Global ETD Search

1	Stable Isotope Characterization and Proxy Records of Hypoxia-Susceptible Waters on the Texas-Louisiana Shelf Strauss, Josiah 2010 December 1900 (has links) Hypoxia, with dissolved oxygen levels < 1.4 ml L-1, is a recurring summer feature of Louisiana shelf bottom waters. Stable isotope characterization (delta^18O and delta D) of surface waters over the hypoxic zone shows a shift of dominant river influence from the Mississippi River during April to the Atchafalaya in July. Carbon isotopes of dissolved inorganic carbon (δ13CDIC) in bottom waters reveal the respiration of terrestrial organic carbon (OC) at inshore localities of 10 m depth and the respiration of marine OC at depths equal to and greater than 20 m. delat^18O and delta^13C profiles of Louisiana shelf Conus shells collected in 1972 show no evidence for summer hypoxia. Comparison with modern Conus records reveal a delta^13CDIC reduction during the last four decades associated with intrusion of ^13C-depleted fossil fuel CO2. Summer delta^13C reductions in Texas shelf Pteria shells may imply dissolved oxygen (DO) was reduced by ≈0.7 ml L-1, although this may be attributed to influence of Brazos River discharge on shell delta^18O and delta^13C. Foraminifera fauna measured in age-calibrated sediments from the Texas shelf reveal a low oxygen conditions on between 1960 and modern sediments. From 1950 to 1960, fauna indicate oxygenated bottom waters. Contemporaneous increases of foraminifera delta^13Cand delta^18O suggest this event is associated with severe drought (the Little Dust Bowl). The synchronicity of these data suggests a link between Brazos River discharge and shelf hypoxia. Hypoxia Stable Isotopes Mollusks Foraminifera Coastal Processes
2	Sedimentation of the Brazos River System: Storage in the Lower River, Transport to Shelf and the Evolution of a Modern Subaqueous Delta Carlin, Joseph A 16 December 2013 (has links) The Brazos River, located predominantly within the state of Texas, has the highest water and sediment discharge of all rivers in the state, and ranks second behind the Mississippi River in terms of sediment load delivered to the Gulf of Mexico. This river is the only Texas river that consistently drains directly into the Gulf of Mexico forming a wave-dominated delta. The delta has experienced dramatic and rapid changes over the last 100-plus years. These changes have resulted from both natural and anthropogenic alterations to the coastal zone proximal to the river mouth and within the rivers watershed. By utilizing high-resolution geophysical data, sediment cores, water column data, and historic shoreline data this study investigated the mechanisms in which sediment is transported to the coastal ocean, the fate of that sediment as it becomes preserved in the modern geological record, and the evolution of a modern delta. Results from this study show that during for a majority of the time a salt-water intrusion in the lower river traps sediment, preventing export to the coastal ocean. The trapped sediment forms an ephemeral mud layer in the lower river that may be remobilized during increased river discharges. When river discharges increase above an observed threshold of 300 m^3/s the salt wedge is pushed seaward of the river mouth and sediment is exported via a buoyant plume. As export of sediment is episodic, accumulation of sediment on the subaqueous delta characterized as non steady-state, and resembles typical foreset delta attributes. These include physical stratification of sediment layers, episodic but relatively high rates of accumulation, and little bioturbation. Currently sediment is primarily accumulating west of the river mouth, and the majority of sediment is bypassing the system. Over the history of the delta, changes both anthropogenic and natural have shifted the relative balance of fluvial sediment supply and marine sediment dispersal. These changes have resulted in dramatic changes in the shoreline, and phases of activation and abandonment of deltaic lobes, which can be seen through historical data and imagery, and is preserved in the recent sedimentary record. Sedimentation River mouths Coastal Processes Delta evolution
3	Evidence for changes in coastline-controlled base level from fluvial stratigraphy at Aeolis Dorsa, Mars Cardenas, Benjamin Thomas 20 January 2015 (has links) There is evidence that a subset of fluvial deposits at Aeolis Dorsa, a basin on Mars, preserve incised valleys carved and filled during changes in base level, which was likely controlled by water surface elevation of a large lake or sea. Three low-albedo, channelized corridors, each several tens of kilometers long, contain relict point bars and scooped boundaries at their bases, indicating that the base and lateral extent of each corridor was defined by a migrating, net-erosional river. Above the basal deposits are stacks several tens of meters thick of “inverted sinuous ridges”, which are channel-filling deposits that have been exhumed and topographically inverted. Indicators of avulsions, channel re-occupations, an overall flattening of basal topography, and confinement of inverted sinuous ridges to the dark corridors are evidence of the gradual filling of a valley cut by the basal migrating river. Valley incision and fill are common responses to sea level change on Earth. Aeolis Dorsa is currently open to the northern lowlands of Mars, where an ocean has been hypothesized to have once existed, although a large lake could have also controlled base level. Cross-cutting valleys require at least two episodes of base level fall and rise. The magnitudes of the base level changes are estimated at about 80 meters, based on the thickness of the valley-filling stratigraphy. Meander asymmetry is consistent with a southeastern flow direction, and is supported by a set of branching fluvial deposits 40 km to the southeast which, qualitatively, appear to be deltaic in origin. / text Mars Geology Ancient ocean Coastal processes Fluvial Incised valley Stratigraphy
4	Convexity, Concavity, and Human Agency in Large-scale Coastline Evolution Ells, Kenneth Daniel January 2014 (has links) <p>Coherent, large-scale shapes and patterns are evident in many landscapes, and evolve according to climate and hydrological forces. For large-scale, sandy coastlines, these shapes depend on wave climate forcing. The wave climate is influenced by storm patterns, which are expected to change with the warming climate, and the associated changes in coastline shape are likely to increase rates of shoreline change in many places. Humans have historically responded to coastline change by manipulating various coastal processes, consequently affecting long-term, large-scale coastline shape change. Especially in the context of changing climate forcing and increasing human presence on the coast, the interaction of the human and climate-driven components of large-scale coastline evolution are becoming increasingly intertwined. </p><p>This dissertation explores how climate shapes coastlines, and how the effects of humans altering the landscape interact with the effects of a changing climate. Because the coastline is a spatially extended, nonlinear system, I use a simple numerical modeling approach to gain a basic theoretical understanding of its dynamics, incorporating simplified representations of the human components of coastline change in a previously developed model for the physical system. </p><p>Chapter 1 addresses how local shoreline stabilization affects the large scale morphology of a cuspate-cape type of coastline, and associated large-scale patterns of shoreline change, in the context of changing wave climate, comparing two fundamentally different approaches to shoreline stabilization: beach nourishment (in which sediment is added to a coastline at a long-term rate that counteracts the background erosion), and hard structures (including seawalls and groynes). The results show that although both approaches have surprisingly long-range effects with spatially heterogeneous distributions, the pattern of shoreline changes attributable to a single local stabilization effort contrast greatly, with nourishment producing less erosion when the stabilization-related shoreline change is summed alongshore. </p><p>Chapter 2 presents new basic understanding of the dynamics that produce a contrasting coastline type: convex headland-spit systems. Results show that the coastline shapes and spatially-uniform erosion rates emerge from two way influences between the headland and spit components, and how these interactions are mediated by wave climate, and the alongshore scale of the system. Chapter 2 also shows that one type of wave-climate change (altering the proportion of `high-angle' waves) leads to changes in coastline shape, while another type (altering wave-climate asymmetry) tends to reorient a coastline while preserving its shape. </p><p>Chapter 3 builds on chapter 2, by adding the effects of human shoreline stabilization along such a convex coastline. Results show that in the context of increasing costs for stabilization, abandonment of shoreline stabilization at one location triggers a cascade of abandonments and associated coastline-shape changes, and that both the qualitative spatial patterns and alongshore speed of the propagating cascades depends on the relationship between patterns of economic heterogeneity and the asymmetry of the wave-climate change--although alterations to the proportion of high-angle waves in the climate only affects the time scales for coupled morphologic/economic cascades.</p> / Dissertation Geomorphology Environmental science coastal processes coastline evolution complex systems coupled human-landscape morphodynamics nonlinear dynamics
5	Geomorphologic evolution of a rapidly deteriorating barrier island system with multiple sediment sources: Eastern Isles Dernieres, Louisiana, 1887 to 2006 Kirkland, Benjamin T 15 December 2012 (has links) Trinity, East, and Wine Islands make up the eastern half of the Isles Dernieres barrier arc in south-central Louisiana. Formed following the abandonment of the Lafourche delta complex, subsidence and storm erosion have led to rapid deterioration of the system. Since 1887, the land area of the islands has decreased seventy-seven percent, and the gulf shoreline has retreated landward more than a kilometer. Wave ravinement on the shoreface of the islands is responsible for the most sediment loss; liberated sediment travels longshore to tidal inlets. The dominant ebb tidal currents then transport the sediment to where it is deposited in ebb tidal deltas or carried to the west, out of the system. A large lobe of sediment bypassing Cat Island Pass is entering the system from the eastern lower shoreface, which helps replace some of the sediment lost through wave ravinement to the upper shoreface. coastal geomorphology coastal processes barrier islands Environmental Monitoring Geology Geomorphology Sedimentology
6	Geomorphic Evolution of Caminada Pass in Southeast Louisiana. Spizale, Jordyn A 06 August 2013 (has links) 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. tidal inlet barrier island Lafourche Barrier Islands Barataria tidal inlets Louisiana coastal processes sediment dynamics Geomorphology
7	The role of large woody debris on sandy beach-dune morphodynamics Grilliot, Michael J. 30 April 2019 (has links) Coastal foredune evolution involves complex processes and controls. Although a great deal is known about the effects of vegetation cover, moisture, and fetch distance on sediment supply, and of topographic forcing on airflow dynamics, the role of large woody debris (LWD) as a modulator of sediment supply and a control on foredune growth is understudied. Large assemblages of LWD are common on beaches near forested watersheds and collectively have a degree of porosity that increases aerodynamic roughness and provides substantial sand trapping volume. To date, no research has attempted to understand the geomorphic role that LWD matrices, as a whole, have as roughness elements affecting airflow and sediment transport across a beach-dune system, or, what the long-term implications of these impacts are on beach and foredune erosion recovery and evolution. This four-year research initiative investigated the role of a LWD matrix on beach-dune morphodynamics on West Beach, Calvert Island on the central coast of British Columbia, Canada. This study integrated data from research that spanned three temporal scales, 1) event-scale (10 min) flow and sediment transport patterns, 2) daily frequency and relative magnitude of landscape changing events, 3) seasonal to interannual-scale volumetric and LWD changes. An event-scale experiment to characterise airflow dynamics and related sand transport patterns showed that LWD distinctly alters wind flow patterns and turbulence levels from that of incoming flow over a flat beach. Overall, mean wind speed and fluctuating flow properties declined as wind transitioned across the LWD. Streamwise mean energy was converted to turbulent energy, however, the reductions in mean flow properties were too great for the increased streamwise turbulence to have an effect on transport. In response to these flow alterations and more limited sand transport pathways to the foredune, sediment flux was reduced by 99% in the LWD compared to the open beach, thereby reducing sand supply to the foredune. Sand grains rebounding off of the LWD were carried higher into the flow field resulting in greater mass flux recorded at 20-50 cm in the LWD as opposed to the flat beach. This effect was only recorded 6 m into the LWD. As such, LWD has the potential to modulate rates of foredune recovery, growth, and evolution. Time-lapse photography collected at 15 min intervals during the study revealed that storm events lead to wave-induced erosion of the backshore and reworking of the LWD matrix. The exposed LWD matrix subsequently traps aeolian sediment that leads to rapid burial of the LWD and building of a raised platform for emergent vegetation. However, infilling of the accommodation space within the LWD matrix is so rapid, that sediment starvation of the foredune is short-lived. While the LWD at this site does trap sediment in the backshore, helping to protect the dune from scarping, LWD at this study site maintains an overall lower impact on transport to the foredune. Critical to this relationship is the frequency and magnitude of nearshore events that erode the beach periodically and re-organize the LWD matrix, which directly impacts the ability of LWD to store sediment and modulate transport to the foredune. A conceptual model exploring these relationships is presented. / Graduate Coastal Processes Foredune Sediment Transport Aeolian Processes Geomorphology Large Woody Debris Driftwood lidar Terrestrial laser scanning Process Geomorphology
8	Wave energy converter strings for electricity generation and coastal protection Alexandre, Armando Emanuel Mocho fernandes e January 2013 (has links) Generation of electricity from ocean waves has seen increasing research and commercial interest in recent years. The development of projects of several hundred megawatts rated capacity is now being considered. There is a clear need for improved understanding of the environmental impact of large-scale wave energy extraction, particularly in nearshore regions where sediment transport and cliff erosion may be affected. This thesis investigates the change in nearshore wave conditions and sediment transport due to energy extraction by long strings of wave energy devices. The influence of wave energy converter (WEC) arrays has been studied using transmission coefficients implemented within a spectral wave model. It is shown that the breaking wave height nearshore is larger (5%) if transmission is defined as frequency dependent. This is due to the energy dissipation processes associated with different wave frequencies. Linear wave theory is employed to determine frequency dependent transmission and reflection coefficients across a line of wave energy devices based onthe amplitude of scattered and radiated waves. This approach is compared with experimental measurements of the wave field in the vicinity of an array of five heaving floats. The transmitted wave amplitude is predicted with reasonable accuracy but additional numerical damping is required to predict the measured float response amplitude. This comparison indicates that linear analysis is an acceptable approach for predicting float response and wave field in the vicinity of the array for a certain range of conditions. Linear wave analysis is subsequently applied to investigate the variation of transmission coefficients with distance inshore of a long array of heaving WECs undergoing free response and with damping specified to optimise power extraction. A method is presented for identifying representative transmission and reflection coefficients such that change in wave energy is equal to energy extraction by the devices. These coefficients are employed to quantify the change in nearshore conditions due to deployment of a long line of wave devices at a site near the East Anglian coastline. Wave conditions are modelled at 12 points along the shoreline over a 140 year period and significant wave height reductions up to 30% were obtained. Importantly, changes in nearshorewave direction are also observed. Analysis using the sediment transport model SCAPE (Soft Cliff and Platform Erosion model) indicates that the introduction of the array reduces both the sediment transport rate and cliff recession rate by an average of 50%. 621.312134
9	Environmental Impacts on the Development and Dune Activity of Oxbow Lake along the Southwest Coast of Lake Michigan at Saugatuck, Michigan USA Baca, Kira J. 22 August 2013 (has links) No description available. Geomorphology Geological Geology Geography Climate Change Earth Environmental Geology Environmental Science Paleoclimate Science dune climate coastal Michigan Lake Michigan Oxbow Lake Suagatuck coastal processes sand signals Glew Livingstone eolian Pb210 age dating gamma spectroscopy climate change
10	Oceanographic Considerations for the Management and Protection of Surfing Breaks Scarfe, Bradley Edward January 2008 (has links) Although the physical characteristics of surfing breaks are well described in the literature, there is little specific research on surfing and coastal management. Such research is required because coastal engineering has had significant impacts to surfing breaks, both positive and negative. Strategic planning and environmental impact assessment methods, a central tenet of integrated coastal zone management (ICZM), are recommended by this thesis to maximise surfing amenities. The research reported here identifies key oceanographic considerations required for ICZM around surfing breaks including: surfing wave parameters; surfing break components; relationship between surfer skill, surfing manoeuvre type and wave parameters; wind effects on waves; currents; geomorphic surfing break categorisation; beach-state and morphology; and offshore wave transformations. Key coastal activities that can have impacts to surfing breaks are identified. Environmental data types to consider during coastal studies around surfing breaks are presented and geographic information systems (GIS) are used to manage and interpret such information. To monitor surfing breaks, a shallow water multibeam echo sounding system was utilised and a RTK GPS water level correction and hydrographic GIS methodology developed. Including surfing in coastal management requires coastal engineering solutions that incorporate surfing. As an example, the efficacy of the artificial surfing reef (ASR) at Mount Maunganui, New Zealand, was evaluated. GIS, multibeam echo soundings, oceanographic measurements, photography, and wave modelling were all applied to monitor sea floor morphology around the reef. Results showed that the beach-state has more cellular circulation since the reef was installed, and a groin effect on the offshore bar was caused by the structure within the monitoring period, trapping sediment updrift and eroding sediment downdrift. No identifiable shoreline salient was observed. Landward of the reef, a scour hole ~3 times the surface area of the reef has formed. The current literature on ASRs has primarily focused on reef shape and its role in creating surfing waves. However, this study suggests that impacts to the offshore bar, beach-state, scour hole and surf zone hydrodynamics should all be included in future surfing reef designs. More real world reef studies, including ongoing monitoring of existing surfing reefs are required to validate theoretical concepts in the published literature. Aramoana Beach Dunedin (New Zealand) ArcGIS ArcSDE artificial surfing reef backscatter Baseline Data Collection bathymetry bathymetric surveying beach morphodynamics beach-state and morphology breaking wave height coastal engineering coastal environment coastal management coastal monitoring coastal processes coastal structures currents economic value EIA environmental data management environmental impact assessment geographic information systems geoid geomorphic surfing break categorisation GIS groin hydrodynamic modelling hydrographic surveying hydrography ICZM incline plane modelling integrated coastal zone management Main Beach Mount Maunganui (New Zealand) Manu Bay Boat Ramp Raglan (New Zealand) measuring water levels morphological coupling multibeam echo soundings oceanography offshore wave transformations Palm Beach Reefs Gold Coast (Australia) RTK GPS salient surf zone hydrodynamics surfing break components surfing reefs surfing tourism surfing wave climate surfing wave parameters Tay Street Mount Maunganui (New Zealand) wave breaking intensity wave climate wave focusing wave modelling wave peel angle wave section length wind effects on waves

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