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。     

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.     

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.     

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.     

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.     

Anisotropic Analysis of I-Walls in New Orleans

Many numerical analyses of New Orleans levee and floodwall sections adopted mostly isotropic soil models partly due to the inherent simplicity of isotropic models. However, the isotropic models may not be sufficient to properly address the anisotropic behavior of soils. To overcome this imperfection, this study incorporated an anisotropic Modified Cam Clay model in a commercially available finite difference code, FLAC^3D, and analyzed a floodwall and levee section in the 17th St. Canal in New Orleans. The analysis showed that the anisotropic model resulted in a similar overall deformation to the Mohr-Coulomb isotropic model. However, the anisotropic model showed more widely spread yielded elements and higher shear strain gradient in the Lacustrine clay layer, reconfirming that the Lacustrine clay layer played a major role for the failure in the 17th St. Canal. This result also signified that the isotropic Mohr-Coulomb model might be good for evaluating overall behavior in moderate deformation problems, while the anisotropic Modified Cam Clay model was good even for large strain problems where more accurate evaluation of yielding is needed.     

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.     

A review of the climatological characteristics of landfalling Gulf hurricanes for wind, wave, and surge hazard estimation

The climatological characteristics of landfalling Gulf of Mexico hurricanes are presented, focusing on the basic parameters needed for accurately determining the structure and intensity of hurricanes for ocean response models. These include the maximum sustained wind, radius of maximum winds, the Holland-B parameter, the peripheral or far-field pressure, the surface roughness and coefficient of drag, and the central pressure for historical hurricanes in the Gulf.Despite evidence of a slight increase in the annual number of named storms over the past 50 years, presently there is no statistically significant trend in tropical storms, hurricanes, or major hurricanes in the Gulf of Mexico. In addition, the long-term variability of tropical cyclones in the Gulf reflects the observed variability in the Atlantic basin as a whole. Analyses of hurricane winds from multiple sources suggest the presence of a bias toward overestimating the strength of winds in the HURDAT dataset from 7% to 15%. Results presented comparing HURDAT with other sources also show an overestimation of intensity at landfall, with an estimated bias of ~10%.Finally, a review of recent studies has shown that hurricane frequencies and intensities appear to vary on a much more localized scale than previously believed. This exacerbates the sampling problem for accurate characterization of hurricane parameters for design and operational applications.     

Bivalve shellfish harvesting and consumption in New Zealand, 2011: data for exposure assessment

We provide an overview of bivalve molluscan shellfish (BMS) availability to New Zealanders. Data on commercial production (aquaculture) and harvesting, non-commercial (recreational and customary) harvesting and international trading (imports, exports) of BMS were assembled. These data were transformed to estimate the total weight (greenweight and meatweight) of each BMS species, and all BMS species, available to New Zealand domestic consumers in 2011. An estimated 68,000 tonnes greenweight, or 13,000 tonnes meatweight, of BMS were available. Mussels (mostly commercially-produced Perna canaliculus) accounted for 96% of the total available BMS by meatweight. Non-commercially harvested BMS were 1% of the total available BMS. BMS availability was estimated as 8 g/person/day for the total New Zealand population and 407 g/person/day for shellfish consumers. These estimates were comparable to published national consumption data. The results can be used as inputs to exposure assessment. Food availability is a useful estimate where consumption data are limited.     

A review of international,regional and national biosecurity risk assessment frameworks

Aquatic nonindigenous species (ANS) have dramatic impact on environmental, economic, social, cultural, and human health values in a variety of coastal, estuarine, and inland ecosystem. Despite efforts to develop biosecurity risk assessment frameworks for the improvement of ANS management, responsible agencies lack a standardized framework to identify and mitigate risk from ANS. This paper reviews the biosecurity risk assessment frameworks of seven international bodies, four regional bodies, and three countries and highlights the similarities, differences and deficiencies in their respective frameworks. Specific deficiencies found by the review include: (i) a lack of national implementation of the international and regional frameworks; (ii) gaps in ANS knowledge; (iii) insufficient guidance for various components of the risk assessment; (iv) limited number and scope of standards and measures related to ANS; and (v) inconsistent terminology between frameworks. To reduce the risk of ANS introductions, this paper concludes with a set of six recommendations to develop aquatic biosecurity risk frameworks that are both comprehensive and precautionary while also in accord with mandates established by other international bodies such as the World Trade Organization.     

The behavior of iron,manganese and silicon in the Peconic River estuary,New York

The behavior of dissolved and particulate iron and manganese and dissolved silicon has been studied as a function of chlorinity in the Peconic River estuary, New York. This study sought to identify important geochemical processes in a relatively pristine estuary facing increasing anthropogenic impact.Dissolved iron behaved in the classical non-conservative manner exhibiting removal of nearly 80% at very low chlorinities, while particulate iron increased by a corresponding amount over the same chlorinity range. Dissolved manganese was enriched by up to 200% over its predicted concentration at low and intermediate chlorinities by desorption from suspended particulates and by a probable benthic flux. Dissolved silicon was enriched by up to 100% at low and intermediate chlorinities also from a probable benthic flux. These fluxes were estimated to be 5 μg cm^?2 day^?1 for dissolved manganese and 70 μg cm^?2 day^?1 for dissolved silicon.The quantity of both particulate iron and manganese increased at high chlorinities due to an influx of suspended inorganic particulates. In the intermediate to high chlorinity region, oxidation of sediment-derived manganese is believed to contribute to the observed increase in particulate manganese.Total iron was essentially conservative throughout most of the estuary, while total manganese was non-conservative presumably due to extensive remobilization of dissolved manganese from the sediments.     

Studies of a mangrove basin,Tuff Crater,New Zealand: III. The flux of organic and inorganic particulate matter

Water samples were collected at 15 min intervals over 11 tidal cycles from a tidal creek draining the mangrove-covered basin of Tuff Crater, Auckland, New Zealand. The samples were filtered and total suspended sediment (TSS), inorganic suspended sediment (ISS) and organic suspended sediment (OSS) were determined. Variation in TSS was high, the concentration varied over a tidal cycle and during over-bank flows concentrations were lowest at or near slack high water. Covariance between TSS concentrations and velocity and discharge meant that the calculation of particulate matter flux over tidal hemicycles was particularly dependent on the method of estimating tidal flux. The hypsometrically-based volumetric method was found to be inappropriate, predicting a positive budget (import) more often than observed. Instead particulate matter budgets were calculated by means of the velocity-area method and indicate a net export of TSS, ISS and OSS. Floating macrodetritus was observed on both the flood and ebb tides, but a net export was found on the two tides monitored. It is considered that on an annual basis floating macrodetritus export accounts for less than 2% of the detrital production in the basin, and organic suspended sediment export from the basin is less than 3 kg C ha^?1 day^?1 and is below the rate of detrital production. It is implied that a proportion of the organic detritus produced in this basin is degraded and recycled in situ.     

Nyctiphanes australis (Euphausiacea) and an upwelling plume in western Cook Strait,New Zealand

Quantitative data are presented on the distribution of adult and larval stages of the euphausiid Nyctiphanes australis G. O. Sars, in western Cook Strait, New Zealand, an area influenced by an upwelling plume. The behaviour of N. australis in the Kahurangi Point region at different stages of its life history appears to ensure its maintenance, in general, over the continental shelf on an upwelling coast. Population structure at the source of the upwelling near Kahurangi Point differed from that in regions “down stream” from the plume. Nyctiphanes australis was most abundant at the “downstream” eastern end of the upwelling plume, and the evidence suggesting that the dense populations there may be resident is discussed. Possible reasons for low densities of furcilia II and III stages in the eastern plume region are considered.     

The chemical, physical and structural properties of estuarine ice in Great Bay, New Hampshire

The purpose of this study was to provide general information on the chemical, physical and structural properties of estuarine ice and show how it compares with sea ice found at higher latitudes in order to determine whether the ice in Great Bay can be used as an analog in the study of arctic sea ice.Ice cores and water samples were collected during the 1983–1984 winter season at Adams Point in Great Bay, New Hampshire. Concentrations of chloride, nitrogen (as nitrate and nitrite), bromide, phosphate, sulfate and silicate were determined for samples chosen on the basis of identifiable stratigraphic layers (i.e. bubble size and shape, sediment layers, etc.).Similarities between ice formation in Great Bay and those in the arctic regions include the nature of the freezing process and the ice types produced. In addition, the distribution and concentration of chemical constituents were found to be similar to those observed in arctic sea ice. Factors affecting the chemistry of the ice in Great Bay include rainfall during the freezing season, the presence of sediment layers in the ice cores, the nature of incorporation of brine into the crystal structure of the ice and the drainage of brine.     

The application of multivariate statistical methods to phytoplankton counts from the Hauraki Gulf,New Zealand

The phytoplankton population from a station in the Jellicoe Channel area of the Hauraki Gulf, New Zealand, was fairly constant, in terms of total population and species composition, throughout the year. Correspondence analysis enabled us to identify 3 groups of species. The largest of these comprised the core species which were present most of the time and included some, such as the coccolithophores, with a strongly seasonal occurrence. The species in the second group were mainly large centric diatoms and appeared for short periods during the winter months, apparently brought in by incursions of oceanic water. The third group of species occurred between April 1970 and October 1971 when there was a period of unusually warm weather: the winds were lighter and more often blowing onshore and this perhaps led to warmer, less nutrient‐rich surface waters being brought into the Gulf.     

Trace element bioaccumulation in reef fish from New Caledonia: Influence of trophic groups and risk assessment for consumers

Fourteen trace elements (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V, and Zn) were analyzed in livers and muscles from 22 fish species from the New Caledonia lagoon, which is subjected to important chemical inputs due to intense land-based mining activities (New Caledonia is the third largest world producer of Ni). The results of this baseline research indicated that livers generally concentrated trace elements to a greater extent than muscles. Nevertheless, the overall trace element concentrations in both tissues were barely above the levels reported in fish and thus contamination at the local scale was poorly discriminated. Although these levels were low, preliminary risk assessment from a global health standpoint suggests that As would be an element potentially leading to exposure of concern for fish consumers. Based on the trace element concentrations in livers and the fish trophic preferences, some trends have been observed among trophic groups: Ag, Cu, Fe, Hg, and Zn concentrations were generally higher in liver of fish with the highest trophic position whereas Cd concentrations were lower in these groups. The use of the leopard coral grouper Plectropomus leopardus as a resident top predator allowed determining the geographical variations in contamination levels with significant differences for six out of the fourteen elements investigated. The sampling sites influenced by anthropogenic inputs were revealed by high Ag, Cd, Cu, Hg, and Pb concentrations. Such geographic differences also applied to Zn but surprisingly not for the typical elements associated with Ni mining, i.e., Co, Cr, Mn and Ni.     

Maintenance of Near-Surface Stratification in Doubtful Sound, a New Zealand Fjord

The surface waters of Doubtful Sound, a glacially carved fjord in south-western New Zealand, feature a quasi-permanent low-salinity-layer (LSL). The LSL is maintained year round by the extreme precipitation in the catchment (7 m yr⁻¹) and discharge from a hydroelectric power station (450 m³ s⁻¹). The robust, stable LSL has been shown to play a major role in controlling intertidal and subtidal community structure. By contrast, little is known about the dynamics of the LSL itself. The work presented here elucidates the response of the LSL to perturbations in the wind stress and rainfall.Frequency-domain analysis of salinity data collected from an array of moored instruments revealed that the LSL responded to perturbations in both the winds and rainfall. However, the specific roles of the wind stress and rain could not be adequately resolved in these analyses. By contrast, simulations of the response of the LSL using a three-dimensional primitive equation model revealed that strong up-fjord directed wind events set up a storm surge at the head of the fjord. This surge significantly deepens the LSL at the head of the fjord and retards or reverses estuarine circulation. The subsequent relaxation of the surge after the abatement of the wind stress resulted in a redistribution of buoyancy throughout the fjord over a two-day period. It is shown that the development and relaxation of the storm surge is a major process controlling the maintenance of the near-surface stratification.     

Studies of a mangrove basin,Tuff Crater,New Zealand: I. Mangrove biomass and production of detritus

The mangrove, Avicennia marina var. resinifera in a tidally-flooded explosion crater, Tuff Crater, near the southern latitudinal limit of mangroves in New Zealand adopts two distinct growth forms, taller tree-like mangroves up to 4 m tall along the banks of the tidal creek, and low stunted shrub mangroves less than 1 m tall on the mudflats. Twelve trees were felled and on the basis of a biomass/height relationship for the taller trees and a biomass/canopy width relationship for the lower, above-ground biomass (excluding pneumatophores) was estimated. Average above-ground biomass for the taller mangrove was estimated to be 104·1 t ha^?1 and for the lower 6·8 t ha^?1. While the value for the taller mangroves is similar to figures reported for more complex tropical mangroves, the fact that 94% of the basin is covered by low generally sparse mangroves means that total biomass for the basin is estimated to be 153 t, an average of only 7·6 t ha^?1. Litter-fall beneath the taller mangroves is estimated as 7·6±2·5 t ha^?1 a^?1 and beneath the lower mangroves 3·3±0·5 t ha^?1 a^?1. The value for the taller mangroves is similar to that reported from mangroves in many other parts of the world, but because of the extensive low sparse mangroves the total for the basin is estimated as 53·7 t a^?1, an average rate of 2·7 t ha^?1 a^?1, a very low rate of litter-fall when compared with elsewhere. Decomposition of mangrove leaves occurs relatively rapidly with leaves losing half their dry weight in 10 weeks and then continuing to degrade but at a slower rate. Substrate sediment samples contain high organic matter content, and although some organic matter appears to be exported via the tidal creek, a proportion of the detrital production is evidently recycled in situ.     

The strengthening East Australian Current, its eddies and biological effects — an introduction and overview

The poleward flowing East Australian Current (EAC) is characterised by its separation from the coast, 100-200 nautical miles north of Sydney, to form the eastward flowing Tasman Front and a southward flowing eddy field. The separation zone greatly influences coastal ecosystems for the relatively narrow continental shelf (only 15-50 km wide), particularly between 32-34°S. In this region the continental shelf has a marked shift in the seasonal temperature-salinity relationship and elevated surface nitrate concentrations. This current parallels the portion of the coast where Australia’s population is concentrated and has a long history of scientific research. However, understanding of physical and biological processes driven by the EAC, particularly in linking circulation to ecosystems, is limited. In this special issue of 16 papers on the EAC, we examine the effects of climatic wind-stress forced ocean dynamics on EAC transport variability and coastal sea level, from ENSO to multi-decadal time scales; eddy formation and structure; fine scale connectivity and larval retention. Comparisons with the poleward-flowing Leeuwin Current on Australia’s west coast show differences in ecosystem productivity that can be attributed to the underlying physics in each region. On average there is double the chlorophyll a concentration on the east coast than the west. In comparison to the Leeuwin, the EAC may have less local retention of larvae and act as a partial barrier to onshore transport, which may also be related to the local spawning and early life history of small pelagic fish on each coast. Inter-annual variations in the EAC transport produce a detectable sea-level signal in Sydney Harbour, which could provide a useful fisheries index as does the Fremantle sea level and Leeuwin Current relationship. The EAC’s eddy structure and formation by the EAC are examined. A particular cold-core eddy is shown to have a “tilt” towards the coast, and that during a rotation the flow of particles may rise up to the euphotic zone and then down beneath. In a warm-core eddy, surface flooding is shown to produce a new shallower surface mixed layer and promote algal growth. An assessment of plankton data from 1938-1942 showed that the local, synoptic conditions had to be incorporated before any comparison with the present. There are useful relationships of water mass characteristics in the Tasman Sea and separation zone with larval fish diversity and abundance, as well as with long-line fisheries. These fisheries-pelagic habitat relationships are invaluable for fisheries management, as well as for climate change assessments.There is further need to examine the EAC influence on rainfall, storm activity, dust deposition, and on the movements by fish, sharks and whales. The Australian Integrated Marine Observing System (IMOS) has provided new infrastructure to determine the changing behaviour of the EAC and its bio-physical interaction with the coasts and estuaries. The forecasting and hindcasting capability developed under the Bluelink project has provided a new tool for data synthesis and dynamical analysis. The impact of a strengthening EAC and how it influences the livelihoods of over half the Australian population, from Brisbane to Sydney, Hobart and Melbourne, is just being realised.