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The coastal planning has been developed in purpose of the ¡§safely¡¨, ¡§landscaping¡¨, ¡§ecology¡¨ and ¡§water affinity¡¨ in Taiwan nowadays. Moreover, the hendland bay beachs and beach nourishment have been hailed for the protection of shoreline. One of the main affection of erosion is a storm, which retreads shoreline and reduces nearshore by storm surge. This essay reports an application of 2-D SBEACH software to simulate the beach profile changes. The data of large wave tank (LWT), which tests by the Coastal Engineering Research Center (CERC), US Army Corps of Engineers, is used to calibrate the parameters by SBEACH. Then, using the results of experimentation to indicate the accuracy of model from Grosser Wellen Kanal (GWK), which tests by the University of Hannor. Finally, simulating beach profile, with a berm (height of 2.5m and width of 100m) and a slope of 1:25, is used to simulate the profile changes and analyze the results by different storm conditions from CECI. The purpose of this paper is to estimate the suitable distance of shoreline and location of bar for a beach buffer zone by SBEACH during different storm conditions. The present study confirms that the simulated results of shoreline erosion rate and the position of bar crest by SBEACH comform to the LWT and GWK experiments. The major parameters of SBEACH, the transport rate coefficient, K influences the sediment transport, coefficient for slope-dependent term, £` controls the slope of beach profile and shape of bar, the transport rate decay coefficient multiplier, Kb affects the shoreline erosion, and the landward surf zone depth, db influences the shape of berm. The result of analysis by SBEACH indicates that a constant slope beach profile changes by different storm conditions and the extent of non-dimensional shoreline retreat Xt/Lo is found in good linear relationship with deepwater wave steepness Ho/Lo. Therefore, the linear regress function is used to compute the less beach buffer zone in different storm conditions.

With the ever increasing population and economic activities in coastal areas, coastal hazards have become a major concern for coastal management. The fundamental requirement of coastal planning and management is the scientific knowledge about coastal forms and processes. This research aims at developing algorithms for automatically extracting coastal morphological information from LiDAR data. The primary methods developed by this research include automated algorithms for beach profile feature extraction and change analysis, and an object-based approach for spatial pattern analysis of coastal morphologic and volumetric change. Automated algorithms are developed for cross-shore profile feature extraction and change analysis. Important features of the beach profile such as dune crest, dune toe, and beach berm crest are extracted automatically by using a scale-space approach and by incorporating contextual information. The attributes of important feature points and segments are derived to characterize the morphologic properties of each beach profile. Beach profiles from different time periods can be compared for morphologic and volumetric change analysis. An object-oriented approach for volumetric change analysis is developed to identify and delineate individual elevation change patches as discrete objects. A set of two-dimensional and three-dimensional attributes are derived to characterize the objects, which includes planimetric attributes, shape attributes, surface attributes, volumetric attributes, and summary attributes. Both algorithms are implemented as ArcGIS extension modules to perform the feature extraction and attribute derivation for coastal morphological change analysis. To demonstrate the utility and effectiveness of algorithms, the cross-shore profile change analysis method and software tool are applied to a case study area located at southern Monterey Bay, California, and the coastal morphology change analysis method and software tool are applied to a case study area located on Assateague Island, Maryland. The automated algorithms facilitate the efficient beach profile feature analysis over large geographical area and support the analysis of the spatial variations of beach profile changes along the shoreline. The explicit object representation of elevation change patches makes it easy to localize erosion hot spots, to classify the elevation changes caused by various mechanisms, and to analyze spatial pattern of morphologic and volumetric changes.

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.

During the onslaught of a storm on the coasts of Taiwan in summer and autumn, large waves and storm surge have often caused beach erosion. In order to mitigate coastal disasters and erosion, soft-options have been promoted in recent years, to fulfill the purpose of shore protection, as well as to meet the new requirements of landscape, ecology and recreation. Consequently, semi-natural approaches have been adopted in stead of the conventional hard-structures. This thesis aims to report a study on the effects of detached submerged breakwater layouts and storm wave types on beach profile changes and berm retreat. In order to establish a practical procedure to assist the assessment of beach profile changes with submerged breakwaters during storm, we first collect and analyze the beach profile change data performed in large wave tanks (CE from the US and PI from Japan), and apply the well known SBEACH model to derive regression relationship between the two key parameters ( and ) in this model against the non-dimensional fall velocity ( ). The suggestion of Larson and Kraus (2000) to include hard bottom option in SBEACH with a set of modified and values, which may be different from that originally developed for a sandy beach environment, is then carried out using the beach profile changes results conducted experimentally with submerged breakwaters (Risio and Lisi, 2010). Consequently, we have conducted the numerical experiments systematically to study the beach profile changes using submerged breakwaters under various environmental combinations (with 10 different offshore distances, 10 breakwater heights, 10 crown widths and 4 types of storm wave conditions derived from storm return periods), from which a new set of and values are derived and used in SBEACH for the investigation of installing submerged breakwaters to mitigate potential beach erosion. Our numerical investigations using SBEACH for a beach with submerged breakwater reveal that: (1) Beach profile changes in erosion (0 m line and berm) and accretion (0 m line) due to regular waves are more significant than that of irregular waves. (2) Storm waves with a long return period cause more erosion to the shoreline (0 m line) and berm, while that with short return period may produce accretion to the shoreline. (3) The further a submerged breakwater away offshore, the more sediment transportation offshore and severe beach and berm erosion. (4).An increase of submerged breakwater height would result in accretion near the 0 line; except during a violent storm event, when an increase of berm height could reduce berm erosion. (5) An increase to the crown width of a submerged breakwater could only become effective to reduce wave energy and berm erosion, if an appropriate breakwater height is used; otherwise, a mere increase in width with insufficient height would increase wave height and berm erosion.

With increasing demands on environmental protection in recent years, the Government agency concerned has recently proposed the strategies for shore protection and management, which aim for prevention and mitigation of coastal disaster and reduction in coastal erosion, as well as the creation of an environment with focus on landscape, ecology and community recreation. Soft and quasi-natural approach will be implemented to restore the glory of a stable coast. Based on the consideration of disaster prevention, this study investigates the beach profile changes, which include beach berm erosion and bar formation resulting from storm waves with different return periods. The SBEACH model is used to estimate the beach changes subject to variable conditions of beach berm width, medium sand grain diameter, beach slope and design water level etc. Regression analysis is then applied to establish a relationship between the storm beach buffer width and relevant physical parameters. Prior to this, the results of large wave tank tests on beach profile changes conducted by Coastal Engineering Research Center in the United States are used to calibrate the two main parameters K and £` used in SBEACH model. Beach profile changes can now be estimated systematically using a set of modified K and £` values. After having performed a series numerical studies, we may conclude that: (1) With storms of different return periods but identical non-dimensional fall velocity (H0/£sT), berm erosion increases and the location of the bar becomes further offshore as storm return period increases ; (2) With different sand grain sizes subject to identical storm wave conditions, beach berm erosion increases as grain size increased, but shoreline retreat decreases; and location of bar is further offshore for a beach consisting smaller sand grains; (3) Under the same storm return period and sand grain diameter (i.e., similar non-dimensional fall velocity), berm erosion increases as storm intensity and design water level increase, but shoreline retreat decreases and bar is located nearer; and vice versa; (4) from a series of calculations based on different sand grains and storm beach buffer width, it is found that larger buffer is required for beach with smaller grain size, in order to absorb the storm wave energy.

On sandy coastlines dunes provide a barrier of protection from strong environmental forces that can naturally occur during storm events including storm surges that expose the dunes to large waves. A set of laboratory experiments were used to investigate the morphological processes during the erosion of a steep dune face under bichromatic wave conditions for two different mean water level elevations, corresponding to storm surges and waves that collide with or overwash the dune. In the collision regime, episodic slumping due to the undercutting of the dune resulted in sudden erosional events followed by long periods of wave-driven reshaping at the dune toe. In the overwash regime, dune erosion was faster and occurred at a more consistent rate. Small scale bedforms (ripples) measured during the overwash test evolved in height faster and to greater overall heights than collision test while bedform lengths were not affected by the change in water level. A numerical model, XBeach, was calibrated to examine the ability to predict erosion of the steep dune due to waves in the two water level regimes. XBeach was not able to recreate the spatial variability of the significant wave height profile from the laboratory measurements; however, mean velocities were in good agreement with observations suggesting that bed shear stress is well estimated. During mobile bed simulations of erosion in the two regimes, the model was in agreement with measured dune erosion after initial adjustment. XBeach was very sensitive to several parameters that control the rate of erosion including the critical avalanching slope under water, the threshold water depth and the sediment transport formulation. The model did not perform well at predicting erosion rates until these parameters had been modified. Overall, XBeach performed better when simulating dune erosion in the overwash regime than the collision regime. / Thesis (Master, Civil Engineering) -- Queen's University, 2014-04-01 14:54:35.257

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Storms play a significant role in beach morphodynamics. Storm-induced beach-profile changes and their longshore variations are investigated in this study. The impacts of four summer tropical storms and two series of winter storms over the last 10 years along the coast of Treasure Island were documented. Tropical storms Alberto in 2006, Fay in 2008, Debby in 2012, Hermine in 2016 and winter storms in winter seasons of 2014 and 2015 are discussed in this study. In general, the Treasure Island beach experienced more erosion generated by tropical storms with greater intensity, but shorter duration, as compared to winter storms due to lower waves, weaker wind and smaller storm surge. Winter storms typically do not generate high storm surge and generally do not cause erosion at the dune and back beach unless the pre-storm beach is very narrow. Based on pre- and post-storm beach-profile surveys along the coast of Treasure Island, the northern end of the barrier island, located directly downdrift of the John’s Pass tidal inlet, experienced erosion along the entire profile during the storms. Along the middle part of Treasure Island, dry beach suffered erosion during both the tropical storms and winter seasons while the nearshore zone suffered erosion during the tropical storms and experienced deposition during the winter seasons. Sunset Beach at the southern end experienced severe erosion during tropical storm Debby, but not during other storms. Winter seasons caused relatively small changes to the morphology of Sunset Beach. Deposition happened in the nearshore zone along Sunset Beach during winter storms. Survey line R143 at the very south end of Treasure Island suffered erosion in tropical storm Alberto, Debby and Hermine. Beach profile changes induced by Tropical storm Fay was different as compared to other tropical storms. Considerably less beach erosion occurred due to the large distance of the storm path from the study area. Overall, Sunshine Beach, bounded by John’s Pass inlet at northern end of Treasure Island, was influenced both by wave conditions and the tidal flows. Sediment transport was to the north along the coast of Sunshine Beach when wind direction was from south, e.g. during tropical storm Fay. However the northward sediment transport was blocked by the John’s Pass jetty. Therefore, deposition occurred at Sunshine Beach during tropical storm Fay. When wind direction was from north (e.g. during tropical storms Alberto and during the winter seasons), southward sediment transport was generated. Erosion occurs during the northerly approaching storms. The morphodynamics of the middle section of Treasure Island are influenced by the sand supply at the attachment point of John’s Pass ebb delta. Sunset Beach experienced various levels of erosion during the tropical storms not only because of the high wave, strong wind and high water level generated by storms, but also due to the higher waves associated with an offshore dredged pit.

On the basis of coastal disaster mitigation and protection, a beach must have sufficient width for preventing the destruction to public facilities, as well as protecting the safety of life and private property during storm events. The requirement of such a horizontal extent from the initial shoreline to the probable erosion landward to safeguard against the onslaught of a storm is referred to as ¡¥storm beach buffer width¡¦. Upon neglecting the effects of global warming and sealevel rise on a beach and berm with profile in equilibrium, numerical calculations are conducted first to validate the range of the most important parameters (K »P £` ) in the SBEACH model using the results of profile changes available from the CERC¡¦s large wave tank (LWT) tests in 1960s. These results are then applied to assess the profile changes for a beach with a vertical seawall and the other without sufficient berm, subject to the normal incidence of storm waves over a specific duration. Finally, a total of 48 cases with sufficient beach width are then investigated, from which a multiple linear regression model is proposed to determine the extent of berm retreat, as well as the location and height of a submerged offshore bar, for the benefit of coastal profession on preliminary design of storm buffer. Our modeling results using SBEACH reveal that: (1) A seawall without or with insufficient fronting beach could result in serious scour at its toe and even the total loss of the entire beach berm; (2) A beach with sufficient berm, natural or artificially nourished, is capable of protecting the back beach, despite the temporary erosion in the early hours of a storm action; (3) Under the same conditions of wave height and period, a wide buffer is necessary for a beach with small mean sand grain, and the berm height should be designed at 1.6 times of the designed storm surge level, in order to effectively absorb storm wave energy and maintain the provision of a storm buffer; and (4) The multiple linear regression model proposed in this study can be used to evaluate the scour depth and retreat of the berm, as well as the width of a storm beach buffer, upon the input of wave conditions and mean beach sand grain etc.