FY 1983

An overview of circulation in the Puget Sound estuarine system

Cannon, G.A.

NOAA Tech. Memo. ERL PMEL-48, NTIS: PB83-258129, 30 pp (1983)

The estuarine system that comprises Puget Sound and the Strait of Juan de Fuca, the southernmost, glacially carved waterways in western North America, is a complex composite of several connecting basins. Observations of circulation were made at a central location in the Main Basin of Puget Sound under various conditions during the past ten years. Intrusions of deep water below sill depth occurred at about fortnightly intervals, but not every fortnight. Flux calculations and water properties suggest a propagation of the intruded water along the Sound between Seattle and Tacoma in a little more than one week. A recent conceptual model, however, implies mixing of seaward-flowing surface water with the intruding deeper water. Present rough estimates are that below about 50 m only about half of the bottom water moving south past Seattle is new water from outside. Observations of mean daily current profiles in the Sound show significant deepening of the level of no-net-horizontal motion from about 50 m to as much as 100 m in approximately 200 m total depth. Winds along the Sound apparently can alter a fairly delicate balance of forces due to relatively small horizontal pressure gradients. In the Strait of Juan de Fuca, the waterway connecting the Sound with the Pacific Ocean, winter storms with predominantly southerly winds along the coast are capable of significantly reversing the normal estuarine flow and causing large intrusions of coastal water lasting several days. Outflow often occurs only in the deeper water with surface water being retained within the Strait.