An Assessment of the Hydrokinetic Energy Potential in Cook Inlet, Alaska

1. An Assessment of the Hydrokinetic Energy Potential in Cook Inlet, Alaska Lyon Lanerolle1,2, Christopher Paternostro3, Gregory Dusek3, Laura Rear McLaughlin3and Sean Skaling4 1NOAA/NOS/OCS/Coast Survey Development Laboratory,1315 East-West Highway, Silver Spring, MD 20910; 2Earth Resources Technology (ERT) Inc., 6100 Frost Place, Suite A, Laurel, MD 2070; 3NOAA/NOS/Center for Operational Oceanographic Products and Services, 1305 East-West Highway, Silver Spring, MD 20910; 4Alaska Energy Authority, 813 West Northern Lights Boulevard, Anchorage, AK 99503.

2. Introduction and Motivation • Alaska Energy Authority (AEA) is interested in optimal locations for siting hydrokinetic energy projects in Cook Inlet, AK • AEA-NOAA/National Ocean Service (NOS) partnership was established • NOAA/NOS/CO-OPS performed field study in Summer 2012 with current meters • NOAA/NOS/Office of Coast Survey (OCS)/CSDL performing numerical ocean model simulations to complement field study • Numerical model output fields are seamless spatio-temporally (no gaps) and gridded – hence, well suited for producing maps, etc. • Final assessment from modeling study will provide AEA with guidance on turbine placement, etc.

3. Field Study Areas and Modeling Domains • Field study had 10 current meters (magenta circles) • Model has a parent domain (blue) • Also 2 high resolution nests to better resolve physics • Kachemak Bay nest (red) • Upper Cook Inlet nest (green) • Model nesting technology previously established at NOAA/NOS/OCS/CDSL

4. Numerical Model Set-up • Use Rutgers University’s Regional Ocean Modeling System (ROMS) for model simulations • ROMS run for 36 days beginning 01/01/2008 • Model forced with tides only (no sub-tidal, river or meteorological forcings included) - ~90% of water level/current signal is purely tidal • Tidal boundary forcing from ADCIRC model tidal harmonic constituent database • Tides ramped over 5-days linearly in time • Used final 30-days of simulation for analysis

5. Model Grid Spatial Resolution (m) Parent Grid Kachemak Bay Nest Upper Cook Inlet Nest Δξ Δη

6. Digital Elevation Map (DEM) • Need DEM to account for heavy tidal flooding-drying • DEM created with best available bathymetry, shoreline, topography data at NOAA/NOS/OCS/CSDL • Bathymetry – NOAA/NOS soundings • Shoreline - NOAA/NGDC, NGS • Topography – USGS gridded product • DEM clipped at 15m height (not a Tsunami model)

7. Maximum Power Density on Parent Grid Near surface Mid-water Near-bottom • Power Density, P=0.5*ρ*|U|3 where |U|=(u2 + v2)1/2 as w << u, v; [P] = W/m2 • Plot P in a Log10 scale for clarity and contrast • Highest P near surface and lowest near bottom but with similar distributions • Geographically, highest P : along axis of Cook Inlet, North Foreland, strait between West Foreland and East Foreland (and some isolated locations in upper CI) • Maximum P ~ 30 kW/m2

8. Maximum Power Density on Nested Grids Kachemak Bay Upper Cook Inlet • Although some differences seen, Parent and Nested grids reflect similar Power Densities • Little power available within Kachemak Bay • Upper Cook Inlet is energetic • High PD values in Upper Cook Inlet due to flooding-drying in narrow channels Parent Parent Nest Nest

9. Vertical Distribution of Power Density Parent Nest Parent Nest • Transects are time snapshots • Transects show the parent and nested domains give similar results • Kachemak Bay less energetic and has weak PD stratification • Upper Cook Inlet more energetic and PD is stratified with higher values in the near-surface region

10. Spatio-Temporal Power Density Evolution Kachemak Bay Upper CI • Hovmoller diagrams for the parent (left) and nested (right) domains are similar • Weak vertical stratification and action of bottom stress apparent • Highest power at flood tide and lowest power at slack tide

11. Power Extraction Times Parent Parent Parent Grid Nest Nest • PE time = available time (hrs.) to extract at least 1 kW/m2 over the 30-day simulation period • Can set the threshold (in this case 1 kW/m2 ) to value we choose • PE times reflect maximum near-surface Power Density distributions • PE times between parent and nested domains similar but also some differences • Highest PE timesin strait between E and W Foreland and in North Foreland • Other “hot spots” : Anchor Pt. (300-400 hrs., ~50% of the time), Pt. Possession (400-450 hrs), • Fire Island (400-450hrs., ~60% of the time), channels in Knik Arm (400-450 hrs)

12. Conclusions and Future Work • The ROMS model was used to provide a numerical assessment of hydrokinetic power in Cook Inlet, Alaska • This initial assessment used only tidal forcing (~90% of current signal) • This study showed that the optimal locations for turbine placement are: • Anchor Point vicinity • the strait between West and East Foreland (near Nikiski) • North Foreland region • Point Possession vicinity • Northern Fire Island region • along the channels in Knik Arm • Typically 300-450 hrs. of power at a threshold of 1 kW/m2is available over 30-days which is ~50%-60% of the time • KachemakBay has little power availability unlike upper Cook Inlet • In the vertical, most power is in upper half of water column • Results between parent domain and higher resolution nests are similar • Future work: run fully synoptic hindcast simulation for summer of 2012 with also sub-tidal, river and meteorological forcing and repeat analysis and compare outcome with present analysis