Beach morphology changes naturally with seasonal and event-driven variability in the wave climate, as well as due to anthropogenic activities such as erosion mitigation efforts. In 2017, category four Hurricane Irma caused beach erosion and dune overwash in Boca Raton, FL. Immediate post-storm perigean spring tides coupled with typical winter high-wind conditions imposed a regime of spatially and temporally extended meteorologic and morphologic variability. This study evaluates the morphologic evolution and post-storm recovery in the first year following Hurricane Irma. Time-series topographic surveys and surface sediment samples were collected. Patterns of accretion and erosion were evaluated with regionally measured water and wind levels. Recovery morphology was generally through berm-building, but lacked shoreline stability. Storm impact regime, mitigation structures, and sediment transport patterns drove the recovery. Total volume lost above the 0 m contour due to the storm was not fully recovered within the year, with a large volume measured in the south. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

The beach profiles pre-and post-the Hurricane Hermine (2016) and Irma (2017) along the Sand Key barrier island were collected to quantify longshore variations in storm induced beach changes as well as to compare the beach changes caused by hydrodynamic conditions of the two different hurricanes. Cross-shore beach profile are examined in 4 sections including dune field, dry beach, sand bar and whole beach to calculate beach change. The volume change for each section and shoreline contour change before and post the hurricane was computed. Hydrodynamic conditions were obtained from adjacent NOAA’s tide and wave gauges. Both hurricanes generated high offshore waves, with Hurricane Hermine generated waves mostly from southwest, and Irma generated waves dominantly from northeast. Hurricane Hermine generated a storm surge of up to 1 m. While hurricane Irma generated negative surge of -1.1 m. Several beach profile parameters such as the foreshore slope, as well as volume changes of dune field, dry beach and sand bar induced by the two hurricanes were computed. Under both storms, the foreshore slope became steeper after the storm north of the headland, while the foreshore slope became gentler south of the headland. Storm surge plays an important role in inducing beach erosion. Hurricane Hermine with 1 m surge caused significant dune erosion in terms of dune volume loss and dune line retreat. On the other hand, hurricane Irma with negative surge only caused minor dune erosion. Sand bar moved seaward during both hurricanes, with Irma induced a much greater offshore movement than that of Hermine. In addition, the sand bar height decreased significantly during Irma. In contrast, during Hermine the sand bar height remained largely similar before and after the storm. Large alongshore variations in beach erosion was observed during both hurricanes as influenced by background erosion rate and direction of incident waves as they approaching the curved shoreline. For both storms, the erosional hot spot at North Sand Key with the highest background erosion rate suffered the most sand loss over the entire profile. More sand was eroded from the dry beach along the broad headland than along the beaches both north and south of it. Corresponding to the higher volume of dry beach erosion, shoreline retreat was also the largest around the headland. During Hurricane Hermine, the headland sheltering of the southerly approaching waves resulted in more erosion to the south than to the north. The opposite happened during Hurricane Irma with northerly approaching wave. More erosion occurred to the north of the headland than that to the south. Systematic measurement of beach profile beach and after hurricanes can improve our understanding on beach morphodynamics on storm induced beach changes.

The prediction of morphological responses of natural and engineered beaches to the prevailing wave, tide and wind conditions continues to be a challenge due to the wide variability in site conditions and the underlying complexities of the processes involved. For this reason, field measurements, especially with a good spatial and temporal resolution, play a critical role in monitoring the performance of intervention work. This thesis presents the results of a five-year study at Aberdeen beach on the North Sea coast of the UK, with the aim of obtaining and analysing high-quality field measurements of beach dynamics before and following beach nourishment and the installation of nearshore breakwaters. Beach topographic data were collected between June 2006 and July 2011 at approximately monthly intervals using real time kinematic GPS, augmented by Argus video monitoring. An assessment of the horizontal and vertical errors of the Argus system found it to be comparable to other similar installations. The initial response of the area of beach subject to recent intervention works was the formation of stable bays in the lee of the nearshore structures, making this zone morphologically distinct from other areas of the beach. Time-synchronous wave data was collected from nearshore wave buoy measurements, or derived from transformed Met Office model-predicted wave data, and were considered in relation to the timing of beach morphology responses to the prevailing wave conditions. A strong link was observed between the 30-day average wave height and the beach dynamic, with erosion commencing when Hm0 rose above 1 m, and antecedence being an important factor in beach response to successive winter storm events. The data and insights from the present study can be used to develop better predictive models and coastal monitoring strategies. Future studies seeking to further understand beach response would benefit from the ability to capture variation within tidal cycles, and to be able to connect the beach to wider nearshore and offshore bedforms and marine processes.

published_or_final_version / Geography and Geology / Master / Master of Philosophy

No description available.

The continuous monitoring of beaches and structures near, or in the surf-zone, has become a vital task from an environmental and economic standpoint. Specifically, the Durban beaches are continually nourished with sand that is dredged south of the Durban Harbour mouth. Constant monitoring is essential to control the erosion and accretion of these beaches. Currently, infrequent and labour-intensive manual surveys are being used to fulfil this task. This dissertation describes the techniques used to process and validate surf-zone video images to extract information, which is equivalent but more frequent and cost effective to that obtained using manual surveying methods. The emphasis is on the extraction of accurate hourly waterlines by analysing video images obtained from Coastal Imaging stations located at Addington Beach and North Beach in Durban, South Africa and the measurement of rip currents in the surf-zone from video images together with the validation of these results. The implementation of a neural network incorporating non-local image pixel data is more reliable than previously used methods, for example, grayscale thresholding or the delta-discriminator. Grayscale thresholding relies on the difference between the water and the sand pixel intensities. The delta-discriminator incorporates hue-saturation-lightness (HSL) values to improve the discrimination between water and sand. These methods could not, however, overcome the problem of varying seasonal and diurnal light intensities and require the prior choice of threshold values. The use of non-local data, such as the average RGB-values, in addition to individual pixel values as inputs to a neural network is shown to give better results in changing ambient lighting conditions. Wavelet and Fourier analysis of the temporal nature of the breaking waves in the surf-zone is also used to calculate more accurate waterlines. These extracted waterlines are validated by data collected from manual surveys. The use of Digital Correlation Image Velocimetry (DCIV) has been proven as a successful method in tracing velocity flow fields in a fluid medium. Typically, the medium is populated with distinct seeds that are tracked through successive video frames using a cross-correlation technique. It is shown that DCIV can be used in surf-zone images to measure surface rip currents by tracking the structure of the advected foam. This technique was validated by simultaneously tracking a large number of yellow corks scattered on the water surface. / Thesis (M.Sc.)-University of Natal, Durban, 2001.

Thesis (Ph.D.)--University of Western Australia, 2006.

Thesis (M.Sc.(Hons.)--Victoria University of Wellington, 2009. / Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin, 1968. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 174-177).

Thesis (Ph. D.)--University of California, Santa Cruz, 2007. / Includes bibliographical references.