Dentre os ambientes costeiros, os estuários são as principais fontes de sedimento para os oceanos. Sua dinâmica sensível é amplamente suscetível a modificações de origem natural e antrópica impactando no balanço sedimentar destes ambientes. O presente trabalho busca compreender a importância da maré meteorológica causada por frentes frias sobre os processos sedimentares do complexo estuarino de Santos aplicando o modelo numérico XBeach com três cenários. O primeiro foi forçado apenas pela maré astronômica outro representando uma condição de frente fria média e um terceiro representando uma frente fria extrema. Buscou-se detectar as frentes utilizando dados de reanálise do NCEP/NCAR. Foram extraídos os cinco dias mais intensos das frentes escolhidas e aplicaram-se ao inicio da série de dados de input do modelo para os ensaios numéricos. Os resultados permitiram compreender que os sistemas frontais atuam como agentes essenciais no balanço sedimentar tendo um papel erosivo compensando os processos deposicionais atuantes no período sem frentes. Frentes muito intensas agravam as feições erosivas e deposicionais, desbalanceando o sistema além da sua capacidade de recuperação. / Among the coastal environments, the estuaries are the main sediment source for oceans. Its sensible dynamic is widely susceptible to changes of natural and anthropogenic impacts the sediment balance of those environments. This work applies the Xbeach numerical model in Santos estuary to understand the storm surges forced by cold fronts on the sediment transport through three scenarios. The first scenario input was astronomic tide sea surface high, the second scenario input was the median cold front and the last scenario input was an extreme cold front. To get the cold front condition we use the NCEP/NCAR reanalysis data. We applied the five most intense days from each cold front condition in the beginning astronomic tide series. With the numerical model results we could understand the erosive action from the cold fronts and how it compensates the depositional period without any cold fronts. The extreme cold fronts intensify the depositional/erosion process unbalancing the system beyond the resilience capacity.

This dissertation investigates the use of remotely sensed data in coastal tide and inundation models, specifically how these data could be more effectively integrated into model construction and performance assessment techniques. It includes a review of numerical wetting and drying algorithms, a method for constructing a seamless digital terrain model including the handling of tidal datums, an investigation into the accuracy of land use / land cover (LULC) based surface roughness parameterization schemes, an application of a cutting edge remotely sensed inundation detection method to assess the performance of a tidal model, and a preliminary investigation into using 3-dimensional airborne laser scanning data to parameterize surface roughness. A thorough academic review of wetting and drying algorithms employed by contemporary numerical tidal models was conducted. Since nearly all population centers and valuable property are located in the overland regions of the model domain, the coastal models must adequately describe the inundation physics here. This is accomplished by techniques that generally fall into four categories: Thin film, Element removal, Depth extrapolation, and Negative depth. While nearly all wetting and drying algorithms can be classified as one of the four types, each model is distinct and unique in its actual implementation. The use of spatial elevation data is essential to accurate coastal modeling. Remotely sensed LiDAR is the standard data source for constructing topographic digital terrain models (DTM). Hydrographic soundings provide bathymetric elevation information. These data are combined to form a seamless topobathy surface that is the foundation for distributed coastal models. A three-point inverse distance weighting method was developed in order to account for the spatial variability of bathymetry data referenced to tidal datums. This method was applied to the Tampa Bay region of Florida in order to produce a seamless topobathy DTM. Remotely sensed data also contribute to the parameterization of surface roughness. It is used to develop land use / land cover (LULC) data that is in turn used to specify spatially distributed bottom friction and aerodynamic roughness parameters across the model domain. However, these parameters are continuous variables that are a function of the size, shape and density of the terrain and above-ground obstacles. By using LULC data, much of the variation specific to local areas is generalized due to the categorical nature of the data. This was tested by comparing surface roughness parameters computed based on field measurements to those assigned by LULC data at 24 sites across Florida. Using a t-test to quantify the comparison, it was proven that the parameterizations are significantly different. Taking the field measured parameters as ground truth, it is evident that parameterizing surface roughness based on LULC data is deficient. In addition to providing input parameters, remotely sensed data can also be used to assess the performance of coastal models. Traditional methods of model performance testing include harmonic resynthesis of tidal constituents, water level time series analysis, and comparison to measured high water marks. A new performance assessment that measures a model's ability to predict the extent of inundation was applied to a northern Gulf of Mexico tidal model. The new method, termed the synergetic method, is based on detecting inundation area at specific points in time using satellite imagery. This detected inundation area is compared to that predicted by a time-synchronized tidal model to assess the performance of model in this respect. It was shown that the synergetic method produces performance metrics that corroborate the results of traditional methods and is useful in assessing the performance of tidal and storm surge models. It was also shown that the subject tidal model is capable of correctly classifying pixels as wet or dry on over 85% of the sample areas. Lastly, since it has been shown that parameterizing surface roughness using LULC data is deficient, progress toward a new parameterization scheme based on 3-dimensional LiDAR point cloud data is presented. By computing statistics for the entire point cloud along with the implementation of moving window and polynomial fit approaches, empirical relationships were determined that allow the point cloud to estimate surface roughness parameters. A multi-variate regression approach was chosen to investigate the relationship(s) between the predictor variables (LiDAR statistics) and the response variables (surface roughness parameters). It was shown that the empirical fit is weak when comparing the surface roughness parameters to the LiDAR data. The fit was improved by comparing the LiDAR to the more directly measured source terms of the equations used to compute the surface roughness parameters. Future work will involve using these empirical relationships to parameterize a model in the northern Gulf of Mexico and comparing the hydrodynamic results to those of the same model parameterized using contemporary methods. In conclusion, through the work presented herein, it was demonstrated that incorporating remotely sensed data into coastal models provides many benefits including more accurate topobathy descriptions, the potential to provide more accurate surface roughness parameterizations, and more insightful performance assessments. All of these conclusions were achieved using data that is readily available to the scientific community and, with the exception of the Synthetic Aperture Radar (SAR) from the Radarsat-1 project used in the inundation detection method, are available free of charge. Airborne LiDAR data are extremely rich sources of information about the terrain that can be exploited in the context of coastal modeling. The data can be used to construct digital terrain models (DTMs), assist in the analysis of satellite remote sensing data, and describe the roughness of the landscape thereby maximizing the cost effectiveness of the data acquisition.

No description available.

Many Climate Scientists believe that global warming will produce more extreme weather events such as tropical storms, hurricanes, intense rainfall, and flooding. These events are considered to be the most catastrophic natural events for transportation systems especially in coastal areas. Due to the severe damage from storm surge and flooding. Evaluating the magnitude of possible storm surges and their impacts on transportation systems in coastal areas is fundamental to developing adaptation plans and impact assessments to mitigate the damage. This thesis focuses on existing transportation systems in the Georgia coastal area that could be affected by several storm surges. An existing storm surge model is used to estimate the storm surges and the surge heights based on the category, direction, and forward speed of a storm. The ground elevation of the ports, interstates, state roads, railroads, and the principal airports on the Georgia coast are identified through a GIS analysis using the national elevation data set. Having the storm surge elevation and the elevation of the existing infrastructure, a GIS study is performed to identify those parts of the transportation system that will be affected by each type of storm giving results such as the length or sections of transportation assets under or above the surge elevation. A literature review of storm surge, rising sea levels, and their impacts on coastal bridges, roads, airports, ports, and railroads is presented in the thesis. Also, a description of the software used to analyze and estimate the impacts of climate change on transportation systems is described.

This thesis reports the development, testing, and application of computer programs for simulating Lagrangian-Stochastic particle dispersion in coastal seas, with particular application to tide and storm induced dispersion in South Australian seas. The three-dimensional tidal equations are briefly discussed for the two types of surge models used, and finite-difference methods for numerically solving these equations are considered. Different methods of simulating flows at open sea boundaries are investigated. The method of particle tracking and the development of the particle tracking model is also described. Various tests are conducted to investigate both the advective and diffusive aspects of dispersion, and a number of scenarios for the simulation of open (ocean) and closed (coastal) boundaries are considered. Various aspects of the particle tracking routine are given specific characteristics according to the nature of the particle being considered. Application of the tide and storm surge model to the Great Australian Bight is described. This uses spherical polar co-ordinates to account for the curvature of the earth, and an oblique boundary element to increase accuracy of the coastline representation. The effect of a low pressure system moving from west to east across the Bight and the resulting significant observed surge at Thevenard during the storm of April 1996 is simulated. This storm resulted in a significant number of deaths in aquaculture farms containing southern bluefin tuna (Thunnas maccoyii) within the Boston Bay region to the extreme east of the Bight due to the agitation of almost neutrally buoyant organic sediments at the sea floor. The effects of this storm are further considered using a Cartesian co-ordinate fine-grid local model of Boston Bay, in Spencer Gulf, South Australia, where both tidal and storm (wind and outside surge) induced flows are simulated. The dispersion of suspended neutrally buoyant sediment throughout the region is considered, and compared with the mortalities of tuna at various farms within the region. Tidal and storm induced currents in the Gulf St. Vincent region, South Australia, have also been modelled using Cartesian co-ordinates. Detailed consideration has been given to the modelling of tides, winds, atmospheric pressures and outside surges from the two open boundaries in Investigator Strait and Backstairs Passage. The information obtained has enabled the modelling of a number of storm surge scenarios. Further to this, various simulations of the dispersion of the larvae of the western king prawn (Penaeus latisulcatus) have been driven using the storm surge model developed. These incorporate currents near the surface and the sea floor, as well as the consideration of changes in behaviour during the life history of the larvae. / Thesis (Ph.D.)--Engineering, Computer and Mathematical Sciences, 2000.

Die Anpassung von Küstenniederungen, Seemarschen und Inseln an klimatische Veränderungen und einen steigenden Meeresspiegel ist eine der großen Herausforderungen des 21. Jahrhunderts. Im Gegensatz zu eingedeichten Küstenmarschen und Inseln besitzen tidebeeinflusste Seemarschen ein natürliches Anpassungspotential an sich verändernde hydrologische Rahmenbedingungen. Überflutungsabhängige Sedimenteinträge führen zu einem Anwachsen der Marschoberfläche und kompensieren somit einen Anstieg des Meeresspiegels. Die 10 verbliebenen nordfriesischen Halligen (Schleswig-Holstein, Deutschland) (Kapitel 1) sind bewohnte Inselmarschen, welche aufgrund ihrer anthropogenen Überprägung von naturbelassenen Seemarschen unterschieden werden müssen. Diese umfasst z.B. den Bau von flachen Sommerdeichen und Sielanlagen. Inwiefern sich diese Veränderungen auf die Sedimentdynamik der Marschen auswirken, ist bislang unzureichend belegt, was eine fundierte Diskussion bezüglich zukünftiger Entwicklungsperspektiven der Halligmarschen verhindert. Die vorliegende Arbeit ist dazu angelegt, diese Wissenslücke zu schließen. Sie untersucht das vertikale Marschwachstum exemplarisch auf den Halligen Hooge, Langeneß und Nordstrandischmoor und beurteilt deren Anpassungsvermögen an einen steigenden Meeresspiegel. Darüber hinaus werden zukünftige Entwicklungsperspektiven diskutiert. Um Faktoren und Prozesse, welche maßgeblich die Sedimentdynamik der Halligen beeinflussen, messbar zu machen, musstengeeignete Methoden entwickelt und angewendet werden. Zur Berechnung jährlicher Überflutungshäufigkeiten wurden Pegelschwellenwerte für Überflutungsereignisse auf Basis von digitalen Geländemodellen (DGMs) und d-GPS (differential global positioning system) Messungen errechnet und auf die verfügbaren, regionalen Pegeldaten angewendet (Kapitel 2). Sedimentfallen, bestehend aus LDPE (low density polyethylene) Flaschen (1 Liter) und Kunstrasenmatten (20 x 30 cm), bilden die Grundlage einer dreijährigen (November 2010 – März 2013) Feld- und Laborstudie zur zeitlichen und räumlichen Erfassung der sturmflutabhängigen Sedimentdeposition (Kapitel 3). Durch die Verwendung regionaler bodenphysikalischer Parameter (Lagerungsdichte und Gehalt an organischer Bodensubstanz) können Depositionsraten in eine vertikale Wachstumskomponente transformiert werden. Dazu werden Ergebnisse einer Rammkernsondierung genutzt, welche 12 Sedimentkerne mit einer Länge von maximal 100 cm umfasst. Die Sedimentbohrkerne sind weiterhin die Grundlage für eine 137Cs- und 210Pb-Datierung. Die Kombination beider Datensätze (Kapitel 4) ermöglicht einen schlüssigen Vergleich der Marschentwicklung seit dem Jahr 1915 mit regionalen Pegeldaten und Projektionen des zukünftigen Meeresspiegelanstiegs. Die Analyse der verfügbaren Pegeldaten (Kapitel 2) zeigt eine hohe Variabilität der jährlichen Überflutungshäufigkeiten. Das zehnjährige Mittel eintretender Ereignisse beträgt 2 Überflutungen auf Hooge, 9 – 10 Überflutungen auf Langeneß und 15 Überflutungen auf Nordstrandischmoor. Aufgrund der künstlichen Überhöhung der Marschkante durch Sommerdeiche mit + 1.54 m ü. mittlerem Tidehochwasser (MThw) auf Hooge und + 0.98 m ü. MThw auf Langeneß werden die betreffenden Halligen lediglich bei selten eintretenden Sturmflutereignissen überflutet. Die Höhe des wasser- und sedimentundurchlässigen Steinpflasters auf Nordstrandischmoor beträgt lediglich + 0.7 m ü. MThw. Die methodischen Untersuchungen bezüglich der Nutzung von Sedimentfallen (Kapitel 3) zeigen, dass beide Typen von Sedimentfallen vergleichbare Ergebnisse liefern. Oberhalb einer Depositionsrate von ~ 2.0 kg/m2 sinkt das Rückhaltevermögen der Kunstrasenmatte im Vergleich zur LDPE Flasche deutlich ab. Die parallele Nutzung beider Fallentypen, insbesondere wenn die Depositionsraten den Schwellenwert (~ 2.0 kg/m2) nicht überschreiten, erlaubt: (1) Die Überprüfung, ob beide Datensätze konsistent sind. (2) Die Identifizierung von Ausreißern. (3) Eine Abschätzung, ob Sediment auf oder in der Sedimentfalle nach der Überflutung remobilisiert wird. Um die Sedimentdeposition in eine vertikale Wachstumsrate zu übersetzen, muss die mittlere Bodendichte als auch der Gehalt an organischer Bodensubstanz des Marschbodens berücksichtigt werden. Die Bohrkernuntersuchungen zeigen, dass diese bodenphysikalischen Parameter auf den unterschiedlichen Halligen stark variieren. Marschen, die häufig überflutet werden lagern weniger organisches Material im Oberboden ein als selten überflutete Marschen. Niedrige Gehalte an leichten organischen Materialien geringer Dichte resultieren wiederum in einer höheren Lagerungsdichte des Marschbodens (Hooge 0.64 g/cm3, Langeneß 0.67 g/cm3, Nordstrandischmoor 0.83 g/cm3). Autochthones organisches Material (welches primär von der Halligvegetation stammt) trägt mit einem Anteil von 9.0 ± 1.4 % (Hooge) bis 21.4 ± 6.6 % (Nordstrandischmoor) zum Marschwachstum bei. Die Ergebnisse der Sedimentfallenuntersuchungen als auch der Datierungen zeigen deutlich ein Ungleichgewicht zwischen Marschwachstum und Meeresspiegelanstieg seit Beginn des 20. Jahrhunderts. Die langjährigen Wachstumsraten, basierend auf der 210Pb-Datierung, liegen mit 1.0 ± 0.3 mm/a auf Hooge, 1.2 ± 0.3 mm/a auf Langeneß und 2.6 ± 0.9 mm/a auf Nordstrandischmoor deutlich unterhalb des MThw-Anstiegs von 5.0 ± 0.3 mm/a (1951 – 2011, Wyk auf Föhr). Projektionen des Meeresspiegelanstiegs bis zum Jahr 2100 (Berechnet durch das fwu, Siegen) weisen darauf hin, dass extreme Wasserstände (höchste, jährliche Tidehochwasserstände, HThw, 6.6 ± 3.8 mm/a) deutlich schneller ansteigen werden als das MThw oder der mittlere Meeresspiegel (2.6 ± 0.4 mm/a). Aufgrund dieser Beobachtungen ist von einem zukünftigen Anstieg des Gefährdungspotentials für die Halligen auszugehen, wenn es nicht gelingt, ein sedimentologisches Gelichgewicht zwischen Meeresspiegel und Marschwachstum herzu stellen. Der Anstieg der Wellenhöhe und Periode, aufgrund von steigender Wassertiefe und einer geringeren Wellentransmissionsrate an den Sommerdeichen, resultiert in einer steigenden hydrodynamischen Belastung der Warften und der Marschoberfläche. Das sedimentäre Ungleichgewicht, besonders auf Hooge und Langeneß, kann eindeutig auf das hydrologische Management der Halligen zurückgeführt werden. Aus sedimentologischer Sicht sind die beiden Hauptkritikpunkte (1) die geringe Anzahl an Überflutungen aufgrund der Deichanlagen und (2) der eingeschränkte Transport suspendierter Feststoffe über die Binnenpriele. Letzteres resultiert aus der Blockade der Binnenpriele durch Sielanlagen und führt zu einer Abnahme der Sedimentdeposition mit zunehmender Entfernung zur Uferlinie. Um dem Ungleichgewicht zwischen Marschwachstum und Meeresspiegelanstieg entgegenzuwirken, ist es dringend erforderlich, neue Managementstrategien für die Halligen zu entwickeln (Kapitel 6), welche sedimentologische/geomorphologische Aspekte sowie die speziellen Bedürfnisse der Halligbevölkerung gleichermaßen berücksichtigen. Letztere beinhalten die Minimierung ökonomischer Schäden wie etwa Einschränkungen der landwirtschaftlichen Nutzung oder des Tourismus. Mögliche Szenarien können ein Abflachen der bestehenden Deiche oder deren Rückbau und Erneuerung durch wasser- und sedimentdurchlässige Rauhstreifen (z.B. Elastocoast®, BASF) beinhalten. Weiterhin erscheint die Reaktivierung der blockierten Binnenpriele eine plausible Maßnahme zu sein. Erste Freilandexperimente auf Hallig Langeneß (Kapitel 5) belegen einen erhöhten Sedimenttransport in die Binnenmarsch aufgrund geöffneter Sielanlagen in Verbindung mit Windstau (Thw-Ereignisse über Springtideniveau). Ob die generelle Umsetzung derartiger Maßnahmen möglich ist, ist in erster Linie davon abhängig, ob die Halligbevölkerung derartigen Veränderungen ihrer Umwelt aufgeschlossen gegenübersteht und diese lokalpolitisch getragen werden. Auf jeden Fall ist ein Umdenken dahingehend erforderlich, die halligtypischen Überflutungen (Land-Unter) nicht ausschließlich als Bedrohung zu verstehen. Sie sind ein natürliches Phänomen, welches notwendig ist, um das Gleichgewicht zwischen Meeresspiegelanstieg und Sedimentdeposition aufrechtzuerhalten.

This thesis reports the development, testing, and application of computer programs for simulating Lagrangian-Stochastic particle dispersion in coastal seas, with particular application to tide and storm induced dispersion in South Australian seas. The three-dimensional tidal equations are briefly discussed for the two types of surge models used, and finite-difference methods for numerically solving these equations are considered. Different methods of simulating flows at open sea boundaries are investigated. The method of particle tracking and the development of the particle tracking model is also described. Various tests are conducted to investigate both the advective and diffusive aspects of dispersion, and a number of scenarios for the simulation of open (ocean) and closed (coastal) boundaries are considered. Various aspects of the particle tracking routine are given specific characteristics according to the nature of the particle being considered. Application of the tide and storm surge model to the Great Australian Bight is described. This uses spherical polar co-ordinates to account for the curvature of the earth, and an oblique boundary element to increase accuracy of the coastline representation. The effect of a low pressure system moving from west to east across the Bight and the resulting significant observed surge at Thevenard during the storm of April 1996 is simulated. This storm resulted in a significant number of deaths in aquaculture farms containing southern bluefin tuna (Thunnas maccoyii) within the Boston Bay region to the extreme east of the Bight due to the agitation of almost neutrally buoyant organic sediments at the sea floor. The effects of this storm are further considered using a Cartesian co-ordinate fine-grid local model of Boston Bay, in Spencer Gulf, South Australia, where both tidal and storm (wind and outside surge) induced flows are simulated. The dispersion of suspended neutrally buoyant sediment throughout the region is considered, and compared with the mortalities of tuna at various farms within the region. Tidal and storm induced currents in the Gulf St. Vincent region, South Australia, have also been modelled using Cartesian co-ordinates. Detailed consideration has been given to the modelling of tides, winds, atmospheric pressures and outside surges from the two open boundaries in Investigator Strait and Backstairs Passage. The information obtained has enabled the modelling of a number of storm surge scenarios. Further to this, various simulations of the dispersion of the larvae of the western king prawn (Penaeus latisulcatus) have been driven using the storm surge model developed. These incorporate currents near the surface and the sea floor, as well as the consideration of changes in behaviour during the life history of the larvae. / Thesis (Ph.D.)--Engineering, Computer and Mathematical Sciences, 2000.

Les submersions marines d’origine météorologique sont des catastrophes naturelles majeures, responsables chaque année de milliers de morts et de milliards d’euros de dégâts. La partie centrale du Golfe de Gascogne est un territoire particulièrement vulnérable à cet aléa, comme nous l’a rappelé la forte submersion engendrée par la tempête Xynthia en 2010. L’objectif de ce travail est d’améliorer la compréhension des surcotes et des submersions marines dans cette zone de France dans une approche pluridisciplinaire mêlant la géomorphologie, l’océanographie et l’analyse d’archives historiques. Afin de juger du caractère exceptionnel de Xynthia, une recherche de l’ensemble des submersions marines qui ont affecté la région d’étude depuis 500 ans a été menée. La modélisation numérique des surcotes des 5 tempêtes engendrant des submersions au 20ème siècle, révélées par ces recherches, montre que des conditions météo-marines variées ont induit des niveaux d’eau et des submersions comparables à ceux provoqués par Xynthia. Ce constat est en désaccord avec les estimations de périodes de retour de niveau marin extrêmes basées sur l’analyse statistique de mesures marégraphiques et met en avant l’apport de l’approche historique dans de telles problématiques. Devant la forte vulnérabilité des Pertuis Charentais aux submersions marines, la modélisation statique de la submersion marine, méthode simple mais néanmoins fréquemment utilisée pour estimer l’extension des zones inondées, a été évaluée. Cette méthode fournit de bonnes estimations de l’extension de l’inondation dans les zones de faibles altitudes caractérisées par une faible distance entre le trait de côte et la limite continentale de la zone inondable, mais mauvaises lorsque cette distance est grande. En effet, lorsque l’inondation se propage loin du trait de côte, la dynamique de l’écoulement ne peut plus être négligée sur ces grandes distances. Afin d’anticiper de futures submersions, deux configurations des digues ont été testées par modélisation numérique au travers de l’exemple de l’estuaire de la Charente. Les hauteurs d’eau et l’inondation de Xynthia sont simulées en augmentant la hauteur des digues de l’estuaire, empêchant toute inondation des zones basses adjacentes ; puis en abaissant les digues bordant l’estuaire au niveau des plus hautes marées astronomiques et en créant une seconde rangée de digues protégeant les zones habitées. Cette seconde configuration permet l’inondation des zones non habitées mais empêche l’inondation des zones à enjeux importants, comme la ville de Rochefort. Il est montré que la rehausse de l’ensemble des digues entraîne des niveaux d’eau supérieurs de 1.2 m à Rochefort par rapport à la simulation sans modification de digues, alors que l’abaissement de celles-ci et la protection des zones à forts enjeux ne modifient pas la hauteur d’eau dans l’estuaire. Ainsi, la rehausse des digues côtières n’est pas une solution systématique car la protection contre l’inondation de toutes les zones côtières peut augmenter la vulnérabilité des zones à forts enjeux. / Storm-induced coastal flooding are major natural disasters, responsible for thousands of deaths and billions of euros of damages each year. The central part of the Bay of Biscay is vulnerable to this hazard, as recently shown by the strong flooding induced by Xynthia in 2010. This study aims to improve the understanding of storm surges and coastal floods in this area of France, using several methods such as numerical or static modeling. To assess the uniqueness of Xynthia, historical researches of coastal floods affecting the study area for 500 years was conducted. Numerical modeling of the storm surges related to 5 storms of the 20th century revealed by these researches shows that various meteo-oceanic settings induced water levels and coastal floods comparable to those caused by Xynthia. This finding challenges return periods estimations of extreme sea levels based on statistical analysis of tide gauges measurements and highlights the contribution of the historical approach to such issues. Given the high vulnerability on coastal floods of Pertuis Charentais, static modeling, a simple but frequently used method to estimate the extension of flooded areas is evaluated. This analysis shows that this method provides good estimations of flood extents in low-lying areas characterized by a small distance between the shoreline and the continental limits of the lower area, but bad estimations when this distance is large. These poor performances when floods spread away from the coastline are explained by the dynamics of the flow, which can no longer be ignored. Two coastal defenses strategies are investigated in the Charente-river Estuary by numerical modeling. Water levels and coastal floods induced by Xynthia are simulated with increased dikes height, preventing flooding of adjacent low-lying areas, and then with dikes lowered to highest high spring tide height and with a second rank of dikes preventing flooding of important issues areas, such as the town of Rochefort. It is shown that raising dikes leads to higher levels of 1.2 m in Rochefort compared to the simulation without changing dikes, while protecting issues do not affect the water level in the estuary. Thus, it is demonstrated that the systematic raising of dikes is not a solution because it can increase the vulnerability of important issues areas.

Coastal forest retreat in the Florida Keys during the 20th century has been attributed to a combination of sea level rise and hurricane storm surge impacts, but the interactions between these two disturbances leading to forest decline are not well understood. The goal of my research was to assess their effects over a period spanning more than two decades, and to examine the relationships between these press and pulse disturbances and freshwater availability in pine rockland, hardwood hammock, and supratidal scrub communities. Impacts and recovery from two storm surges, Hurricanes Georges (1998) and Wilma (2005), were assessed with satellite-derived vegetation indices and multiple change detection techniques. Impacts were greater at lower elevations, and in hardwood hammock, spectral signatures indicative of plant stress and productivity returned to pre-disturbance levels within a few years. In pine rockland, impacts were predominately related to Hurricane Wilma, however, a similar return to pre-disturbance conditions was absent, suggesting that trajectories of disturbance recovery differed between the two communities. Long-term monitoring of forest composition, structure, and groundwater salinity showed that compositional shifts in the low shrub stratum were associated with salinization of the freshwater resource attributable to sea level rise. Throughout the course of twelve months of climate and groundwater monitoring (2011-2012), groundwater salinity generally decreased in response to large precipitation events. Modeling of geophysical data indicated that groundwater salinity was an important predictor of community type. Isotopic analysis of d18O in plant stem water and foliar d13C was used to determine temporal and spatial patterns in water use and plant stress in two community dominants, slash pine, Pinus elliottii var. densa, and buttonwood, Conocarpus erectus. Both species relied heavily on groundwater, and plant stress was related to increasing groundwater salinity. The results of this work suggest that the interaction of press and pulse disturbances drive changes in community composition by causing mortality of salt-sensitive species and altering the freshwater resource.

No description available.