ACCESS NUMBER: M14AC00014

STUDY TITLE: Cook Inlet Circulation Model Calculations

REPORT TITLE: Cook Inlet Circulation Model Calculations

CONTRACT NUMBER: M14AC00014

SPONSORING OCS REGION: Alaska

APPLICABLE PLANNING AREA: Cook Inlet

FISCAL YEARS OF PROJECT FUNDING: FY 2014

COMPLETION DATE OF REPORT: 18 November 2016

COSTS BY FY: FY 2014: $ 499,428

CUMULATIVE PROJECT COST: $ 499,428

PROJECT MANAGER: Dr. Seth L. Danielson

AFFILIATION: University of Alaska Fairbanks

ADDRESS: 905 N. Koyukuk Dr., Fairbanks, AK, 99775-7220

PRINCIPAL INVESTIGATOR(S)*: Dr. Seth Danielson, Dr. Katherine Hedstrom, Dr. Enrique Curchitser

KEY WORDS: Cook Inlet, circulation, model, hydrography, tide

BACKGROUND: 

BOEM proposes to lease within the Cook Inlet Planning Area in its proposed 2012-2017 Five-year 

Program. Oil Spill Risk Analysis (OSRA) is a cornerstone for evaluating impacts and alternatives in OCS 

oil and gas leasing Environmental Impact Statement preparation and for evaluating mitigation, such as oil 

spill contingency plans. BOEM needs updated model fields of the winds and surface currents in Cook 

Inlet and adjacent areas to create OSRA estimates of oil-spill trajectories.

The purpose of this study is to develop up-to-date ocean circulation hindcast model simulations for the 

area of Cook Inlet, Shelikof Strait and adjacent portions of the Gulf of Alaska using a state of the science 

general circulation model. This study will provide the scientific information needed by the State of Alaska, 

the Cook Inlet Regional Citizens Advisory Committee and other stakeholders to understand and mitigate 

potential impacts associated with development of offshore energy resources.

OBJECTIVES:

• Modify an existing ocean circulation model that includes Cook Inlet, Shelikof Strait and adjoining 

areas of the Gulf of Alaska to maximize overall skill in the target area. 

• Conduct sensitivity testing and validation of the modified model.

• Produce gridded velocity fields (wind, surface water, three-dimensional currents) for a 5-10 year

hindcast simulation. 

• Provide documentation through a model manual and disseminate significant findings in the peerreviewed literature.

DESCRIPTION:

The main research tool used for this work is a state-of-the-art coupled ocean/sea ice model based on the 

Regional Ocean Modeling System (ROMS). The model was setup regionally for the Gulf of Alaska at 

moderately high resolution (~ 1.5 km). Model features include a modern high-resolution bathymetric 

digital elevation dataset, sea ice, a wetting-and-drying algorithm, moderately high-resolution reanalysis 

atmospheric forcing, tidal forcing with eight constituents, and a spatially explicit high-resolution coastal 
ACCESS NUMBER: M14AC00014

fresh water discharge time series. Extensive qualitative and quantitative model skill assessments were

carried out as part of the effort.

SIGNIFICANT CONCLUSIONS:

We find that the model exhibits appreciable skill in reproducing observed tidal current directions, 

magnitudes and phases; tidal amplitude magnitudes and phases; and wind and buoyancy forced mean 

flow features on and near the northern Gulf of Alaska continental shelf. Observed tidal currents that are 

poorly reproduced by the model generally occur in constricted regions that are not well resolved by the 

model’s grid spacing and bathymetry. We also find that the model hindcasts of the temperature and 

salinity fields reproduce those observed in Cook Inlet with a nearly 1:1 relation on average for 79 

hydrographic CTD transects occupied during the model integration’s time range, although there is a 

depth-dependent bias such that the model tends to be somewhat too saline and cool at depth and 

somewhat too fresh and warm at the surface. For all CTD data on these transects the average 

temperature offset is 0.65 °C (σ = 1.07), with the model slightly cooler than the observations; for salinity, 

the model hindcast is slightly more saline than the observations with a mean offset of 0.47 (σ = 1.05). 

Combined, 43% of the hindcast/observation pairs simultaneously agree to within 1 for both temperature 

and salinity and 86% agree to within 2 (°C and salinity units). The model results provide new insights to 

the pathways of fresh coastal discharges and nutrient-rich basin waters and their variability. 

STUDY RESULTS:

Model simulations using the coupled circulation-sea ice model were carried out for the ten-year period of 

1999-2008 and archived. Extensive model evaluation was carried out with an analysis of 1. Tidal 

amplitudes, 2. Tidal currents, 3. Sub-tidal currents, 4. Temperature and salinity, and 5. Sea ice cover. The 

comparisons show significant skill in the model capability to reproduce observed circulation and sea ice 

patterns in the Cook Inlet, Shelikof Strait and greater Gulf of Alaska.

STUDY PRODUCTS:

The following were created as part of this project:

• A new ocean circulation model for the Cook Inlet and Shelikof Strait region

• A 10-year model hindcast with 3-d fields of velocity, temperature, salinity and 2-d fields of surface 

stress, air-sea fluxes, and ice.

• An updated Regional Ocean Modeling System (ROMS) users manual.

• Final report

• Study results were presented at regional (Alaska Marine Science Symposium) and national 

(AGU-ALSO Ocean Sciences meeting) scientific conferences

Map of Study Area: