Also of interest is the fact that the channels have substantially shifted in position. It is however incontrovertible, based on either analysis, that the bay is in active bathymetric evolution. It is important to recognize that available data are insufficient to satisfactorily evaluate this hypothesis. However, the combination of an existing bathymetric survey in mid- 1995 with the occurrence of extreme flooding in early 1996, suggests that a comparable bathymetric survey in 1996 would go a long way towards clarifying the importance of episodic floods in the bathymetry changes in Tillamook Bay. Tides Under non-flooding conditions, tides are the most dominant forcing in Tillamook.
Tides are semi-diurnal, with significant diurnal asymmetries.
The entrance channel and the extensive mud flats are both key controlling elements of the tidal propagation in the bay. Mud flats, in particular, induce significant non-linear generation of shallow water tides, leading to distortion of the tides. This hypothesis is difficult to prove based on tidal data, as tidal gauges have, both in this and in past studies, been typically installed away from mud flats. However, numerical simulations provide strong and convincing evidence. This is illustrated by the comparison of the amplitudes and phases of individual tidal constituents , for simulations performed respectively with the 1956 and 1995 bathymetries.