FY 1984

Tides and tidal currents of the inland waters of western Washington

Mofjeld, H.O., and L.H. Larsen

NOAA Tech. Memo. ERL PMEL-56, NTIS: PB84-237379, 52 pp (1984)

The tides enter the inland waters of Western Washington from the Pacific Ocean. They form a pattern of nearly standing waves with large areas of relatively constant amplitude and phase separated by channels where both change rapidly. The tides are either mixed-semidiurnal or mixed-diurnal. Usually the tides have nearly equal high waters with large differences in the low waters. The diurnal range decreases from 2.4 m at the western end (Neah Bay) of the Strait of Juan de Fuca to a minimum of 1.9 m at the southern end of Vancouver Island (Victoria, British Columbia) and then increases to 4.4 m at the southern end of Puget Sound (Olympia). There is an increase in phase lag away from the ocean due to tidal dissipation. This dissipation is large compared with inland waters with smooth bottom topography and is concentrated in the rugged channels such as Admiralty Inlet and Haro Strait with strong tidal currents. The tidal currents often exceed 1 m/s in many channels and the Strait of Juan de Fuca. Weaker currents occur in the main basins and side-embayments. Strong vertical shear occurs over sills but the tidal currents are relatively independent of depth in the deeper reaches. The tidal currents are rectilinear and flow parallel to the local channel or shoreline except at the intersection of several channels where broad tidal ellipses can occur. In Admiralty Inlet there are major diurnal inequalities in both the flood and ebb currents while in The Narrows the ebb currents are nearly equal in strength. The tidal prism of Puget Sound amounts to 4.8% of its total volume. Associated with the tidal currents are numerous eddies, fronts and internal waves.