An application of Boussinesq modeling to Hurricane wave overtopping and inundation

Wave and combined wave-and-surge overtopping was significant across a large portion of the hurricane protection system of New Orleans during Hurricane Katrina. In particular, along the east-facing levees of the Mississippi River-Gulf Outlet (MRGO), the overtopping caused numerous levee breaches. This paper will focus on the MRGO levees, and will attempt to recreate the hydrodynamic conditions during Katrina to provide an estimate of the experienced overtopping rates. Due to the irregular beach profiles leading up to the levees and the general hydrodynamic complexity of the overtopping in this area, a Boussinesq wave model is employed. This model is shown to be accurate for the prediction of waves shoaling and breaking over irregular beach profiles, as well as for the overtopping of levees. With surge levels provided by ADCIRC and nearshore wave heights by STWAVE, the Boussinesq model is used to predict conditions at the MRGO levees for 10 h near the peak of Katrina. The peak simulated overtopping rates correlate well with expected levee damage thresholds and observations of damage in the levee system. Finally, the predicted overtopping rates are utilized to estimate a volumetric flooding rate as a function of time for the entire 20 km stretch of east-facing MRGO levees.     

Development of storm surge which led to flooding in St. Bernard Polder during Hurricane Katrina

Hurricane Katrina caused devastating flooding in St. Bernard Parish, Louisiana. Storm surge surrounded the polder that comprises heavily populated sections of the Parish in addition to the Lower 9th Ward section of Orleans Parish. Surge propagated along several pathways to reach levees and walls around the polder's periphery. Extreme water levels led to breaches in the levee/wall system which, along with wave overtopping and steady overflow, led to considerable flood water entering the polder. Generation and evolution of the storm surge as it propagated into the region is examined using results from the SL15 regional application of the ADCIRC storm surge model. Fluxes of water into the region through navigation channels are compared to fluxes which entered through Lake Borgne and over inundated wetlands surrounding the lake. Fluxes through Lake Borgne and adjacent wetlands were found to be the predominant source of water reaching the region. Various sources of flood water along the polder periphery are examined. Flood water primarily entered through the east and west sides of the polder. Different peak surges and hydrograph shapes were experienced along the polder boundaries, and reasons for the spatial variability in surge conditions are discussed.     

Reconstruction of Hurricane Katrina's wind fields for storm surge and wave hindcasting

As the most costly US natural disaster in history, Hurricane Katrina fostered the IPET forensic study to better understand the event. All available observations from several hundred space-, land-, sea-, and aircraft-based measurement platforms were gathered and processed to a common framework for height, exposure, and averaging time, to produce a series of wind field snapshots at 3 h intervals to depict the wind structure of Katrina when in the Gulf of Mexico. The stepped-frequency microwave radiometer was calibrated against GPS sondes to establish the upper range of the instrument and then used to determine the wind field in the storm's core region in concert with airborne Doppler radar winds adjusted to the surface from near the top of the PBL (500 m). The SFMR data were used to develop a method to estimate surface winds from 3 km level reconnaissance aircraft observations, taking into consideration the observed azimuthal variation of the reduction factor. The “SFMR method” was used to adjust reconnaissance flight-level measurements to the surface in the core region when SFMR and Doppler winds were not available. A variety of coastal and inland mesonet data were employed, including portable towers deployed by Texas Tech University, University of Louisiana at Monroe, and the Florida Coastal Monitoring Program, as well as fixed mesonet stations from Louisiana State Universities Marine Consortium, University of Southern Mississippi, and Agricultural Networks from Louisiana, Mississippi, and Alabama, and the Coastal Estuarine Network of Alabama and Mississippi. Also included were land- (WSR-88D VAD and GBVTD, ASOS, Metar, LLWAS, HANDAR), space- (QuikScat, GOES cloud drift winds, WindSat), and marine- (GPS sondes, Buoys, C-MAN, ships) platforms. The wind fields serve as an analysis of record and were used to provide forcing for wave and storm surge models to produce hindcasts of water levels in the vicinity of flood control structures.     

Numerical simulation of a low-lying barrier island's morphological response to Hurricane Katrina

Tropical cyclones that enter or form in the Gulf of Mexico generate storm surge and large waves that impact low-lying coastlines along the Gulf Coast. The Chandeleur Islands, located 161 km east of New Orleans, Louisiana, have endured numerous hurricanes that have passed nearby. Hurricane Katrina (landfall near Waveland MS, 29 Aug 2005) caused dramatic changes to the island elevation and shape. In this paper the predictability of hurricane-induced barrier island erosion and accretion is evaluated using a coupled hydrodynamic and morphodynamic model known as XBeach. Pre- and post-storm island topography was surveyed with an airborne lidar system. Numerical simulations utilized realistic surge and wave conditions determined from larger-scale hydrodynamic models. Simulations included model sensitivity tests with varying grid size and temporal resolutions. Model-predicted bathymetry/topography and post-storm survey data both showed similar patterns of island erosion, such as increased dissection by channels. However, the model under predicted the magnitude of erosion. Potential causes for under prediction include (1) errors in the initial conditions (the initial bathymetry/topography was measured three years prior to Katrina), (2) errors in the forcing conditions (a result of our omission of storms prior to Katrina and/or errors in Katrina storm conditions), and/or (3) physical processes that were omitted from the model (e.g., inclusion of sediment variations and bio-physical processes).     

Disaster prevention design criteria for the estuarine cities:New Orleans and Shanghai The lesson from Hurricane Katrina

1Introduction IntheendofAugust2005,HurricaneKatrina assaultedAtlanticcoastandcoastofGulfofMexico coastswithamaximumwindspeedof175m/h,a bout1200peoplewerekilledinthecatastrophic storm,NewOrleanswasseriouslydamagedbythe turbulenthurricanewindandtheassociate…     

Disaster prevention design criteria for the estuarine cities: New Orleans and Shanghai The lesson from Hurricane Katrina

The accurate prediction of the typhoon （hurricane） induced extreme sea environments is very important for the coastal structure design in areas influenced by typhoon （hurricane）. In 2005 Hurricane Katrina brought a severe catastrophe in New Orleans by combined effects of hurricane induced extreme sea environments and upper flood of the Mississippi River. Like the New Orleans City, Shanghai is located at the estuarine area of the Changjiang River and the combined effect of typhoon induced extreme sea en- vironments, flood peak runoff from the Changjiang River coupled with the spring tide is the dominate factor for disaster prevention design criteria. The Poisson-nested logistic trivariate compound extreme value distribution （PNLTCEYD） is a new type of joint probability model which is proposed by compounding a discrete distribution （typhoon occurring frequency） into a continuous multivariate joint distribution （ typhoon induced extreme events）. The new model gives more reasonable predicted results for New Orleans and Shanghai disaster prevention design criteria.     

Potential impact of sea level rise on coastal surges in southeast Louisiana

Potential impacts of 0.5 and 1.0 m of relative sea level rise (RSLR) on hurricane surge and waves in southeast Louisiana are investigated using the numerical storm surge model ADCIRC and the nearshore spectral wave model STWAVE. The models were applied for six hypothetic hurricanes that produce approximately 100 yr water levels in southeastern Louisiana. In areas of maximum surge, the impact of RSLR on surge was generally linear (equal to the RSLR). In wetland or wetland-fronted areas of moderate peak surges (2-3 m), the surge levels were increased by as much as 1-3 m (in addition to the RSLR). The surge increase is as much as double and triple the RSLR over broad areas and as much as five times the RSLR in isolated areas. Waves increase significantly in shallow areas due to the combined increases in water depth due to RSLR and surge increases. Maximum increases in wave height for the modeled storms were 1-1.5 m. Surge propagation over broad, shallow, wetland areas is highly sensitive to RSLR. Wave heights also generally increased for all RSLR cases. These increases were significant (0.5-1.5 m for 1 m RSLR), but less dramatic than the surge increases.     

A hydrodynamics-based surge scale for hurricanes

Record hurricane surges over the last several years have demonstrated the need for an improved surge hazard warning scale for hurricanes. Here, a simple hydrodynamics-based surge scale for hurricane surge hazard is presented. This surge scale incorporates readily available meteorological information along with regional-scale bathymetry into a single measure of expected surge levels at the coast. We further outline an approach for estimating expected flood inundation and damages based on the alongshore extent of high surges during hurricanes. Comparisons between this new surge scale and historical hurricane observations show a measurable improvement over existing surge indices, including the Saffir-Simpson scale. It is anticipated that the proposed surge scale will improve public awareness of surge hazard and assist governments in communicating critical decisions regarding evacuation and emergency response.     

Long-term regional hurricane hazard analysis for wind and storm surge

This paper introduces a new method to estimate the long-term regional hurricane wind and storm surge hazard. The output is a relatively small set of hurricane scenarios that together represent the regional hazard. For each scenario, the method produces a hazard-consistent annual occurrence probability, and wind speeds and surge levels throughout the study area. These scenarios can be used for subsequent evacuation or loss estimation modeling. This optimization-based probabilistic scenario (OPS) method involves first simulating tens of thousands of candidate hurricane scenarios with wind speeds and approximate surge depths. A mixed-integer linear optimization is then used to select a subset of scenarios and assign hazard-consistent annual occurrence probabilities to each. Finally, a surge model is used to estimate accurate surge depths for the reduced set of events. The method considers the correlation between winds and surge depths and the spatial correlations of each; it is computationally efficient; and it makes explicit the tradeoff between the number of scenarios selected and the errors introduced by using a reduced set of events. A case study for Eastern North Carolina is presented in which a final set of 97 hurricanes provides unbiased results with errors small enough for many practical uses.     

Physical model study of wave and current conditions at 17th Street Canal breach due to Hurricane Katrina

A 1:50 scale physical model was constructed for the 17th Street Canal region, New Orleans, on the southern coast of Lake Pontchartrain, as part of the Interagency Performance Evaluation Task Force (IPET) study of Hurricane Katrina. The purpose of the 1350 m² physical model that represented about 3.4 km² of the local area was to aid in defining wave and water velocity conditions in the 17th Street Canal during the time period leading up to the breaching of the floodwall within the Canal. In the immediate period following this disaster, there were many hypothesis of failure put forth in the media. Some of these hypothesis indicated wave action may have been the underlying cause of the failure of the 17th Street Canal floodwall. Some performed numerical work with inappropriate boundary conditions, which indicated strong wave-generated currents may have caused erosion along the floodwalls. This physical model study indicated a number of wave-attenuating processes occurring as waves approached the location of the breach. Wave height reduction resulted due to: (1) refraction of wave energy over the shallower submerged land areas surrounding the harbor away from the canal; (2) reflection of energy off vertical walls in the region between the entrance to the canal near the Coast Guard Harbor and the bridge; and (3) interaction of the wave with the Hammond Highway bridge, including reflection and transmission loss. Wave heights near the lakeside of the bridge were 0.3-0.9 m in height, reduced from 1.8 to 2.7 m wave heights in the open lake. Waves on the south side of the bridge, near the breach, were further reduced to heights below 0.3 m. These results supported the conclusion that waves were not a significant factor for the 17th Street Canal floodwall failure. Other IPET investigations determined floodwall failure was of a geotechnical nature due to the high surge water level. The physical model also provided calibration information for numerical wave models. The effects of debris on flow and waves after the breach was formed were also investigated.     

Efficient joint-probability methods for hurricane surge frequency analysis

The Joint-Probability Method (JPM) was adopted by federal agencies for critical post-Katrina determinations of hurricane surge frequencies. In standard JPM implementations, it is necessary to consider a very large number of combinations of storm parameters, and each such combination (or synthetic storm) requires the simulation of wind, waves, and surge. The tools used to model the wave and surge phenomena have improved greatly in recent years, but this improvement and the use of very large high-resolution grids have made the computations both time-consuming and expensive. In order to ease the computational burden, two independent approaches have been developed to reduce the number of storm surge simulations that are required. Both of these so-called JPM-OS (JPM-Optimal Sampling) methods seek to accurately cover the entire storm parameter space through optimum selection of a small number of parameter values so as to minimize the number of required storm simulations. Tests done for the Mississippi coast showed that the accuracy of the two methods is comparable to that of a full JPM analysis, with a reduction of an order of magnitude or more in the computational effort.     

台风移行速度与登陆角度对风暴潮的影响:一个理想模型数值实验

The effects of hurricane forward speed(V) and approach angle(θ) on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before. Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model(FVCOM).The hurricane track is simplified as a straight line, such that V and θ fully define the motion of the hurricane. The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane.Among the free waves, Kelvin-type waves can only propagate in the down-coast direction. Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component. The optimal values of V and θ that maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry. For a constant bathymetry, the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal; for a stepped bathymetry, the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing; a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry, with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity. For other cases, the storm surge is smaller, given other parameters(hurricane size, maximum wind speed, etc.)unchanged.     

新奥尔良防洪工程体系破坏原因分析与研究

通过飓风卡特里娜对新奥尔良防洪工程体系破坏情况的回顾并分析其破坏原因,结合其它海堤的建设情况,总结防洪工程体系建设经验教训。认为防洪工程建设应有系统工程的观念,并基于风险分析进行设计;筑堤土料尽量采用抗冲能力强的粘土或采用抗冲性能差的土料时应有相应的防护措施;注意堤防的防护设计,特别是生物措施的利用;强调应重视工程地质参数的正确选取。     

The impact of the 2005 hurricane season on the Louisiana Artificial Reef Program

The 2005 hurricane season in the Gulf of Mexico was the worst in the history of offshore production, with Hurricanes Katrina and Rita destroying 110 oil and gas structures and eight mobile offshore drilling units. Infrastructure destroyed by accident or natural catastrophe are decommissioned according to the same federal regulations that guide normal decommissioning operations, but depending on the nature of the destruction and the market conditions in the months following the event, special conditions and delays may occur. Historically, offshore infrastructure destroyed by hurricanes or other unusual circumstances have been considered for inclusion in the Louisiana Artificial Reef Program (LARP) under the Special Artificial Reef Site (SARS) category. The purpose of this paper is to review the impact of the 2005 hurricane season on the LARP and the current status of the SARS program. We examine the criteria employed in project evaluation and approval as well as aggregate program statistics. The characteristics and risks associated with decommissioning destroyed infrastructure are also described. At the end of 2006, 10 projects representing 35 platforms destroyed in the 2005 hurricane season have been approved as SARS in the Gulf of Mexico, effectively doubling the number of sites and structures classified as SARS.     

南麂海域台风影响过程中的波浪特征

根据１９８３－１９８９年南麂海洋站在台风影响过程中的实测风和浪资料，分析了该海域的波浪特征。结果表明，这个海域的台风波浪通常是混合浪，在台风影响过程中出现的最大值波高，既有较大波陡的风浪，也有波陡较小的清浪；各向波高的均值变化不大，各向最大波高却有较大幅度的差距；本区的台风浪以４级波高占优，风浪以ＮＮＥ向、涌浪以Ｅ向为常浪向；波高为４级的风浪和涌浪，其周期分别在４．０－４．９Ｓ和７．０－７．９Ｓ之     

Quadrature-based approach for the efficient evaluation of surge hazard

The Joint Probability Method (JPM) has been used for hurricane surge frequency analysis for over three decades, and remains the method of choice owing to the limitations of more direct historical methods. However, use of the JPM approach in conjunction with the modern generation of complex high-resolution numerical models (used to describe winds, waves, and surge) has become highly inefficient, owing to the large number of costly storm simulations that are typically required. This paper describes a new approach to the selection of the storm simulation set that permits reduction of the JPM computational effort by about an order of magnitude (compared to a more conventional approach) while maintaining good accuracy. The method uses an integration scheme called Bayesian or Gaussian-process quadrature (together with conventional integration methods) to evaluate the multi-dimensional joint probability integral over the space of storm parameters (pressure, radius, speed, heading, and any others found to be important) as a weighted summation over a relatively small set of optimally selected nodes (synthetic storms). Examples of an application of the method are shown, drawn from the recent post-Katrina study of coastal Mississippi.     

Numerical modeling of wind waves generated by tropical cyclones using moving grids

A version of the WAVEWATCH III wave model featuring a continuously moving spatial grid is presented. The new model option/version is intended for research into wind waves generated by tropical cyclones in deep water away from the coast. The main advantage of such an approach is that the cyclones can be modeled with spatial grids that cover much smaller areas than conventional fixed grids, making model runs with high spatial resolution more economically feasible. The model modifications necessary are fairly trivial. Most complications occur due to the Garden Sprinkler effect (GSE) and methods used to mitigate it. The basic testing of the model is performed using idealized wind fields consisting of a Rankine vortex. The model is also applied to hurricane Lili in the Gulf of Mexico in October 2002. The latter application shows that the moving grid approach provides a natural way to deal with hurricane wind fields that have a high-resolution in space, but a low resolution in time. Although the new model version is originally intended for tropical cyclones, it is suitable for high-resolution modeling of waves due to any moving weather pattern.     

Analysis of the coastal Mississippi storm surge hazard

Following the extreme flooding caused by Hurricane Katrina, the Federal Emergency Management Agency (FEMA) commissioned a study to update the Mississippi coastal flood hazard maps. The project included development and application of new methods incorporating the most recent advances in numerical modeling of storms and coastal hydrodynamics, analysis of the storm climatology, and flood hazard evaluation. This paper discusses the methods that were used and how they were applied to the coast of the State of Mississippi.     

一维海洋混合层模式应用于二维数值模拟的试验研究

基于一个一维湍能海洋混合层模式,发展了一个易于与大气或海洋模式耦合的,可应用于水平二维空间的模块化海洋混合层模式。并加入垂直上翻参数化方案,引入日平均海面温度及气候态松弛项,进行二维海洋模拟理想气旋实验和飓风实例模拟实验。理想气旋强迫实验表明,垂直上翻过程的参数化方案可有效地弥补原有一维海洋混合层模式无法形成气旋中心动力上翻的不足,消除了虚假暖水核心。卡特里娜飓风个例实验的结果表明,加入垂直上翻后,飓风中心附近的海表面温度误差明显减小。海洋混合层模式对海洋表面温度日变化模拟能力在二维应用中依然表现良好。经过上述改进,发展的海洋混合层模式可以较为真实地模拟平常海表温度高频日变化的同时,还对剧烈天气过程也有一定的模拟能力,具有广泛的应用前景。     

Open-boundary conditions for open-coast hurricane storm surge

Harper, B.A. and Sobey, R.J., 1983. Open-boundary conditions for open-coast hurricane storm surge. Coastal Eng., 7: 41–60.The specification of realistic open-boundary conditions for the numerical simulation of hurricane (or tropical cyclone) storm surge is considered in the context of the very considerable spatial extent of the meteorological forcing. Existing practice is reviewed and an alternative approach, a Bathystrophic Storm Tide approximation to open-boundary water levels, is presented. Results from a series of numerical experiments demonstrate the advantages of this approach over existing methods.