Seawater exchange rates for harbors based on the use of MIKE21 coupled with transport and particle tracking models

The water self-purification capacities of coastal areas can be affected by the extension of adjacent harbors. Studies of the seawater exchange capacities of harbors are viewed as an important index and means of protecting coastal water environments. In this paper, the MIKE21 hydrodynamic model (HD) is established and coupled with the transport model (TR) and particle tracking model (PT). Taking the Budai Harbor of Chiayi County along the southwestern coast of Taiwan as an example, five scenarios of upstream river inflow and corresponding pollutant distributions are explored. The tidal exchange rates (TER) of the five scenarios are quantitatively calculated. The results show the following: (1) Water exchange and self-purification capacities of the coastal area are stronger than those of other areas of the wetland region. (2) The self-purification capacities of the wetland are improved close to estuary due to upstream inflows. (3) With an increase in upstream flows, the wetland TER increases from 0.85 to 0.95, showing that inflows improve the water exchange capacity of the wetland. These have results applications for quantifying the influence of engineering construction in coastal areas close to harbors, for revealing the rates of seawater exchange that govern areas within and outside of harbors.