This investigation applies non-stationary time-series analysis methods and the St.Venant equations to model tidal range, tidal species amplitudes, and phases of water surface elevation in the Lower Columbia River in reach from the ocean entrance to Bonneville Dam, 234 km upriver. Future use of this model, together with a low-frequency river stage model, will include the reconstruction of historical water levels in the Lower Columbia River. These can be used in efforts to restore salmon habitat in the Columbia River below Bonneville Dam.