Water-Level Fluctuations and Flow in Tidal Inlets

Equations are derived to describe the water motion in a tidal inlet connecting the ocean with a relatively small basin. The boundary conditions considered are the ocean tide and fresh water inflow. No density effects are taken into account. A dimensionless resistance coefficient is introduced to express the influence of the inlet channel resistance on the water motion. A numerical method to solve the equations is presented. For a better physical insight, the analytic solution is presented for a simplified set of equations, in which the quadratic resistance term is replaced by a linear term. It appears that after a certain transition period the water-level fluctuations in the bay become steady, the steady state fluctuations being independent of the initial conditions. Numerical computations are carried out for the Inlet of Macquarie Harbour, Tasmania. The results, for a case in which no fresh water inflow is considered, are compared with the results obtained according to Keulegan's method and with the results obtained with the help of the simplified (linear) set of equations. They appear to be in close agreement.