Browsing by Subject "coastal"
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Item Aquatic macrophyte and animal communities in a recently restored brackish marsh: possible influences of restoration design and the invasive plant species Myriophyllum spicatum(2012-07-16) Bell, Michael ThomasThe numerous benefits that wetlands provide make them essential to ecosystem services and ecological functions. Historically, wetland losses have been caused by natural and anthropogenic changes. In Texas, nearly 50% of coastal wetland habitat has been lost since the 1930s and losses in the Lower Neches watershed have been some of the most extensive. Restoration is a way to mitigate these losses and can be accomplished in many ways. Each restoration design creates different aquatic habitats that can influence both submerged aquatic vegetation (SAV) and faunal communities. The restoration of the Lower Neches Wildlife Management Area (LNWMA) has created the conditions for the growth of the invasive submerged macrophyte, Myriophyllum spicatum (Eurasian watermilfoil) which may be competing with the native aquatic grass, Ruppia maritima (widgeongrass) for essential nutrients. In this study, an attempt was made to link restoration design with both SAV and aquatic fauna community structures by using a throw trap to characterize assemblages observed in three different types of restored marshes. We also performed two controlled mesocosm experiments in 0.5 gal aquariums to determine growth inhibition by M. spicatum on R. maritima. Analyses using Kruskal-Wallis non-parametric test determined that temporal variations in fauna and SAV community composition was greater than any restoration effect. Discriminant Function Analyses (DFAs) determined two to three key faunal species that best predicted association among restoration designs, but linear regressions could not determine any consistent relationship between individual species density and biomass of the dominant SAV species, M. spicatum. For the mesocosm experiments, M. spicatum inhibited the biomass production and branch count of R. maritima when the two species are grown together (ANOVA, p = 0.004 and 0.003, respectively). Changes in SAV assemblages due to competition and habitat characteristics could play a major role in determining faunal community. In order to minimize the temporal effect observed and better determine any habitat pattern that may be present, a much longer study is necessary.Item Calibration studies of the Hayes Coastal Engineering Laboratory(Texas A&M University, 2006-04-12) Thurlow, Aimee RebeccaThe Hayes Coastal Engineering Laboratory is a new laboratory with two water basins: a 45.72-meters long, 3.66 meters wide and 3.06 meters deep Tow Tank with sediment pit for dredging and current flow studies, and a 36.58 meters long, 22.86 meters wide and 1.22 meters deep 3D Wave Basin for coastal wave studies. In order to assess the capabilities of the lab a series of tests were done in both tanks. Hydrodynamic tests in the Tow Tank using a Micro Acoustic Doppler Velociometer measured current flow in the tank and assessed the efficacy of different filters to stabilize flow patterns. A concrete dam structure installed near the reversed diffusers most effectively stabilized flow of all the configurations tested. Wave tests were conducted in the 3D Wave Basin with the newly-installed 48 paddle Rexroth wave generator at 0.5 and 1.0 meter water depths using wired and wireless capacitance wave gauges. These tests measured characteristics of the generated waves and reflection from the rubble-mound beach. In addition, initial testing of the Active Reflection Absorber (ARA) system was done. Correlating the wave data to the theoretical wave being produced showed that with water depth of 0.5 meters the 0.1 meter waves were well-formed, but the 0.2 meter waves showed energy loss and lower correlation. The results from one meter water depth wave tests showed good formation of 0.2 meter waves. In nearly all wave tests with pool buoys installed the waves were better formed with good correlation and a better fitting power spectrum. The beach reflection was within the expected value range, being ten percent and below for most tests. ARA, while operational, needs to be further tuned to find the settings that will increase its effectiveness.Item Coherent structures and aeolian saltation(2009-05-15) Ellis, Jean TaylorAeolian sand transport models, widely employed by coastal scientists and managers, assume temporal and spatial homogeneity within the saltation field. This research questions that assumption by demonstrating that the saltation field is event-driven, therefore indicating that the saltation field is not temporally steady. The findings from this research may explain a portion of the conclusions from previous studies that indicated inequalities between model-estimated and field-measured aeolian sand transport. The relationship between unsteadiness in a turbulent wind field and pulses in a sand transport field was investigated on a beach near Shoalhaven Heads, New South Wales, Australia. Microphone-based saltation sensors, ?miniphones,? and thermal anemometers (both instruments constructed exclusively for this field experiment) were co-located (0.02 m separation on center) and deployed between 0.01 and 0.0225 m above the bed, and sampled at 6000 Hz. Average grain size at the field site was 0.30 mm. Five runs totaling 2050 seconds of wind and saltation data were analyzed. The continuous wavelet transform, using the Morlet wavelet base, was the principle method for analyzing the wind and saltation records. The cross continuous wavelet transform was used to analyze the wind and saltation time series concurrently. Wind, saltation, and cross events were discerned by selecting wavelet power coefficients between wavelet scales of 0.4 and 3.0 seconds and with coefficients exceeding the 95% confidence interval. Average event spacing was 6.10, 6.50, and 6.73 seconds for the wind, saltation, and cross events, respectively. The average event spacing measured in this research was compared to the empirical-based model presented by Rao, Narashimha, and Narayanan (1971). The correspondence between the model and this research strongly suggests that bursting-type coherent structures were present. The durations of average wind, saltation, and cross events were 1.87, 2.10, and 1.73 seconds, respectively. Integral time scales, calculated using normalized auto correlation and power spectral density analysis, were approximately two seconds for the wind and saltation systems. The temporal coincidence of the integral time scale estimations and the event durations for the wind and saltation system strongly suggests that wind events are driving sand transport events.Item Development and Progression of Aeolian Blowouts in Padre Island National Seashore(2013-05-28) Jewell, Mallorie EThis study characterizes the development and migration of blowouts within Padre Island National Seashore (PAIS). A combination of aerial photographs and Light Detection and Ranging (LIDAR) are used to track the migration of eighteen blowouts, while Ground-penetrating Radar (GPR) is used to investigate the subsurface at two smaller sites in the study area. This data, coupled with beach morphology and changing anthropogenic factors, helps understand why the dune blowouts develop and are restricted to a particular section of the National Seashore. Aerial Photographs taken at least twice a decade since 1969 were used to track blowouts. Each blowout was digitized in order to understand its morphometric characteristics by studying its length, width, area, segmentation, perimeter, and the width of the neck, when present, through the foredune. The velocity and direction of movement were also calculated. Cluster analysis was used to analyze the blowouts using these morphological variables. Based on this data, blows appear to group into two morphologically different clusters. Blowouts grouped into Cluster 1 are longer, thinner, have smaller perimeters and areas, smaller throat widths, and are furthest from the beach access road. A lower dune elevation leads to a larger wave runup to crest height ratio. A larger ratio suggests that the dunes are more easily overtopped during large storms, thus scarping, a precursor to blowout development, is increased. Cluster 2 blowouts tend to be longer, wider, and stabilized faster leading to a more undulated perimeter in addition to a smaller wave runup potential due to a higher dune elevation. Historically blowouts covered the entire northern portion of PAIS. In the 1970?s the portion of the beach north of Park Road 22 was designated as non-driving. Since then all blowouts in this section have revegetated, while, blowouts in the driving section are still active. Beach driving pulverizes seaweed leading to less deposition along the dune toe and therefore a lower elevation of the backshore. As a result there is a greater wave runup in storms leading to an increase in susceptibility to scarping, and therefore, blowouts. Despite the fact that storms are the primary mechanism for blow development, anthropogenic effects, such as vehicle traffic, flatten the beach profile allowing for lower areas to become inundated during storms. This, along with decreased sediment budget and increased storm frequency increases the potential for blowouts to form events and leave the island vulnerable to an increased rate of sea level rise. GPR surveys were completed at two sites; an active blowout with a foredune that is not completely reestablished (Site 1) and a blowout that is stabilized by vegetation (Site 2). Six GPR surveys were completed at Site 1 and four surveys were completed at Site 2 that show the preservation of historic phases, surfaces, and facies used to interpret sequences and compare to aerial photography and LiDAR data. Site 1 moves through five phases that begin in 1969 and end at the present location, while Site 2 moves through three active phases and then ends in a fourth phase by becoming completely stabilized with vegetation in 2010.Item Evaluating Florida's Coastal Protected Areas: A Model for Coastal Management Plan Evaluation(2011-02-22) Bernhardt, Sarah PraegerThis research presents the first coastal and marine protected areas specific quantitative management plan evaluation protocol. This critical research gap in the coastal and marine protected area (CMPA) research literature was addressed by creating a protocol for evaluating CMPA plan quality utilizing a combination of marine protected area (MPA) and land use planning techniques for the first time, then applying it to a sample of CMPAs providing both descriptive results of CMPA plan quality and analysis of factors that might influence plan quality. A sample of CMPAs (n=40) under the jurisdiction of Florida?s Coastal and Aquatic Managed Areas (CAMA) was evaluated for plan quality using 96 indicators scored as 0, 1, or 2 and then divided into five plan components: factual basis, goals and objectives, policies, tools and strategies, inter-governmental coordination and cooperation, and implementation and monitoring. Total CMPA plan quality averaged 29.40 out of a possible 50.00. CMPA plan quality ranged from 20.00 to 47.00 with a standard deviation of 7.07. Regression analysis examined the effects of CMPA context, participation, environmental threats and socioeconomic factors on CMPA plan quality. The age of CMPA plans was found to be a significant indicator of CMPA plan quality. Other significant indicators of plan quality included threatened biodiversity, participation, and percent of adjacent developed or agricultural land.Item Forms and Distributions of Hurricane Ike Backflow and Scour Features: Bolivar Peninsula, Texas(2011-08-08) Potts, Michael KillgoreThe storm surge from Hurricane Ike inundated Bolivar Peninsula as well as pooled up (~4 meters above sea level) in the Galveston Bay System behind Bolivar. After the hurricane passed, this water flowed back over the peninsula for about 19 hours, causing a great deal of coastal destruction. Analysis of post-Hurricane Ike aerial photography and Lidar data revealed the development of dramatically different scour and backflow features in the beach and dune environments along Bolivar Peninsula, Texas. Using Ward's cluster analysis, the 454 identified features were grouped according to shape and size characteristics generated by an object-oriented shape analysis program. Five distinct groups of features emerged from the cluster analysis. Group 1 features were small and compact, distributed mostly in the west; Group 2 features were large and dendritic in nature, distributed where the peninsula was narrow. Group 3 features had a longshore orientation with many of them resembling piano keys, distributed in the east. Group 4 features were oriented longshore and ornate in shape. Many of them were similar in shape to Group 2 or 3 features though statistically different enough to be grouped alone; they were distributed mostly in the eastern half of the study area. Group 5 features tended to be elongated, oriented cross-shore, nonbranching, and distributed mostly in the east. At least four flow environments caused characteristic forms. The first flow environment is typified by seaward flowing water encountering a road parallel with the coastline. The water flowing over the road scours deeply on the leeward side (seaward side), denuding beach sediments down to the resistant mud layer (Groups 3 and 4). The second flow environment was caused by a geotube, which breached during the storm and channelized flow through the breaches (Groups 2 and 5). The third flow environment had a comparatively high elevation, high development, and shore-perpendicular roads (Group 2). The fourth flow environment was typified by wide beaches backed by dunes (lost in the storm) as well as flat vegetated areas. Water flowing seaward over the vegetation scoured deeply into troughs after it came off the vegetation (Groups 1, 3, and 4).Item Phylogeographic Patterns of Tylos (Isopoda: Oniscidea) in the Pacific Region Between Southern California and Central Mexico, and Mitochondrial Phylogeny of the Genus(2012-08-17) Lee, Eun Jung 1974-Isopods in the genus Tylos are distributed in tropical and subtropical sandy intertidal beaches throughout the world. These isopods have biological characteristics that are expected to severely restrict their long-distance dispersal potential: (1) they are direct developers (i.e., as all peracarids, they lack a planktonic stage); (2) they cannot survive in the sea for long periods of immersion (i.e., only a few hours); (3) they actively avoid entering the water; and (4) they are restricted to the sandy intertidal portion that is wet, but not covered by water. Because of these traits, high levels of genetic differentiation are anticipated among allopatric populations of Tylos. We studied the phylogeographic patterns of Tylos in the northern East Pacific region between southern California and central Mexico, including the Gulf of California. We discovered high levels of cryptic biodiversity for this isopod, consistent with expectations from its biology. We interpreted the phylogeographic patterns of Tylos in relation to past geological events in the region, and compared them with those of Ligia, a co-distributed non-vagile coastal isopod. Furthermore, we assessed the usefulness of the shape of the ventral plates of the fifth pleonite for distinguishing genetically divergent lineages of Tylos in the study area. Finally, mitochondrial phylogenenetic analyses to identify the most appropriate outgroup taxa for Tylos in the study area, which included 17 of the 21 currently recognized species, provided important insights on the evolutionary history of this genus.Item The nonlinear dynamics of the sea breeze(Texas A&M University, 2004-11-15) Walter, Kevin RobertThe response of the land and sea breeze circulation to two highly simplified dynamical models is presented. The first dynamical model is the explicit specification of an oscillating interior heat source analogous to that from Rotunno (1983). Emphasis is placed on the variation of the response with heating amplitude and latitude. In addition, a weakly nonlinear analysis focuses on the dynamic forcing of nonlinear features such as a semi-diurnal gravity wave, fronts, and asymmetry in the magnitude of onshore and offshore flow. One surprising result is the identification of a cycle-mean surface divergence pattern at both 0? and 45?. At 45?, this divergence pattern is accompanied by a cycle mean shore-parallel response due to the Earth's rotation. The second dynamical model is the explicit specification of an oscillating surface heat flux. Again, comparison is made between simulations at different heating amplitudes, and between simulations at different latitudes. To address changes in the solution due to the heating method itself, comparison is made between solutions from the surface heating method and solutions from the interior heating method. Finally, solutions across the planetary continuum are explored for critical latitude dependence in high-amplitude simulations.Item Variations in Nearshore Bar Morphology: Implications for Rip Current Development at Pensacola Beach, Florida from 1951 to 2004(2012-10-19) Barrett, Gemma ElizabethIn 2002, Pensacola Beach was identified by the United States Lifesaving Association as being the most hazardous beach in the continental United States for beach drowning by rip currents. Recent studies suggest that the rip currents at Pensacola Beach are associated with a transverse bar and rip morphology that develops with the migration of the bars and recovery of the beachface following an extreme storm. Combined with an alongshore variation in wave forcing by transverse ridges on the inner-shelf, the bar cycle (of bar response and recovery to extreme storms) is hypothesized to create both rip current hotspots and periods of rip activity. However, it is unknown at what stage, or stages, the bar cycle is associated with the formation of these hotspots and the greatest number of rips. To determine how the accretional rip hazard varies in response to the nearshore bar cycle, this thesis will quantify the alongshore variation in the nearshore bar morphology on Santa Rosa Island from 1951 to 2004. Aerial photographs and satellite images are collected for the study area and nearshore features are digitized in ArcGIS and evaluated using wavelet analysis. Specifically, a continuous wavelet transform is used to the identify times and locations when a transverse bar and rip morphology is present or is in the process of developing. The findings suggest that the rip-scale variation in bar morphology (~100-250m) is superimposed on an alongshore variation consistent with the scale of the transverse ridges (~1000m). From the outer bar to the shoreline, and as the bar migrates landward, the variation becomes increasingly dominated by the rip-scale variation. Hotspots of rip current activity were found consistently between years at Fort Pickens Gate, San Souci, Holiday Inn, Casino Beach, Avenida 18 and Portofino, as clusters of rip-scale variation.