One Analytical Method for Salinity Intrusion into Estuaries of Well-Mixed Type

摘要

An analytical expedient for salinity intrusion of well-mixed estuaries is to solve one dimensional convective diffusion equation in any kind of way. As the stream of estuary is unsteady due to tide and the flow area is nonuniform in longitudinal direction, the flow velocity, the cross sectional area and the dispersion coefficient in estuary vary with time and position. Therefore it is very difficult to solve analytically the convective diffusion equation which has these functions of time and position for hydraulic coefficients. In this paper the complex problems are made simple as follows, solving the equation of salinity convective diffusion in estuaries. Considering that the diffusion equation holds good averagely during a tidal cycle and solving the diffusion equation in wihch velocity is transformed into constant river discharge velocity, longitudinal salinity distribution at low tide slack is determined. Next, the salinity distribution at low tide slack is carried through the estuary by means of tidal velocity. The solutions obtained by this method are presented and are applied in the Chikugo River. The analytical results show fairly good agreement with the field observed data.