The Change Of Wave Dynamic Environment For Bohai Bay In Recent30Years

In according to the change of the coast line of the Bohai Bay in the recent ten years, we establish the SWAN (Simulating Waves Nearshore) wave model to simulate the wave fields of the Bohai Bay in order to know about coastal reclamation affects wave fields, especially the influence of the wind waves. The large-scale reclamation projects lead to the coastal natural wetlands reduced, and the destruction of their natural attributes and ecological environment, along with the area and shoreline length are changed in different regions, consequently, wave fields are changed. There is a close relationship between waves and winds. Wave fields are influenced by the wind speed, wind direction and different wind zones. Based on the variations of wind fields nearly30years the impacts of natural factors on wave fields in Bohai Bay are analysed. Changes in natural factors such as climate winter monsoon weakened, strengthened gale frequency change elements of change, change to simulate the wave field changes by the wind fields, and further compared to the size of the reclamation projects environmental impact of wave power.We use the SWAN model forced by the ERA wind fields to simulate the wave fields of the Bohai Bay in the years of2000and2010. The variations of the wave fields near the four harbors in which that the coastlines have been changed significantly are analyzed. The results revealed that the significant wave heights decrease after the coastal reclamation, and the magnitude of decrease of the significant wave heights in the harbor basin and the tidal channels is bigger than the other area. Moreover, the locations of the four ports and the topography around them have the combined effects on the distributions of the wind waves near the three ports area.From the impact of the four port projects, the region where the significant wave heights decrease in the Caofeidian wave field is in the southeast wave field of the building where the influence scale is no more than20km. When the northwest wind prevailed in the winter, the influence scale is about15km in the region where the significant wave heights decrease20%in the southeast wave field of the Caofeidian Harbor. When the northwest wind prevailed in the summer, the influence scale is only about5km in the region where the significant wave heights decrease20%. The significant wave heights decrease greatly within the range of approximately100km2of the northeast wave field of the Caofeidian Harbor. Because of geographical reasons, the change of the wave fields is smaller of Tanjin port. The Tanjin port has little influence of the wind waves. The Huanghua Harbor wave field is under the influence of building shape and topography. The significant wave heights decrease greatly in the southeast of the project and the proportion of the decrease is about 50%. The affected wave field is about100km2. Because of the south wind in the summer, the degree of the significant wave height decreases increase in the north wave field of the Huangye port and the influence scale is about2km. The South Harbor project has minimal impact on the wind wave and the influence can be negligible.We use the SWAN model forced by the NECP wind fields to simulate the wave fields of the Bohai Bay from1981to2010. The research results revealed that the wave elements of Bohai Bay had little changed for30years and the significant wave heights was a decrease trend. The change trend of the significant wave height and period is silimar to the trend of the wind speed. There is a high degree of correlation between the wind fields and the wave fields of the Bohai Bay. The first model contribution rate of the significant wave heights in winter of the Bohai Bay is94.5%and it has an increasing trend.But the summer is85.3%with a decreasing trend.From the entire Bohai Bay, the impacts of natural factors on wave fields leads to a larger change and influence in the variations of the wave field than the coastal reclamation. For the wave field where the building scale is within7km, the result is contrary. For the wave fields where the coastal reclamation influence the location and orientation of the building have great influence on the wave fields.