FY 1984

Synthesis of current measurements in Puget Sound, Washington—Volume 1: Index to current measurements in Puget Sound from 1908–1980, with daily and record averages for selected measurements

Cox, J.M., C.C. Ebbesmeyer, C.A. Coomes, J.M. Helseth, L.R. Hinchey, G.A. Cannon, and C.A. Barnes

NOAA Tech. Memo. NOS OMS-3, 38 pp. & 4 microfiche (1984)

Puget Sound is an estuary in northwestern Washington consisting of three branches joined near their mouths to an entrance sill zone. In turn, this zone connects to the Pacific Ocean via the Strait of Juan de Fuca. The branches consist largely of basins embraced by sill zones; the largest or Main Basin accounts for half of Puget Sound's volume and the other half occurs mostly in three secondary basins. The estuarine flow is strongly modified by vertical mixing of surface and deep water over the sills as the water moves between the basins. As a result, the major portion of the surface flow is mixed downward and returned inland before exiting Puget Sound. This downwelling has raised concerns that primary fractions of municipal and industrial wastes are also refluxed inland and may be retained in the fjord complex for considerable periods. To describe the characteristics of the circulation in Puget Sound, a synthesis of historical measurements of currents, water properties, and meteorological conditions has been undertaken. The results of this project are presented in three volumes: Volume 1: Index to current measurements made in Puget Sound from 1908–1980, with daily and record averages for selected measurements; Volume 2: Indices of mass and energy inputs into Puget Sound: runoff, air temperature, wind, and sea level; and Volume 3: Circulation in Puget Sound: an interpretation based on historical records of currents. Volume 1 contains the locations and statistics of the recorded currents, and describes the types of equipment used to obtain the data. Volume 2 describes indices of the mass and energy inputs into Puget Sound which influence Puget Sound's water properties and circulation. This volume (Volume 3) contains an interpretation of the circulation based on the data contained in Volumes 1 and 2. Two aspects have been addressed: regional variability within Puget Sound's basins of mean currents, variance, and volume transport; and the temporal variability within the Main Basin. The mean circulation consists primarily of two-layer flow, but there are sizeable flows which occur as single layers in and between some sill zones. Many of the sill zones are quite energetic (variance of order 10⁴ cm² s^–2) compared with the basins. Two of the most energetic sill zones embrace the Main Basin and cause it to have a vigorous, rapid circulation through the year which is modulated largely by wind action. The Main Basin's volume transport in each layer is an order of magnitude larger, and the temporal scale is sixfold larger, than in the secondary basins. The computations of volume transport show that approximately two-thirds of the Main Basin's upper layer is refluxed downward into its lower layer via the sill zone at its mouth. Because of the refluxing in this and other sill zones, and because of the mismatch of the time scales between the basins, the fluxing time for a conservative substance in Puget Sound may be on the order of years.