Three-Dimensional Numerical Study Of Sediment Transport In Coastal Areas Based On ECOMSED/SWAN Model

Coastal region is the intersection of land and sea. In this region there are a number of environmental factors, and the hydrodynamic system is complex. In the coastal, estuarine areas,the wave and tide are the main dynamic factor with the change of water depth. Wave and tidal interaction is very necessary on the study of sediment transport. This paper analyzes the wave and tide interactional sediment transport mechanisms using ECOMSED 3-dimensional hydrodynamic and sediment model and SWAN wave model in Jiaozhou Bay.In this paper, it analyzes the distribution of sediment concentration and hydrological characteristics based on a lot of observations in Jiaozhou Bay. The sediment transport applicability of SWAN and ECOMSED coupled model was validated by considering tidal influence, wave influence and sediment distribution. The sediment transport under tidal current, ocean waves was simulated and the influence to transport by them was studied respectively.The main work in the paper is described as follows. It summarized the progress in numerical simulation of sediment, ocean waves and sediment transport under tidal current and waves. Ocean waves simulation in Jiaozhou Bay was constructed by SWAN model by adopting triple-nested manner. It got the wave parameters and their evolution such as significant wave height and mean periods. The harmonic constants S2, M2, N2, K1, P1, O1 were calculated by the tide gauge stations nearby, which were given as the boundary conditions of ECOMSED model. It showed a good performance of ECOMSED from the comparisons with observations of tidal current and water level. In order to understand the role of the waves in the sediment transport, the simulated wave elements were added to the ECOMSED sediment module, which give a comprehensive simulation of sediment evolution. The results show that ECOMSED hydrodynamic model give a good simulation of water level and tidal current in Jiaozhou Bay, where the tidal type is typical semidiurnal nature. The significant wave height derived from Jason-1 is similar to the simulated results by SWAN. It shows that Jiaozhou Bay is always in smooth sea states, which is correspond to the observations.Current speed plays an important role in the suspended sediment concentration evolution. Only considering the action of current, the contour lines of suspended sediment concentration are parallel to contour lines of water depth. The concentration decreases gradually when the water depth becomes deeper and most of the suspended sediment concentration is 10mg/~50mg/L in the deep water. The suspended sediment concentration is greater below 5m isobaths nearshore. Overall, the suspended sediment under the action of tidal current is low, which is about dozens of grams per cubic meter.Some characteristics under joint influence of wave and tidal current are similar to that under tidal current. The sediment concentration contours are parallel to depth contours and the suspended sediment concentration decreases accompany with the deeper of water depth. The current plays an important role in the sediment transport. The simulated results shows that most of the suspended sediment concentration is 10mg/L~100mg/L. The suspended sediment concentration is greater below 5m isobaths nearshore. Overall, the suspended sediment concentration is higher than under the action of tidal current, which is about dozens to 100 grams per cubic meter.In the case of wind waves, the suspended sediment concentration distribution near-shore will change significantly. It becomes greater than simply under the tidal current. That means that ocean waves are an important factor in coastal sediment transport. The joint influence by wave and current will have a rise about 2%~68% in the suspended sediment concentration. The average value is abou 14%.