Coastal Hazards

The tsunami generated by the 2010 Chilean earthquake was recorded at several tide gauge stations along the Pacific coast from 02/27/2010 to 03/02/2010. The marigram at the tide gauge station in Crescent City Harbor in Northern California is analyzed in detail because Crescent City is well known for its tsunami vulnerability. The energy spectrum as a function of frequency has been found to contain several spikes corresponding to the frequency range of 3×10^-4 ~ 8×10^-4 Hz. This behavior is different from several prior tsunamis observed and analyzed for Crescent City Harbor. A finite element numerical model has been used to compute the resonant response at Crescent City Harbor to incident waves with different wave directions. It is found that the spectral spikes are associated with the first fundamental mode of oscillation at the dimensionless wave number kl = 1.10 for different water depth due to the varying tide levels (0.6 to 3.9 meters). A closer view of the spectral density curves found that everyday tide gauge record also contained the same multi-spectral-spikes because of the significant variation of water depth from low tide to high tide. In order to correctly decipher the resonant response characteristics to incident wave the response curve plotted as a function of the dimensionless wave number is essential.

The objective of this work is to build a high performance computing framework for simulating, analyzing and visualizing oil spill trajectories driven by winds and ocean currents. We adopt a particle model for oil and track the trajectories of oil particles using 2D surface currents and winds, which can either be measured directly or estimated with sophisticated coastal storm and ocean circulation models. Our work is built upon the Cactus computational framework. The numerical implementation of the particle model as well as the model coupling modules will become crucial parts of our upcoming full 3D oil spill modeling toolkit. Employing high performance computing and networking, the simulation time can be greatly reduced. Given timely injection of the measurement data, our work can be helpful to predict oil trajectories and facilitate oil clean up, especially after a tropical cyclone.

Due to the retreat of sea ice coverage in the Arctic Ocean, increasing wave intensity is becoming a significant concern for coastal erosion and offshore operations. In order to better assist environmental protection and human activities in the Arctic, a predictive model is needed for wave conditions in the ice-covered seas. Recently, a continuum viscoelastic model has been developed to describe the wave propagation characteristics in all types of ice cover. However, this model is not ready to be integrated into wave models until sufficient validation and parameterization is completed. In this paper, theoretical results are presented to demonstrate the complexity of the problem. Additional study needed to complete the theoretical model is discussed. A conceptual experiment is described as a validation and parameterization plan.

A two phase compressible finite volume numerical model based on Navier Stokes equation and k-ɛ equations is used to investigate interaction of regular waves with a 1:5 scale reinforced concrete model of a typical section of I-10 Bridge over Escambia Bay, Florida which was extensively damaged by Hurricane Ivan. Simulation results are validated by comparing to experimental data available from large scale laboratory experiments of wave forces on Highway Bridge superstructures conducted at Oregon State University. In addition, effect of air compressibility and the viscous effects on total hydrodynamic forces applied to the bridge superstructure are evaluated.

Surge and waves generated by hurricanes and tropical storms often cause severe damage and loss of life in coastal areas. It is widely recognized that wetlands along coastal fringes reduce storm surge and waves. Yet, the potential role and primary mechanisms of wave mitigation by wetland vegetation are not fully understood. Knowledge of wave attenuation is essential for assessing the ability of vegetation to limit wave damage. The goal of the work reported here was to use a laboratory wave flume to quantify the attenuation of waves as a function of vegetation type, density, and height. The properties of waves passing through rigid and flexible model vegetation as well as live Spartina alterniflora and Juncus romerianus were measured. An automated system was developed and used to generate regular and random waves and to record time series of water surface elevation. A technique was developed for extracting the water surface profile through the vegetation field from images recorded with a consumer grade digital video camera. The new method was also tested for wave setup measurements along a plane sloping beach.

A numerical study is conducted to simulate the oscillations in Lake Pontchartrain induced by Hurricane Katrina. The physical mechanisms of the wind-induced oscillation in Lake Pontchartrain are modeled by the depth-averaged, non-linear shallow-water equations. Finite-volume method (FVM) is used in the model with the model results verified by the extensive field data compiled by IPET. The present model is further applied to investigate the oscillations in Lake Pontchartrain induced by two synthetic hurricanes scenarios within the time-span of 00:00 UTC August 29 to 00:00 UTC August 30, 2005. Scenario 1: Hurricane Katrina tracks on its original route under the condition if the dikes in several drainage canals are not breached. Scenario 2: Hurricane Katrina tracks on its original route with reduced forward speeds. It is found that much more severe damages in metro New Orleans and neighboring parishes could be expected if Hurricane Katrina passes through the regions nearby the east shore of Lake Pontchartrain with reduced forward speeds.

Based on Hurricane Ivan condition, numerical modeling of extreme waves under hurricane wind condition was investigated in this study in Pensacola Bay. Results from two popular wave models, STWAVE 4.0 and SWAN 48.8 models, were compared in three numerical experiments. Under regular incidental wave forcing, predictions of progressive wave heights from SWAN and STWAVE model are very close. However, under strong wind forcing condition of 120 mph wind speed, the spatial distributions of waves predicted by SWAN and STWAVE show substantial differences, even though the overall maximum wave height is close. Outside the bay, wind-induced wave heights predicted by SWAN are generally higher than those predicted by STWAVE. Inside the bay, along the direction from the southern shoreline to the northern shoreline, wave predicted by SWAN is generally higher than those predicted by STWAVE near the southern shoreline. It then becomes smaller than those estimated by STWAVE as wind driving waves to the north.

The catastrophic damages caused by hurricane Katrina and Rita in 2005 focused new attention on accurately predicting storm surges and efficiently evaluating coastal risks. Numerous storm surge models (i.e., SLOSH, CH3D-SSMS, ADCIRC) have been developed and used in real-time for estimating local storm surges from an approaching hurricane. One of the state-of-the-art techniques is to run high resolution storm surge models such as ADCIRC utilizing hundreds of computers (or CPUs) in parallel (Fleming et al. 2007). Even with the parallel computing resources, it can take hours to predict high resolution local storm surge in real time once a hurricane advisory is issued from the National Hurricane Center (NHC). As an alternative, we have developed a robust and efficient method to predict local storm surge using data mining. This data mining method is programmed into a simplified Graphical User Interface (GUI) which operates in real time and it is desktop based, fast and very easy to use. The algorithm uses a weight based Storm Similarity Index (SSI) which is calculated by using current hurricane position, Central Pressure (C_P), Pressure Scale Radius (R_max) along with hurricane track, forecasted landfall location, storm forward speed, and forecasted storm track published by the National Hurricane Centre (NHC) and then correlated with the characteristics of hundreds of synthetic storm simulations archived in a central database. Based on the values of SSI (scales from 0 to 1), the GUI then identifies a group of synthetic storms that closely matches with the characteristics of the approaching hurricane and then display high resolution results (e.g., maximum surge elevation and hydrographs) in Google Earth environment. The method has been verified against two historical hurricanes, Katrina and Camille which made landfall in the Mississippi coast. With the help of this tool, the emergency personnel can quickly estimate high resolution local storm surge and can make quantitative decisions by evaluating "what-if-scenarios" starting two to three days ahead of the landfall.

This paper presents an experimental investigation of solitary wave induced fluid motions in a submerged cavity. The evolution of the vortices and wave elevations were recorded for analysis. The tests were conducted in a glass-walled wave flume. A piston-typed wavemaker was installed on one end of the flume for generating desired solitary waves. A cavity of changeable size was positioned in the flume with two up-leveled acrylic panels. Three resistance-typed wave gauges were placed along the flume to record the wave profiles. The Planar Laser Induced Fluorescence (PLIF) technique was utilized to visualize and study the flow patterns as a solitary wave propagating past the cavity zone. The laser module used for the study had wavelength, output power, and projection fan angle of 532 nm (green light), 20 mW, and 100 degree, respectively. The laser excited the molecules of the fluorescent dyed fluid. As the incident wave passed by, any flow field feature would be illuminated. Each test was recorded with a video camera, and all the image frames could be further processed for comparison with the results obtained from a finite-analytic based two-dimensional (2-D) viscous flow model. This flow model solves combined stream function and vorticity equations. In terms of wave elevation and transformation of the formed vorticity, fairly good agreements are obtained between the numerical solutions and experimental observations. The results are presented and discussed.

A calibrated three-dimensional model was used to investigate the transport of pollutants in the Yangtze estuary in China. The pollutant was drained from one anabranch into the Yangtze estuary. The investigation focuses on the tidal forcing transport of pollutants, and analyzed the potential optimization of the real-time management of pollutant draining scheme. In this study, the pollutant was drained through one sluice, and the sluice was constructed in one anabranch with a distance about 300 m from the Yangtze River. The hydrodynamics and the transport of pollutants nearby the sluice were also investigated, and some interesting phenomena were discussed.

Tsunami waves can cause large forces on coastal structures. This study carried out experiments on a horizontal flume to simulate tsunami waves with the dam-break method making impact on a vertical plexiglass wall. The forces obtained were compared with forces estimated by various available methods. It was found that the forces predicted by two methods (ASCE and Miles) are lower than those measured in the experiments, while three other methods (Honolulu building code, Coastal Engineering Technical Note, and Cross) estimated larger forces than measured in this study. Ramsden and Raichlen's method seemed to predict forces that match our experimental results closely, but at least one prediction was lower.

Salinity intrusion, as one of the main coastal hazards, has a significant influence to the Yangtze Estuary. To describe the characteristics of salt intrusion, the modified ECOMSED is applied to establish a three dimensional baroclinic salinity transport model. An approach to represent a moving boundary is introduced and the improved model is validated through the observed field data of tidal height, current and salinity distribution. Since the saline intrusion is mainly affected by the upstream discharge and out sea tidal ranges, several combinations of discharge and tidal ranges conditions have been carried out to discuss the impact of saline intrusion due to the South-to-North Water Transfer Project in the dry seasons. Based on the simulation result, the salinity intrusion under different computational conditions is discussed.

Surface-level turbulence in the Hurricane Boundary Layer is an important factor in the determination of wind load characteristics for coastal structures. While the necessary data has been collected from fixed stations, very little of it has been collected during an eyewall passage and/or in suburban terrain. Recent field research by the Florida Coastal Monitoring Program using portable mobile towers has enabled us to collect and to analyze the data that could not be obtained previously. This paper analyzes high fidelity wind velocity data collected during Hurricane Ike (2008) to better understand the effect of the terrain conditions in hurricane wind turbulence. Two 10-m instrumented towers were co-located in close proximity to compare suburban and open condition. Their turbulence intensities and power spectra are compared for. In order to deal with the non-stationarity of the data, empirical mode decomposition is employed to de-trend the signal.

This paper presents the design process of a new full-scale Wall of Wind (WoW) facility for wind engineering testing. Computational fluid dynamics (CFD) was used for a preliminary design of the facility, followed by an experimental verification of the wind field conducted with a small-scale replica. Results showed good agreement between mean wind speed profiles predicted by the CFD modeling and those measured experimentally, attesting to the growing importance of CFD simulations for wind engineering applications. The proposed full-scale 12-fan WoW facility will be able to engulf large- and full-scale models for future testing. The facility has been designed to generate wind and wind-driven rain with proper characteristics to mimic hurricanes up to Category 4 as defined by the Saffir-Simpson hurricane scale. The intent of the new facility is to improve wind-related building code provisions, to develop innovative hurricane mitigation techniques, and to help strengthen the resiliency of coastal communities to hurricane hazards.

The paper presents the use of a sophisticated hydrodynamic model to evaluate the response of the estuarine residence time (ERT) to flow in the Lower Peace River (LPR) estuary located on the southwest coast of Florida, USA. Here, the ERT is defined, following Miller and McPherson (1991, Limnol. Oceanogr., 36: 602–612), as the time required to flush out a certain percentage of conservative particles that were evenly distributed at time = 0. With the use of a multi-block hydrodynamic model that dynamically couples a 3D model with a laterally averaged 2D model, ERT values for a total of 16 freshwater flow scenarios were calculated. Unlike most previous tracer simulations which did not allow tracers that left the domain during the ebb tides to return back to the estuary, this study allows some of them to return during the flood tides, resulting in a more realistic estimation of the ERT in the LPR. Based on a careful analysis of calculated ERTs, it was found that the ERT in the LPR is a power function of the gauged in-stream flow (Q) from the Peace River watershed and the ERT in the LPR can be expressed as ERT = [240.83−51.76ln(L)]Q^-0.556, where L represents the percentage of remaining conservative mass within the estuarine system after ERT days.

This paper presents a practical engineering application of an integrated coastal model in coastal and estuarine planning for flood and erosion protection against hazardous hydrological forcing such as river floods, storm surges, waves, and high tides in an estuary in Taiwan. It demonstrates the advancement of the integrated modeling system to simulate hydrodynamic and morphodynamic processes in the estuarine area including rivers and adjacent coastal zones in responses to combined tides, waves, river flood, and winds. In order to identify the best engineering plan for the purpose of flood prevention and erosion protection, the integrated coastal models are applied to evaluate a number of engineering plans by simulating long-term variations of hydrodynamic and morphodynamic processes under a hypothetical storm-monsoon event which contains a 100-year storm and a three-month-long monsoon. Numerical results on flood water stages and morphological changes enable engineers to find the most desirable engineering plan for protecting the estuarine area from flood inundation and erosions. The integrated modeling system provides a comprehensive assessment tool for coastal and estuarine planning in complex hydrological and geomorphologic conditions.