ABSTRACT Storm waves affect beach berm and even dunes, resulting in shoreline retreat accompanying by the formation of a submerged bar in the vicinity of the breakers. After a storm wanes, bar material originally may removed from the beachprogressively move landwards by subsequent swell which prevails at the time to assist beach recovery. Such repetitive processes are the nature way to maintain a beach profile in dynamic condition. This research essay reports an application of SBEACH software to simulate beach profile changes induced by different storm conditions. Upon applying the wave module within SBEACH , the range of broken waves during a storm is first calculated, which is in turn to help locate the range of bar crest. Comparisons are then given for bar crest position and the extent of shoreline recession simulated by SBEACH and the original beach profile data obtained from large wave tank (LWT) tests conducted of the Coastal Engineering Research Center (CERC), US Army Corps of Engineers. The effect of resetting the values to several key parameters in the sediment transport equation is also investigated. The present study confirms that cross-shore distribution of the maximum wave heights, one of the many important outputs from SBEACH, can be successfully applied for the estimation of wave breaker heights and the prediction of bar crest positions. In addition, from setting different values to some key calibration parameters used in the model (e.g., the default calibration values and Larson¡¦s (1996) calibration parameters for monochromatic waves), bar crest distance offshore Xc/Lo can be linearly related to deep-water wave steepness Ho/Lo, while bar crest position Xc/Lo versus surf similarity parameter

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 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.

The objective of this study is to quantify the accuracy of two engineering models for dune erosion (SBEACH and EDUNE), and to determine which of the two models is best suited for predicting barrier island vulnerability due to extreme storm events. The first model, SBEACH, computes sediment transport using empirically derived equations from two large wave tank experiments. The second model, EDUNE, theoretically relates excess wave energy dissipation in the surf zone to sediment transport. The first mechanism for model comparison is sensitivity testing, which describes the response of the model to empirical, physical, and hydrodynamic variables. Through sensitivity tests, it is possible to determine if responses to physical variables (e.g. grain size) and hydrodynamic variables (e.g. wave height) are consistent with theoretical expectations, and whether the function of each variable is properly specified within the governing equations. With respect to empirical parameters, model calibrations are performed on multiple study sites in order to determine whether or not the empirical parameters are properly constrained. Finally, error statistics are generated on four study sites in order to compare model accuracy. Cross-shore profiles of dune elevation are extracted from coastal lidar (light detecting and ranging) surveys flown before and after the impact of major storm events. Three study sites are taken from 1998 lidar surveys of Assateague Island, MD in response to two large northeasters that produced significant erosion along the Assateague shoreline. Two additional study sites are obtained from 2003 lidar surveys of Hatteras Island, NC in response to erosion caused by Hurricane Isabel. Error statistics generated on these study sites suggest that the models are statistically equivalent in their ability to hindcast dune erosion due to extreme storm events.

Le littoral Est dunkerquois, comme la plupart des côtes méridionales de la Mer du Nord, est constitué de larges plages sableuses à barres intertidales et de dunes côtières qui protègent des zones basses densément peuplées particulièrement vulnérables dans le contexte actuel de montée du niveau marin associée au changement climatique. Les objectifs de ce travail et la démarche méthodologique adoptée reposent sur une approche à plusieurs échelles spatiales et temporelles afin dévaluer l'impact des tempêtes sur l'évolution d'une côte basse macrotidale à fetch limité. A l'échelle évènementielle, les mesures ont souligné une réponse morphologique très différente de la côte face aux conditions énergétiques et tempétueuses, sur deux secteurs d'étude situés à 4 km de distance. Cette réponse très contrastée se traduit par des conditions hydrodynamiques différentes sur les deux sites, avec un secteur Ouest plus sensible à l'érosion que le secteur Est, plutôt stable voire en accrétion. Sur une échelle saisonnière à pluriannuelle, l'évolution de la côte et notamment sa capacité à se reconstruire durant les phases post-érosives a été mise en évidence, soulignant notamment l'efficacité des transports éoliens dans l'alimentation et la cicatrisation des dunes. A moyen terme, de 1957 à 2010, l'évolution du trait de côte a montré une grande variabilité à la fois spatiale et temporelle, qui semble être expliquée par une variabilité spatiale de l'énergie de la houle à la côte, en partie liée à la bathymétrie de l'avant-côte, mais aussi par les variations des forçages météo-marins et des interventions anthropiques locales. Certaines conditions météorologiques plus morphogènes ont été mises en évidence, telles que des vents persistants de secteur N-NW soufflant à plus de 8 m/s pendant plus de 48 heures, par exemple. Les mesures réalisées dans cette étude ont également permis la mise en place et la validation de deux codes morphodynamiques de modélisation à court terme de la réponse de la côte aux évènements de tempête, SBEACH et X-BEACH, qui ont tous deux donné des résultats cohérents sur le littoral étudié. Si le premier restitue mieux l'évolution morphodynamique et le second les conditions hydrodynamiques mesurées in-situ, ils restent tous les deux pertinents voire complémentaires.