Spatial Variability of Currents Across Key Navigation Passages in Puget Sound, Washington

Currents are an important factor in estuarine circulation, stratification and exchange.  Their accurate predictions are critically important for safe and efficient marine navigation.  Puget Sound, Washington is a dynamic, complex and spatially variable estuary with strong currents and significant environmental concerns including ocean acidification, hypoxia and pollutant transport.  Puget Sound is also a major hub for both recreational and commercial interests.  The NOAA NOS Center for Operational Oceanographic Products and Services is performing a large-scale, 3-year study to measure currents through the water column at nearly 140 different locations in Puget Sound, the Strait of Juan de Fuca and the San Juan Islands.  A spatial analysis of the cross-channel variability of tidal and residual currents was performed at three physically dynamic locations in Puget Sound: The Tacoma Narrows (south-Sound), Alki Point (mid-Sound) and Admiralty Inlet (Sound entrance).  Cross-channel variability was assessed through the deployment of three current profilers across narrow passages at each location.  Co-located conductivity, temperature and depth (CTD) sensors were also deployed at several locations, and CTD casts were made at each location while performing deployment and recovery operations.  The spatial and temporal variability of the currents at each location is related to tidal dynamics; topographic and bathymetric influences; and density gradients.  The observations and analyses will result in more accurate tidal current predictions for marine navigation, contribute to a better understanding of the circulation of the Sound, and aid in the development of numerical hydrodynamic models to help mitigate the many environmental issues facing the Sound.