Modeling wave, currents and sediment transport in Ystad Bay

Abstract: Coastal areas around the world are being shaped by many natural phenomena, as well as by man-induced activities. Hydrodynamic phenomena such as wind-generated waves, extreme storms and seasonal tides cause a continued change in topography and the natural sediment formation in the nearshore zone as a result of erosion and accumulation. Therefore, the nature of the nearshore zone and its protection through different structures and activities is of great importance for coastal engineers and project managers. In the recent decades, numerical modelling has been an engineering tool for the simulation of waves and sediment transport in coastal waters and bays. Nowadays, there are a number of developed models in terms of simulating nearshore hydrodynamics and sediment transport. The results of these models in practical applications have been validated and shown to be in good agreement with observations. However, due to the complexity of morphological phenomena in coastal waters, especially in the nearshore regions, these models usually deal with some specific processes and are limited by time and space scales. The main objective of this study is employ two advanced numerical models, SWAN and EBED (modified) model to determine the sediment transport patterns and their implications for topographic changes due to waves and currents in the Ystad Bay, Skåne, Sweden. This work was performed with emphasis on different time scales and various types of wave conditions. In order to derive a sediment pattern for the Ystad Bay, a preliminary study of the background data for the Ystad Bay was performed. The SWAN and the EBED-modified model were numerically implemented to calculate the wave field in the bay for the wave conditions from 2004 to 2010 for both extreme situations and for long-term representative conditions, and the simulation results were illustrated afterwards. Furthermore, the EBED-modified model was applied to derive two-dimensional current fields. A numerical model developed by Nam (2010) was subsequently implemented to calculate the sediment transport with focus on longshore transport. The simulation results from the application of the numerical models show that waves from south and southwest, which have the long fetches for Ystad Bay, will cause erosion in the western parts of the bay and accretion along the lower southeastern part of the bay. These results are in a good agreement with observations. However, the sediment transport model should be improved to include cross-shore transport in the future.