• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 245
  • 120
  • 27
  • 17
  • 16
  • 13
  • 10
  • 5
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • Tagged with
  • 590
  • 112
  • 90
  • 74
  • 53
  • 49
  • 49
  • 47
  • 44
  • 41
  • 38
  • 36
  • 33
  • 30
  • 30
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
111

Spatial and temporal variability of sandy beach sediment grain size and sorting

Prodger, Sam January 2017 (has links)
Beach grain size plays a major role in controlling beach slope and sediment transport rates and is a crucial criterion in selecting the appropriate fill material for beach nourishment. Yet, little is known about how and why beach grain size (and sorting) varies both spatially and temporally on high-energy sandy beaches. Therefore, in this PhD research project, the presence, magnitude and predictability of any spatio-temporal sediment variability was investigated on a number of contrasting high-energy (average significant wave height = 0.8 to 3.5 m), predominantly macrotidal (MSR = 3.1 – 6.2 m), sandy (0.26 – 0.64 mm) beach sites around the southwest peninsula of the United Kingdom (UK). The spatial extent of the data collected ranges from regional (one off snapshot of the sediment conditions on 53 beaches over 485 km of coastline) to local scales (repeated high-resolution samples from across the inter- and subtidal zone of a single high-energy sandy beach; Perranporth, UK). The temporal scales of the sampling ranges from tidal scale (~12 hours) up to monthly (long-term monitoring since 2008). A combination of traditional and modern field data collection methods has provided new insights into the sediment dynamics of sandy beaches. Surface and 0.25 m core sediment samples from the 53 beaches around the southwest UK and high-resolution digital measurements with longer 1 m sand cores from the intertidal zone, plus grab samples from the subtidal zone, at Perranporth, indicated the presence of three quasi-permanent spatial trends. On all sandy beaches, surface sediments became coarser (and better sorted) in the seaward direction across the intertidal zone. Peak sediment sizes were observed on the lower beach around mean low water springs, which were an average 19% coarser (and 8% better sorted) than sediments sampled on the upper intertidal beach. Sediment size (and sorting) also increased (improved) with distance down the sediment column over the top 0.25 m to 1 m. Peak sediment sizes at depth were an average 16% coarser (and 16% better sorted) than surface sediments. In the subtidal zone, surface sediments became finer and poorer sorted with increasing offshore distance. Minimum sediment size occurred on the subtidal bar crest and were an average 21% finer (and 51% poorer sorted) than the lower beach sediments and 5% finer (and 38% poorer sorted) than upper beach sediments. The coarsest sediments were usually the best sorted at all locations. The intertidal coarsening was deterministically linked to the location and amount of breaking wave-induced turbulence. The peak sediment sizes (and sorting) on the lower beach correlated with the location of peak wave dissipation (sediment size to amount of wave dissipation, r2 = 0.86) and the finer sediment sizes on the upper beach and bar were coincident with reduced amounts of wave dissipation in these regions. Long-term seasonal monitoring of the surface sediments at Perranporth indicated a background seasonality, where the winter months were an average 35% coarser and 22% better sorted than samples collected in summer. This seasonal pattern was punctuated by episodic storm events that promoted a significant coarsening (up to 112% in the extreme winter storms of 2014) of the surface sediments and significant beach erosion up to 175 m3/m. An empirical model forced by the degree of disequilibrium between an instantaneous and antecedent (weighted average) wave steepness time series was able to capture up to 86% of the sediment grain size and sorting variability, incorporating both the seasonal and storm driven change. The same model, applied to daily observations of sediment size and sorting changes was able to explain 72% of the variability. A conceptual model is proposed that extends the cross-shore sediment transport shape functions to include the various sediment (size and sorting) responses alongside the morphodynamic evolution during persistently high and low wave steepness conditions. Under high steepness waves, the finer material is preferentially removed from the lower intertidal beach, leaving behind coasrer sediments. This fine material is transported to the subtidal bar, which becomes finer (and more poorly sorted) inversely with the coarsening (and improved sorting) of the intertidal zone sediments. Under low steepness waves, this fine material is returned from the bar to the intertidal beach. This work provides a detailed, quantitative insight into the magnitude of sediment grain size and sorting changes exhibited by sandy beaches on a number of spatial and temporal scales. Several consistent trends were observed on a range of sandy beaches despite their different environmental conditions and geological histories. This improved understanding of sediment grain size and sorting changes on beaches will hopefully aid future research efforts and ensure that this fundamental aspect of coastal science is not overlooked or oversimplified.
112

Characteristics of a Chronically, Rapidly Eroding Beach: Long Key, Pinellas County, Florida

Saint John, Alyssa L 19 November 2004 (has links)
Long Key, on the central western coast of Florida, has been nourished repeatedly since 1975. Following nourishment, the beach has rapidly eroded. This study documents rates, processes, and mechanisms for the rapid erosion. To better understand the beach performance, it is crucial to quantify the background erosion rate when artificial beach fill is at its minimum. This year long study from February 2003 through March of 2004 provides a detailed examination of the performance of a natural beach experiencing intense erosion. The primary objective is to analyze the performance of Long Key through detailed investigation of shoreline and beach-volume changes at a time when the effects of the most recent nourishment in the summer of 2000 are a minimal influence, and the natural performance of the beach, i.e, the background erosion/accretion rate, can be determined. This study also examines, in detail, shore-parallel and cross-shore sediment properties in an attempt to link erosional, stable and accretional areas to sediment grain-size composition. Finally seasonal variations of the nearshore morphology and sediment properties of the Long Key beach were determined to identify the significance of seasonal variations on long-shore and cross-shore sediment transport. This study was conducted using monthly beach profile data and monthly sediment samples. Net longshore sediment transport at the eroding north end (Upham Beach) is to the south at a rate of 34,000 cubic meters per year. Eighty-five percent of this sediment is deposited on the central and southern portions of the island, mainly in the central portion. This is an elevated sediment transport rate as compared to the generally accepted rate of 15,000 to 20,000 cubic meters per year, which explains the rapid erosion at the north end. The greatest volume loss occurs in the winter months, ostensibly due to the passage of winter storms. There is also no significant cross-shore sediment transport in the northern portion of Long Key, beach profile results demonstrate a stable shape. However, there is slight cross-shore sediment transport in the central and southern regions of the island. At location LK 3 in the north end of the island lost 35 meters of shoreline above NGVD and 25 meters below NGVD. At location LK 11 in the south end there was a gain of 3 meters above NGVD and 15 meters below NGVD. Based on detailed sediment analysis, it is not possible to determine distinctive and persistent temporal or spatial sediment characteristics, nor are the sediment properties of Long Key indicative of longshore sediment transport.
113

Evolution and Equilibration of Artificial Morphologic Perturbations in the Form of Nearshore Berm Nourishments Along the Florida Gulf Coast

Brutsché, Katherine Emily 26 June 2014 (has links)
Inlets and channels are dredged often to maintain navigation safety. It is beneficial to reintroduce the dredged material back into the littoral system, in the form of beach or nearshore nourishments. Nourishment in the nearshore is becoming an increasingly utilized method, particularly for dredged material that contains more fine sediment than the native beach. This research examines the morphologic evolution of two different nearshore nourishments. A nearshore berm was constructed at Fort Myers Beach, Florida using mixed-sized sediment dredged from a nearby channel. The nearshore berm was placed in water depths between 1.2 and 2.4 m with the berm crest just below MLLW in the shape of a bar. The nearshore berm migrated onshore while the system was approaching a dynamic equilibrium. Near the end of the fourth year, the beach profiles had returned to the equilibrium shape characteristic of the study area. Gaps in the berm allowed water circulation and should be considered as a design parameter. The fine sediment fractions in the original placed material was selectively transported and deposited offshore, while the coarser component moved onshore. The dry beach maintained the same sediment properties throughout the study period and was not influenced by the fine sediment in the initial construction of the berm. Another nearshore nourishment was placed along eastern Perdido Key, Florida in 2011-2012 using maintenance dredged material from nearby Pensacola Pass. Different from the Fort Myers Beach berm, the material was placed within the swash-zone, with a maximum elevation of +0.91 m NAVD88 (or 0.62 m above MHHW). The low constructed berm elevation allowed natural overwash processes to occur frequently, which resulted in net onshore sediment transport and growth of the active beach berm. Sediment volume gain west of the project area due to longshore spreading of the nourishment occurred mostly in the trough between the shoreline and the bar, rather than on the dry beach. The swash-zone berm evolved back to the natural equilibrium profile shape maintained in the study area within 8 months. The performance of the swash-zone nourishment was compared to two previous beach nourishments at the same location in 1985 and 1989-1991, with higher berm elevations, at +3 m and +1.2 m NAVD88, respectively. The 1.2-km 1985 nourishment performed the poorest with a shoreline retreat rate of 40 m/year. The 7.3-km 1989-1991 nourishment performed the best with a retreat rate of 11 m/year. This suggests that high berm elevations do not necessarily lead to better nourishment performance. Longshore extent of a nourishment may play an essential role. The distant passage of two tropical storms (Tropical Storm Debby and Hurricane Isaac) generated high waves for the study areas. The two berm nourishments responded differently to the storm. Response was also compared to a beach nourishment in Sand Key. The bar-shaped Fort Myers Beach berm was split into two smaller bars, while a storm berm developed for the swash-zone nourishment at Perdido Key. In both cases, the energetic storm conditions accelerated the evolution of the berm profiles toward equilibrium. As compared to the measured nearshore waves by this study, CMS-Wave accurately propagated the WIS Hindcast waves. SBEACH accurately captured the maximum water elevation, consistent with measured upper limit of morphology change. The model correctly predicted beach and nearshore erosion during the storms. The growth of the storm berm at the Perdido Key swash-zone nourishment was predicted reasonably well by the SBEACH model. However, the magnitudes of the storm-induced erosion and the locations of the offshore bar were not accurately predicted consistently.
114

Attitudes and Information Effects in Contingent Valuation of Natural Resources

Raybould, Michael, n/a January 2006 (has links)
This thesis investigated the effects of photographic and text information on respondents' attitudes and willingness-to-pay for a proposed beach protection scheme in the erosion prone Gold Coast region on the east coast of Australia. The research developed two alternative expectancy-value attitude-behaviour models to test residents' attitudes toward relevant targets and behavioural intention, expressed through stated willingness-to-pay, and compared the proposed models with one established attitude-behaviour model. The thesis set out to investigate three central research questions; one question relating to the effects of information on attitudes and willingness-to-pay, and two questions relating to the relationships between attitudes and willingness-to-pay. It was hypothesised that photographs that depicted severe erosion damage would result in more positive attitudes toward, and greater willingness-to-pay for, beach protection than photographs that showed only mild levels of erosion damage. Positive relationships were hypothesised between variables representing attitudes toward beach erosion, attitude toward beach protection, attitude toward paying for beach protection, and willingness-to-pay. Finally, it was hypothesised that the relationships between attitudes and willingness-to-pay could be adequately explained by the proposed attitude-behaviour models. The thesis describes how seven information treatments and eight attitude measurement scales were developed and tested in a pilot experiment before use in a survey of homeowners in the region of interest. Analysis of variance showed that, while respondent's attitude toward beach protection was affected by the information treatments, their willingness-to-pay for the proposed program was insensitive to information. There were no significant effects that could be attributed exclusively to text descriptions of the good but there were significant effects that could be attributed to photographic information treatments. However, none of the effects on attitudes resulted in significant effects on the behavioural intention expressed in stated willingness-to-pay. Analysis of respondents with low previous knowledge of the proposed good revealed more extensive information effects on attitudes, but still not on willingness-to-pay, and this suggests that high levels of previous knowledge in a large proportion of the sample had a moderating effect on attitude change caused by the information treatments. Regression analysis showed that seven of the eight attitude and behaviour variables in the proposed attitude-behaviour model were significant predictors of willingness-to-pay. In the final phase of the analysis, goodness-of-fit indices, estimated using Structural Equation Modelling, indicated a good fit between the data and the attitude-behaviour models tested. Standardised coefficients on the model indicated that perceived behavioural control, expected utility of outcomes, and subjective norms all had strong direct relationships with stated willingness-to-pay, and strong indirect relationships on willingness-to-pay via attitudes toward payment. These results are consistent with the relationships proposed in attitude-behaviour models and the moderating effects of these variables explain why significant information treatment effects were observed on attitude to beach protection but not on willingness-to-pay. This research showed that respondent's willingness-to-pay in a contingent valuation experiment is quite insensitive to photographic treatments when previous knowledge is high and that costly and time consuming testing procedures, recommended by authorities, may not be necessary under these conditions. It also demonstrated that measures of attitude, consistent with an attitude-behaviour model, can be collected easily in a contingent valuation study and can contribute to understanding of participant responses and to identification of protest responses.
115

Rip Channel Morphodynamics at Pensacola Beach, Florida

Labude, Daniel 14 March 2013 (has links)
80% of all lifeguard related rescues along the beaches of northwest Florida are believed to be related to rip currents. A rip current is the strong flow of water, seaward extending from the beach to the breaker line. It has previously been shown that there are rip current hot spots at Pensacola Beach, forced by a ridge and swale topography offshore, but the annual evolution/behavior of these hotspots (i.e. location, size, frequency, and orientation) have not been examined in detail. Remote imagery from Casino Beach was rectified to a planar view in order to examine the rip channel characteristics. These characteristics were analyzed to determine variations and patterns on a daily, monthly, and seasonal basis and in relation to reset storms, wind and wave characteristics, and the beach states of Casino Beach in order to characterize the rip development and variation throughout a year. Beach states and rip configurations were impacted by many frontal storms and one tropical storm, which were classified as a reset storm when reconfigurations of the beach state and rips occurred. Given sufficient time between reset storms, the bar migrated onshore in a manner consistent with the Wright and Short (1984) model, transitioning from LBT, to RBB, and finally to TBR state. The lack of reset storms after March 2010 resulted in a large frequency of observed rip channels (64) between April and May. It is shown that these rip channels are clustered into 7 statistically significant groups based on their location alongshore at the 95 % confidence interval. It is argued that the rip channel clusters are a direct result of the wave forcing caused by the ridge and swale topography. This situation causes the bar to move onshore that without interruption of a reset storm will attach at certain locations creating a transverse bar and rip morphology. The bar appears to attach to the beach at consistent locations throughout the year creating similar rip locations and subsequently the rip clusters. The risk posed to beach users by these rip currents is concentrated in certain locations which are persistent throughout the year.
116

Establishing a Coastal Protection and Planning System in Taiwan

Yu, Meng-Jiuan 05 September 2011 (has links)
In the last few decades, academic and institutions advanced in coastal research in Europe and America have rigorously engaged in developing numerical models for coastal wave hydrodynamic simulations. The notable products include MIKE21 from DHI in Denmark, CEDAS (with GENESIS and SBEACH) from Veri-Tech in the United States, and the SMC from University of Cantabria in Spain. Among them, the Spanish Coastal Modeling System (SMC) is the only integrated package for coastal planning and modeling. With a unique preprocess module which pre-stores the bathymetry and wave data, the SMC provides a user-friendly interface directly using the screen display for a series of coastal planning and design applications which comprise artificial nourishment with headland-bay beach, breakwater construction and extension, and dredging of navigation channel etc., as well as the usual wave-current simulation for countermeasures in coastal protection and disaster mitigation. Despite the availability of several numerical programs for wave-current simulations and beach changes that have been developed by the coastal professional in Taiwan, and the continuous effort of the Water Resources Agency, Ministry of Economic Affairs to establish a national coastal database, it is imperative to develop/setup an integrated bathymetry-hydrodynamics-protection system, such as the Spanish SMC, as the key element in the national platform for coastal planning and modeling. This dissertation first describes the coastal environment in Taiwan, major causes for shoreline evolution and then reviews the history of shore protection since 1970s, together with the current prospective for coastal environment and strategies to sustain the natural shoreline ratio. To accomplish these goals, the Water Resources Agency has endeavored to implement artificial nourishment with headland-bay beaches, in order to raise the ratio of natural shoreline, in addition to establish a national coastal planning and simulation platform. As a response to this call for eco-engineering approach, we recommend that headland-bay beach in static equilibrium be adopted for mitigating coastal erosion, beach restoration and creation of recreational beaches, which can be designed directly on the screen using the empirical bay shape equation in conjunction with the SMC. Based on the framework of the Spanish SMC, this writer has successfully attempted the preliminary pre-process module of Baco (bathymetry) and Odin (wave climate) for Taiwan, using data from digitized nautical charts, nearshore depth surveys, and long-term wave observation results around Taiwan from the International Comprehensive Ocean-Atmosphere Data Set (ICOADS). The effort generates the first version of SMC in Taiwan. Having pre-stored the bathymetry and wave data for Dapeng bay in Pingtung County and Sizihwan Bay in Kaohsiung City, a series of coastal planning and modeling procedures for these two model sites are demonstrated in this dissertation, including a series of calculations of wave-current distribution for monsoon and storm waves, as well as planning of bay beach using artificial nourishment. Upon executing the Taiwanese version of SMC introduced in this dissertation, the modeling results can be applied to assist the planners and decision makers in comprehending the coastal environment, devising a feasible shore protection strategy, and promoting an earlier accomplishment of the so-called ¡ugeo-engineering ¡u in our country. Finally, the writer also wishes the outcome of this study could help relevant government agency to accomplish the prospective of sustainable coastal development upon implementing the strategies of establishing an appropriate coastal planning platform and promoting a systematic approach for coastal planning and design, as revealed in the "Sustainable Regeneration of Coastal Environment Project (98 ~ 103 fiscal year)".
117

Beach profile and sediment changes in Tai Long Wan, Hong Kong.

To, Ka-yan. January 1977 (has links)
Thesis (M. Phil.)--University of Hong Kong, 1978.
118

Distinguishing Processes that Induce Temporal Beach Profile Changes Using Principal Component Analysis: A Case Study at Long Key, West-central Florida

Davis, Denise Marie 01 January 2013 (has links)
The heavily developed Long Key is located in Pinellas County in west-central Florida. The structured Blind Pass at the north end of the barrier island interrupts the southward longshore sediment transport, resulting in severe and chronic beach erosion along the northern portion of the island. Frequent beach nourishments were conducted to mitigate the erosion. In this study, the performance of the most recent beach nourishment in 2010 is quantified through time-series beach profile surveys. Over the 34-month period, the nourished northern portion of the island, Upham Beach, lost up to 330 m3/m of sand, with a landward shoreline retreat of up to 100 m. The middle portion of the island gained up to 25 m3/m of sand, benefiting from the sand lost from Upham Beach. The southern portion of Long Key lost a modest amount of sediment, largely due to Tropical Storm Debby, which approached from the south in June 2012. The severe erosion along Upham Beach is induced by a large negative longshore transport gradient. The beach here has no sand bar and retreated landward persistently over the 34-month study period. In contrast the profiles in the central section of the island generally have a sand bar which moved landward and seaward in response to seasonal and storm-induced wave-energy changes. The sand volume across the entire profile in the central portion of the island is mostly conserved. Two typical example beach profiles, LK3A and R157, were selected to examine the ability of the commonly used principal component analysis (PCA), also commonly known as empirical orthogonal function analysis (EOF), to identify beach profile ix changes induced by longshore and cross-shore sediment transport gradients. For the longshore-transport driven changes at the non-barred profile LK3A, the principal eigenvector accounted for over 91% of the total variance, with a dominant broad peak in the cross-shore distribution. At the barred R157, the profile changes were caused mainly by cross-shore transport gradients with modest contribution from longshore transport gradient; eigenvalue one only accounted for less than 51% of the total variance, and eigenvalues two and three still contributed considerably to the overall variance. In order to verify the uniqueness of the PCA results from LK3A and R157, five numerical experiments were conducted, simulating changes at a barred and non-barred beach driven by longshore, cross-shore, and combined sediment transport gradients. Results from LK3A and R157 compare well with simulated beach erosion (or accretion) due to variable longshore sediment transport gradients and due to both cross-shore and longshore sediment transport gradients, respectively. Different PCA results were obtained from different profile change patterns.
119

Cerebral syrebrist hos sövda patienter som genomgår axelkirurgi i Beach-chair position

Tegnér, Lena January 2015 (has links)
Bakgrund: Cerebral syrebrist är ett problem som kan ge katastrofala konsekvenser även hos friska individer. Patienter som skall genomgå axeloperation i beach-chair position är en patientgrupp som har högre risk att drabbas av cerebral syrebrist (CDE). CDE är dock svårt att detektera med konventionell intraoperativ övervakning.Syfte: Att undersöka förekomst av CDE hos sövda patienter som genomgår axelkirurgi i beach-chair position samt att identifiera de specifika riskfaktorer för CDE och åtgärder som anestesisjuksköterskan kan utföra för att reducera dessa.Metod: Deskriptiv litteraturstudie med systematisk ansats.Resultat: Incidensen av uppmätta CDE varierade i de olika studierna mellan 3 % och 80 %. Anestesisjuksköterskan kan minska risk för CDE genom att preoperativt bedöma riskfaktorer i patientens anamnes samt intraoperativt genom blodtrycksreglering, ventilationsförändring, kontroll av beach-chair position samt kontroll av huvudets position.Slutsats: Genom att anestesisjuksköterskan uppmärksammar specifika riskfaktorer i patientens anamnes samt utför intraoperativa åtgärder som syftar till att säkerställa adekvat blodtryck och optimal syresättning kan risken för CDE minska. Mätning av cerebral syresättning med NIRS rekommenderas som ett komplement för att detektera förekomst av CDE. / Background: Cerebral desaturation is a problem, which may result in catastrophic consequences even with healthy individuals. Patients who will undergo shoulder surgery in beach-chair position are at higher risk to be affected by cerebral desaturation events (CDE). However, CDE is hard to detect with conventional intraoperative surveillance.Purpose: To investigate incidence of CDE with anesthetized patients undergoing shoulder surgery in beach-chair position, and to identify the specific risk factors and measures the nurse anesthetist may perform to reduce those.Method: Descriptive literature review with systematic approach.Result: The incidence of measured CDE varied between 3% and 80% in the different studies. The nurse anesthetist may reduce the risk for CDE by preoperatively assess the risk factors in the medical history of the patient and intraoperatively by regulation of the blood pressure, changes in ventilation, control of beach-chair position and control of the patients head position.Conclusion: By paying attention to specific risk factors in the patients medical history and performing intraoperative measures to ensure adequate blood pressure and optimal saturation the risk for CDE may be lowered. Measuring cerebral saturation with NIRS technology is recommended as a complement to be able to detect incidence of CDE.
120

Stranden och det främmande : En undersökning av ”den Andres” roll och tematisering i Alex Garlands The Beach

Hall, Nina January 2013 (has links)
In this essay I point out that the presence of  ”Otherness” plays a key role in the novel The Beach by Alex Garland, and that the text relates to a colonial literary tradition. I’ve mainly used the distinction of Otherness and cultural representation presented by the postcolonial theorist Edward W. Said to guide me. In my examination of the text the presence of Otherness, how it is described and the effects that it has on the story’s central group of characters, has been my focus point. I’ve investigated the occurrence of different elements in the text which creates the sense of Otherness and identified the two most prominent opposition groups in relation to the protagonist of the story. On the story’s setting level aside, a colonial and imperialist theme can also be found on an intertextual level by made references to American war movies like Apocalypse Now, a specifically good example as the script of that movie is based upon the colonial themed novel Heart of Darkness by Joseph Conrad. I will summarize how the opposition between the Self and the Other throughout The Beach effects the plot’s outcome, and present my conclusion: that the author Alex Garland intentionally places his novel in a tradition of colonial storytelling to give a critical comment on the modern world’s similarities with its colonial past, especially when it comes to contemporary tourism. In my opinion the novel is also questioning the human’s civilized state and social evolvement.

Page generated in 0.0626 seconds