Simulation of different sea-crossing traffic route structures’ effects on the marine environment for the Dalian large-scale offshore airport island

China is developing a 21km(2) artificial island for the Dalian offshore airport in Jinzhou Bay, and a sea-crossing bridge traffic route scheme and an impervious seawall road traffic route scheme are under consideration. To compare the effects of the development of the airport island with these two schemes on the marine environment, a two-dimensional hydrodynamic model and a pollutant transport model have been developed. The data from field observations have been used for the calibration and validation of the models. The numerical simulation results of the effects on hydrodynamics, morphological evolution, water pollution, and biological losses indicate that the sea-crossing bridge traffic route scheme is less damaging to the marine environment than that of the seawall road scheme. This study's conclusions provide an important foundation for the Dalian offshore airport programme and can be used as a reference for similar coastal engineering and marine environmental protection programmes.