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FY 2003

Tidal datum distributions in Puget Sound, Washington, based on a tidal model

Mofjeld, H.O., A.J. Venturato, V.V. Titov, F.I. González, and J.C. Newman

NOAA Tech. Memo. OAR PMEL-122, NTIS: PB2003-102259, NOAA/Pacific Marine Environmental Laboratory, Seattle, WA, 35 pp (2002)

To improve the spatial estimates of tidal datums in Puget Sound, Washington, the harmonic constant datum method has been applied to the harmonic constants from a channel tide model of the Sound. This was done using the FORM180 Version 1.8 program. The model datums, harmonic constants, and associated geospatial information are available on the website Focusing on mean high water (MHW) relative to mean lower low water, it increases in height from 2.16 m at Port Townsend to 4.10 m at Olympia and 4.17 m at the head of Oakland Bay. Larger increases per km occur in Admiralty Inlet (1.66 cm/km) and the Tacoma Narrows (2.92 cm/km); smaller gradients occur in the Main Basin (0.44 cm/km) and South Sound (0.70 cm/km). The model MHW in Hood Canal closely follows MHW along the main axis with distance away from the main entrance to the Sound, to a maximum of 3.23 m at the head of Lynch Cove. This is also true for MHW in Whidbey Basin, except for a maximum of 3.17 m in southern Skagit Bay before decreasing northward toward Deception Pass. The model datums relative to MLLW tend to be slightly less than values derived from tide gage observations. For MHW, an average deviation of –3.6 cm occurs in the Main Basin, with smaller deviations in Admiralty Inlet (–1.1 cm) and the South Sound (–1.8 cm) and larger ones in Whidbey Basin (–7.8 cm) and Hood Canal (–8.5 cm). Further improvements to the datums should include adjusting the model datums to tide gage observations and applying high-resolution models to high-current areas and large tideflats.

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