Localized Tidal Energy Extraction in Puget Sound Can Adjust Estuary Reflection and Friction, Modifying Barotropic Tides System‐Wide

Harvesting energy via tidal stream turbines is being increasingly considered as a renewable energy resource in estuaries with strong tidal currents. It remains unclear how localized energy extraction changes basic tidal physics throughout real systems. Here, we analyze the influence of an extensive synthetic tidal turbine array on barotropic tides in the Salish Sea, a complex, tidally energetic estuary, using a realistic numerical model. Tidal energy fluxes are calculated at 15 sections throughout the system and decomposed into incident and reflected components, as well as by frequency. Results show the dominant semidiurnal constituent, M2, controls the total tidal energy flux everywhere. When turbines are placed in Tacoma Narrows, the M2 energy flux is enhanced at sections seaward of the array in Puget Sound and reduced landward. The principal diurnal constituent, K1, contributes little to the total energy flux, but behaves similarly. Changes to each constituent are primarily attributed to turbine enhanced frictional dissipation which reduces the estuary's natural resonant period (∼10 hr) amplification. Being close to the semidiurnal frequencies, the resonance adjustment reduces M2 tidal reflection seaward of the turbines and free surface amplitude (particularly landward of the turbines) thereby increasing (decreasing) tidal energy fluxes at seaward (landward) locations. K1 is further from the natural frequency and insensitive to resonance changes. We hypothesize K1 is directly sensitive to increased frictional dissipation which acts to reduce reflection and tidal amplitude, regardless of the estuary natural frequency. Spatial variability in dynamics is discussed, as well as potential environmental implications. Plain Language Summary Energy can be extracted from strong tidal currents present in many coastal estuaries via tidal stream turbines. We still lack a thorough understanding of how tidal turbine farms can modify tides and currents throughout the estuarine system they are installed in. Here, we use a computer model of the Salish Sea in the Pacific Northwest to simulate a large, synthetic tidal turbine farm in Tacoma Narrows to investigate impacts on tides elsewhere: from the Straits of Juan de Fuca and Georgia to South Puget Sound. We find that the tide occurring twice daily (M2) is more energetic than the once daily (K1) tide throughout the Salish Sea and so the M2 is more important to the transfer of tidal energy through the estuary (tidal energy