This study set out to investigate the shear stress behaviour at the bed under combined wave and current action. The intention of the study was to make experimental measurements to determine how wave and current shear stresses combine, so that theoretical models describing the combined flow condition could be proposed. Two types of experiment were conducted, and theoretical models for the combined flow were assessed. One set of experiments attempted to use a shear plate to make direct measurements of the combined flow shear stress, and of the shear stresses for the component waves and steady currents. This approach failed because the large correction terms introduced by the non-uniform wave pressure field could not be accurately estimated. The second set of experiments used a laser doppler anemometer to make detailed velocity profile measurements over flat sediment beds. The onset of sediment motion was used as a criterion to carefully control the experiments. It is assumed that the threshold of sediment motion represents a specific shear stress intensity at the bed for sediments of narrow size ranges. As the shear stresses can be determined from the velocity fields under waves and currents, their additive nature under combined flow conditions could be investigated. For each sediment size range, it is shown that the same maximum velocity very near the bed can be used to specify the threshold of sediment motion condition for all flow types, be they under waves, currents, or combined waves and currents. It is also shown that the near-bed velocity under a laboratory wave can be predicted accurately from second order wave theory and that the velocity under a current can be predicted from combining Manning's relation with the universal log velocity law. It is further shown that the near-bed velocity under a combined wave and current can be described by the vectorial addition of the maximum component wave velocity and the average component current velocity. The shear stress for the onset of motion is calculated for the steady current using Manning's relation, for the wave by combining the oscillatory shear stress formula with Kamphuis's rough turbulent friction factor relation, and for the combined wave and current by the simple vectorial addition of the component shear stresses, and is shown to be comparable with Shields's threshold criterion for nearly all conditions tested. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Objective To determine the cardiopulmonary and blood gas status of elephants during chemical capture (immobilisation) with a thiafentanil-azaperone drug combination kept in lateral recumbency. Study design Prospective descriptive study. Animal population Ten free-ranging adult African elephant bulls (estimated weight range 3000 to 6000 kg). Methods Elephants were immobilised using a thiafentanil (15-18 mg) and azaperone (75-90 mg) by darting from a helicopter. Once recumbent, the tidal volume, minute volume, end-tidal carbon dioxide, arterial blood pressure and pulse rate were recorded immediately after instrumentation and at five-minute intervals until T20. Arterial and venous blood gases were analysed at the time of initial instrumentation and at 20 minutes. On completion of the data collection, the thiafentanil was antagonised using naltrexone (10 mg mg-1 thiafentanil). A stopwatch was used to record time to recumbency (dart placement to recumbency) and time to recovery (administering antagonist to standing). Data was checked for normality and was found to be parametric. Data were compared using a one-way analysis of variance and reported as mean (± SD). Results All elephants were successfully immobilised and all physiological variables remained constant with minimal non-significant variation over time. Average time to recumbency was 12.5 minutes. The estimated expiratory tidal volume was 21 (± 6) L breath-1 or 4.8 ± 0.8 mL kg-1, and the measured minute volume was 103 (± 31) L minute-1. The heart and respiratory rates were 49 (±6) beats and 5 (± 1) breaths minute-1, respectively. The mean arterial blood pressure was 153 (± 31) mmHg. The elephants were acidaemic (pH 7.18 ±0.06; bicarbonate ion 20 ±4 mmol L-1; lactate 11 ± 4 mmol L-1), mildly hypoxemic (PaO2 68 ± 15 mmHg) and mildly hypercapnic (PaCO2 52 ± 7 mmHg). Average time to recovery was 2.2 minutes. Conclusion and clinical relevance African elephant bulls can be successfully immobilised using thiafentanil-azaperone. Recumbency was rapid, the cardiopulmonary variables were stable and within acceptable ranges, and recovery was rapid and complete. Mild hypoxaemia and hypercapnia were evident, but does not necessarily require oxygen supplementation. / Dissertation (MSc)--University of Pretoria, 2020. / Companion Animal Clinical Studies / MSc / Unrestricted

Research in salt marshes dominated by the grass Sporobolus alterniflorus indicates that plant characteristics affect fiddler crab burrowing and in turn, crab activity can enhance primary productivity by increasing soil oxygen and nutrient cycling. Crab-plant interactions are less understood in microtidal Gulf Coast marshes compared to Atlantic Coast tidal marshes. It is unknown how structure of the dominant Gulf Coast vegetation zones (salt marsh, brackish marsh, fresh marsh and salt pannes) affects density of crab burrows and how burrows may influence primary productivity. I hypothesized that fiddler crabs would be most abundant in marsh zones with intermediate substrate hardness and vegetation density (Goldilocks Hypothesis). A seasonal habitat preference study was conducted during 2016-2017 in tidal marshes at Grand Bay National Estuarine Research Reserve in coastal Mississippi using burrow density as a proxy for crab abundance. Plant above- and below-ground biomass, burrow proximity to vegetation, and soil hardness were also surveyed as potential drivers of fiddler crab populations. The results indicated that fiddler crabs burrow in all four zones, but to varying degrees, and that burrow density was highest during autumn. The fresh marsh had the highest average density of burrows, as well as vegetation and soil parameters most representative of intermediate habitat, thereby supporting the “Goldilocks Hypothesis”. The brackish marsh also proved to be important fiddler crab habitat. Preferential fiddler crab usage of habitat upslope of salt marsh, e.g., fresh and brackish marsh, in Gulf Coast sites suggests that they may avoid immediate impacts of rising sea levels and possibly even migrate to higher ground if needed.

Every marine energy source presents advantages and disadvantages. For example, they are not atthe same stage of maturity. Tidal range power is fully mature but the limited number of sitesavailable, combined with the large environmental impacts and investment costs limit itsdevelopment. The idea of artificial lagoons that will be offshore tidal range plant could create a newinterest for this technology. But for the moment, no plant of this type has been constructed yet. Tidalstream power is the next mature technology of marine energy after tidal range. Its development willrequire public subsidies but is supposed to be commercial in 2015. Systems are already indemonstration in several countries (UK, France and Canada). Wave power is less mature but it willbenefit from the development of tidal stream power and will probably be commercial in 2020. Somesystems are also in demonstration but challenges seem greater in wave power than in tidal power.Wave power conversion systems have to extract energy from the waves, even the largest ones, butat the same time resist to them. Contrary to tidal stream which has a predictable resource, waves areway less predictable and systems will have to be able to resist and valorize waves. OTEC (OceanThermal Energy Conversion) has been studied for years but it is still not mature. Its development forelectricity production needs technology research to develop cheaper and more compact systems(heat exchangers, pipes…). Air conditioning applications are developing and also require the use ofpipes and heat exchangers. Advances in this utilization could maybe help the development of OTECsystems for electricity production. Osmosis is the less mature and the most challenging technology. Atechnological breakthrough in the membrane could allow a rapid development. This breakthroughwill probably come from other sectors so it is important for the industries to get ready in order todevelop the system as soon as this technological improvement will be made.

Numerous studies have identified the west coast of Canada as an attractive place for the development of wave energy projects. To evaluate the viability of these projects, an accurate description of the wave resource is crucial. Most of the previous efforts to characterize the wave climate in B.C. at shallower waters, where wave energy converters (WECs) are most likely to be deployed, lack the necessary nearshore spatial resolution, and were driven by overly simplistic wave boundary conditions. In addition, none of the previous studies have included the effect of tidal currents, which have been proven to be significant in wave resource characterizations in other locations. This work increased the fidelity of the wave resource characterization and developed an understanding of the impact of tidal currents on the wave conditions in this region by generating two most accurate, long-term (14 years, 2004 to 2017), high resolution (in space and time) datasets of the wave resource for the west coast of Canada. The two datasets were generated using nearly identical SWAN wave models, which their only difference was that one of them (V5), did not incorporate the effect of currents, while the other (V6) included tidal currents as forcing. Thus, the pure influence of the tidal currents on the wave characteristics was able to be identified when comparing the two wave model results. This study developed simple, robust, and objective metrics to support the calibration process and to evaluate the performance of the models. Utilizing these metrics, the V5 and V6 models presented substantial improvements in reproducing the wave conditions of about 18% and 20%, respectively and in relation to the previous most complete and accurate wave model of the region (V4). Their better performance was largely achieved by a significant increment in their ability to reproduce the significant wave height (H_m0) and energy period (T_e). The inclusion of tidal currents in the wave model increased the accuracy of the wave resource characterization, mainly by improving the model’s ability in simulating T_e by 5.1%. The most sensitive wave parameter to the tidal currents was the peakedness of the wave spectrum (Q_p), which was consistently and significantly reduced by values even larger than 2.5. In some regions, directions characterized by the mean wave direction (D_m) and the directional spreading (D_spr) were also noticeably very sensitive to the currents, which even deflected D_m to its opposite direction and drove changes in D_spr that reached values of up to 40°. However, these significant transformations were less frequent and reduced in magnitude at exposed (to swell-waves) sites, where strong currents have affected waves in a reduced part of their trajectory. Typically, tidal currents had the effect of reducing the wave power density (P), but in a relatively small amount, however, during rare events, tidal currents were able to induce changes in this parameter ranging -140 kW/m to 75 kW/m. At these extreme events, it was observed that the peak of the wave spectra became flatter, with some of its wave height variance redistributed to near increasing and decreasing frequencies and directions, regardless to the magnitude and direction of the local tidal currents. Impacts of the tidal currents on P were largely attributed to the induced changes in H_m0 and T_e. Although D_spr and Q_p were greatly transformed by the action the tidal currents, they account very little in explaining the variations in P. These four wave parameters together, and how they are transformed under the presence of currents, can explain a large part of the changes in P, however, other transformations of the wave spectrum due to the currents, not investigated in this study, must account for a considerable part of the changes in P. / Graduate

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 91-92. / by François-Marc Turpin. / M.S.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20922号 / 理博第4374号 / 新制||理||1628(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 James Mori, 教授 中西 一郎, 准教授 久家 慶子 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

The Sacramento San Joaquin Delta has been highly altered by human activity since the mid-1800s from mining, agriculture, dredging, and urbanization. Did the resulting modifications to channel width, depth, and length alter tidal range in the Sacramento San Joaquin Delta? In this study, archival tidal records were evaluated at many stations throughout the San Francisco Bay and Delta, with a focus on San Francisco, Rio Vista, Sacramento, and Stockton daily, monthly, and annual tidal ranges. Monthly and seasonally averaged tidal ranges were analyzed to determine seasonal changes. In addition, tidal range was compared to daily Delta discharge to consider the effects of river flow. Results show that the spatial pattern of tidal amplitude through the San Francisco Bay and Delta system have changed since the mid-nineteenth century and the changes are consistent with human and climate change impacts on the Delta landscape. There is a general 7% increase in mean annual tidal range in San Francisco from 1860 to 2018. In Stockton, mean annual tidal range increased from 0.6 meters to 0.9 meters between 1908 and the 1930s but decreased approximately 9% from the 1930s to 2011. Mean annual tidal range in Sacramento increased from zero to 0.5 meters between 1890 and the late 1930s and then decreased by 50% through the early 2000s to approximately 0.25 meters. Lower tidal ranges in the early 1900s are consistent with the effects of hydraulic mining. Increased tidal ranges in the mid-20th century are consistent with dredging throughout the system. Recent decreases in tidal ranges are consistent with wetland restoration, increased water storage, and further modifications to the geometry and management of the Delta. A peak river flow shift from late spring/early summer to early spring has contributed to increased tidal range between February and June by 0.1 and 0.6 meters in San Francisco and Stockton, respectively. In Sacramento, the least decrease in tidal range between 1939 and the present occurred during spring months, due to the decrease in river discharge during this period. Tides have recorded the history of environmental change within the highly altered San Francisco Bay and Sacramento San Joaquin system. While not as notable as similarly altered systems, the changes described here were most significant in Sacramento where mean annual tidal range has ranged between zero and 0.5 meters since 1890 and, for any discharge below 1,000 cubic meters per second, mean daily tidal range is higher from 1938 to 1939 than from 1997 to 2018. Change in tidal range implies potential change in tidal velocities, salinity intrusion dynamics, and flood risk within the system, especially in Sacramento.

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Civil Engineering, 1980 / Bibliography: leaves 173-175. / by David William Ostendorf. / Sc. D. / Sc. D. Massachusetts Institute of Technology, Department of Civil Engineering

Millions of people in low-lying areas are already affected by flooding, and the number will increase substantially in the future. Tidal flooding, the form of flooding caused by a combination of high tides and sea level rise to overcome protection levels, can cause damage and inconveniences such as road closures, overwhelmed drainage systems, and infrastructure deterioration from water damage. Tidal flooding already occurs annually in cities along the U.S. east coast, most notably Miami. However, the time it will take for other regions globally to begin to experience tidal flooding has not yet been assessed. Therefore, there is a limited understanding of how and when human populations will be exposed to this type of flooding. Tide gauge data from the GESLA-2 data base are used to obtain information about the highest astronomical tide (HAT) and extreme value statistics for 571 locations globally. For a complete spatial analysis, modelled water levels from the Global Tide and Surge Reanalysis (GTSR) are also used. Estimated protection levels are extracted from the DIVA database and translated to absolute heights based on the extreme value statistics of high water levels. This analysis is based on calculating the difference between the existing protection level and HAT, which indicates how much sea levels can rise before tidal flooding occurs, and evaluating in what decade this is expected to happen under different sea-level rise (SLR) scenarios. Tidal trends from the nodal and perigean are also taken account and used to modify 1000 different sea level rise scenarios to provide a more comprehensive analysis of possible tidal flooding years. Our results indicate that tidal flooding may occur within a few decades in many locations (under the assumption that no adaptation will take place), and therefore awareness should be heightened so that actions can be taken to minimize the impacts.