such as the local average power density (W/m8) in a vertical plane perpendicular to the average current at each model grid cell. Visualizations of average power density could, in principle, be used to estimate the power available from a single turbine or a few turbines (an array small enough not to have a significant back effect on the currents). The ArcView GIS database developed by the tidal resource assessment group was well designed and executed, and it allows for downloading of the tidal modeling results for further analysis by knowledgeable users. Based on the final assessment report, the assessment group produced estimates of the total theoretical power resource. However, this was done for complete turbine fences, which essentially act as barrages. The group did not assess the potential of more realistic deployments with fewer turbines, nor did they incorporate technology characteristics to estimate the technical resource base. It is clear, however, that the practical resource will be very much less than the theoretical resource.
Methodology and Validation
ROMS is a structured-grid, open-source coastal ocean model. It has performed well in the prediction of coastal circulation and tides in a large number of applications (e.g., Warner et al., 2005; Patchen, 2007; NOAA, 2011a). Finer grid resolution may be needed to represent bathymetry accurately in high tidal current regions. Increasing the grid resolution in local areas of a ROMS model often results in a significant increase of the total model grid size, owing to the structured-grid framework. In contrast, unstructured-grid models, which have greater flexibility for high grid resolution in complex waterways, could provide an alternative, especially for areas of complex geometry with high tidal energy (see, e.g., Patchen, 2007). An evaluation of the effect of grid resolution in the most promising high tidal energy regions would be a critical next step for future studies.
The location of the offshore boundary, partway out onto the continental shelf, is adequate for this effort, assuming that only a single turbine or a limited number of turbines is represented. Extension of the model boundary farther away to minimize the boundary effect (e.g., to the shelf edge [see, for example, Garrett and Greenberg, 1977]) may be necessary in the future if models are rerun with representations of a large turbine array that would be extensive enough to have a back effect on offshore tides. Estimates of available power may not be accurate without considering the effect of the locations of open boundaries. This question could be evaluated in future studies. Comparisons of model bathymetry to acoustic Doppler current profiler (ADCP) measurements at selected stations indicated