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A nested three dimensional numerical modeling application was developed to determine the fate of pathogen indicators in Lake Pontchartrain discharged from its tributaries. To accomplish this, Estuarine, coastal and ocean model with sediment (ECOMSED) was implemented to simulate various processes that would determine the fate and transport of fecal coliform bacteria in the lake. The processes included hydrodynamics, waves, sediment transport, and the decay and transport of the fecal coliforms. Wind and tidal effects were accounted along with the freshwater inflows. All the components of the modeling application were calibrated and validated using measured data sets. Field measurements of the conventional water quality parameters and fecal coliform levels were used to calibrate and validate the pathogen indicator transport. The decay of the fecal coliforms was based on the literature and laboratory tests. The sediment transport module was calibrated based on the satellite reflectance data in the lake. The north shore near-field model indicated that the fecal coliform plume can be highly dynamic and sporadic depending on the wind and tide conditions. It also showed that the period of impact due to a storm event on the fecal coliform levels in the lake can be anywhere from 1.5 days for a typical summer event to 4 days for an extreme winter event. The model studies showed that the zone of impact of the stormwater from the river was limited to a few hundred meters from the river mouth. Finally, the modeling framework developed for the north shore was successfully applied to the south shore of Lake Pontchartrain to simulate fate and transport of fecal coliforms discharged through the urban stormwater outfalls.

Tidal inlets play a significant role in barrier island sustainability along the barrier islands of southern Louisiana. With increasing tidal prism, major changes are taking place within and adjacent to the inlets. The purpose of this thesis is to examine how Caminada Pass, a tidal inlet along the Caminada-Moreau headland, has evolved through time. Fundamental to this effort is evaluating which processes have contributed toward inlet evolution and what is the response of the inlet-bordering barrier island shorelines of Grand Isle and Elmer’s Island. This effort summarizes previous results and utilizes published bathymetric data, aerial photographs, vector shorelines, satellite images, and seafloor grab samples. The intent of this research is to document the variety of data that are available for future studies of Caminada Pass, an evaluation of long and short-term changes to the system, and an overall better understanding of the inlet dynamics of Caminada Pass.

A expansão agrícola no Cerrado brasileiro vem causando severos impactos negativos decorrentes do manejo inadequado das terras. Um destes impactos é a erosão em campos de cultivo que gera grande quantidade de sedimentos, os quais podem ser interceptados em faixas vegetadas com espécies arbóreas ou gramíneas. Várias medidas conservacionistas são indicadas para a minimização destes impactos, dentre elas a presença de cobertura florestal nativa ao longo dos cursos dágua. As matas ciliares funcionam como corredores ecológicos que favorecem a biodiversidade e colaboram na manutenção da qualidade do solo e da água. A largura fixa e simétrica dessa faixa de vegetação conforme proposto pela legislação, em algumas situações se mostra ineficiente, porém a largura ideal ainda permanece controversa. Com o objetivo de propor novas informações acerca da largura ótima para Áreas de Preservação Permanente (APP´s) o presente estudo analisa as matas ciliares de forma multidisciplinar, onde são considerados diversos fatores que influenciam na dinâmica do ecossistema ripário. Fatores climáticos, geomorfológicos e pedológicos são relacionados e focados na interação das matas ciliares com os processos erosivos e seus impactos intrínsecos. Foram utilizadas técnicas convencionais para estudos de solos, como análise estrutural, análise granulométrica em soluções dispersantes (NaOH e H2O) e micromorfologia, técnicas pertinentes a estudos geomorfológicos como uso de pinos de erosão, além de técnicas inovadoras como a dendrogeomorfologia que utiliza as árvores como testemunho temporal de processos ambientais. Dessa forma foram avaliados espaço-temporalmente os sedimentos depositados nas nascentes da zona ripária da microbacia hidrográfica do Rio Meia Ponte. A análise integrada da granulometria e da micromorfologia dos solos e sedimentos revelou a predominância da sedimentação ao longo da borda da mata ciliar. A deposição de sedimentos na área de estudo varia intensamente (coeficiente de variação de 77,76%) tanto no espaço como no tempo, tendo sido observada a deposição de até 37 cm de sedimentos em alguns locais e, a erosão de até 14 cm na superfície em outros. Sendo que de um mês para outro também foi observada alternância entre sedimentação e erosão num mesmo local. A análise dendrogeomorfológica evidenciou que nos últimos 15 anos houve a deposição de até 50 cm de sedimentos. A deposição de sedimentos na área de estudo ocorre distribuída de forma geral na área numa média de 12 cm, bem como de forma localizada próxima aos sulcos de erosão (voçorocas efêmeras) e às raízes tabulares de árvores como figueiras (Ficus insípida).Os maiores índices de sedimentação ocorreram no verão de 2008/2009 quando chuvas muito intensas atingiram o solo descoberto. A ocorrência de voçorocas que atravessam tanto o campo de cultivo quanto a zona ripária reduz a eficiência da mata ciliar na retenção de sedimentos. Outro impacto negativo de grande proporção é o soterramento das nascentes e plântulas que afetam a regeneração da floresta. / Agricultural expansion in the Brazilian Savanna causes several negative impacts due to inappropriate land use. One of these impacts is represented by soil erosion in agricultural fields producing big amounts of sediment, which can be intercepted by vegetated areas with pastures or arboreous species. Several conservationist techniques are indicated to minimize these impacts, including maintenance of native vegetal coverage along water courses.Riparian forests act as ecological corridors promoting biodiversity and collaborating in water and soil quality maintenance. The symmetric and fixed width of vegetated stripes proposed by law is inefficient in some situations, and the ideal width is still controversial . With the purpose of proposing new data about the ideal width for permanent preservation areas (APPs), this study analyzes riparian forests in an integrated way taking into account several factors that influence the dynamic of riparian ecosystems. Climatic, geomorphological and pedological factors are related and focused in interaction with riparian forests, erosion processes and related intrinsic impacts. Conventional techniques were used for the soil studies such as structural analysis, particle size distribution analysis with dispersive solutions (NaOH and H2O) and micromorphology. Other techniques were used for geomorphological studies like erosion pins and dendrogeomorphology that uses trees as a temporal evidence of environmental processes. Using these techniques the spatial-temporal distribution of sediments deposited on the sources located in the riparian zone of the basin of Meia Ponte river, was studied. The integrated analysis of particle size and morphology of soils and sediments revealed the dominance of sedimentation along the edge of the riparian forest. The deposition of sediments in the study area varies greatly (coefficient of variation of 77.76%) both in space and time, the deposition was observed up to 37 cm of sediments in some locations, and erosion of up to 14 cm in surface in others. From one month to another was also observed alternation of sedimentation and erosion in one place. The dendrogeomorphic analysis showed that in the last 15 years there was deposition of sediment of up to 50 cm. Sediment deposition in the study area is generally distributed in an average of 12 cm, and locally next to rills (ephemeral gullies) and tabular roots of trees such as figs (Ficus insipida). The biggest rates of sedimentation occurred in the summer of 2008/2009 when very intense rains hit bare soil. The occurrence of gullies that cross both the field and the riparian zone and reduces the efficiency of riparian forest on sediment retention. Another negative impact is the large proportion of the springs and seedling burial that affect forest regeneration.

A expansão agrícola no Cerrado brasileiro vem causando severos impactos negativos decorrentes do manejo inadequado das terras. Um destes impactos é a erosão em campos de cultivo que gera grande quantidade de sedimentos, os quais podem ser interceptados em faixas vegetadas com espécies arbóreas ou gramíneas. Várias medidas conservacionistas são indicadas para a minimização destes impactos, dentre elas a presença de cobertura florestal nativa ao longo dos cursos dágua. As matas ciliares funcionam como corredores ecológicos que favorecem a biodiversidade e colaboram na manutenção da qualidade do solo e da água. A largura fixa e simétrica dessa faixa de vegetação conforme proposto pela legislação, em algumas situações se mostra ineficiente, porém a largura ideal ainda permanece controversa. Com o objetivo de propor novas informações acerca da largura ótima para Áreas de Preservação Permanente (APP´s) o presente estudo analisa as matas ciliares de forma multidisciplinar, onde são considerados diversos fatores que influenciam na dinâmica do ecossistema ripário. Fatores climáticos, geomorfológicos e pedológicos são relacionados e focados na interação das matas ciliares com os processos erosivos e seus impactos intrínsecos. Foram utilizadas técnicas convencionais para estudos de solos, como análise estrutural, análise granulométrica em soluções dispersantes (NaOH e H2O) e micromorfologia, técnicas pertinentes a estudos geomorfológicos como uso de pinos de erosão, além de técnicas inovadoras como a dendrogeomorfologia que utiliza as árvores como testemunho temporal de processos ambientais. Dessa forma foram avaliados espaço-temporalmente os sedimentos depositados nas nascentes da zona ripária da microbacia hidrográfica do Rio Meia Ponte. A análise integrada da granulometria e da micromorfologia dos solos e sedimentos revelou a predominância da sedimentação ao longo da borda da mata ciliar. A deposição de sedimentos na área de estudo varia intensamente (coeficiente de variação de 77,76%) tanto no espaço como no tempo, tendo sido observada a deposição de até 37 cm de sedimentos em alguns locais e, a erosão de até 14 cm na superfície em outros. Sendo que de um mês para outro também foi observada alternância entre sedimentação e erosão num mesmo local. A análise dendrogeomorfológica evidenciou que nos últimos 15 anos houve a deposição de até 50 cm de sedimentos. A deposição de sedimentos na área de estudo ocorre distribuída de forma geral na área numa média de 12 cm, bem como de forma localizada próxima aos sulcos de erosão (voçorocas efêmeras) e às raízes tabulares de árvores como figueiras (Ficus insípida).Os maiores índices de sedimentação ocorreram no verão de 2008/2009 quando chuvas muito intensas atingiram o solo descoberto. A ocorrência de voçorocas que atravessam tanto o campo de cultivo quanto a zona ripária reduz a eficiência da mata ciliar na retenção de sedimentos. Outro impacto negativo de grande proporção é o soterramento das nascentes e plântulas que afetam a regeneração da floresta. / Agricultural expansion in the Brazilian Savanna causes several negative impacts due to inappropriate land use. One of these impacts is represented by soil erosion in agricultural fields producing big amounts of sediment, which can be intercepted by vegetated areas with pastures or arboreous species. Several conservationist techniques are indicated to minimize these impacts, including maintenance of native vegetal coverage along water courses.Riparian forests act as ecological corridors promoting biodiversity and collaborating in water and soil quality maintenance. The symmetric and fixed width of vegetated stripes proposed by law is inefficient in some situations, and the ideal width is still controversial . With the purpose of proposing new data about the ideal width for permanent preservation areas (APPs), this study analyzes riparian forests in an integrated way taking into account several factors that influence the dynamic of riparian ecosystems. Climatic, geomorphological and pedological factors are related and focused in interaction with riparian forests, erosion processes and related intrinsic impacts. Conventional techniques were used for the soil studies such as structural analysis, particle size distribution analysis with dispersive solutions (NaOH and H2O) and micromorphology. Other techniques were used for geomorphological studies like erosion pins and dendrogeomorphology that uses trees as a temporal evidence of environmental processes. Using these techniques the spatial-temporal distribution of sediments deposited on the sources located in the riparian zone of the basin of Meia Ponte river, was studied. The integrated analysis of particle size and morphology of soils and sediments revealed the dominance of sedimentation along the edge of the riparian forest. The deposition of sediments in the study area varies greatly (coefficient of variation of 77.76%) both in space and time, the deposition was observed up to 37 cm of sediments in some locations, and erosion of up to 14 cm in surface in others. From one month to another was also observed alternation of sedimentation and erosion in one place. The dendrogeomorphic analysis showed that in the last 15 years there was deposition of sediment of up to 50 cm. Sediment deposition in the study area is generally distributed in an average of 12 cm, and locally next to rills (ephemeral gullies) and tabular roots of trees such as figs (Ficus insipida). The biggest rates of sedimentation occurred in the summer of 2008/2009 when very intense rains hit bare soil. The occurrence of gullies that cross both the field and the riparian zone and reduces the efficiency of riparian forest on sediment retention. Another negative impact is the large proportion of the springs and seedling burial that affect forest regeneration.

Les estrans du bassin d’Arcachon sont en grande partie colonisés par des herbiers de Zostera noltii. La surface de ces herbiers connaît actuellement une régression importante. Il est donc essentiel de comprendre le rôle des herbiers de Zostera noltii sur les processus hydrodynamiques et sédimentaires afin d’anticiper les conséquences de la régression sur les bilans morpho-sédimentaires du bassin d’Arcachon.Des expérimentations en canal sur herbiers naturels ont mis en évidence une importante atténuation de la vitesse près du fond, associée à une augmentation de la turbulence, diminuant au cours du développement des herbiers. Il en résulte dans le même temps, une augmentation de l’effet de protection contre l’érosion et des flux de dépôt.Des tests d’érodabilité ont montré une variation saisonnière de la résistance des sédiments face à l’érosion, associée à la modification des sédiments superficiels. La stabilisation induite par la présence de la rhizosphère et sa saisonnalité a également été mise en évidence. Un paramétrage satisfaisant de la loi d’érosion a été obtenu.Un suivi in-situ du niveau sédimentaire, des paramètres sédimentaires et biométriques a mis en évidence des tendances nettes au dépôt en présence d’herbier, et à l’érosion en l’absence d’herbier. En présence d’herbiers, l’évolution des caractéristiques des sédiments superficiels est corrélée au cycle de croissance des herbiers. Les sédiments deviennent plus fins durant la période de croissance alors qu’un enrichissement en sable intervient durant la période de dégénérescence automnale.Le modèle hydrodynamique MARS-3D a été exploité pour simuler finement les profils de vitesse en présence des herbiers, en prenant en compte la flexibilité de leurs feuilles. / The intertidal flats in the Arcachon lagoon are extensively colonized by seagrass meadows of Zostera noltii. The last ten years these meadows experienced a drastic regression of their surface area. Understanding the impact of seagrass on hydrodynamics and sediment dynamics is required to anticipate the consequences of meadows regression on the sediment dynamics of the Arcachon lagoon.Flume experiments with natural seagrass highlighted a strong velocity attenuation associated with a turbulence increase near the bed within seagrass canopies. An increase in sediment protection from erosion and in deposition fluxes related to the seagrass growth was found.Erosion tests showed seasonal variability of sediment resistance against erosion associated with changes in sediment characteristics. The bed stabilization induced by the root system and its seasonality was also observed. A parameterization of the erosion law was found.The in-situ survey of sediment altimetry, sediment and biometric characteristics showed a significant trend to sediment deposition on colonized sites, while erosion occurred on the unvegetated site. On the vegetated sites, surface sediment evolutions are correlated to the seagrass growth. Sediment became finer during the growth while the sand content rose during the end-of-season die-off.The hydrodynamic model MARS-3D was modified to take into account for seagrass and its flexibility on hydrodynamics and produced good simulation of velocity profiles in presence of seagrasses.

Seagrasses are ecosystem engineers, forming extensive meadows that provide critical habitat and modulate local morphodynamics. Their canopies induce drag on flow to attenuate mean flow and reduce near-bed flow velocities, which can shield the bed from erosion and sediment suspension. Alternatively, seagrass loss can enhance erosion and sediment suspension, which can be initiated through short-lived extreme events, or chronic long-term disturbances. Physical process and disturbances can govern the evolution of seagrass meadow ecosystems. In two separate chapters, this research examined 1) the influence of climate variability and storms on seagrass loss and erosion at a high spatial resolution, and 2) how flow attenuation by seagrass varies across tidal cycles and at different locations in the Choked Passage meadow, on the Central Coast of British Columbia. We used high resolution multibeam echosounder (MBES) bathymetry and backscatter data from 2018 to 2021, drone mapped seagrass delineations from 2014 to 2021, and wind and wave data from 2014 to 2021. Flow data (i.e. velocity magnitude, velocity direction, and acoustic backscatter) above the seagrass canopy was collected with an Acoustic Doppler Current Profiler (ADCP) along transects and moored to the seafloor over a tidal cycle. Sediment samples were collected from the bed to estimate critical shear stress and verify sediment classes from an acoustic backscatter analysis. From 2018 to 2021, the meadow experienced significant erosion (net surface lowering of -18,768 m3) and loss of seagrass (10% reduction), which we attribute to the preceding winter storm activity driven by moderate La Niña conditions. The spatial patterns of erosion and seagrass loss was non-uniform across the meadow. Coupled erosion and seagrass loss resulted in the generation and/or expansion of blowouts. We observed a trend of a reduction in seagrass coverage following winters with a high number of storm events and/or high recorded storm intensity from 2014 to 2021. We believe the Choked Passage seagrass meadow undergoes cyclic behaviour with reduction in seagrass coverage during energetic ENSO years, followed by a recovery period during weak years. The ADCP was used to detect the seagrass canopy height, measure flow, and estimate shear stress. Overall, flow is fastest in the northern section of the main meadow, particularly in the north-west corner where the meadow is patchy. Moreover, flow appears to accelerate through the meadow interior, which suggests that topographic steering and the strength of incoming currents exceeds the ability of seagrass to dampen flow velocity. During the transition from peak flood to ebb, flow velocity remained heightened for longer above the southern meadow and lagged the other sections. Shear stress results indicate that sediment can be transported as bedload and in suspension under peak flow velocities at some of the sites examined within the meadow. Shear stress is largest in the meadow center and lower towards the southern margin of the main meadow. Based on our results, when sediment transport is initiated under peak tidal and/or extreme conditions, sediment is likely primarily transported as bedload, creating the observed sand wave and blowout bedforms. This research demonstrated linkages between extreme storms (during ENSO years), seabed morphology, and seagrass coverage, and examined the variability in the interaction between flow, seagrass, and sediment transport. Geomorphic processes and disturbances have an important influence on ecosystem structure and function over time, therefore, it is important to understand how these processes operate and are modified by external drivers. The results of this study have significant implications on seagrass conservation, restoration, and the evolution of coastal landscapes. / Graduate

Seabed surface sediments vary with active geomorphodynamics and sediment remobilization processes. Understanding relations between geotechnical sediment properties and sediment mobilization processes can potentially improve predictions of coastal erosion and hazard mitigation. Portable free fall penetrometers have emerged as an economic and useful tool for rapid geotechnical site characterization and uppermost sediment layer investigation. Acoustic methods have been used to assess seabed layering, scour evolution, and seabed morphology. However, there still exist major limitations in using these methods for classification and characterization of seabed sediment surface layers in the context of local sediment dynamics. Therefore, the goal of this research is to advance field data collection methods and field data availability towards advancing the current understanding and prediction of nearshore sediment dynamics. Geotechnical and geophysical measurements were conducted at different sites: Delaware Bay, Delaware; Pea Island, North Carolina; York River, Virginia; Potomac River, Maryland; Guadalupe River, Brazos River, Colorado River, Texas with different soil types and properties, hydrodynamic conditions, and morphological settings. The data collected was utilized to address the research goals through: (1) combining geotechnical and acoustic measurements to get better insight on sediment dynamics and erodibility, (2) proposing a framework that utilizes PFFP data to classify soil and estimate certain sediment properties (relative density and friction angle for sand and undrained shear strength for clays), relevant for local sediment dynamics, and (3) investigating how relevant geotechnical properties are reflected in acoustic, and specifically chirp sonar measurements. The findings of this research support the capability of portable free fall penetrometer to estimate sediment properties in topmost layers for different soil types such as friction angles, with an accuracy of ± 1° and undrained shear strength values, with <10% mismatches. Geoacoustic parameters such as acoustic impedance can also be calculated from acoustic measurements and correlated to certain sediment properties such as porosity and bulk density. Combining both measurements can yield better site characterization and accurate estimation of sediment properties for a better prediction of sediment dynamics. / Doctor of Philosophy / As the impacts of climate change seem to worsen, the likelihood of extreme events increases. This includes more frequent and severe events such as erosion, storm surges, melting glaciers, and sea level rise that impacts coastlines and coastal infrastructure. The increase in water levels increases the frequency of coastal hazards and flooding. These events result in devastating consequences, economically and environmentally, and disrupt people's lives all over the world. To adapt and reduce the severity of these consequences, there is a need to capture the changes in seabed, and a better understanding of seabed properties and their erodibility. This requires a reliable site characterization and an accurate estimate of seabed properties, which remain a challenge for different marine environments. There exist different site investigation methods to estimate seabed sediment properties that fall under geotechnical or geophysical types. One of the common geotechnical methods is a Portable free fall penetrometer (PFFPs), that presents a robust and economical tool for a rapid site assessment of topmost seabed layers. Geophysical tools, and mainly acoustic methods, are also often used to complement geotechnical methods due to their ability to cover vast areas in efficient time. However, both methods still face limitations in assessing seabed layers and properties. Therefore, the objective of this research is to develop a framework that paves the way for a reliable assessment of seabed properties using geotechnical and geophysical methods. Both methods were utilized for data collection in different locations across the US: Delaware Bay, Delaware; Pea Island, North Carolina; York River, Virginia; Potomac River, Maryland. Three additional sites Guadalupe, Brazos River, and Colorado Rivers, Texas were surveyed post hurricane Harvey that resulted in extreme flooding events. The measurements are collected from different coastal environments. This better account for the diversity in seabed to achieve a more generalized and well-integrated methodology to assess seabed layers under different conditions.