Amphibious landings and small boat operations are normally conducted only in benign wave conditions. An unexpected encounter with an isolated freak wave may damage equipment and prevent mission accomplishment. This study examines the occurrence of unusually large waves using data sets obtained with bottom mounted pressure sensors and wave buoys in the DUCK 94, SHOWEX, and SAX 04 experiments. All of the experiments include wave records from high energy events. After correcting the raw pressure data for hydrodynamic attenuation over the water column, the statistics of wave heights were evaluated and compared with the theoretical Rayleigh distribution of a narrow-band linear wave field. Observations from deep water sites follow the Rayleigh distribution well, even in extreme sea states, indicating that strong nonlinearity does not have a major effect on wave height statistics. However, during high energy events at shallow water sites, there are significantly less measured wave heights in the right-hand tail of the distribution of wave heights than the theoretical Rayleigh distribution would predict. These results show that waves become more homogeneous in height as they propagate into shallower water, possibly owing to breaking and nonlinear effects. While the observed wave statistics do not suggest a frequent occurrence of freak waves, isolated large waves were indeed observed, even in benign conditions. Further studies are needed to assess their risk to Navy operations.

Changes in the marine environment have been reported for over three decades in terms of mean annual wave heights, exceedance probabilities and extreme conditions. More recently, the existence of a link between these changes and anthropogenic climate change has been postulated. This is not unreasonable, as climatic changes in regional warming and cooling are likely to alter wind patterns, and therefore the wave climate as well. In an attempt to mitigate climate change and increase energy security, the offshore environment is being looked at to provide sustainable energy from wind, waves and tides. As a result the number of marine structures is only likely to increase. While survivability in this environment is essential for all such installations, some devices such as wave energy converters also rely on the environment for energy production. In designing these offshore structures to survive the harshest conditions as well as to ensure optimum operation, knowledge of the evolution of the wave climate is essential. This study aims to identify and evaluate any historical trends that may be exhibited by the wave climate in the North East Atlantic and North Sea region. The study also aims to investigate the link between any observed changes and atmospheric greenhouse gas levels and projected wave conditions for the 21st century. This is achieved by producing a long-term, high resolution hindcast of wave conditions for 1871-2010 using the third-generation spectral wave model WAVEWATCH III. A dataset of wave climate projections for the high, medium and low emissions scenarios is also prepared by forcing the model with GCM winds for 2001-2100. In addition to dynamically projecting the wave climate in the 21st century for different IPCC climate change scenarios, statistical methods were applied to historic data to estimate extreme events in terms of 100-year return values of significant wave height. These, together, provide some idea of the plausible wave climate up to 2100. The results of the work show the existence of long-term trends in the historical wave climate in the region from 1921 onwards. However, based on the findings of the study, it is unlikely that these are a result of changes in atmospheric greenhouse gas concentrations and are more likely due to internal variability in the system.

Approved for public release; distribution is unlimited / Under meteorological conditions associated with extreme cold air outbreaks (CAO) off the U.S. East Coast, large ocean waves sometimes develop along the North Wall of the Gulf Stream. These wave events produce wave heights above those expected given the short fetch and moderate winds. The highest waves are often very localized, which suggests localized forcing by the atmosphere. In this study, results from four cases are examined to characterize the role of high resolution, mesoscale wind forcing in generating localized regions of large ocean waves during events with large air-sea temperature differences. A known "true" atmosphere is simulated through the use of the Navy's Coupled Oceanographic and Atmospheric Mesoscale Prediction System (COAMPS). Model surface wind output from COAMPS is used to generate a wave field using Wavewatch Three (WW3), which is then compared to buoy observations and ship reports. Results of these cases show the mesoscale wind forcing of ocean waves during CAO and the importance of mesoscale atmospheric modeling in localized generation of ocean wind waves. Additionally, empirical wave forecast techniques are compared to WW3 model output for these cases to further reinforce the mesoscale atmospheric forcing during rapid growth of wind wave events in fetch limited environments. / Lieutenant Commander, United States Navy

In 1996, Beach et al. first proposed the idea of mounting an echo-sounder on a Waverunner to measure nearshore beach profiles. This thesis discusses the Coastal Profiling System, an extension of the original work, which has been utilized to measure nearshore bathymetry at selected sites along the coasts of North Carolina, Oregon, and Washington. Position of the Coastal Profiling System is accurately measured five times per second using a differential global positioning system (DGPS), while depth below the hull is measured by an acoustic echo-sounder. Surveys can be conducted in waves up to 3 m and in depths of 1-15 m. The effects of waves, tides, and set-up are eliminated by the co-collection of position and depth data. In October 1997, extensive testing of the system took place at the SandyDuck '97 field experiment in Duck, NC. Nearshore bathymetric surveys were taken simultaneously by the Coastal Research Amphibious Buggy (CRAB) and the Coastal Profiling System (CPS). Comparison of the CPS with CRAB measurements interpolated to the same locations showed a mean bias of 4.6 cm too shallow in the vertical and standard deviations about the bias of 5.5 cm. The largest differences occur over the steeply sloping flanks of sand bars. The bias statistic, of central interest to these tests, is confused by the potential of boat tilt and by possible errors in the CRAB data itself. In July & August 1998, the system was tested as a tool for long-term coastal monitoring by the Southwest Washington Coastal Erosion Study in a regional morphology monitoring program (Ruggiero et al., 1997). A 2-3 km section in approximately the center of each of the four sub-cells of the Columbia River littoral cell, and an anomalous fifth site, was surveyed to map the morphology of each region. Alongshore-averaged profiles were decomposed into underlying AX[superscript m] profiles and deviations from this equilibrium profile. The mean of the exponents was close to 2/3 with m=0.70, but ranged between sites from 0.56 to 0.79. Shape parameters between 0.027 and 0.038 were estimated. Nearshore slopes (0-1 km cross-shore) were calculated from the exponential profile in the dissipative range with a minimum of 0.0067 and a maximum of 0.0089. However, no correlation was seen between the shape parameters and the 1 km nearshore slopes. An analysis of the deviations of the alongshore-averaged profiles from the equilibrium profile provided an objective method to determine sand bar positions from zero-down-crossings. Each site was characterized by a minimum of two sand bars in 2-6.5 m (NAVD 88) depths with heights of 0.2-2 m, lengths of 164-949 m and volumes of 48-534 m��/m. An additional bar in the swash zone between the +1 m elevation and 1 m depth contour was resolved in some cross-shore profiles. The crest of the bar largest in height was located at 3-4.5 NAVD 88 m at four of the five sites suggesting the profiles vary on similar cross-shore length scales amongst the sub-cells. A series of surveys in April, June, and October 1998 at the northern most site in Ocean City, WA demonstrated onshore bar migration and seaward accretion of the foreshore. This seasonal response was further quantified between August and October at Fort Canby. Three nearshore profiles surveyed by Willard Bascom et al. (1954) in the 1940s were reoccupied to compare the shape of the morphology 50 years ago to present. These profiles demonstrate accretion of approximately 2 m elevation gains in the nearshore and 26-165 m of shoreline change. Although the Coastal Profiling System is a highly accurate, mobile and efficient method to obtain nearshore profiles, several improvements have been suggested. Future modifications to the system should include an increase in the precision of the echo-sounder measurements, higher sampling rates, and improvement of the user interface. Additional components may include an onboard navigation system, a thermister to measure temperature and salinity, and a motion sensor to measure roll and pitch of the vehicle. / Graduation date: 1999

Thesis (M.C.E.)--University of Delaware, 2005. / Principal faculty advisor: James T. Kirby, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 46-49). Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 1993. / Typescript (photocopy). Includes bibliographical references (leaves 123-129). Also available on the World Wide Web.

Thesis (doctoral)--Technische Universiteit Delft, 1997. / Also published in the series: Communications on hydraulic and geotechnical engineering ; no. 97-4. Vita. Includes bibliographical references (p. [127]-136).

Thesis (Ph. D.)--University of Nevada, Reno, 2008. / "August, 2008." Includes bibliographical references (leaves 184-188). Online version available on the World Wide Web.

Thesis (Ph.D.)--University of Rhode Island, 2007. / Includes bibliographical references (leaves 124-131).