Note
A numerical model is derived which describes the flushing of a coastal bay through tidal exchanges with the adjacent continental shelf. An expression for the renewal of bay water as a function of the number of elapsed tidal cycles involves a series of binomial coefficients which is equal in length to the number of tidal cycles. The model describes temporal variability in bay seltntty.-or any other measure of water quality, and indicates an asymptotic approach to a final value equal to that characteristic of shelf waters. The model is applied to Corpus Christi Bay, along the central Texas Gulf coast, and to Sarasota Bay, on the Gulf coast of Florida.