Presentation Abstract

Hood Canal is a deep and long estuarine sub-basin within the Salish Sea that exhibits characteristics of classic fjords. Presence of the Hood Canal Bridge (HCB), a floating barge-like block near the mouth of Hood Canal is under investigation for potential environmental impacts on water quality and pelagic ecosystem. In this study, the effect of HCB on Hood Canal stratification and transport were evaluated using the Salish Sea Model, a 3-D hydrodynamic model with Hood Canal Bridge embedded at a high local resolution. The effects of the bridge as an obstruction to tidal currents and circulation were examined near the structure with the objective of characterizing the nearfield zone of influence (ZOI). This was accomplished through a combination of field measurements, and model simulations. ZOI was defined as the 3-D space near the floating bridge where ambient water properties were noticeably affected relative to background or natural water approaching the bridge during ebb or flood conditions. Field measurements included tides, currents, salinity, and temperature profile time series data collected from locations near the bridge over a 4-week period. These included stations upstream, downstream, and directly below the structure. The model results were in good agreement with the observed data. The simulated results show significant reduction of velocities in the surface layers near the structure. The Effect of HCB on temperature and salinity was also noticeable and extended over a larger zone predominantly during peak ebb and flood periods. HCB blocks the advection of warmer temperature and brackish water from the inner part of Hood Canal to the Salish Sea, creating significant backwater effect and associated temperature and salinity gradients during ebb as well as flood. ZOI(s) relative to the ambient current, salinity, and temperature structure were computed and will be presented.

Session Title

Big Objects Need Big Solutions: Addressing the Environmental Effects of Major Infrastructure Around the Salish Sea

Keywords

Hood Canal, Bridge impact, Hydrodynamics, Zone of impact, Nearfield

Conference Track

SSE1: Habitat Restoration and Protection

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE1-553

Start Date

6-4-2018 1:45 PM

End Date

6-4-2018 2:00 PM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 6th, 1:45 PM Apr 6th, 2:00 PM

Hood canal bridge effect on hydrodynamics and nearfield zone of influence

Hood Canal is a deep and long estuarine sub-basin within the Salish Sea that exhibits characteristics of classic fjords. Presence of the Hood Canal Bridge (HCB), a floating barge-like block near the mouth of Hood Canal is under investigation for potential environmental impacts on water quality and pelagic ecosystem. In this study, the effect of HCB on Hood Canal stratification and transport were evaluated using the Salish Sea Model, a 3-D hydrodynamic model with Hood Canal Bridge embedded at a high local resolution. The effects of the bridge as an obstruction to tidal currents and circulation were examined near the structure with the objective of characterizing the nearfield zone of influence (ZOI). This was accomplished through a combination of field measurements, and model simulations. ZOI was defined as the 3-D space near the floating bridge where ambient water properties were noticeably affected relative to background or natural water approaching the bridge during ebb or flood conditions. Field measurements included tides, currents, salinity, and temperature profile time series data collected from locations near the bridge over a 4-week period. These included stations upstream, downstream, and directly below the structure. The model results were in good agreement with the observed data. The simulated results show significant reduction of velocities in the surface layers near the structure. The Effect of HCB on temperature and salinity was also noticeable and extended over a larger zone predominantly during peak ebb and flood periods. HCB blocks the advection of warmer temperature and brackish water from the inner part of Hood Canal to the Salish Sea, creating significant backwater effect and associated temperature and salinity gradients during ebb as well as flood. ZOI(s) relative to the ambient current, salinity, and temperature structure were computed and will be presented.