Christopher Curran | USGS Science

USGS2007

Nearshore circulation and water-column properties in the Skagit River Delta, northern Puget Sound, Washington: Juvenile Chinook Salmon habitat availability in the Swinomish Channel

Time-series and spatial measurements of nearshore hydrodynamic processes and water properties were made in the Swinomish Channel to quantify the net direction and rates of surface water transport that influence habitat for juvenile Chinook salmon along their primary migratory corridor between the Skagit River and Padilla Bay in northern Puget Sound, Washington. During the spring outmigration of Skagit River Chinook between March and June 2007, currents measured with fixed acoustic doppler current profilers (ADCP) at the south and north end of the Swinomish Channel and with roving ADCP revealed that the currents are highly asymmetric with a dominant flow to the north (toward Padilla Bay). Maximum surface current velocities reached 1.5 m/s and were generally uniform across the channel near McGlinn Island Causeway. Transport times for surface water to travel the 11 km from the southern end of Swinomish Channel at McGlinn Island to Padilla Bay ranged from 2.1 hours to 5.5 days. The mean travel time was ~1 day, while 17 percent of the time, transport of water and passive particles occurred within 3.75 hours. Surface water in the Swinomish Channel during this time was generally very saline 20-27 psu, except south of the Rainbow Bridge in the town of La Conner where it ranged 0-15 psu depending on tide and Skagit River discharge. This salinity regime restricts suitable low salinity (<15-20 psu) surface waters for fry Chinook salmon to the southernmost 2 km of the channel. The mean change in salinity along the channel was 10-13 psu. The high northward current velocities have the capacity to transport Chinook fry into less suitable, high-salinity waters toward Padilla Bay within hours. The rapid transport times of 2.1 to 3.75 hours between McGlinn Island and Padilla Bay that occur 17 percent of the time, are considerably less than the time considered adequate for juvenile Chinook to acclimate and produce a temporal salinity gradient for pre-smolt salmon that can exceed 4 psu/hour during high northward current flow.>

Washington↗

USGS2006

Transport pathways in the lower reaches of Hood Canal

In 2003, studies revealed that the waters in the lower reaches of Hood Canal in Washington State had very low dissolved-oxygen concentrations, low enough to cause some fish kills between June and October of that year. In order to determine the transport patterns and the persistence of the low oxygen level in this portion of the canal, the U. S. Geological Survey deployed two instrumented platforms on the seabed near the head of the canal that measured currents over the whole water column, water level, near-bed temperature, salinity and oxygen for 2 months in the fall of 2004. Tidal currents, the dominant current component in the canal, flowed primarily along the canal axis and had speeds of 15-20 cm/s. There was also a persistent internal seiche that caused currents to flow along the canal axis with speeds of a few cm/s. The seiche, which had a period of a few days, caused currents in the surface layer to flow in an opposite direction to currents in water depths deeper than 15 m. A pool of warmer, saltier and more oxygenated water moved past the measurement sites toward the head of the canal with a speed of 1 cm/s. CTD measurements taken near the 2 measurement sites during the deployment indicated that this more oxygenated layer of water extended from the bed to the thermocline. Oxygen data from the tripods showed that this water remained in the region until at least the end of October 2004, when the tripods were recovered.

Washington↗