Taiwan is a small island state surrounded by the oceans but with large population. With limited land space, it would be worthwhile considering how to stabilize the existing coast or to create stable artificial beaches. Under the onslaught of storm surge and large wave from typhoons, beach erosion would occur accompanying by formation of a submerged bar beyond the surf zone with the sand removed from the beach. After the storm, the bar material maybe transport back by the swell and predominant waves which helps recover the original beach, thus producing a beach profile in dynamic equilibrium. The main purpose of this research is to use the back-propagation neural network¡]BPNN¡^, which trains a sample model and creates a system for the estimation, prediction, decision making and verification of an anticipated event. By the BPNN, we can simulate the key characteristic parameters for the storm beach profile resulting from typhoon action. Source data for training and verification are taken from the experimental results of beach profile change observed in large-scale wave tank¡]LWT¡^conducted by Coastal Engineering Research Center¡]CERC¡^in the USA in the 1960s and that from the Central Research Institute of Electric Power Industry in Japan in the 1980s. Some of the data are used as training pairs and others for verification and prediction of the key parameters of berm erosion and bar formation. Through literature review and simulation on the related parameters for storm beach profile, methodology for the prediction of the beach profile and bar/berm characteristics can be established.

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.