Clearly this open-boundary transport is required to balance salt transport in estuaries. Less obviously, it can be an important source or sink for nutrient transport between estuaries and the coastal ocean. Obviously this equation can be solved only if there is a quantifiable salinity difference between the system and the ocean, yet some systems lack a salinity gradient.
V X is still an important variable.
We offer an alternative way to estimate the mixing volume V X without relying on a salinity difference between the system and the ocean. In the case of Hakata Bay, the agreement is about a factor of two. Further examples should be explored to evaluate the general agreement between these two methods. U, the K's, and D H are reported both in notation commonly given in the oceanographic literature and in the notation used here, in order to facilitate both comparison with that literature and calculations reported here.