Preston Spicer

The resilience of a power system to withstand a high-impact, low-frequency event is a growing concern, especiallyin coastal communities that tend to be densely populated and very prone to extreme events such as storms and flooding. In such areas, marine renewable energy can be integrated with existing renewable energy sources to enhance generation diversity and improve power system resiliency. This paper proposes an empirical study to investigate the impact of marine resources, particularly tidal energy, on power system resiliency. A set of quantitative metrics with intuitive physical interpretations is used to evaluate the resiliency of a power system enhanced with distributed generation in the form of rooftop photovoltaic systems, battery energy storage systems, and tidal generators. The effectiveness of resource diversification on the power system resiliency is demonstrated through simulations on a model of a real-world coastal distribution feeder located in Sequim, Washington.

In the United States (US) Caribbean Sea, Puerto Rico and the US Virgin Islands (USVI) are planning to transition to renewable energy. Being surrounded by water, the use of marine energy within Puerto Rico and the USVI represents an opportunity to increase renewable energy usage. Marine energy includes wave, tidal, and current energy as well as thermal and salinity gradient energy, and has a large potential to provide reliable and efficient power. While marine energy is usually perceived to bring power to the grid, it can also be used to power activities at sea, particularly offshore aquaculture. In the US Caribbean islands, the development of co-located offshore aquaculture and marine energy could help boost the ocean economy. This study highlights a real-world assessment of the suitability to co-locate offshore integrated multi-trophic aquaculture (IMTA) and wave energy off Puerto Rico and the USVI. The feasibility for co-location was determined through a spatial analysis to identify suitable areas for co-location, field work to collect environmental data, and a readiness analysis of wave energy devices. Combining key environmental, regulatory, and logistical parameters, the spatial analysis identified potential suitable areas for co-location off the coast in the northwest corner of Puerto Rico, northwest of Culebra, east of Vieques, and north of St. Thomas in the USVI. Wave energy was identified as the most limiting parameter for co-location in the study area. The wave energy data collected were comparable to the model predictions, showing the usefulness of fine-scale environmental conditions from wave models to assess the feasibility for co-location. Through the combination of spatial analysis, environmental monitoring, and information on wave energy device readiness, several key components for the technical feasibility of co-locating offshore IMTA and wave energy have been demonstrated in the US Caribbean islands.

The Duwamish River Estuary (DRE) of Washington is prone to compound flooding during atmospheric river (AR) events. The processes contributing to such flooding (coastal and fluvial) have remained opaque to municipalities that are increasingly impacted. Here, we conduct a suite of coupled atmosphere‐hydrology‐ocean model simulations with varying forcing combinations (tide, surge, and/or river discharge) to identify the primary drivers of compound flooding during a recent AR event. We also test year 2,100 climate forcing to project how flooding and drivers may change in the future for the same event. We identify a clear distinction between dynamics in the downstream, engineered portion of the DRE compared to the upstream, “natural” river. Downstream, tides dominate water levels but contributions from storm surge and nonlinear tide‐surge interaction elevate tide‐only high waters from no flooding to major flooding. Upstream, total water levels during the event are ∼6 cm higher than downstream due to an increasing influence of river discharge over surge and tides. Notably, nonlinear surge‐river and tide‐river interactions act to reduce upstream water levels up to 50% compared to estimates which linearly sum tides, surge, and river, likely reducing flood vulnerability. Under two future climate scenarios: one with only sea level rise (SLR) and another with SLR plus atmospheric warming, we find little change in mechanism contributions to water levels. Expanded flooding in both cases is largely due to SLR, as a ∼50% increase to river discharge under the warming scenario has no impact downstream and marginally increases (∼3 cm) water level upstream.

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.

The Connecticut River plume is influenced by energetic ambient tides in the Long Island Sound receiving waters. The objectives of this modeling study are (a) characterizing the spatial heterogeneity of turbulent buoyancy fluxes, (b) partitioning turbulent buoyancy fluxes into bottom‐generated and interfacial shear contributions, and (c) quantifying contributions to plume‐integrated mixing within the tidal plume. The plume formed during ambient flood tides under low river discharge, spring tides, and no winds is analyzed. Turbulent buoyancy fluxes (B) and depth‐integrated B through the plume (Bd) are characterized by pronounced spatial heterogeneity. Strong mixing (Bd ∼ 10⁻⁵‐10⁻⁴ m³/s³) occurs near the mouth, in the nearfield plume turning region, over shoals, and nearshore shallow areas. Low to moderate mixing (Bd ∼ 10⁻⁸‐10⁻⁶ m³/s³) occupies half the plume. Buoyancy fluxes are first partitioned based on the depth of the shear stress minimum between plume‐generated and bottom‐generated shear maxima. Four other tested partitioning methods are based on open channel flow and stratified shear flow parameterizations. Interfacial and bottom‐generated shear contribute to different areas of intense and moderate mixing. All methods indicate a significant plume mixing role for bottom‐generated mixing, but interfacial mixing is a bigger contributor. Plume‐integrated total and interfacial mixing peak at max ambient flood and the timing of peak bottom‐generated mixing varies among partitioning methods. Two‐thirds of the mixing occurs in concentrated intense mixing areas. A parameter space with the ambient tidal Froude number and plume thickness to depth ratio as axes indicates many tidally modulated plumes are moderately to dominantly influenced by bottom‐generated tidal mixing.

Microstructure profiling was utilized to estimate vertical mixing (via vertical turbulent buoyancy flux) during a tidal pulse in the interior Merrimack River plume in calm winds. Multiple stratified shear mixing regimes appear and evolve with time. Initially the plume acts as a nearfield jet, with mixing in the plume (plume layer mixing) and over the plume‐ambient interface (nearfield interfacial mixing). As the plume grows, interfacial mixing is suppressed offshore of the nearfield as currents slow, diminishing turbulent exchange between plume and shelf. At the end of ebb, ambient tidal currents reverse direction below plume, initiating another mode of internal, interfacial mixing (coined here as tidal interfacial mixing), allowing exchange between plume and ambient waters offshore. This work highlights previously unreported tidally modulated mixing within the near and midfield of a river plume.

River plumes transport and mix land‐based tracers into the ocean. In tidally pulsed river plumes, wind effects have long been considered negligible in modulating interfacial mixing in the energetic nearfield region. This research tests the influence of variable, realistic winds on mixing in the interior plume. A numerical model of the Merrimack River plume‐shelf system is utilized, with an application of the salinity variance approach employed to identify spatial and temporal variation in advection, straining, and dissipation (mixing) of vertical salinity variance (stratification). Results indicate that moderate wind stresses (∼0.5 Pa) with a northward component countering the downcoast rotation of the plume are most effective at decreasing stratification in the domain relative to other wind conditions. Northward winds advect plume and ambient shelf stratification offshore, allowing shelf water salinity to increase in the nearshore, which strengthens the density gradient at the plume base. Straining in the plume increases with winds enhancing offshore‐directed surface velocities, leading to increased shear at the plume base. Increased straining and larger density gradients at the plume base enhance variance dissipation in the near‐ and midfield plume, and dissipation remains enhanced if the shelf is clear of residual stratification. The smaller spatial and temporal scales of the Merrimack plume allow the mechanisms to occur at tidal time scales in direct response to instantaneous winds. This is the first study to show tidal time scale wind‐induced straining and advection as controlling factors on near‐ and midfield mixing rates in river plumes under realistic winds.