotidal lines from concurrent coastal water level measurements,

generally run east-west directly across the waterway (Figure 5). Cook Inlet fishermen

commented in meetings for this project that they observed differences in tide phase between the
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Fire

Island

Augustine

Island

Barren Islands

Figure 3. Water depths in fathoms in Cook Inlet, Alaska (Sharma and Burrell 1970).

One fathom equals 1.8 meters.

Middle

Ground Shoal

Kalgin Island

Homer Spit
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East Riptide

West Riptide

Middle Riptide

Middle Riptide

Figure 4. Water circulation patterns in Cook Inlet, Alaska (Wapora Inc. 1979).
Figure 5. Cotidal lines for Cook Inlet, Alaska (graphics provided by Center For Operational

Oceanographic Products and Services [CO-OPS]/NOAA).

Figure 6. Corange lines for Cook Inlet, Alaska (graphics provided by CO-OPS/NOAA).
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center of the Inlet and the opposite eastern shore. These observations are as yet unverified by

measurements.

Corange lines, along which the tidal range is equal, are not parallel to cotidal lines in Cook

Inlet. Ranges on the east shore are considerably higher than those on the opposite west shore

(Figure 6). Ranges on both sides of the Inlet increase northward, reaching a 9.1-m daily range at

Anchorage with recorded spring tide extremes in excess of 12.2 m (NOAA 1999). In summary,

tides in Cook Inlet are extraordinarily complex and energetic, dominating all other

hydrodynamic forces in the waterway. Though other forces, such as wind, waves and ice, may

affect the detection of rip tides, tidal forces drive rip tides.

2.4 Bottom Friction Effects On Cook Inlet Currents

Measurements of currents in upper Cook Inlet have revealed that bottom friction influences

the speed and alters the direction of tidal currents (USACE 1993, 1996). Currents are slowed

and veered several meters above the bottom. In this way, friction created by sloping inlet banks

and shoals steer tidal currents. These trends are particularly notable when an acoustic Doppler

current profiler measures continuous profiles of currents. A bottom boundary layer several

meters thick tends to reverse direction before surface tidal currents. High sediment

concentrations near the bottom may also affect the balance of friction forces. Recent multi-beam

hydrographic surveys of central Cook Inlet reveal large sand dunes on the bottom with heights

on the order of 2 m (unpublished charts by Terra Surveys, Ltd. and Racal Pelagos, Inc. under

contract to NOAA). These bed forms appear in constricted areas and in the vicinity of rip tides.

Their presence is indirect evidence of vertical shear extended several meters above the bottom.

2.5 Cook Inlet Roll Cells

Observations from fishermen, scientists, and satellite imagery interpretation suggests that

horizontal current speeds in Cook Inlet have large and frequent fluctuations, routinely near banks

and shoals. These fluctuations create zones of divergence marked by upwelling that appears to

boil on the water surface. Upwelling currents on one side of a rip tide exaggerate the upward

motion of wind-generated surface waves, creating a steep random chop at the water surface. The

choppiness on the small scale of capillary waves appears bright on a SAR satellite image.

Parallel zones of downwelling occur on the opposite side of a rip tide, causing surface slicks

(smooth water surface) and lines of flotsam. Slicks appear dark on SAR images. Both the

choppy and slick types of surface signatures are associated with rip tides in Cook Inlet,

indicating vertical circulation in the form of spiraling roll cells. Water spirals across the strong

surface current from upwelling to downwelling zones. The spiral is completed beneath the

surface from downwelling to upwelling zones. Figure 7 is a visualization of this concept of

circulation associated with rip tides in Cook Inlet. This explains patterns observed at the surface.

A phenomenon with similar behavior, known as Langmuir circulation, can be induced by

steady wind friction on the water surface. Parallel lines of foam and floating debris, known as

“windrows,” are common sights on a windy water surface from an airplane. These lines of

flotsam are oriented along the direction of the wind and maintain themselves because buoyant

matter is drawn together at zones of convergent downwelling.

Linear slicks are also associated with downwelling induced by internal waves propagating

along a density layer beneath the surface. The upper layer of water is forced to converge ahead of
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the crest of the undulating density interface below. Slow moving surface slicks are observed to

move parallel to wave crests of internal waves as they slowly advance along a thermocline

(temperature layer) or halocline (salinity layer) beneath the surface.

These two more commonly observed ocean phenomena have similar surface signatures due

to vertical circulation. Future studies of Cook Inlet rip tides would be more revealing if they

involve measurements of both vertical and horizontal currents. Shipboard acoustic Doppler

current profiler (ADCP) measurements could accomplish this.
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3.0 METHODS

The following methods were used to map rip tides in Cook Inlet: (1) gathering “local

knowledge” from Cook Inlet drift gillnet salmon fishery stakeholders; (2) ground–truthing

contemporary satellite images to develop an accurate method of identifying rip tides and

examining remote sensing images of the Inlet for rip tides; (3) obtaining information from the

Alaska Department of Fish and Game’s (ADF&G) test fishery regarding the occurrence of rip

tides in Cook Inlet throughout July 1999; (4) conducting aerial surveys of Cook Inlet to locate

potential rip tides and reviewing historical ADF&G surveys of the salmon fishery; and

(5) conducting a literature search for Cook Inlet rip tide information. Also, public testimony

regarding possible offshore development in Cook Inlet was reviewed for fishermen’s concerns.

3.1 Local Knowledge

Communications with Cook Inlet stakeholders provided critical information (i.e., local

knowledge) on the location of rip tides and on identifying the surface signatures of rip tides. In

addition, local fishermen collected GPS locations of rip tides that allowed satellite imagery to be

correlated to surface information (ground-truthed). Data concerning the rip tides were collected

by means of interview sessions, mass-mailings, a public outreach initiative, and a workshop with

driftnet fishermen.

3.1.1 Interviews

Twenty-seven phone interviews with Cook Inlet driftnet fishery shareholders were

conducted from late April through June 1999 (Appendix A). Personal interviews were

conducted with 13 of the stakeholders on the Kenai Peninsula. During interviews, the following

four topics were discussed: (1) Cook Inlet rip tide dynamics; (2) fishermen’s use of rip tides and

their adjoining waters; (3) potential conflicts between Cook Inlet fishermen and future offshore

oil and gas industry activity; and (4) opportunities for fishermen to contribute to ground-truthing

satellite data. This information was used to develop our field sampling approach and

interpretation.

Cook Inlet driftnetters indicated that they typically use nets that are three shackles (274.3 m)

long. Fishermen suggested that they could be “working” a rip tide anywhere within a distance of

926 m (0.5 nautical miles—or 3.4 net lengths) from a rip tide. That standard was employed

when analyzing fishing proximity to rip tide data. The 926-m (0.5 nm) distance was broken

down into three categories: (1) in the rip tide, (2) less than or up to 463 m (0.25 nm) from the rip

tide, and (3) between 463 m and 926 m from a rip tide.

3.1.2 Mailings

In addition to direct communication with driftnet fishery stakeholders, brochures describing

the rip tide project and its purpose were mailed to all (575) active Cook Inlet driftnet salmon

fishery permit holders. The mailings appealed to fishermen to contribute to the project.

3.1.3 Meetings and Publicity

Study personnel attended the United Cook Inlet Drifter’s Association (UCIDA) annual

meeting in June 1999 to present the rip tide project to Cook Inlet fishermen and request their

help with the project. Public Service Announcements were printed in the Kenai Peninsula
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newspapers, the Peninsula Clarion and the Homer News, regarding the project and the project

team’s attendance at the UCIDA meeting (Appendix B1, B2).

3.1.4 Workshops

A workshop was conducted with Cook Inlet driftnet salmon fishery stakeholders to present

preliminary findings on 8 November 1999. The purpose of the workshop was to review and add

to the local knowledge the study team had gathered from fishermen during the 1999 fishing

season. A total of 37 people participated, including fishermen, municipal, borough and industry

representatives, and scientists. A final workshop was held 6 March 2000 during which we

reviewed our findings with nine attendees.

3.2 Satellite Imagery

Satellite-borne SAR technology was used to provide remote sensing imagery of Cook Inlet.

This method had the following advantages: (1) a large area could be surveyed, (2) data were

available for several years, and could be collected at different tidal stages, (3) acquisition of data

was not affected by weather conditions, and (4) the imagery from this technology was relatively

inexpensive.

Radar imagery can be collected day and night and in all weather conditions and there is an

archive of images for the Cook Inlet area dating back to 1992. Two types of SAR satellite

images were examined, those from the European Radar Satellites ERS-1 and ERS-2 and those

collected by the Canadian Space Agency RADARSAT 1 satellite. Both ERS and RADARSAT

measure radar returns in the C-band (5.6 cm wavelengths), but they differ in polarization and

incidence angle (Table 1). The steep viewing angle and vertical polarization of ERS radar is

sensitive to surface roughness and was designed to gather information about ocean water

conditions, including subtle surface water features. RADARSAT imagery is more efficient at

detecting point sources, such as fishing vessels, due to horizontal polarization and shallower

viewing angles. Consequently, rip tides are more likely to be detected using ERS images,

whereas RADARSAT is better suited to vessel detection. Depending on the operating mode,

RADARSAT images may also show pronounced rip tides and thus document both the rip tide

and any vessels in its vicinity.

Table 1. Operating parameters, RADARSAT and ERS.

Parameter RADARSAT ERS

Altitude (km) 793–821 km 780–785 km

Period (min) 101 minutes 100 minutes

Orbits/day ~ 14 ~ 14

Revisit cycle (days) 24 days 35 days

Wave length C Band, 5.66 cm C Band, 5.66 cm

Polarization HH VV

Incidence Angle 20–60 degrees 20–26 degrees

Swath 50–500 km 100 km

Range resolution ~ 10-100 m ~ 30 m
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3.2.1 RADARSAT Data Collection

One objective of the project was to confirm that rip tides interpreted from satellite radar

were in fact rip tides as classified by Cook Inlet fishers, or to “ground-truth” the satellite

imagery. Because the RADARSAT satellite may be programmed to operate in multiple beam

modes and at different viewing angles, the same region of Cook Inlet could be repeatedly

surveyed at frequent intervals. These capabilities allowed us to ensure fishermen were on the

water when the RADARSAT satellite was collecting images overhead.

The Canadian Space Agency (CSA), owner of the RADARSAT 1 satellite, programmed the

satellite to image Cook Inlet during the 1999 driftnet fishery openers (Table 2). To obtain

appropriate coverages, beam mode and viewing angle were adjusted differently for each fishery

opener. Also, RADARSAT had not previously been used for the detection of rip tides, or small

(10 to 15 m) fishing boats, so no prior information was available with which to establish

appropriate settings.

The ground-truth program in this study was designed to collect as much locational data as

possible at or near the time of the scheduled RADARSAT overpasses. Members of the Cook

Inlet driftnet fishery were asked to log their locations during five of the seven scheduled passes

over Cook Inlet (Table 2). Data sheets, in the form of self-addressed, stamped post cards, were

mailed along with brochures in the mass mailing to Cook Inlet fishermen for this purpose

(Appendix C). We asked fishermen to record their GPS positions, their proximity to any rip tide,

and weather conditions during the time of the five satellite overpasses. Nine fishermen offered

to assist the project beyond recording data once per opener. The study team asked those

fishermen to provide the same information at hourly intervals throughout six, 12-hour openers

(the 22 July opener was added), between 7:00 a.m. and 7:00 p.m.

In addition, LGL personnel were on board a commercial fishing boat and a private vessel

during the first two openers (28 June and 1 July 1999) to record coordinates of rip tide locations.

These data were added to the rip tide location information from fishermen. GPS locations of rip

tides recorded by fishermen and study team personnel were entered into a database for

comparison with the satellite imagery.

3.2.2 Analysis of Historical Satellite SAR Images of Cook Inlet

ERS satellite images of North America are archived at the Alaska SAR Facility (ASF) at the

University of Alaska Fairbanks. A visit to the ASF was made to select appropriate ERS imagery

archived since the satellite was launched in 1992. Photographic imagery for ERS-1 was

available for the years 1992–1995.

ERS digital data are available as either “Full-Resolution” or “Low-Resolution” data. The

“Full-Resolution” data are processed by ASF to 8-bit data (256 grey levels) at 12.5-m cell size.

The standard scene is 100 km by 100 km, and the digital scene is 64 megabytes (mb) in size.

The “Low-Resolution” data have a pixel spacing of 100 m, and are about 1 mb each in size.

We examined 247 separate images of lower Cook Inlet acquired on 69 separate dates

between 14 May 1992 and September 1995. For each date, there was a minimum of one and a

maximum of three consecutive images that imaged part of the study area. We identified 26 dates

in the 1992–1995 period during which linear features (possibly rip tides) were evident in the
RADARSAT Ascending

Local Incidence or Range Azimuth

Acquisition Angle Descending Resolution Resolution No. Aerial

Date Fishery Time Beam Mode (mid) Orbit (m) (m) Scenes Survey Comments

*990628 District wide 7:07 XH EH-3 53.1 D 25 28 2 Yes Good coverage West

and Mid Rip areas.

*990701 District wide 7:19 N2 W-2 38.5 D 100 100 2 No Overview - water is

uniformly black.

*990705 District wide 7:03 XH EH-3 53.1 D 25 28 2 Yes Good coverage East 

and Middle Rip areas.

*990708 District wide 18:44 SB S-4 36.5 A 25 28 2 Yes Good coverage of 

both coastlines.

990712 Western, S. of Redoubt Pt. 6:59 XH EH-4 55.5 D 25 28 3 No Good coverage,

Excessive range ambiguities

990712 Western, S. of Redoubt Pt. 6:59 FB F-4 44.7 A 9 9 3 No Mostly Land on

Kenai Peninsula.

*990715 District wide 18:39 WB W-2 35.1 A 27 28 2 Attempted Good coverage East 

and Middle Rip areas.

990722 Inside 3 miles only 7:07 XH EH-3 53.1 D 25 28 3 No Good coverage West 

and Mid Rip areas.

990722 Inside 3 miles only 18:35 SB S-2 27.7 A 25 28 1 No Restricted coverage Kalgin

 Island and north.

990726 no fishery 7:07 XH EH-6 58.1 D 25 28 3 No Mostly over Kenai Peninsula.

* Indicates dates of commercial fishery openers during which Cook Inlet driftnet fishermen were asked to record location, proximity to rip tide, and weather 

conditions during the RADARSAT overpass.

Table 2. RADARSAT acquisitions from satellite overflights of Cook Inlet, Alaska, Summer 1999. Beam modes include N2 (ScanSAR mode), 

XH (extended high beam mode), W (wide beam mode), S (standard beam mode), and F (fine beam mode). Incidence angle ranges within a beam 

mode are shown as -2,-3,-4. 
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ASF images. The images were ranked both by extent of coverage of the study area, as well as the

definition of linear features in the surface waters of the Inlet. We subsequently acquired lowresolution digital images for each of those dates.

Thirteen of the 26 dates evidenced both good coverage of the study area and good definition

of linear hydrological features. Full-resolution images of these dates were also acquired and

processed for extraction of rip tide information.

Photographic Quick-Looks or preview images were not produced for ERS acquisitions after

1995. We therefore checked ERS scene coverage over Cook Inlet for every orbit collected June

through September for the years 1996 through 1999. Low-resolution images were ordered for

those orbits on which Kalgin Island was imaged.

Table 3 lists the 61 dates for which ERS imagery was acquired over Cook Inlet.

3.2.2.1 Digital Processing of Full-Resolution Data

Fifteen full-resolution ERS scenes collected on 13 dates in the period 1992–1995 were

processed to aid in the extraction of information about rip tide dynamics in Cook Inlet. The

following processing steps were applied to each scene:

1. Data rotation/mirroring to correct scene orientation.

2. Geometric rectification and projection to Universal Transverse Mercator grid using U.S.

Geological Survey digital raster graphics or Ground Control Points acquired from

previously-rectified SAR images.

3. Spatial filtering for reduction of SAR noise.

4. Custom Look-Up Table for enhancement of surface water features.

The rectified and enhanced images were investigated for the presence or absence of a rip

tide. This information was compared with the tidal stage at the time of the image acquisition.

3.2.2.2 Digital Processing of Low-Resolution Data

During analysis of the 1992–1995 imagery at both full (12.5 m) and low (100 m)

resolutions, we determined that the lower resolution data were equally useful for delineating and

mapping rip tides. For reasons of efficiency we therefore decided to utilize only the lowresolution data in future work:

1. The low-resolution images were much cheaper, allowing the acquisition of additional

images from the ASF archive.

2. Digital processing times would be reduced from about 8 hours per scene for fullresolution data to about 2 hours per scene for the low-resolution imagery.

3. The cost and time savings would increase the number of images analyzed, improving the

ability to statistically evaluate different factors that might affect rip tide locations.

Forty-eight low-resolution ERS images were subsequently digitally processed (Table 3).

Each image was rotated, rectified, and contrast enhanced. It was not necessary to filter the

images for noise due to the averaging effect of reduced resolution. Image features that were

interpreted as possible rip tides were extracted by tracing the cursor over the feature of interest

and saving the traced linework as polylines. This method is commonly known as “Heads Up
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Table 3. ERS scenes and tide conditions. ADT = Alaska Daylight Time.

Scene

ID Image

Full (F) or

Low (L)

Resolution

(A)scend

or (D)esc

ERS

Acquistn

ADT

High

Tide

ADT

Low

Tide

ADT

High

Tide

ADT

ERS Tide

Height at

Ninilchik

FT

Time from

start of

Flood Tide

Time from

start of

Ebb Tide

1 920514 L D 13.22 8.68 14.70 5.62 4.53

2 920602 L D 13.27 11.17 17.35 (4.49) 2.10

3 920618 L D 13.22 12.32 18.53 0.04 0.90

4 920621 F D 13.32 7.50 14.12 7.61 5.82

5 920703 L A 0.02 (6.20) (0.05) 1.85 6.22

6 920723 F D 13.22 9.75 15.63 11.99 3.47

7 920726 F D 13.32 7.47 13.73 10.14 5.85

8 920827 L D 13.23 9.55 15.55 1.21 3.68

9 920830 F D 13.32 11.60 17.47 (2.44) 1.72

10 920915 F D 13.28 11.87 17.57 2.82 1.42

11 930502 L D 13.32 7.10 12.93 14.01 6.22

12 930518 F D 13.27 8.52 14.43 7.51 4.75

13 930606 L D 13.32 11.57 17.75 (3.73) 1.75

14 930622 F D 13.27 11.93 17.42 (2.95) 1.33

15 930727 L D 13.27 10.82 16.75 14.46 2.45

16 930815 F D 13.32 8.53 14.67 6.90 4.78

17 930916 L D 13.22 10.12 15.97 (0.16) 3.10

18 940526 L D 13.28 11.13 17.28 (5.74) 2.15

19 940702 F D 13.30 11.18 17.18 12.86 2.12

20 940722 F D 13.25 9.97 16.10 (1.43) 3.28

21 950527 L D 13.22 9.30 15.32 3.22 3.92

22 950615 L D 13.27 11.93 18.10 (4.71) 1.33

23 950720 F D 13.27 10.35 16.43 13.30 2.92

24 950808 L D 13.32 8.32 14.48 7.37 5.00

25 950824 F D 13.27 9.38 15.38 4.14 3.88

26 950912 L D 13.32 12.07 17.88 1.46 1.25

27 950924 F A 0.02 (2.32) 3.47 3.09 2.33

28 960615 L A 0.07 (2.55) 3.13 6.17 2.62

29 960619 L D 13.32 12.38 18.52 0.45 0.93

30 960705 L D 13.28 6.82 13.48 3.59 6.47

31 960720 L A 0.07 (5.43) 0.85 6.39 5.50

32 960721 L D 13.23 7.15 13.67 6.62 6.08

33 960724 L D 13.33 10.12 16.22 12.91 3.22

34 960824 L A 0.07 (5.57) 0.13 17.20 5.63

35 960825 L D 13.23 7.33 13.50 11.95 5.90

36 960828 L D 13.32 9.82 15.83 (0.28) 3.50

37 960913 L D 13.28 10.50 16.35 0.82 2.78

38 970604 L D 13.32 9.72 15.77 (0.32) 3.60

39 970706 L D 13.22 11.08 17.18 (2.53) 2.13

continued
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Table 3 (continued). ERS scenes and tide conditions. ADT = Alaska Daylight Time.

Scene

ID Image

Full (F) or

Low (L)

Resolution

(A)scend

or (D)esc

ERS

Acquistn

ADT

High

Tide

ADT

Low

Tide

ADT

High

Tide

ADT

ERS Tide

Height at

Ninilchik

FT

Time from

start of

Flood Tide

Time from

start of Ebb

Tide

40 970718 L A 0.00 (3.67) 1.97 11.43 3.67

41 970720 L A 0.02 (2.08) 3.56 3.92 2.10

42 970806 L A 0.00 (6.45) (0.18) 2.81 6.45

43 970810 L D 13.23 8.17 14.43 10.00 5.07

44 970813 L D 13.32 11.95 17.80 13.27 1.37

45 970914 L D 13.22 8.25 14.33 9.10 4.97

46 980726 L D 13.22 12.15 18.20 (0.95) 1.07

47 980729 L D 13.32 7.47 13.95 7.92 5.85

48 980830 L D 13.30 9.68 15.63 12.47 3.62

49 980922 L D 13.32 11.15 16.93 0.38 2.17

50 990602 L A 0.00 (6.15) (0.15) 4.60 6.15

51 990606 L D 13.22 8.42 15.25 10.32 4.80

52 990609 L D 13.32 12.17 18.52 14.47 1.15

53 990620 L A 0.02 (1.97) 4.42 14.60 1.99

54 990621 L A 0.02 (2.05) 4.60 16.16 2.07

55 990710 L A 0.07 (4.93) 0.88 15.88 5.00

56 990711 L D 13.22 8.88 15.00 3.74 4.33

57 990714 L D 13.32 11.23 17.35 4.26 2.08

58 990811 L A 0.00 (2.30) 3.43 4.09 2.30

59 990815 L D 13.22 6.32 13.47 2.72 6.90

60 990818 L D 13.32 8.65 14.87 11.44 4.67

61 990830 L A 0.02 (6.27) 0.18 1.77 6.28

 Dates for which high resolution images acquired and processed 13

 Dates for which low resolution images acquired and processed 48
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Digitizing.” Automatic feature extraction, using an edge-filter and raster-to-vector process,

generated either too many lines and artifacts or insufficient detail to be useful for our purpose.

We found manual digitizing to be more accurate and much faster.

Interpretation Keys

During the preliminary work, a set of Interpretation Keys was developed to help identify rip

tides. Many of the SAR images show water surface features in lower Cook Inlet that may be

caused by factors other than rip tides including water depth, currents, salinity changes, or local

weather conditions—particularly near-surface winds.

The following four Interpretation Keys were initially used: (1)location—between the Forelands and Iniskin Peninsula (Figure 1) to cover the driftnet fishing grounds; (2) linearity—

longitudinal, parallel to the coastline in NNE-SSW direction; (3) length—several tens of miles in

extent; and (4) persistence—feature should be present in other images.

These criteria were later modified after the 8 November 1999 workshop, when Cook Inlet

fishermen stated that

1. rip tides can appear anywhere in lower Cook Inlet,

2. rip tides can be less than a mile long, and

3. rip tide orientation is generally NNE-SSW, but small rip tides can also appear running

E-W across the Inlet.

Consequently, interpretation of rip tides was expanded to include linear features as little as a

mile in length, and those of any orientation. Also the “persistence” interpretation key was

discarded.

3.3 Test Fishery

Information on rip tide locations was collected from ADF&G during their July 1999 test

fishery (a contracted fishing vessel fishes short time periods in specific locations to “test” the

strength of the salmon run entering Cook Inlet). The vessel captain conducting the test fishery

collected data on rip tide location, time, and weather conditions on a daily basis during July

1999. These data were checked for temporal coincidence with 1999 fishing season RADARSAT

images and then examined for locational coincidence with rip tides evident in historical SAR

satellite images.

3.4 Aerial Surveys

Aerial surveys were flown during three driftnet fishery openings in Cook Inlet (28 June, and

5 and 8 July 1999), concurrent with the satellite overpasses, to provide an additional opportunity

to photograph and document rip tide locations. Aerial surveys were flown in a Piper Navajo

twin engine aircraft over the fishing grounds (between the 60o46.38’ and 59o46.2’ parallels) in

areas where fishing vessels were present. In addition, historical aerial survey data were

incorporated into this project. Ken Tarbox of ADF&G in Soldotna, Alaska allowed the project

team to review aerial survey charts of fishery openers dating back to 1978. These charts

indicated the locations of fishing vessels and occasionally included the location of rip tides. The

charts were also examined for the co-occurrence of fishing boats and rip tide zones.
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3.5 Literature

A literature search for Cook Inlet rip tides was conducted through the Alaska Resources

Library and Information Services (ARLIS) and the Internet.
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4.0 RESULTS AND DISCUSSION

Both quantitative and qualitative information was gathered to map Cook Inlet rip tides.

Quantitative information included fishermen logs, test fishery observations, satellite data, and

tide data; qualitative information included interviews, workshop input, and historical aerial

survey charts. The two types of information were examined, compared, and synthesized to

create the most accurate charts of Cook Inlet rip tides possible.

4.1 Location and Dynamics of Rip Tides

4.1.1 Qualitative Local Knowledge About Cook Inlet Rip Tide Location and Dynamics

Conversations with 27 Cook Inlet driftnet fishery stakeholders in 1999 indicated that rip

tides in the Inlet vary in form, force and location (Appendix D). Burbank (1977) reported a

similar finding: “The various persons consulted have indicated somewhat differing

configurations and locations for some of the rip tides, and the actual locations of the rip tides

apparently can vary significantly at times.”

During the 8 November 1999 workshop with Cook Inlet driftnet fishery stakeholders,

fishermen reviewed definitions of rip tides and clarified the difference between “rip tides” and

riplines (or zones).” They indicated rip lines are distinct features along the edge of a rip tide,

whereas a rip tide can be miles wide. However, obvious rip lines do not necessarily materialize

along the side of a rip tide.

From interviews and on-the-water experience, the project team learned that fishermen use

five indicators to locate a rip tide: (1) large waves or “boiling” water—surface roughness,

(2) change in water color, (3) lines of debris or flotsam, (4) concentrations of birds on the water

surface, and (5) temperature change.

4.1.1.1 General Locations of Cook Inlet Rip Tides

Fishermen, in general, reported three re-occurring main rip tides in Cook Inlet: the west,

middle (or main), and east rip tides (see Figure 2 for historic locations). The middle rip tide is

the largest and deepest of the Cook Inlet rip tides, extending along a 40+ fathom (73 m) channel

through the center of the Inlet. Initially, the middle rip tide was believed to be as wide as 1.9 to

2.8 kilometers (1 to 1.5 nautical miles). However, fishermen at the November 1999 workshop

reported that the middle rip tide can be 1.9 km wide during a flood, but that it might be as wide

as 7.4 to 11.1 km (4 to 6 nm). The middle rip tide generally occurs between 13 and 22.2 km (7

and 12 nm) off the east coast of the Inlet and sometimes joins with the east rip tide in the lower

portion of the Inlet. A flood tide can push the middle rip tide as far as 3.7 km (2 nm) to the west.

The middle rip tide typically divides the clear, relatively warmer incoming Gulf of Alaska water

to the east and silty, fresh outflowing water to the west.

Some fishermen occasionally use the term “violent” to characterize the surface appearance

and water mass movement in Cook Inlet rip tides. Fishermen have indicated that the east rip tide

is not as violent as the middle rip tide, and some fishermen fish across the east rip tide. The east

rip tide tends to align with a 10-fathom (18 meters) contour along the east shore of the Inlet. It

can be as far offshore as 7.4 km and as close as 3.7 km off Cape Kasilof during a flood tide (refer

to Figure 1 for geographic locations).
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Burbank’s (1977) findings reflected the fishermen’s knowledge at that time. He reported

that ocean water flowing up the east side of Cook Inlet during a flood tide wedged between the

east and middle rip tides. The flood tide forced the middle rip tide 3.7 km (2 nm) to the west and

the east rip tide 3.7 km (2 nm) to the east, west of Kasilof, separating the two from a “typical”

distance of 9.3 km (5 nm) during an ebb to an approximate 16.7 km (9 nm) distance during the

flood (Burbank 1977).

The west rip tide forms approximately 3.7 km east of Kalgin Island and follows the shelf of

the island’s east shoal along a 10-fathom (18 m) contour (Figure 8). The west rip tide can bend

to the west across the shoal south of Kalgin Island.

4.1.1.2 Cook Inlet Rip Tide Dynamics

Aside from the three main rip tides, fishermen also reported that rip tides can materialize at

almost any location in central Cook Inlet, although they tend to run along deep channels and

follow bathymetric contours. This study focused on central Cook Inlet where the salmon driftnet

fishery occurs. Occasionally, several rip tides have been seen over the Kalgin Island shoals.

These rip tides join together south of the shoals and the associated navigational buoy or can

(USCGS light list #26270). A small rip tide has also been observed north of the can to the east

of the middle rip tide, but generally lasts for only 1 to 1.5 hours. Another rip tide has been seen

along a 50-fathom (91 m) contour finger, or “hole,” near the 152°20′W parallel between the

latitudes of 59°52′N and 60°00′N (Figure 8).

Fishermen have reported that rip tide current velocity in the Inlet can range between four

and six knots, and can be as swift as eight knots near the Forelands (Figure 1). Fishermen also

acknowledged that water speed can vary significantly across a rip tide. On three separate

occasions during July, the ADF&G test fishery captain recorded a noticeable difference in

velocity between one side of a rip tide and the other (Table 4). All rip tides dissipate during

slack tide for approximately 1.5 hours.

Table 4. Test fishery observations of velocity difference within Cook Inlet rip tides.

Day Time Latitude Longitude Wind Speed Wind Direction Comments

11-Jul 11:15 59o49.99' 152o15.42' 0 E side moving N much faster than

W side of rip, strong rip during

flood

12-Jul 11:25 59o49.19' 152o14.76' 20 SE E side calmer that W side of rip,

large rip, 5- to 6-ft seas, 0.25 mile

wide

19-Jul 12:45 59o49.48' 152o15' 10 SE W side moving much faster to

south than E side, 2-ft seas,

distinct 2 colors of water, ebb tide

Fishermen reinforced the fact that the rip tides are relatively predictable. They emphasized

that tide stage, wind and weather can influence rip tide manifestation and location, and that the

development and location of lesser rip tides are not as predictable.
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Figure 8. Driftnet fishery area with highlighted 10-fathom contours and 50-fathom

hole in Cook Inlet, Alaska. One fathom equals 1.8 meters.
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4.1.2 Quantitative Information About Cook Inlet Rip Tide Location and Dynamics

4.1.2.1 Fishermen Surveys

Twelve percent (68 of 575) of all active Cook Inlet driftnet permit holders responded to

mailed brochures and recorded data during five fishery openers. On average, 10% of the

fishermen participating in each of the five fishery openers collected GPS locations of rip tides

during the satellite overpass (Table 5).

Table 5. Percent of fishermen recording observations of Cook Inlet rip tides per total fish

delivery during satellite overpasses. Overall percent of recordings per fish deliveries

during satellite overpasses = 10%.

Date Total Fish Deliveries Total Observations

Fishery Participants

Recording Data

28-Jun 224 28 13%

1-Jul 372 37 11%

5-Jul 430 45 10%

8-Jul 402 34 8%

15-Jul 477 36 8%

4.1.2.2 Remote Sensing

Our interpretation of SAR images of central Cook Inlet is consistent with the hypothesis that

rip tide currents are bounded at the surface by lines of upwelling, where the surface appears to

boil, and downwelling, where a surface slick occurs on the opposite side of the rip tide. Zones of

upwelling have a chaotic surface texture that causes a bright return to the SAR. Zones of

downwelling tend to calm the sea and have a low (dark) return to the SAR.

Figure 9 shows an ERS image of Kalgin Island in central Cook Inlet, taken at mid-flood tide

on 22 July 1994. The northward flowing, west rip tide is usually found by fishermen along the

10-fathom (18 m) contour offshore of Kalgin Island. The image shows a bright line near the

eastern shore of the island, just inshore of the 10-fathom (18 m) contour on nautical charts. A

distinct parallel dark line occurs beyond the 10-fathom (18 m) contour east of Kalgin Island.

The bright line probably indicates a zone of upwelling and the dark line indicates a surface slick

associated with downwelling. The strongest currents of the west rip tide probably occurred

between these lines. A spiraling roll cell along this current would have a secondary west-east

current component across the rip tide at the surface and a secondary east-west current component

some distance beneath the surface.

Figure 10 shows another ERS SAR image collected 30 August 1998 at mid ebb tide. A rip

tide is interpreted between Kalgin Island and the Kenai Peninsula running approximately parallel

to the coastline. In this image the rip tide is 11 km (6 nm) offshore at Humpy Point (near the top

center of the image), and is more than 1.9 km (1 nm) wide. The location of this rip tide is in the

undefined area between the east and middle rip tides defined by fishermen at the November 1999

workshop (Section 4.1.1.1). Rip Tides were identified in most of the ERS images, but rarely

were they as clear and well defined as in Figure 10.
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Figure 9. Synthetic aperture radar (ERS–1) image of Kalgin Island in central Cook Inlet, Alaska

on 22 July 1994. Image provided by Pacific Geomatics Ltd., Surrey, B.C. Clearly

visible are a dark line and a white line/band east of Kalgin Island which are interpreted

to be zones of downwelling and upwelling in a rip tide.

Text refers to

this dark line
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Figure 10. Synthetic aperture radar (ERS-2) image of Kalgin Island in Cook Inlet, Alaska,

30 August 1998. Imagery collected during ebbing tide, 3.62 hours after a high

tide of 3.8 meters at Ninilchik. Copyright 1992–2000 European Space Agency,

prepared by LGL Alaska Research Associates, Inc. and Pacific Geomatics Ltd.,

February 2000.

N
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During our search of ERS images we were able to identify the presence of rip tide features

in the 1992–1995 period using the ASF photographic images (Section 3.2.2). This process

ensured that the full-resolution images later purchased from ASF would be useful for mapping

Cook Inlet rip tides. We attempted to correlate the presence or absence of rip tides in the 1992–

1995 imagery with stage of tide in order to guide purchase of 1996–1999 imagery, for which no

previews were available. No simple correlation was found. We then decided to acquire lowresolution digital data for every pass of the ERS satellite having good coverage of lower Cook

Inlet during summer months (June through September) in the 1996–1999 period.

4.1.2.3 Aerial Surveys

Aerial surveys of the Cook Inlet salmon driftnet grounds were conducted on 28 June, 5 July

and 8 July 1999, coinciding with RADARSAT coverage. Distinct rip tides were visible from

the air on the fishing grounds (between the 60o46.38’N and 59o46.2’ parallels) during the 28 June

aerial survey of Cook Inlet. On both 28 June and 5 July prominent rip tides were evident from

the air north of the fishing grounds. On 5 July, a rip tide was apparent, running for

approximately 5.6 km (3 nm) southwest from the south side of Fire Island. Consistent, rigorous

winds churned Cook Inlet’s water surface during the satellite’s overflight on 8 July and may

have made it difficult to observe any rip tides that day, whereas previous aerial flights occurred

on better weather days (Table 6).

Table 6. Weather conditions reported by fishermen on the grounds during aerial surveys,

Cook Inlet, Alaska.

Date Wind Speed Cloud Cover

28 June 8–15 knots Clear—broken clouds

5 July 0–10 knots Clear—overcast

8 July 15–35 knots clear

4.1.2.4 Literature

The most comprehensive report that expressly addresses Cook Inlet rip tides is Burbank

(1977). Burbank (1977) described rip tides in Cook Inlet based on information provided by local

fishermen, pilots and others with experience in the Inlet. This anecdotal information was

incorporated in Burbank’s map of the three main rip tides in Cook Inlet (Figure 2). No

quantitative, inlet-wide description of Cook Inlet rip tides is currently published.

4.2 Fishermen’s Use Of Cook Inlet Rip Tides

4.2.1 Qualitative Information About Fishermen’s Use of Cook Inlet Rip Tides

4.2.1.1 Local Knowledge

The use of rip tides by fishermen varies widely, apparently in response to the dangers

associated with fishing such areas. Although most fishermen indicated they fish the rip tides in

Cook Inlet at least some of the time, individual use ranged from always to never.
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Many fishermen are wary of setting nets on rip tides because of the danger involved. Rip

tides can (1) accumulate debris that can clog fishing nets, (2) turn a net very dramatically, and

(3) even submerge a net along or down into itself. In addition, there can be a large shear in

current velocities immediately at or adjacent to a rip tide. Some fishermen avoid rip tides

completely, while others set their nets beside them. Fishermen have indicated that the east rip

tide is not as violent as the middle rip tide, and some even fish across it. Although rip tides can

be a dangerous location to fish, fishing along rip tides can also be very productive.

Biological, physical, practical and personal factors influence whether fishermen fish rip

tides. For example, salmon behavior has varied over the years, and fishing tactics have followed

this pattern. During some years, fish have migrated along the east side of a rip tide, while during

other years fish migrated along the west side of a rip tide. During years when a particularly large

jellyfish bloom occurs, a heavy concentration of jellyfish floats along the rip tides.

Consequently, fishing success along the rip tides was reduced, causing fishermen to avoid the rip

tides with large jellyfish concentrations.

Two Cook Inlet salmon fishermen allowed the project team to peruse their charts marked

with fishing locations and catch. Each fisherman stated a preference to fish the rip tides, and

each pointed out fishing locations along a rip tide that had been very productive. However, each

fisherman also pointed out fishing locations, miles away from present rip tides, that were also

very productive. Both fishermen use rip tides as markers where fish are likely to be, but they

may fish anywhere in the Inlet—sometimes based on intuition. Both charts were spattered with

seemingly random, “good” fishing locations. Each fisherman has studied the high-catch

positions on his chart in conjunction with logs of weather, tide stage and other variables. Neither

was able to find any predictable pattern. Other fishermen claimed to have attempted the same.

 4.2.1.2 Historical Aerial Survey

ADF&G’s historical aerial survey charts of the Cook Inlet salmon fishery provided a very

general view of fishing locations. The charts were reviewed for apparent fishing trends along

acknowledged rip tide zones; the boats seemed to fish in the general area of rip tides

(Appendix E).

4.2.2 Quantification of Fishermen’s Use of Cook Inlet Rip Tides

During 1999, sixty-eight fishermen collected GPS positions of their fishing locations once as

the satellite passed overhead during five fishery openers; nine of these provided the same

information throughout six 12-hour openers at, roughly, hourly intervals. These data offered an

indication of “how” fishermen used the rip tides. The once-an-opener records provided a

snapshot of participants’ locations during an opener, and the hourly observations presented a

profile of how some fishermen change their fishing locations throughout the duration of an

opener.

4.2.2.1 Distance Fishing to Rip Tide

The snapshots (once-an-opener records) of fishermen’s locations during openers as the

satellite collected data indicated that between 35% and 68% of fishermen participating in this

project set nets within 926 m (0.5 nm) of a rip tide (Table 7). The average percent of

participating fishermen fishing within 926 m of a rip tide for all five openers was 51% ± 12.4

(mean ± SD; 91 of 180 fishermen). Across all five openers, the average of these fishermen
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fishing in the rip tide was 19% ± 10.5, the average of these fishermen within 463 m of a rip tide

was 58% ± 7.1, and the average of these fishermen between 463 m and 926 m of a rip tide was

23% ± 7.2.

Table 7. On-ground observations of Cook Inlet rip tides from data forms on 28 June 1999 during

the commercial fishery.

Distance From Rip Tide

Date In Rip < 463 m

426 m–

926 m > 926 m

No Rip

in Sight

Total

Observations

% Total Participating Fishermen

Fishing within 926 m of Rip

28-Jun 1 10 6 3 10 30 57%

1-Jul 6 8 3 4 17 38 45%

5-Jul 5 14 5 11 12 47 51%

8-Jul 2 8 2 7 15 34 35%

15-Jul 4 12 5 1 9 31 68%

Overall 18 (10%) 52 (29%) 21 (12%) 26 (14%) 63 (35%) 180 51%

4.2.2.2 Profiles of Fishermen’s Use of Rip Tides

The periodic data (profiles) of locations and proximity to rip tides collected by nine

fishermen during the six, 12-hour openers indicated that they positioned themselves at various

proximities to rip tides while fishing (Table 8). On average, the largest percentage of fishermen

fished out of sight of a rip tide. This was followed by those fishing within 463 m of a rip tide,

those fishing in a rip tide, those fishing greater than 926 m from a rip tide, and finally those

fishing between 426 m and 926 m of a rip tide. The largest variation in fishing use occurred

within the rip tide, with between 1% and 55% of the observations recorded in this area. The

second greatest variance occurred in the “no rip tide in sight” category, ranging from 17% to

61%. The least variance appears in the 426-m to 926-m category where the least percentage of

recordings was taken (4% to 8%). Overall, the data indicate that the fishermen recording data for

the project were within 926 m (i.e., the rip tide working area) 51% of the time they recorded their

positions.

Table 8. Percent of time fishermen spent fishing in or adjacent to rip tides in Cook Inlet, Alaska

during six, 12-hour fishery openers in June and July 1999. Each value represents the

percentage of observations recorded by all fishermen combined on that day. The Cook

Inlet salmon fishery on 22 July was limited to a three-mile open corridor along the east

shore, reducing the opportunity to fish a rip tide.

Date In Rip < 463 m

426 m –

926 m > 926 m

No Rip in

Sight

# of

Fishermen

28-Jun 15% 22% 5% 10% 48% 5

1-Jul 55% 14% 5% 8% 18% 3

5-Jul 22% 42% 4% 14% 17% 7

8-Jul 9% 16% 8% 6% 61% 4

15-Jul 23% 44% 4% 1% 28% 7

22-Jul 1% 25% 4% 20% 50% 5

Grand Mean ± SD 21% ± 18.7 27% ± 12.9 5% ± 1.5 10% ± 6.6 37% ± 18.5 9
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4.3 Remote Sensing

4.3.1 RADARSAT Imagery

A total 23 RADARSAT images of lower Cook Inlet were collected on 10 orbits between

28 June 1999 and 26 July 1999 (Table 9). Figure 11 shows examples of these images.

The Scan SAR image acquired 1 July 1999 provided a good overview of Cook Inlet with its

300-km swath, but the 100-m resolution and 8-bit quantization provided little information about

water surface features. The water surface was uniformly black. A series of three fine-beam

images (50-km footprint, 8-9 m resolution) was collected on 12 July. Unfortunately, the

coverage was mostly land on the Kenai Peninsula.

The remaining RADARSAT images were all at approximately 25 m resolution at incidence

angles ranging from 27 to 58 degrees. In Figure 11, water appears uniformly dark in the high

incidence angle Extended High Beam 3 (EH-3) image acquired 28 June 1999. This appearance

is misleading as image processing of the 28 June image showed there was valuable information

in the image.

Conversely, images generated at lower incidence angles (16 July, 23 July, and 9 July) appear

to show more features in surface water (Figure 11). Again, this initial observation should be

treated with caution as certain “surface features” are in fact artifacts caused by topographic

“ghosting.” This effect is most evident in the EH-3 images of 12 July 1999 and 26 July 1999. It

was also observed in the EH-3 image of 28 June 1999.

4.3.1.1 EH-3 RADARSAT Image, 28 June 1999

We were able to examine in detail only one of the RADARSAT images due to time and

budget constraints. On 28 June 1999, an EH-3 RADARSAT image was collected within one

hour of the start of a driftnet fishery. Coverage of the image included Kalgin Island and more

than 100 km to the south and west (Figure 12). This image was selected for detailed processing.

The north and south scenes were geometrically rectified and mosaicked together. All

processing was performed at 16-bit radiometric resolution. Figure 13 shows the 28 June image

after processing. The white lines represent rip lines and the white dots are fishing vessels.

As explained in Section 3.2, RADARSAT is less useful than ERS for detection of sea

surface conditions due to the horizontal polarization of the radar signal and shallower viewing

angle. In Figure 12, which shows the area between Chisik Island (NE) and Anchor Point (SW)

during a driftnet fishery, the water surface shows very little current or tide information compared

to ERS images. Linear features that appear to be rip lines are evident in the image in midchannel south of the Kalgin Island shoal. Fishing boats of the Cook Inlet driftnet fleet are also

detected by the RADARSAT satellite.

The “topography” that appears in the RADARSAT image is an artifact of the imaging

geometry and local environment. Images from SAR are comprised of multiple signal returns that

are integrated over time. At low viewing angles, bright returns from high elevation features in

the background can contaminate foreground features. In this case, signal returns from the west

coast mountains show in the dark waters of Cook Inlet.
Table 9. ERS images used to map rip lines.

West Rip Middle/East Rip Other Rip Lines

(Date of ERS image) (Date of ERS image) (Date of ERS image)

920622 920723 920726

920723 940722 940702

920830 950824 940722b 

930518 970706 950720

930622 970810 950924

930815 970813 960615

940722 970914 960619

 950824a 980830 960705

 950824b 990606 960720

960705 990621 960721

960721 990711 960724

960824 990811 960825

960828 980729

960913 980922

970604 990620

970706 990815

970720 990818

970806

970914

980726

980830

990606

990609

990621

990710

990711

990714

990811

990815

990830
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Figure 11. RADARSAT images of lower Cook Inlet collected between

28 June and 26 July 1999.
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N

Figure 12. Synthetic aperture radar (RADARSAT EH-3) image of central Cook Inlet, Alaska

between Chisik Island and Anchor Point, 28 June 1999. The white lines represent

rip tides and the white dots are fishing boats.
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N

Figure 13. Boat positions and RADARSAT imagery of 28 June 1999 fishery opener, Cook

Inlet, Alaska. Rip lines have been enhanced, and are plotted with logged fishing

boat positions at the time of imaging. Circle radius is distance to nearest boat from

logged position. Also shown is the time difference between logged position and

imaging time. Ghosting is evident in this image as apparent “mountains” in the

water (see text).
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Because Daylight Savings Time was not incorporated into our ground-truthing design, Cook

Inlet fishermen recorded their positions one hour before the RADARSAT satellite imaged the

study area. Consequently, we have near-synchronous positions (+/- 10 minutes) for only five

boats that logged their positions at hourly intervals throughout that day.

A fishing vessel appears in the RADARSAT image as a small bright dot, one or two pixels

in size. It is not possible to differentiate between boats, only to determine whether a vessel is

detectable in the image at a particular location. We were able to identify the presence of the five

logged vessels within a one-mile radius of reported position (Figure 13). Two of the vessel

captains reported being in the rip tide at that time (vessels B, C), a third was 500 yards away

(vessel D), and two were in open water (vessels A, E). Rip Tides or rip lines can also be seen in

the RADARSAT image (Figure 12). The fishing fleet is aligned along these lines. Even though

individual vessels cannot be identified, the following conclusion is reached by comparing the

imagery with the fishing location logs: Although our sample size is small, the imagery

represented in Figure 13, together with the information in the fishermen’s logs, provide evidence

that rip tides are correctly identified in the RADARSAT imagery.

Information collected by the RADARSAT satellite on 28 June 1999 was incorporated with a

1995 ERS image of Cook Inlet. This compilation of radar satellite image data was printed as

posters for presentation at the second workshop (Appendix G). The base of the map is the ERS

satellite image acquired during a flood tide 24 August 1995. Surface water features, interpreted

to be the middle rip tide, are highlighted in light blue. Overlaid on the ERS image is information

collected by the RADARSAT satellite during an ebb tide 28 June 1999. Fine white lines on the

image are interpreted rip tides from the 1999 RADARSAT image, and white dots are positions of

boats participating in the Cook Inlet driftnet fishery at the time of the satellite overpass. The

compilation of satellite images on the poster supports Burbank’s (1977) findings and fishermen’s

reports that the middle rip tide can move as much as 3.6 km to the west during a flood tide

[Section 4.1.1.1].

4.3.2 Historic ERS Imagery

We examined 61 ERS images of lower Cook Inlet (Table 3), and almost all displayed

evidence of rip tides. We followed the description provided by fishermen at the November 1999

workshop as well as our own experience of interpreting the ERS SAR imagery. “Rip lines are

distinct features along the edge of a rip tide, whereas a rip tide can be miles wide. However,

obvious rip lines do not necessarily materialize along the side of a rip tide” [Section 4.1.1]. “Rip

tides can materialize at almost any location in central Cook Inlet” [Section 4.1.1.2].

Figure 14 compares two ERS images acquired two years apart, both at mid-flood tide. The

west rip tide is seen offshore of Kalgin Island in the same position in both images. This rip tide

remains quite constant in its location off Kalgin Island, but appears to be further south in the

1999 image. It is more difficult to identify the limits of the middle and east rip tides in

Figure 14, although the east rip tide appears much closer in-shore off Cape Ninilchik in the July

1997 image.

This image pair reflects the project team’s experience analyzing the other 59 ERS images.

From the Forelands to southern Kalgin Island, the west rip tide boundaries are very well defined

and consistent, but they start to widen south of Kalgin Island. The middle and east rip tides seem

to move laterally across the inlet much more, and the project team was unable to distinguish

between them.
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Figure 14. The west rip tide line during mid-flood tide off Kalgin Island, Cook Inlet, Alaska

in July 1997 and August 1999.
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4.3.2.1 West Rip Tide Location

The interpreted rip lines were sequentially overlaid on a background ERS image of Cook

Inlet, and the linework for each date was visually examined for presence of lines in the general

area of the west rip tide. Where such lines were present, they were copied to a new file and

assembled with similarly classified linework from the other dates.

The west rip linework was taken from 30 images acquired at all tide stages in the period

1992–1999, and this linework was edited to remove lines outside the general area of the west rip

tide. Figure 15 shows the maximum east and west boundaries of the interpreted west rip lines.

Between the Forelands and southern Kalgin Island, the west rip tide is very stable. The east-west

bounds rarely vary by more than 3.7 km (2 nm), and are often less than 1.9 km (1 nm) apart. The

eastern boundary closely follows the 20-fathom (37 m) contour in this area, and the western

boundary appears at about 5 fathoms (9 m). South of Kalgin Island the west rip tide bounds

widen to as much as 18.5 km (10 nm) and may join with the middle rip tide. Table 9 lists the

ERS images used to map west rip linework.

4.3.2.2 Middle and East Rip Tide Locations

The middle and east rip linework was classified in the same manner as for the west rip

linework (Table 9). Rip lines in the central channel and east side of the Inlet were mapped from

twelve ERS images. These lines were assembled and edited. Figure 16 shows the maximum

east and west boundaries from this work.

We were unable to differentiate between the middle and east rip tides. Rip lines were found

at all areas between the classical locations of the east and middle rip tides. The eastern boundary

closely follows the 10-fathom (18 m) contour 3–5 miles off the Kenai Peninsula. The western

boundary is in the central Inlet at 30–40 fathoms (55–73 m) depth.

4.3.2.3 Other Rip Tide Lines

Figure 17 shows rip lines interpreted from the ERS images that occurred in other parts of the

Inlet (Table 9). At the 8 November 1999 workshop, fishermen reported seeing rip tides over the

Kalgin Island shoals and south of the navigation buoy (USGGS light list #26270). Figure 17

shows that many ERS images had rip lines in this area.

Two other areas of rip tide activity are indicated in Figure 17. Interpretation of the ERS

imagery suggests rip tides can develop along a 40-fathom (73 m) trench that occurs in the

narrows between Harriet Point and the southern tip of Kalgin Island. The second area where rip

tides occur frequently is along the 10-fathom (18 m) contour on the west side of the Inlet.

4.4 Potential Conflicts Between Fishermen And Offshore Industry Development

4.4.1 Obstacles

The establishment of fixed drilling platforms or other industry equipment may pose a hazard

to fishermen. Numerous fishermen recounted problems with nets getting caught on the

stationary navigational buoy south of Kalgin Island and on the Sisters, south of the Kasilof River

(Figure 8).
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Figure 15. Maximum east and west boundaries of interpreted west rip lines at all tide stages

from ERS synthetic aperture radar images of Cook Inlet, Alaska from 1992–1999.
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Figure 16. Maximum east and west boundaries of interpreted middle and east rip lines at all tide

stages from ERS synthetic aperture radar images of Cook Inlet, Alaska, 1992–1999.
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Figure 17. ERS synthetic aperture radar image lines of rips interpreted as other than the west,

middle, or east rips in Cook Inlet, Alaska from 1992–1999.
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Avoiding fixed objects while drifting with a 274.3-m long net is difficult given the distance

a boat may float while hauling up a net. For example, fishermen reported taking 15 minutes to

pull in an empty net, if nothing goes wrong. During this time, a boat and gear might travel 1 nm,

given a conservative current of 4 knots. Consequently, avoiding stationary objects in Cook Inlet

is difficult during an active fishing operation. New stationary objects, such as surface oil and gas

platforms, might require fishermen to allow 1.9 to 3.7 km (1 to 2 nm) buffer zones to avoid

entangling nets.

To eliminate a fishing gear conflict, the use of “non-surface” oil and gas production

methods, such as directional drilling, was suggested by fishermen. The operation of mobile

exploration platforms during the off-season was also proposed. One stakeholder suggested

development be limited to less-fished areas of the Kalgin Shoals, north of the navigational buoy

and to the west of Kalgin Island.

4.4.2 Discharges/Spills

Further concerns were expressed regarding the potential discharge or spills of drilling fluids,

other substances, and oil. Rip tides may concentrate oil within or along their edges. In July

1987, spilled crude oil from the M/V Glacier Bay concentrated and persisted in rip tides (U.S.

Coast Guard 1988). Some of the oil was difficult to collect as it submerged after being boomed

(Whitney 1994). In addition, the spiraling circulation of a rip tide current provides a powerful

dispersion mechanism for contaminants. Understanding the short- and long-term ramifications

of oil spills is difficult given that the transport of such materials by tides and currents in Cook

Inlet is unpredictable.
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5.0 COMMENT

In this study we examined 61 Synthetic Aperture Radar (SAR) images acquired by the

ERS-1 and ERS-2 satellites, and one SAR image collected by the RADARSAT satellite.

RADARSAT images from another nine dates in summer 1999 were inspected but not analyzed.

ERS radar images can provide valuable information concerning surface feature information in

ocean waters. RADARSAT images are most useful for detection of point-source reflectors, such

as fishing boats or other vessels on the ocean surface.

Time and budget constraints did not allow a comprehensive analysis of the SAR imagery

with state of tide. Our preliminary work found no obvious correlation between tide state and rip

tide location. ERS coverage of Cook Inlet is predictable. It is recommended that any planned

oceanographic work in the Inlet consider the possibility of synchronizing on-water studies with a

scheduled ERS image acquisition program. A fisherman reported that salmon cannery operators

customarily conduct fish spotting flights along rip tide lines the night before salmon openings.

These aerial surveys could provide opportunities to coordinate with satellite overpasses and

further ground-truth rip tide interpretations of satellite images.
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6.0 SUMMARY

6.1 Rip Tide Location

Cook Inlet rip tides vary in form, force and location, but there are certain areas of the Inlet

where rip tides persist. The major rip tides in the Inlet tend to run along deep channels and

follow bathymetric contours. Satellite mapping of Cook Inlet rip tides supports the generalized

chart of Cook Inlet rip tides produced by Burbank (1977; Figure 2). The satellite mapping

further supports the fishermen’s reports that rip tides can appear almost anywhere in the Inlet,

that they occur over Kalgin Island shoals, and that they are found south of the navigation buoy

(USCGS light list #26270).

Thirty satellite images acquired at different tide stages over eight years showed the west rip

tide consistently in one location, whereas the middle and east rip tides in the central channel

occur over a wider area of the Inlet. The satellite mapping was unable to differentiate clearly

between the middle and east rip tides.

In addition to the rip tides discussed above, the satellite mapping has repeatedly identified

other areas where rip tides have been reported by Cook Inlet fishermen. These include the

Kalgin Island shoals and south of the navigation buoy, in a 40-fathom (73 m) trench between

Harriet Point and the southern tip of Kalgin Island, and following the 10-fathom (18 m) contour

along the west coastline of Cook Inlet.

6.2 Fishermen’s Use of Rip Tides

Cook Inlet fishermen indicated that they fish rip tides inconsistently. Some prefer to work

rip tides, but do not limit their fishing to the rip tides. Both the fishery “snapshot” and fishing

“profile” data suggest there is a wide range of fishing methods fishermen use to factor rip tide

locations into their fishing practices.

A RADARSAT image of the 28 June 1999 fishery opener was able to document the position

of the driftnet fleet 67 minutes after the opening. Most fishing boats were aligned along rip tides,

which is an indicator of the importance of the rip tides to the Cook Inlet driftnet fishery.

6.3 Potential Conflicts with Oil and Gas Industry Development

Cook Inlet driftnet fishery stakeholders indicated the addition of surface obstacles and

potential for pollution associated with oil and gas development could pose problems for their

fishery. Planning for discharges or spills is further compounded by the fact that the transport of

such materials by tides and currents in Cook Inlet is unpredictable. Understanding and

predicting circulation associated with rip tide currents would allow prediction of pollutant

dispersion patterns so that a rational response plan could be formulated.
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7.0 ACKNOWLEDEMENTS

The U.S. Department of Interior, Minerals Management Service (MMS) sponsored this

work. We are grateful for the assistance provided by Dr. Richard Prentki, the MMS Contracting

Officer’s Technical Representative, who helped plan logistics and reviewed work products and

reports. We thank Ms. Valerie Elliott of the MMS who provided logistical help regarding the

use of the Service’s vessel, Launch 1273, during two fishery openers. The Contracting Officer

for the program, Wallace Adcox, cheerfully helped the study team navigate the government

procedures necessary to complete this project.

This study was supported in part by the Canadian Centre for Remote Sensing (CCRS). The

CCRS subsidized an expansion of the project to examine the utility of using its satellite,

RADARSAT 1, to identify, characterize and enumerate the various types of fishing vessels in

Cook Inlet. The CCRS paid for the printing and mailing of the post card questionnaires in

support of their part of the project.

Drs. Mark Johnson and Steve Okkonen of the University of Alaska showed interest in this

project, provided comment on the approach, and invited us to a Cook Inlet oceanography

workshop to present this work. Wanda Seamster of the University of Alaska prepared the artist’s

illustration of a Cook Inlet rip tide.

We thank all fishermen who participated in the project, and especially those 13 who spent

the extra time with us during interviews (Appendix A). Special thanks is extended to Darwin

and Alison Waldsmith who operated the MMS Launch 1273 and shared their experiences of

fishing Cook Inlet, and to Ridgely Stier who allowed personnel onboard his boat, F/V Blueback.

Marc Zimmerman shared his fishing charts and logs, and Bruce Gabrys shared his historic

fishing locations with our study team. We thank the Cook Inlet Aquaculture Association for

hosting stakeholder workshops, and the United Cook Inlet Drifters Association who let us

participate in their annual meeting.

Finally, we thank the staffs of LGL Alaska Research Associates, Inc. and Pacific Geomatics,

Ltd. for their technical support and assistance throughout this study, especially Peggy Kircher,

Jessy Coltrane, Matt Nemeth, and Drs. Rick Lanctot and Dale Funk.
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8.0 REFERENCES

Burbank, D.C. 1977. Circulation Studies in Kachemak Bay and Lower Cook Inlet. In: Trasky,

L.L., Flagg, L.B., and Burbank, D.C., eds. Alaska Department of Fish and Game;

Marine/Coastal Habitat Management. Anchorage, Alaska.

Commercial Fisheries Entry Commission. 1999. CFEC Commercial Fishing Data [Web Page],

available at www.cfec.state.ak.us/bit/S03H.htm.

National Oceanic and Atmospheric Administration (NOAA). 1999. NOAA National Ocean

Service, Center for Operational Oceanographic Products and Services [Web Page],

available at http://co-ops.nos.noaa.gov/.

Sharma, G. and D. Burrell. 1970. Sedimentary environment and sediments of Cook Inlet,

Alaska.

Tarbox, K.E. and R.E. Thorne. 1996. ICES Journal of Marine Science, p. 53.

U.S. Army Corps of Engineers (USACE). 1993. Deep Draft Navigation Reconnaissance

Report, Cook Inlet, Alaska. Alaska District, U.S. Army Corps of Engineers. Anchorage,

Alaska.

U.S. Army Corps of Engineers (USACE). 1996. Deep-Draft Navigation Interim Feasibility

Report and Environmental Impact Assessment, Cook Inlet, Alaska. Alaska District, U.S.

Army Corps of Engineers. Anchorage, Alaska.

U.S. Coast Guard (USCG). 1988. Federal On-Scene Coordinator's Report: Major Oil Spill M/V

Glacier Bay: Cook Inlet, Alaska: 2 July to 3 August 1987. U.S. Coast Guard Marine

Safety Office. Anchorage, Alaska.

Wapora Inc. 1979. Lower Cook Inlet, Alaska, Environmental Impact Review Manual. Report

for Environmental Protection Agency.

Whitney, J.W. 1994. Oil Spill Response in Dynamic Broken Ice. NOAA Hazardous Materials

Response and Assessment Division, Anchorage, Alaska.
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LIST OF APPENDICES

APPENDIX A. Cook Inlet driftnet stakeholders interviewed April through June, 1999.

APPENDIX B1. Sunday, 20 June 1999 Peninsula Clarion article.

APPENDIX B2. Thursday, 24 June Homer News Public Service Announcement.

APPENDIX C. One of five data sheets mailed to all active Cook Inlet driftnet fishermen,

May 1999.

APPENDIX D. Cook Inlet rip tide notes from interviews of driftnet fishermen.

APPENDIX E1. ADF&G aerial fishery survey on 13 July 1983, Cook Inlet, Alaska.

APPENDIX E2. ADF&G aerial fishery survey on 18 July 1986, Cook Inlet, Alaska.

APPENDIX E3. ADF&G aerial fishery survey on 20 July 1979, Cook Inlet, Alaska.

APPENDIX E4. ADF&G aerial fishery survey on 20 July 1990, Cook Inlet, Alaska.

APPENDIX F. Technical presentations resulting from this study.

APPENDIX G. Poster: Compilation of Cook Inlet radar satellite image data.
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APPENDIX A. Cook Inlet driftnet stakeholders interviewed April through June, 1999.

Name Occupation Date Interview

Roy Self ADF&G test fisher 19 April phone

Paul Dale seafood processor 19 April phone

Susan Saupe RCAC scientist 19 April phone

Ken Tarbox ADF&G biologist 3 May personal

Jeff Fox ADF&G biologist 3 May personal

Drew Sparlin fisherman 4 May personal

Bill Sullivan fisherman 4 May personal

Dan Mahan retired fisherman 4 May personal

George Jackinsky retired fisherman 5 May personal

Bill Holt fisherman 5 May personal

Phil Squires UCIDA/fisherman 5 May personal

Loren Flagg retired fisherman/guide 6 May personal

Chris Kempf fisherman 6 May personal

Theo Matthews UCIDA/retired fisherman 6 May personal

Marc Zimmerman fisherman 7 May personal

Ridgely Stier fisherman 8 May personal

Emmet Heidemann fisherman 12 May phone

Karl Kirscher fisherman 17 May phone

Marvin Peters fisherman 7 June phone

Mike Wade fisherman 7 June phone

M.L. “Moon” Mullin fisherman 7 June phone

Jim Williamson fisherman 7 June phone

Mark Mahan fisherman 9 June phone

John Lindeman fisherman 10 June phone

Darwin Waldsmith retired fisherman 14 June phone

Alexander Stuart fisherman 17 June phone

Grace Kendall fisherman 7 July phone
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APPENDIX B1. Sunday, 20 June 1999 Peninsula Clarion article discussing the Mapping Cook

Inlet Using Local Knowledge and Remote Sensing Project. Reproduced with permission of the

Peninsula Clarion.
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Local Knowledge and Remote Sensing B-2 Final Report 9/1/00

APPENDIX B2. Thursday, 24 June Homer News Public Service Announcement of the Mapping

Cook Inlet Rip Tides Using Local Knowledge and Remote Sensing Project and LGL personnel

presence at the annual UCIDA meeting. Reproduced with permission of the Homer News.
Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing C-1 Final Report 9/1/00

APPENDIX C. One of five data sheets mailed to all active Cook Inlet driftnet fishermen, May

1999. Each differed in date and time of satellite overpass.
Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing D-1 Final Report 9/1/00

APPENDIX D. Cook Inlet rip tide notes from interviews of driftnet fishermen.

Review Area We’re Discussing

Where: Upper Cook Inlet—about 156 miles long by 40 miles long at the southern boundary

fish—from can just north of Kalgin to line across from Anchor Point Light to Chinitna width and

breadth of inlet—along 59 degree 46.25’ (or 46’12”) area of fishery over which MMS has

jurisdiction from southwest of Kalgin Island to see above.

Corridor openers are 3 miles wide in “stock specific” area (including 600 feet of driftnets

Fish 900 foot (3 shackle) long nets

Location And Dynamics Of Rips

• Incoming tide like hose—soars through deeper areas, showers on shallows

• Cook Inlet is home of tidal fluctuations that can be greater than 30 ft. and can produce

current velocities in excess of 8 knots

• More “regular” current will run 4 to 6 knots

• Rips tend to run along area (channel) of deep water—shoulder to shoulder

• A rip acts like a vacuum and sucks debris and fish into it

Three main rips: West, Middle (or Main), East

• Mid-channel deepest rip—40 plus fathom channel

• Middle rip is dividing line between clear ocean water in east inlet and silty, fresh water to

west

• Middle rip may be 1 to 1.5 miles wide

• MAIN rip 8 to 10 miles offshore, can be as far as 7 to 12 miles off east coast, main and

east sometimes joins to the south

• EAST and west rips follow 10-fathom depth

• East tide can be 7 to 8 miles off east coast

• Some days east can be 8 miles offshore

• Especially on east channel—no obvious bathymetric expression

• WEST rip 2 miles east of Kalgin

• WEST may bend to west over Kalgin Island shoal south of island

• Rip on west side of middle inlet follows shelf from west forelands pretty much along 10-

fathom line to east of Kalgin

• Probably preferred fishing ~ 8 miles off shore; avenue most fish take as mixed stock

heads up middle along the greatest movement of water, often more clear (ocean water) on

its east side

• Clear (ocean) water in the west and dirty (fresh) in the east—to main rip, agrees with

circulation profile.
Appendix D. Continued

Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing D-2 Final Report 9/1/00

Relative To Tide Stage

• Rips predictable depending on tide stage

• Rips fairly steady as tide increases

• Flood pushes rips north, sometimes of Forelands

• East tides head toward the beach with the flood

• EAST rip 4 miles offshore—during flood as close as 2 miles off Humpy point

(Cape Kasilof).

• Flood pushes east rip 2 nm to east and mid rip ~ 2 nm to west

• FLOOD – east rip not as violent as main – can straddle rip or fish across towing; during

flood east side of rip will usually pull you into rip; Main rip is stronger on flood

• Southern extent of east/west rips dissipate

• mid channel rip dissipates during ebb, collects debris and can spread out as much as

1.5nm, during flood converges into narrow bank ~0.125 nm wide, can create swath 1.5

nm of boiling water and large waves. Noise can be heard up to 0.25 nm away

• Kalgin Island reef—ebb rip lines more obvious and violent especially near Forelands—

rip follows shelf

• EBB—main (middle) and east meet below Kalgin can; tide pushes to west below

• During ebb—east and middle rip about 5nm apart; during flood ~ 9 nm

• The tide change by Kalgin can is 2.5 to 3 hours different from the east coast (Ninilchik to

can approximately)

• 4-hour difference in tide between Ninilchik to can

• 1-hour difference in high tide between Ninilchik and Kenai

• Stage of tide rip fluctuates from 7 miles off east shore at low to 2 miles off east shore

• West rip follows Kalgin to shoal and then veers west south of Kalgin island on the flood

• Along line “Lower Cook Inlet” tides generally run 2 to 3 hours later than Seldovia

• All rips dissipate during slack

• SLACK: slack may last 1.5 to 2 hours when no obvious rips

• Tides (per se) not the only factor—winds have strong influence, tide pushes to the east on

flood and then west on ebb

• DRIFT PATTERNS: flood—north of Ninilchik between mid and east rips strong drift to

west—can float distance between east and mid channel rip

• Ebb tide drift—parallel to rips

• MANY RIPS: a small rip to east of middle lasts only 1 to 1.5 hours north of the can

• Several rips around Kalgin shoals that come together on the south side of the can

• Rips can be everywhere
Appendix D. Continued

Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing D-3 Final Report 9/1/00

• Rip along 50-fathom finger—see chart

• RIP SIDES: west side of rip you can either hold or get kicked out while you’re fishing—

east side will suck you in

• INDICATOR: water color, fish finder indicates turbulence

• Can have mucky water then clear patches appear, almost boiling up

• Look for color change, trash; west rip especially bad for trash

Fishermen’s Use Of Rips And Adjacent Water

• Drew usually fishes east

• Some days east can be 8 miles offshore; usually fish in east rip during flood; during ebb,

would rather fish in restricted east side fisheries

• Drew won’t fish in them—too much stuff, some folks right in the middle

• Work two most significant rips—one on east and one on the west

• Where fish depends on weather, stage of fishery, where fish is headed—shallower tides

could fish anywhere

• WIND: west wind fish to shore to NE

• FISH always at surface in heavy waves; rips can be everywhere, fish like middle of rips

as two join

• What stock is coming in, may follow the west rip during shallower tides

• Fish travel back and forth across rips

• Earlier in the season the fish are loosely distributed less concentration boats scattered and

concerned less with rip

• Most of fleet fishes middle rip then will travel to east

• Will fish rips about 50% low tides looks for likes rip to SW of can on ebb

 Indicators

• TEMPERATURE VARIATIONS? Look for warmer incoming water

• Drew sees change in water temperature of 47 – 48degrees to 50 or 52 degrees. Some

fishermen actually use thermometers to track variations

• TEMP – variations and thermocline suck fish into it

• one side is usually better than the other - Chris believes that warmer side is better for

fishing

• DOESNOT use TEMP (doesn’t need)

• INDICATORS: birds, debris, waves, color, surface action, fish finder

• Most active fishing during incoming tide /during FALL fish west side (different runs)

• FISH sound as tide ebbs – if fish near beach, fish in shallows

• George will set the net in muddy water with the boat “bumping” against the rip – the fish

can’t see the net and the muddier water more likely to be warmer water with incoming

fish

• Wind helps move the fish, but tide stays the same – in a circulation report in the late 70’s

• Most times fishes east side of rip, but not predictable
Appendix D. Continued

Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing D-4 Final Report 9/1/00

• Never just sits in rip to fish

• FISH enter from the SW

• Fishes rips 80% of the time

• By mid-JULY, fish are more to the east, so fishermen follow them

• Always fishes off rip

Potential Conflict With Offshore Industry

• Setnetters’ corks thrown overboard with dates and locations, near east bench rip

recovered west of Kalgin (NW)

CONCERNS – obstacles!

• Platforms – rips move conservatively at 6 knots if platform in path take 15 minutes to

pull in an EMPTY net – in that 15 minutes the boat would have traveled one mile

• Doesn’t want oil development

• UCIDA has already suggested using bar on west side of Kalgin Island and shoal south of

island for platforms

• Advises mobile exploration units – no permanent platforms, Force Energy does use

mobile units

• Already countless evidence of people getting caught on the Kalgin can and the sisters

(between Kasilof and Clam Gulch)

• Since oil spill, rips not very productive; can still see oil come up in rips

• After 1987 Glacier Bay oil spill on 7/2, one fishermen trashed three nets – 7/10, 7/20, and

7/22 (second opener he was fishing a rip) continued to try to avoid oil through 8/10. Did

not make 8/17 opening in Chinitna but no nets available
Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing E-1 Final Report 9/1/00

APPENDIX E1. ADF&G aerial fishery survey on 13 July 1983, Cook Inlet, Alaska. Rip tides

are indicated on the chart.
Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing E-2 Final Report 9/1/00

APPENDIX E2. ADF&G aerial fishery survey on 18 July 1986, Cook Inlet, Alaska. Rip tides

are indicated on the chart.
Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing E-3 Final Report 9/1/00

APPENDIX E3. ADF&G aerial fishery survey 20 July 1979, Cook Inlet, Alaska. Rip tide are

indicated on the chart.
Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing E-4 Final Report 9/1/00

APPENDIX E4. ADF&G aerial fishery survey 20 July 1990, Cook Inlet, Alaska.
Mapping Cook Inlet Rip Tides Using Contract No.01-98-CT-30906

Local Knowledge and Remote Sensing F-1 Final Report 9/1/00

APPENDIX F. Technical presentations resulting from this study.

Venue Title Date

No. of

Attendees Location

Workshop Mapping Cook Inlet Rip

Tides Using Local

Knowledge and Remote

Sensing

8 Nov 1999 37 Cook Inlet Aquaculture Assn.

Kalifornsky Beach Road

Soldotna, Alaska

Workshop Cook Inlet

Oceanography

Workshop

9 Nov 1999 59 Kenai Cultural and Visitors Ctr.

Kenai, Alaska

Workshop Mapping Cook Inlet Rip

Tides Using Local

Knowledge and Remote

Sensing

6 Mar 2000 9 Cook Inlet Aquaculture Assn.

Kalifornsky Beach Road

Soldotna, Alaska
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