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Rick Dinicola,
Associate Director, WA Water Science Center,
934 Broadway,
Suite 300
Tacoma, WA 98402

(253) 552-1603
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Duwamish River Estuary

Project Summaries

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WA218 - Flux of Toxicants Through the Duwamish Estuary to Puget Sound - Completed FY1979

Problem - The Puget Sound ecosystem could be changed by toxic substances entering it as a result of man's activities. The Seattle area is the largest urban/industrial area on the sound and thus has the potential of being a major source of toxic substances to the Sound. One of the major pathways for these toxicants from the Seattle area is the Duwamish River estuary. The Duwamish is a salt-wedge estuary for the Green River. Probable toxic sources on the Duwamish are the Renton Sewage Treatment Plant, stormwater drainage, drainage from agricultural areas, food processing wastes, and accidental or planned discharges from boats and industries.

Objectives - The USGS, in cooperation with Metro, proposes to: (1) document the presence of toxic substances in the Duwamish estuary; (2) make the necessary concentration and discharge measurements to estimate the annual flux of toxic substances from the Duwamish to Puget Sound through a cross-section located near the mouth of the estuary, and (3) estimate annual fluxes to the estuary from the Green River through a cross-section at the Tukwila gaging station as well as from the Renton Treatment Plant. The storage and transport of toxic substances in the bottom sediments of the estuary and Green River will also be examined. Metro is collecting data on stormwater discharge to the estuary. The other potential toxic source will be investigated briefly as part of this study.

Approach - The sampling program to estimate the flux of toxicants is in three phases. The first is a preliminary survey. A few water bed-sediment samples will be taken and analyzed to determine which toxicants are present. The second phase is a detailed sampling of the cross-sections to determine when and where phase three representative samples would be collected for best estimating fluxes. The third phase, will be a routine weekly sampling program to supply data for computing the annual toxicant fluxes. Samples from the 2nd and 3rd phases will be analyzed primarily for those species found in significant concentrations in the samples taken in the preliminary survey. Concentrations of samples multiplied by appropriate discharges will give estimates of toxicant fluxes into the Duwamish estuary and from the estuary into Puget Sound.

WA137 - Flow Patterns in the Duwamish Estuary - Completed FY1972

Problem - The port of seattle is planning to fill part of the Duwamish River estuary and narrow and deepen the channel in the east waterway. In order to meet the differing stream-velocity requirements for shipping, pollution, and fish migration, a study of the present stage and distribution of discharge and velocity in the lower estuary is needed and a projection of the effects of the physical changes required.

Objectives - To determine the stage relationship, velocity patterns, and flow distribution in the lower three miles of the estuary under present conditions and project the effects of certain physical changes proposed by the Port of Seattle.

Approach - Four temporary water-stage recorders were used to determine the stage relationship. Velocity observations were obtained over half a tidal cycle at high and low fresh-water discharge at three locations. Velocity observations were taken in 11 verticals once each hour. Data were used to compute discharge, develop velocity distribution, and estimate high and low velocities for present and proposed channel changes.

WA068 - The Influence of Industrial and Municipal Wastes in Estuarine and Offshore Waters - Completed FY1977

Problem - The discharge of municipal and industrial wastes, which received varying degrees of treatment, from many sewage treatment plants and other outfalls was seriously deteriorating the quality of waters in the Metropolitan Seattle area. A comprehensive sewerage plan includes interception and transport of these wastes to four plants that dispose of "primary-treated" wastes at great depths in Puget Sound and one plant that dispose of "secondary-treated" wastes into the Duwamish River estuary. The changes in waste-disposal practices probably will cause changes in the water quality of Puget Sound and the Duwamish River estuary.

Objectives - The study is to determine the effects of changes in disposal of municipal and industrial wastes on quality (physical, chemical, and biological) of the receiving waters, the Duwamish estuary and Puget Sound. Involved in the study are the effects of changes in: (1) degree and type of waste treatment; (2) amount of treated-waste effluent; (3) geometry of the Duwamish estuary caused by proposed widening and deepening of ship and barge channels; and (4) water quality of inflowing waters to the Duwamish River estuary.

Approach - Spatial and temporal variation of variable values in the estuary and Puget Sound are observed by continuous monitoring at several ocations and by data collected during field investigations. Analysis and interpretation of data include use of graphical and regression-analysis techniques to determine relations among variables and use of time-series analysis to determine structure of spatial and temporal variation of variables. A numerical (digital) model of the Duwamish River estuary is being developed to simulate observed variation of variables and to predict changes in variable values generated by possible changes in the causative factors.

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