Far-field impacts of tidal energy extraction and sea level rise in the Gulf of Maine

The dynamics of tides in the Gulf of Maine are unique due to the tidal resonance, which generates the largest tidal range in the world (about 16 m). Consequently, a large tidal energy resource is available in this area, particularly in the Bay of Fundy, and is expected to be harvested in the future. Currently, more than 6 projects are operational or under development in this region (in both US and Canadian waters). Understanding the far-field impacts of tidal-stream arrays is important for future development of tidal energy extraction. The impacts include possible changes in water elevation, currents, and sediment transport. Accordingly, a number of previous studies have assessed the impacts of the tidal energy development in the Gulf of Maine. Further, due to the sea level rise (SLR), those impacts may also change during the project lifetime, which is usually more than 25 years. The objective of this study is to assess the combined effects of SLR and tidal energy extraction on the dynamics of tides in the Gulf of Maine. A tidal model of the Gulf of Maine was developed using Regional Ocean Model System (ROMS) at one arcminute scale. The model extends from 71.5W to 63.0W and from 39.5N to 46.0N. After validation of the model at NOAA tidal gauge stations and NERACOOS buoys, several scenarios; including SLR scenario, and tidal extraction scenario, were examined. Recent studies suggest that the global dynamics of tides will change due to SLR; therefore, SLR not only affects the bathymetry of the model inside the domain, it also changes the boundary forcing, which was considered in this effort. The results of the impacts of the tidal energy extraction with and without the SLR were presented, and compared with those from literature. Up to 4% decrease in tidal range and M2 amplitude was estimated in Minas Basin due to the 2.5 GW extraction scenario without SLR. On Massachusetts coastal area, the impacts of the same scenario can be considered negligible, 0.94%. In summary, the implementation of modified boundary forcing due to SLR, which was ignored in the previous works, can change the results of the impact assessment. Based on the results, the far-field impact is more threatening in coastal regions of US. However, the impact of energy extraction in Minas Passage is relatively small. Compared to the model validation, the impacts were inside the uncertainty level of the model. For example, maximum change in Boston coastal area was calculated up to 1.65%, which is inside the level of uncertainty in models, about 10%. Furthermore, the impact of SLR on the dynamics of tides is much more than energy extraction assuming 2.5 GW extraction in Minas Passage