Tidal current observations through Admiralty Inlet from ferry-mounted current profilers


Admiralty Inlet is a narrow sill located at the northern end of Puget Sound (WA, USA). Circulation through Admiralty Inlet is complex, with tidal currents exceeding 3 \(\hbox {ms}^{-1}\), large variations in fresh water input to the system, and seasonal ocean water intrusions. Long-term observations of the currents across the entire inlet are crucial for understanding circulation through Puget Sound. In this context, the Washington State Department of Transportation (WSDOT) Ferries, which run year round through Admiralty Inlet, provide a cost-effective platform to mount instruments and obtain long time series of currents distributed across the inlet. Through the Ferry-Base Monitoring of Puget Sound Currents project, two down-looking acoustic Doppler current profilers (ADCPs) are installed on board two WSDOT ferries, providing depth profiles of velocities across the inlet since May 2014. All data are quality controlled and organized in an horizontal and vertical grid across the inlet. Data within each grid cell are analyzed to capture tidal current harmonic components. Results agree well with data from fixed bottom-mounted ADCPs, and show large spatial variability in the amplitude of harmonic components, probably related to the bathymetric features of the inlet. Further analysis provides estimates of tidal asymmetry and residual currents through the inlet, which are relevant to water quality within the Puget Sound.

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The authors would like to thank the support of Washington State Department of Transportation Ferries, in particular Mark Scoville and Cotty Fay. The authors acknowledge NOAA, PMEC, and Dr. Kevin Haas for facilitating the additional data sets used in this investigation, as well as Alex de Klerk for design and implementation of data acquisition systems. Maricarmen Guerra thanks the support of Fulbright and Becas Chile doctorate fellowship programs. This project has been funded wholly or in part by the United States National Estuary Program funded by the US Environmental Protection Agency under assistance agreement PC00J20101 to Washington Department of Ecology. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

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Correspondence to Maricarmen Guerra.

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Guerra, M., Thomson, J., Prusa, T. et al. Tidal current observations through Admiralty Inlet from ferry-mounted current profilers. J. Ocean Eng. Mar. Energy 5, 159–172 (2019). https://doi.org/10.1007/s40722-019-00135-w

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  • Vessel mounted ADCP
  • Tidal currents
  • Residual currents
  • Ferry-based measurements
  • Tidal energy