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STUDY TITLE: Mapping Cook Inlet Rip Tides Using Local Knowledge And Remote Sensing 

REPORT TITLE: Mapping Cook Inlet Rip Tides Using Local Knowledge And Remote Sensing 

CONTRACT NUMBER: 01-98-CT-30906 

SPONSORING OCS REGION: Alaska 

APPLICABLE PLANNING AREA: Cook Inlet 

FISCAL YEARS OF PROJECT FUNDING: 1998–2000 

COMPLETION DATE OF REPORT: September 2000 

COSTS: FY 1998 – $127,976; FY 2000 – $13,000 

CUMULATIVE PROJECT COST: $140,976 

PROJECT MANAGER: William J. Wilson 

AFFILIATION: LGL Alaska Research Associates, Inc. 

ADDRESS: 4175 Tudor Centre Dr., Suite 202, Anchorage, AK 99508 

PRINCIPAL INVESTIGATORS: Beth Haley, Geoff Tomlins, Orson Smith, William Wilson, Michael Link 

KEY WORDS: Cook Inlet, salmon fishery, rip tides, satellite, imagery 

BACKGROUND: 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. This study was designed to map rip tides in Cook Inlet, gather baseline 

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

tides. 

OBJECTIVES: 

1. Quantify the spatial and temporal variability of rip tide locations. 

2. Determine the locations of rip tides used by the fishing fleet. 

3. Collate information on fishery use of rip tides and identify potential conflicts between fishermen 

and the oil and gas industry. 

DESCRIPTION: The study area consisted of waters within the Cook Inlet salmon driftnet fishery 

(between the 60o46.38’ and 59o46.2’ parallels) under MMS jurisdiction. The MMS is responsible for 

permitting oil and gas exploration and development in areas under its jurisdiction (three or more nautical 

miles offshore). 

The particular emphasis of the study was to use both local knowledge and remote sensing to examine rip 

tide locations and their use by fishermen in the Cook Inlet driftnet fishery. Local knowledge was obtained 

from Cook Inlet fishermen through interviews and two workshops. The locations of rip tides also were 

interpreted and mapped using satellite-borne Synthetic Aperture Radar (SAR) imagery. During the 

summer of 1999, the Canadian Space Agency’s RADARSAT 1 satellite was programmed to image the 
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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.

SIGNIFICANT CONCLUSIONS: Interpretation of satellite imagery of Cook Inlet suggests that major rip 

tides tend to run along deep channels and follow bathymetric contours. Satellite imagery mapping of 

Cook Inlet rip tides also supports a generalized chart of three main rip tides, west middle and east, 

produced in 1977. The satellite mapping further supports the fishermen’s reports that rip tides can 

appear almost anywhere in the Inlet. 

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 fishery “snapshot” (one point of time during a fishery) and 

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

locations into their fishing practices. 

The satellite imagery interpretation of rip tides in Cook Inlet from RADARSAT 1, acquired 28 June 1999, 

is verified when compared to fishing location logs that include rip tide proximity for that time. 

STUDY RESULTS: Conversations with 27 Cook Inlet driftnet fishery stakeholders in 1999 indicated that 

rip tides in the Inlet vary in form, force and location. Fishermen, in general, reported three re-occurring 

main rip tides in Cook Inlet: the west, middle (or main), and east rip tides. 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. 

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 (USCGS light list #26270). A small rip 

tide has also been observed north of the buoy 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. 

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. 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. 

Thirty satellite images acquired at different tide stages over eight years show 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, 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. 
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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. 

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. 

STUDY PRODUCTS: 

Haley, B.E., G. Tomlins, O.P. Smith, W.J. Wilson, and M.R. Link. 2000. Mapping Cook Inlet Rip Tides 

Using Local Knowledge And Remote Sensing. A final report for the U.S. Department of the Interior, 

Minerals Management Service, Alaska OCS Region, Anchorage, AK, Contract No. 01-98-CT-30906. 

OCS Study MMS 2000-025. 67p. 

Link, M.R., W.J. Wilson, and G. Tomlins. 1999. Mapping Cook Inlet Rip Tides Using Local Knowledge 

and Remote Sensing in MBC Applied Environmental Sciences, Preparers. Alaska OCS Region Seventh 

Information Transfer Meeting Proceedings. Anchorage, AK: USDOI, MMS, Alaska OCS Region. OCS 

Study MMS 99-0022. p. 10. 

Wilson, W.J. and G. Tomlins. 2000. Mapping Cook Inlet Rip Tides Using Local Knowledge and Remote 

Sensing in: Johnson, M.A. and Okkonen, S.R., eds. Proceedings Cook Inlet Oceanography Workshop. 

Fairbanks, AK: University of Alaska, CMI and Oil Spill Recovery Institute; OCS Study MMS 2000-043. 

pp. 1-10. 

POSTER: Compilation of Cook Inlet radar satellite image data. 

* P.I.’s affiliation may be different than that listed for Project Manager(s).