The study begins with an application of a state-of-the-art storm surge model to examine the effects of meteorological forecast errors on coastal flooding predictions along the North Carolina (NC) coastline. As Hurricane Arthur (2014) moved over Pamlico Sound, it increased the total water levels to 2.5 m above sea level; this water pushed first into the river estuaries and against the inner banks, and then moved eastward to threaten the sound-side of the barrier islands. It is hypothesized that a combination of storm track and intensity errors caused errors in the forecast winds and water levels along the NC coast during Arthur. Model results reveal that, as the forecast storm track and intensity errors increase, the errors in forecast wind speeds also increase, but the errors in forecast water levels remain relatively the same, signifying the non-linear response of the coastal ocean to wind effects. By separating the forecast errors in storm track and storm strength, this study quantifies their effects on the coastal ocean, which provides useful guidance for designing relevant forecast ensembles.
In addition to flooding impacts, storms can also cause dramatic changes in estuarine salinities, which can negatively impact estuarine ecosystems. Baroclinic models are useful tools for predicting estuarine salinity response under changing environmental conditions. In the present work, the features of wind- and plume-driven circulation in the vicinity of Choctawhatchee Bay (CB) and Destin Inlet, Florida, are analyzed with a recently-enhanced, three-dimensional, baroclinic model. Satellite imagery showed a visible brackish surface plume at Destin during low tide. The goal of the present study is to quantify variability in the plume signature due to changes in tidal and wind forcing. Modeled tides, salinities and plume signature are validated against in-situ observations and satellite imagery and then applied to analyze plume response in two scenarios. In the first case, model plume behavior is analyzed on successive days of near-constant tidal amplitudes and changing wind directions due to passing cold fronts. In the second case, plume response is investigated during consecutive days of neap-spring variability in the tides and near-constant wind speeds. Model results reveal a larger plume during spring tides and periods of weak wind forcing. Oshore winds enhance the north-south expansion of the plume, whereas onshore winds restrict the plume to the coastline.
Finally, the validated model is applied to identify salinity and transport characteristics within CB. Based on past studies, it is hypothesized that CB is a stratified system with limited flushing and zones of distinct salinity gradients. These hypotheses are tested by analyzing bay salinities from the validated model during a period of low river flows. Model surface salinities indicate brackish conditions (20 psu) throughout the bay except for near the river mouth. Stratification (10 to 15 psu) within the bay is unaffected by the passage of cold fronts and neap-spring tidal variability. The residence time within the Choctawhatchee Bay, an important indicator of estuarine health, is computed via particle tracking and is equal to roughly 40 days.
This work advances the scientific understanding of multiple aspects of estuarine circulation including wind-driven surge and flooding, brackish plume behavior through inlets and onto the shelf, and salinity transport and stratication properties within estuaries. Research ndings lead to a better understanding of estuarine response under a wide range of atmospheric conditions, and the resulting technologies will be useful for oil spill response operations, fisheries and pollution management.
Coastal Louisiana and Mississippi are especially prone to large hurricanes due to their geographic location in the north-central Gulf of Mexico. Several recent hurricanes have devastated the region, creating complicated environments of waves and storm surge. Katrina (2005) and Gustav (2008) made landfall in southeastern Louisiana, and their counter-clockwise winds pushed surge onto the Louisiana-Mississippi continental shelf, into the low-lying wetlands surrounding the Mississippi River, and over and through the levee system that protects metropolitan New Orleans. Rita (2005) and Ike (2008) passed farther to the west, moved across the Texas-Louisiana continental shelf, and created surge that flooded large portions of southwestern Louisiana.
Hydrodynamic models are used for a variety of purposes, such as the modeling of hurricane storm surges, the study of tidal circulation patterns, and the planning of naval fleet operations. One such hydrodynamic model is ADCIRC (ADvanced CIRCulation), which was developed more than 20 years ago and has been refined continuously by researchers across North America. ADCIRC is based on the shallow water equations and includes many of the features necessary to model complex hydrodynamic systems. However, some of these features were implemented in an attempt to solve specific problems, and their behaviors were never rigorously assessed. For instance, the model uses a wetting and drying algorithm to simulate the ebb and flow of tides in coastal regions. This behavior is important in many applications, and it must be modeled correctly. This research thesis will: (1) refute an attack on the usefulness of the finite volume method for computing mass balance errors, (2) lay the groundwork for a future study that will automate the placement of grid points based on a minimization of local mass balance error, (3) implement and assess the wetting and drying algorithm in one-, two-, and three-dimensional versions of the ADCIRC model, (4) identify a set of optimal parameters for wetting and drying simulations, (5) prove that recent updates to the wetting and drying algorithm were beneficial, and (6) show that smaller mass balance errors are obtained when they are computed for each vertical element in the water column.