Numerical study of water age influenced by tide and runoff in Daliaohe Estuary in China

Based on the concept of the age, the water transport characteristics as the response to the runoff and the tide in Daliaohe Estuary in China are studied under different hydrodynamic conditions using a three-dimensional convection-diffusion model. The results show that the relationship between the average age at a specific position and the runoff could be expressed by a power function approximately. In the river channel, the runoff controls the water transport: it might take about 52 d, 27 d and 15 d for the water parcel to be transported from Sanchahe to the mouth during the dry, normal and rainy seasons, respectively. Outside the mouth, the tide is dominant even though the difference between the spring tide and the neap tide is less than 5 d, and the water parcel transports mainly along the northwest direction through the West Waterway and the southeast direction through the East Waterway. A significant age stratification emerges in the vicinity of the mouth, in which there exists a strong interaction between the tide and the runoff, and the age differences between the surface and the bottom could reach 7 d.