Tide and Storm Surge Dynamics in Estuaries of Variable Morphology

Storm surges are the most destructive component of coastal storms, and climate change is predicted to enhance the frequency of intense storm events in the future. Currently, most storm surge forecasting assumes linear surges and the extent to which this assumption leads to model inaccuracies is currently unknown. The goals of this research are to characterize storm surge in estuaries and determine the contribution of nonlinear tide-surge interaction to total inland surges. A citizen science experiment was conducted in four estuaries in Maine. Results show the estuary shape influences surges through convergence, friction and man-made constrictions. These mechanisms modified total surge levels by more than 50% from estuary mouth to head. The mechanisms behind higher order tide-surge interactions were also identified for the first time. The D6 and D8 bands were recognized as the dominant frequencies in tide-surge interaction, sometimes creating a total storm surge that was more than double that of the low-frequency, linear surge. Enhancement of quadratic friction from storm-induced currents is the primary mechanism causing the D6 interaction. The D8 interaction scales with the D6 and resonates in a portion of the estuary, amplifying the total surge. Sea level rise from climate change is expected to enhance inland storm surges as higher sea levels bring the system closer to the resonant depth for the D8 tide

Mixing Processes in Tidally Pulsed River Plumes: Mechanisms, Significance, and Variability

River plumes form at the river-ocean interface when fresh, buoyant river water merges with salty, dense ocean water and can significantly modify coastal water properties and circulation. It is important to understand how plumes physically mix into the ocean to inform predictive modeling of river-borne tracers to coastal seas. In tidally energetic regions such as New England, river plumes can form and evolve with each new tide and are referred to as “tidally pulsed”. In this dissertation, we explore the numerous mechanisms which can contribute to mixing tidally pulsed plumes (i.e., frontal, stratified shear [interfacial], and bottom-generated tidal mixing) their spatiotemporal variability, controlling processes, and the relative importance of each to plume dilution by utilizing numerical modeling and field observation techniques. The contributions of frontal, interfacial, and bottom-generated tidal mixing are first investigated using an idealized numerical model broadly inspired by the Connecticut River plume. A mixing budget is applied, and river discharge and tidal amplitude are varied between experiments to isolate the influence of each forcing on the budget. Results indicate bottom-generated tidal mixing can dominate the mixing budget for large tide, small discharge events, when the product of the nondimensional Estuarine Richardson number and inverse Rossby number ( ) exceeds 1. When the nondimensional parameter is below 1, interfacial mixing dominates. Frontal mixing was found to never exceed 10% of total mixing in the budget. This is the first study to identify the potential for bottom-generated tidal mixing to dominate mixing in surface-advected river plumes. Wind controls on stratified shear mixing in tidal plumes is investigated using a realistic model of the Merrimack River plume system. A salinity variance approach is applied, allowing for the quantification of stratifying and de-stratifying processes (straining, mixing, advection) throughout the tidal plume. Winds countering the right-turning tendency of the plume are found to be most effective at increasing plume mixing. During the wind events, ambient shelf stratification is advected offshore, which creates a saltier shelf condition beneath the plume and increases the vertical salinity gradient. Simultaneously, plume layer velocities are enhanced, increasing shear and straining. The larger salinity gradient between plume and ambient coupled with increased shear leads to enhanced stratified shear mixing in the near and mid-field plume. The wind mechanism was found to be effective at modulating mixing at short, tidal time scales. The evolution of stratified shear mixing throughout the interior Merrimack River plume is characterized using observational data. Three source-to-front transects were conducted over a ~6-hour tidal pulse during low wind conditions. Data collection on each transect included continuous sampling of current magnitude and direction supplemented by profiles of turbulent kinetic energy dissipation rates and conductivity, temperature, and depth (CTD). Analysis shows stratified shear mixing transforms spatially and temporally over a tide and is characterized by three distinct regimes: plume layer mixing, nearfield interfacial mixing, and tidal interfacial mixing. Plume layer mixing is confined within the plume and decreases offshore of the nearfield as the tide progresses. Nearfield interfacial mixing facilities exchange between the plume and underlying ambient shelf throughout the tidal pulse. Tidal interfacial mixing mixes plume with ambient waters offshore of the nearfield at the end of ebb tide when shelf currents reverse direction beneath the plume. These observations provide some of the most robust spatiotemporal plume mixing estimates to date. This dissertation highlights the highly variable nature of mixing in tidally pulsed river plumes and the oftenimportant influence of the ambient shelf condition on mixing. Winds and tides impact the collective plumeshelf system to varying degrees which subsequently modulates mixing in a spatiotemporally varying manner. Analyses of static locations or times likely omit essential processes contributing to mixing. This research provides important context for future coastal model development

Coastal windstorms create unsteady, unpredictable storm surges in a fluvial Maine estuary

Storm surges create coastal flooding that can be damaging to life and property. In estuaries with significant river influence (fluvial), it is possible for tides, storm surge, and river discharge to interact and enhance surges relative to the immediate coast. These tide-surge-river interactions were previously identified in a fluvial Maine estuary as higher frequency (\u3efour cycles per day) oscillations to storm surge which were proposed to be incited by enhanced friction and resonance during certain windstorm events (Spicer et al. 2019). The relative contributions to tide-surge-river interaction from atmospheric forcing variables (wind, barometric pressure, and externally generated surge) remains unclear. This work seeks to decompose and analyze a recent windstorm surge event to better isolate the effects of atmospheric forcing on tidesurge-river interaction. Results show total storm surges in the fluvial estuary to be two times larger than at the estuary mouth because of tide-surge-river interaction. Analysis indicated at least 50% of the magnitude of tide-surge-river interactions are created by non-tidal forcing, in the form of wind, enhancing frictional energy in the estuary. The remaining tide-surge-river interaction is likely a result of changes in tidal wave propagation speed due to surge deepening the mean estuary water level

Wind Effects on Near- and Midfield Mixing in Tidally Pulsed River Plumes

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

Managing for Stakeholders, Stakeholder Utility Functions, and Competitive Advantage

A firm that manages for stakeholders allocates more resources to satisfying the needs and demands of its legitimate stakeholders than what is necessary to simply retain their willful participation in the productive activities of the firm. Firms that exhibit this sort of behavior develop trusting relationships with stakeholders based on principles of distributional, procedural and interactional justice. Under these conditions, stakeholders are more likely to share nuanced information regarding their utility functions, which increases the ability of the firm to allocate its resources to areas that will best satisfy them (thus increasing demand for business transactions with the firm). In addition, this information can spur innovation, as well as allowing the firm to deal better with changes in the environment. Competitive advantages stemming from a managing-for-stakeholders approach are argued to be sustainable because they are associated with path dependence and causal ambiguity. These explanations provide a strong rationale for including stakeholder theory in the discussion of firm competitiveness and performance

Supporting Data for Figures in "Localized, tidal energy extraction in Puget Sound can adjust estuary resonance and friction, modifying barotropic tides system-wide"

<p>Supporting data for figures in "Localized, tidal energy extraction in Puget Sound can adjust estuary resonance and friction, modifying barotropic tides system-wide" by Preston S. Spicer, Zhaoqing Yang, and Parker MacCready. The manuscript is being considered for publication in Journal of Geophysical Research: Oceans (2023). The article analyzes the effect of a tidal turbine farm on tidal energy fluxes in the Salish Sea. Files are in MATLAB data and .m format with some .txt and shape files. Files named figX.m create the corresponding Figure X using provided .mat and other files. Variable names and units correspond to graphed data of each figure in the journal article.</p&gt

Supporting Data for Figures in "Localized, tidal energy extraction in Puget Sound can adjust estuary resonance and friction, modifying barotropic tides system-wide"

<p>Supporting data for figures in "Localized, tidal energy extraction in Puget Sound can adjust estuary resonance and friction, modifying barotropic tides system-wide" by Preston S. Spicer, Zhaoqing Yang, and Parker MacCready. The manuscript is being considered for publication in Journal of Geophysical Research: Oceans (2023). The article analyzes the effect of a tidal turbine farm on tidal energy fluxes in the Salish Sea. Files are in MATLAB data and .m format with some .txt and shape files. Files named figX.m create the corresponding Figure X using provided .mat and other files. Variable names and units correspond to graphed data of each figure in the journal article.</p&gt

Observations of Near-Surface Mixing Behind a Headland

Field observations were collected near the mouth of the Bagaduce River, Maine, in order to understand how complex features affect the intratidal and lateral variability of turbulence and vertical mixing. The Bagaduce River is a low-inflow, macrotidal estuary that features tidal islands, tidal flats and sharp channel bends. Profiles of salinity, temperature, and turbulent kinetic energy dissipation (ε) were collected for a tidal cycle across the estuary with a microstructure profiler. Lateral distributions of current velocities were obtained with an acoustic doppler current profiler. Results showed intratidal asymmetries in bottom-generated vertical eddy diffusivity and viscosity, with larger values occurring on ebb (Kz: 10−2 m2; Az: 10−2 m2/s) compared to flood (Kz: 10−5 m2/s; Az: 10−4 m2/s). Bottom-generated mixing was moderated by the intrusion of stratified water on flood, which suppressed mixing. Elevated mixing (Kz: 10−3 m2; Az: 10−2.5 m2/s) occurred in the upper water column in the lee of a small island and was decoupled from the bottom layer. The near-surface mixing was a product of an eddy formed downstream of a headland, which tended to reinforce vertical shear by laterally straining streamwise velocities. These results are the first to show near-surface mixing caused by vertical vorticity induced by an eddy, rather than previously reported streamwise vorticity associated with lateral circulation