ACCESS NUMBER: TO-15172

STUDY TITLE: Cook Inlet Workshop Support

REPORT TITLE: Proceedings Cook Inlet Oceanography Workshop

CONTRACT NUMBER: 14-35-001-30909; TASK ORDER (TO): 15172

SPONSORING OCS REGION: Alaska

APPLICABLE PLANNING AREA: Cook Inlet

FISCAL YEAR OF PROJECT FUNDING: 1999

COMPLETION DATE OF REPORT: June 2000

COST: FY 1999: $31,669; CUMULATIVE PROJECT COST: $31,669

PROJECT MANAGERS: Mark A. Johnson, Stephen R. Okkonen

AFFILIATION: University of Alaska Fairbanks

ADDRESS: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775-7220

PRINCIPAL INVESTIGATORS*: Mark A. Johnson, Stephen R. Okkonen

KEY WORDS: Cook Inlet circulation, tide-rip front, ADCP, oil-spill trajectory models

BACKGROUND:

A one-day Cook Inlet oceanographic workshop was held on 9 November 1999 at the Kenai Cultural and

Visitors Center. More than 70 people attended the workshop to assess our understanding of the physical

oceanography in Cook Inlet. More than a dozen experts presented their views on Cook Inlet circulation,

the use and validation of oil-spill trajectory models, the use of satellite imagery for understanding the

temporal and spatial variance of tidal rips, and the use of free-drifting surface buoys and acoustic Doppler

profilers for direct estimates of Cook Inlet currents. Utilizing this information, we examined the utility of

numerical models used to predict oil-spill trajectories.

OBJECTIVES:

The workshop goal was to review Cook Inlet circulation using present and past hydrographic information,

identify the essential circulation features, and examine the utility of the oil-spill trajectory models currently

in use.

DESCRIPTION:

Invited speakers described Cook Inlet circulation as complex, with variability at tidal, seasonal, annual,

and inter-annual time scales. The circulation is dominated by tidal flow which generates three major rip

currents with roughly north–south axes aligned with local bathymetry. The tidal rips have speeds of up to

six knots, and account for most of the volume transport through Cook Inlet. The geographical size of

Cook Inlet and the tidal velocities produce out-of-phase tidal heights for Seldovia and Anchorage.

Significant non-tidal circulation features exist in Cook Inlet. There is a southward-flowing buoyancy-driven

current along the western shore of Cook Inlet, a concentrated, intense, bathymetrically-steered westward

flow across lower Cook Inlet, and a slow flow to the north in central and eastern Cook Inlet. These are

driven by the freshwater flux from Cook Inlet’s western shore, and the flow from the Gulf of Alaska.
ACCESS NUMBER: TO-15172

SIGNIFICANT CONCLUSIONS:

The workshop participants recommended additional field-based research specifically targeted at

improving our understanding of Cook Inlet circulation and validating numerical models. The strong need

for direct measurements to validate the numerical models was recognized, specifically the use of acoustic

Doppler profilers. The use of remote sensing to quantify the spatial and temporal variability of the tide rips

was strongly encouraged. The importance of additional moored instrumentation was recognized, along

with the continued use of surface drifting buoys. It was recognized that long-term planning reduces startup costs associated with shorter term-studies.

STUDY RESULTS:

There was consensus among participants that oil-spill trajectory models appear to be reasonably

accurate, but that the models continue to develop in complexity. Improvements include better model

resolution, the addition of vertical structure, the inclusion of freshwater buoyancy driving, and addressing

boundary forcing from the Gulf of Alaska. It was agreed that future studies should be systematic in their

measurements of currents, winds, tides, ice, temperature and salinity. Field work should take place in the

very near future so that data sets can be acquired and analyzed as developmental pressure continues in

Cook Inlet.

STUDY PRODUCTS:

Johnson, M.A. and S.R. Okkonen [eds.]. 2000. Proceedings Cook Inlet Oceanography Workshop.

November 1999, Kenai, AK. Final Report. OCS Study MMS 2000–043, University of Alaska Coastal

Marine Institute, University of Alaska Fairbanks, 118 p.

*P.I.’s affiliation may be different than that listed for Project Manager(s).
ACCESS NUMBER: TO-15172

MMS Gulf of Alaska Subregion

Cook Inlet