Abstract
Yakutat is a community along the northeast coast of the Gulf of Alaska that is currently considering utilizing renewable, wave based electricity generation in order to lessen their reliance on diesel fuel for electricity generation. As part of this effort the University of Alaska Fairbanks carried out a study to assess the wave energy resource off of Yakutat’s Cannon Beach. Funding for the assessment was provided by the Alaska Energy Authority and the City and Borough of Yakutat. The study described herein utilized a combination of in situ observations and numerical modeling. The central piece of the assessment was an in situ wave measurement campaign. An Acoustic Doppler Current Profiler (ADCP) equipped to measure surface gravity wave spectra (i.e. wave height, direction and frequency) was deployed in 40 m of water approximately 6 km offshore of Cannon Beach and adjacent to the Yakutat Airport. The ADCP recorded a full annual cycle of wave spectra at the site over the course of a ~1.5 year deployment between August 2013 and April 2015. The ADCP mooring was also equipped with a Seabird Microcat CTD that measured and recorded hydrography at the site (e.g. Conductivity/salinity, Temperature and pressure/Depth) for the full length of the deployment. Additionally, the ADCP recorded water column velocity between the ADCP transducer and the surface (from ~5 meters above the bottom and the surface). Finally, ~6 months of passive acoustic data were collected at the site during this period. Neither the CTD data nor the passive acoustic data are discussed in this report.
As part of the assessment, wave height and frequency recorded by two nearby NDBC buoys are compared to ADCP wave data. Gaps in both the ADCP and NDBC record do not allow for a comparison for the full length of the ADCP record but for the periods where there is overlapping data, the buoys and ADCP agree very well (R=0.84, 0.79 for the ADCP and each of the two buoys). Additionally, a coarse, regional wave model hindcast utilizing the SWAN spectral wave model was implemented for the northern Gulf of Alaska including the nearshore zone off Yakutat. The coarse model forced a finer scale, nested SWAN model for the region immediately adjacent to Yakutat. Results of both the regional and fine scale models compare well with both the ADCP and NDBC wave data from the region (R=0.86 for significant wave height between the model grid point nearest the ADCP and the ADCP measured values and R=.92, 0.93 for the two buoys for significant wave height). The goal of the modeling is to quantify the annual variability in the wave resource and to aid in identify the most promising sites for installation of a wave energy converter (WEC) or an array of WECs. Since only a single ADCP was deployed, a validated model is needed to ensure that the regional wave climate was well characterized and understood.
The mean annual available wave energy at the mooring site is approximately 19.2 kW/m. While on an annual basis, this is less than sites off of Oregon or Hawaii (e.g. Kilcher, 2015), there is a large interannual variability in the Yakutat resource due to the frequent passage of storms over the Northern Gulf of Alaska. Winter values of the monthly mean available wave kinetic energy exceed 35 kW/m. Thus the resource is more than enough to satisfy Yakutat’s relatively modest electrical demand (e.g. Previsic and Bedard, 2009).