Algorithmic improvements and analyses of the generalized wave continuity equation based model, ADCIRC.

Second, nearly all GWC-based models utilize a velocity-based, non-conservative momentum equation (NCM) to obtain the depth-averaged velocity profile. It has been hypothesized that the conservative momentum equation (CM) may improve accuracy, mass balance and stability. Results show that the CM equation improves mass balance, both globally and locally, especially in areas of steep bathymetry gradients, and improves local spatial accuracy in these same regions, yet does so without significantly impacting stability, temporal accuracy and global spatial accuracy.First, the current time marching algorithm is semi-implicit, with the nonlinear terms evaluated explicitly. It has been hypothesized that the explicit treatment of the nonlinear terms can lead to instabilities. An iterative, implicit treatment of the nonlinear terms is implemented and studied. Results show an increase in the maximum time step of at least eight-fold, depending on the domain, and an increase in temporal accuracy from first to second order. A parallel implementation of the algorithm scales as well as the original algorithm.Shallow water equations are based on conservation of mass and momentum and can be used to model the hydrodynamic behavior of oceans, coastal areas, estuaries and lakes. The model used in this research ADCIRC, an advanced three-dimensional circulation model, is based on the shallow water equations. ADCIRC provides elevation changes and velocity profiles that can be utilized by themselves or coupled with other models, such as water quality models, thus lending itself to a wide-variety of applications. Three research areas are investigated in this dissertation in an effort to improve the predictive capabilities of ADCIRC through improved numerics.Third, baroclinic models that are used to simulate density-driven flows require an accurate and stable computation of the baroclinic pressure gradient (BPG). In this study, four methods for computing the BPG are investigated, along with resolution requirements (horizontal and vertical). Numerical experiments thus far indicate that the z-coordinate method provides the least amount of error, and a hybrid method, which switches from sigma to z-coordinates at a prescribed depth, also shows promising results

Hurricane Storm Surge Modeling for Southern Louisiana

Coastal Louisiana is characterized by low-lying topography and an intricate network of sounds, estuaries, bays, marshes, lakes, rivers and inlets that permit widespread inundation during hurricanes, such as that witnessed during the 2005 hurricane season with Katrina and Rita. A basin to channel scale implementation of the ADCIRC hydrodynamic model has been developed that simulates hurricane storm surge, tides and river flow in this complex region

Use of 1D Unsteady HEC-RAS in a Coupled System for Compound Flood Modeling: North Carolina Case Study

The research presented herein develops and compares an ADCIRC and ADCIRC/HEC-RAS (1D) paired model for the purpose of compound flood modeling within the Tar River and Pamlico Sound basins of North Carolina. Both the ADCIRC and 1D HEC-RAS models are capable of simulating river systems but differ in their underlying numerical formulations. A case-study comparison of each model’s ability to simulate flooding accurately and quickly in a riverine/estuarine system is investigated herein; results may serve as a valuable reference to forecasters and model developers. Individual models of the Tar River and Pamlico Sound area in North Carolina were used, and pairings of these models were devised to determine the benefits and drawbacks of using ADCIRC alone, or ADCIRC + 1D HEC-RAS, to simulate the response of the Tar River and Pamlico Sound during three test events: Hurricane Irene, Hurricane Floyd, and an unnamed April 2003 event. With increased emphasis on predicting total water levels, the results of this study can provide information for the possible development of similarly paired models for coastal river systems across the US and improve the body of knowledge about each model’s relative performance in riverine and estuarine areas.Ye

The CI-FLOW Project: A System for Total Water Level Prediction from the Summit to the Sea

Kildow et al. (2009) reported that coastal states support 81% of the U.S. population and generate 83 percent [$11.4 trillion (U.S. dollars) in 2007] of U.S. gross domestic product. Population trends show that a majority of coastal communities have transitioned from a seasonal, predominantly weekend, tourist-based economy to a year-round, permanently based, business economy where industry expands along shorelines and the workforce commutes from inland locations. As a result of this transition, costs associated with damage to the civil infrastructure and disruptions to local and regional economies due to coastal flooding events are escalating, pushing requirements for a new generation of flood prediction technologies and hydrologic decision support tools

An Integrated Scenario-Based Framework for Evacuation Modeling

Processes and cast study for creating a integrated scenario-based evacuation (ISE) framework

Improvements for the Eastern North Pacific ADCIRC Tidal Database (ENPAC15)

This research details the development and validation of the updated Eastern North Pacific (ENPAC) constituent tidal database, referred to as ENPAC15. The database was last updated in 2003 and was developed using the two-dimensional, depth integrated form of the ADvanced CIRCulation coastal hydrodynamic model, ADCIRC. Regional databases, such as ENPAC15, are capable of providing higher resolution near the coast, allowing users to more accurately define tidal forcing for smaller sub-regions. This study follows the same methodology as the EC2015 updates for the eastern coast of the United States and six main areas of improvement in the modeling configurations are examined: (1) placement of the open ocean boundary; (2) higher coastal resolution; (3) updated global bathymetry; (4) updated boundary forcing using two global tidal databases; (5) updated bottom friction formulations; and (6) improved model physics by incorporating the advective terms in ADCIRC. The skill of the improved database is compared to that of its predecessor and is calculated using harmonic data from three sources. Overall, the ENPAC15 database significantly (52% globally) reduces errors in the ENPAC03 database and improves the quality of tidal constituents available for sub-regional models in the ENPAC region

Improvements for the Western North Atlantic, Caribbean and Gulf of Mexico ADCIRC Tidal Database (EC2015)

This research details the development and validation of an updated constituent tidal database for the Western North Atlantic, Caribbean and Gulf of Mexico (WNAT) region, referred to as the EC2015 database. Regional databases, such as EC2015, provide much higher resolution than global databases allowing users to more accurately define the tidal forcing on smaller sub-region domains. The database last underwent major updates in 2001 and was developed using the two-dimensional, depth-integrated form of the coastal hydrodynamic model, ADvanced CIRCulation (ADCIRC), which solves the shallow-water equations in the generalized wave continuity equation form. Six main areas of improvement are examined: (1) placement of the open ocean boundary; (2) higher coastal resolution using Vertical Datum (VDatum) models; (3) updated bathymetry from global databases; (4) updated boundary forcing compared using two global tidal databases; (5) updated bottom friction formulations; and (6) improved model physics by incorporating the advective terms in ADCIRC. The skill of the improved database is compared to that of its predecessor and is calculated using harmonic data from the National Oceanic and Atmospheric Administration Center for Operational Oceanographic Products and Services (NOAA CO-OPS) stations and historic International Hydrographic Organization (IHO) data. Overall, the EC2015 database significantly reduces errors realized in the EC2001 database and improves the quality of coastal tidal constituents available for smaller sub-regional models in the Western North Atlantic, Caribbean and Gulf of Mexico (WNAT) region

Application of the Forward Sensitivity Method to a GWCE-Based Shallow Water Model

The Forward Sensitivity Method (FSM) is applied to a GWCE-based shallow water model to analyze the sensitivity to the numerical parameter, G, that determines the balance between the wave and primitive forms of the continuity equation. Results show that the sensitivity to G calculated in the sensitivity evolution portion of the FSM is consistent with the actual sensitivity to G computed from multiple simulations using finite differences. The data assimilation step in the FSM is shown to be effective in selecting G that minimizes an objective function, in this case model errors based on sensitivities. Additionally, the FSM sensitivity results show 2 Δ x oscillations in the elevation and velocity fields develop when G is increased too high, suggesting the FSM may be an effective tool for determining the upper limit of G for real-world applications

Development and Validation of Accumulation Term (Distributed and/or Point Source) in a Finite Element Hydrodynamic Model

During tropical storms, precipitation and associated rainfall-runoff can lead to significant flooding, in both the upland and coastal areas. Flooding in coastal areas is compounded by the storm surge. Several hurricanes in recent history have exhibited the destructive force of compound flooding due to precipitation, rainfall-runoff, storm surge and waves. In previous work, various coupled modeling systems have been developed to model total water levels (defined as tides, waves, surge, and rainfall-runoff) for tropical storms. The existing coupled system utilizes a hydrologic model in the upland areas of the domain to capture the precipitation and rainfall-runoff associated with the storms; however, in the coastal areas the precipitation and rainfall-runoff is not captured. Herein a source/sink term is incorporated within the hydrodynamic model itself to capture precipitation and rainfall-runoff over the already inundated coastal areas. The new algorithm is verified for several idealized test cases, and then it is applied to Hurricane Irene. Validation indicates that the new methodology is comparable to the existing river flux forcing under most conditions and allows for the addition of streamflows due to overland runoff, as well as the actual precipitation itself

The Predictability of Near-Coastal Currents Using a Baroclinic Unstructured Grid Model

A limited domain, coastal ocean forecast system consisting of an unstructured grid model, a meteorological model, a regional ocean model, and a global tidal database is designed to be globally relocatable. For such a system to be viable, the predictability of coastal currents must be well understood with error sources clearly identified. To this end, the coastal forecast system is applied at the mouth of Chesapeake Bay in response to a Navy exercise. Two-day forecasts are produced for a 10-day period from 4 to 14 June 2010 and compared to real-time observations. Interplay between the temporal frequency of the regional model boundary forcing and the application of external tides to the coastal model impacts the tidal characteristics of the coastal current, even contributing a small phase error. Frequencies of at least 3 h are needed to resolve the tidal signal within the regional model; otherwise, externally applied tides from a database are needed to capture the tidal variability. Spatial resolution of the regional model (3 vs 1 km) does not impact skill of the current prediction. Tidal response of the system indicates excellent representation of the dominant M2 tide for water level and currents. Diurnal tides, especially K1, are amplified unrealistically with the application of coarse 27-km winds. Higher-resolution winds reduce current forecast error with the exception of wind originating from the SSW, SSE, and E. These winds run shore parallel and are subject to strong interaction with the shoreline that is poorly represented even by the 3-km wind fields. The vertical distribution of currents is also well predicted by the coastal model. Spatial and temporal resolution of the wind forcing including areas close to the shoreline is the most critical component for accurate current forecasts. Additionally, it is demonstrated that wind resolution plays a large role in establishing realistic thermal and density structures in upwelling prone regions