A tidal model always has to be calibrated with measured data in order to proof that the model is reliable. The long wave equations can be approximated in many ways. The most important difference in approximation is a one or two dimensional approach. A one dimansional computation is much simpler and requires less calibration data, but can only be applied where the flow has indeed a one dimensional character. In rivers and river mouths with clear channels, a one dimensional model can mostly be applied with succes.
Boundary conditions can be e.g. a tidal curve at the river mouth and an upland river discharge.
Calibration data will be water levels and velocities or discharges along the river stretch being studied. Along a coastal area, the flow usually has no distinct direction and a two dimensional approach will be necessary. This requires also more data for boundary conditions and calibration. In all cases, the boundaries of the model have to be chosen well outside the area where changes can be expected. This also depends on the magnitude of the disturbance in the area.