NUMERICAL-MODELS AND INTERCOMPARISONS OF BEACH PROFILE EVOLUTION

A modified non-linear cross-shore sediment transport relationship is d eveloped based on equilibrium beach profile concepts and scaling relat ionships. This non-linear relationship provides a reasonable explanati on for the significantly different time scales of beach evolution evid ent in various laboratory experiments. The proposed non-linear model c alled ''CROSS'' is calibrated and compared with the commonly employed linear transport relationship using laboratory data. A total of seven large scale wave tank experiments from three different facilities are examined. The results demonstrate that the non-linear transport model provides better overall predictions than the linear transport equation s. The CROSS model and three other commonly used models are applied to predict beach erosion at Ocean City, Maryland during the November 11, 1991 and January 4, 1992 storms. Seven survey lines are available for comparison with the numerical simulations. Overall, CROSS, EDUNE and SBEACH (version 3.0) provide reasonable predictions for both dune eros ion and the entire profiles. The sensitivity of CROSS to the transport coefficient, active water depth, storm surge levels and the storm wav e heights are examined for the storm erosion at Ocean City. It appears that CROSS is quite insensitive to the transport coefficient. The sub aqueous part of a profile is quite sensitive to the wave height and th e subaerial part is less affected. The CROSS model provides better pre dictions with the ratio of active water depth to incoming wave height of 1 than with the ratio of 1.28, and the 20% increased storm surge yi elds a better simulation.