Ferries For Science: Monitoring Flow in Puget Sound

Ferries making their regular trek across the Puget Sound will now be also helping scientists better understand water flow and changes in tides and currents.

The Applied Physics Laboratory (APL) at the University of Washington in Seattle installed powerful sensors on the bottom of the Coupeville, a Port Townsend ferry as part of a new research initiative that will hopefully help scientists collect a massive amount of data on the interaction between water flows in the unusual Puget Sound inlet.

"The ferries cross the entire span twelve times per day," Jim Thompson, principal oceanographer for the new study, said in an APL release.  "By having our instruments on the ferries, we can start to get a total estimate as to how much water is intruding at the bottom from the ocean and how much water is leaving at the top from the rivers and the fresh water than comes in."

Thompson has been studying the turbulence and flow of the Puget Sound for years, as it is an excellent model for the study of the turbulent clash of fresh and salt water.

"That turbulence is one of the reasons we're out here. The whole area has very strong tides - a lot of energy here," he added.

The other reason is water quality prediction and management. The APL research team believes that patterns of water exchange and circulation between water basins in cross-sections of the Puget Sound may help them predict potential threats before they occur. Better understanding flow patterns could help contain a toxic spill, prevent harmful algae blooms or halt contributors to ocean acidification.

Two ferries in all will be equipped with an instrument known as an Acoustic Doppler Current Profiler (ADCP) at the start of this new study. Using sound wave pings, these sensors will measure current velocities and how they differ between the surface and the bottom of the Sound. After multiple passes, the combined data should allow the researchers to map out salt water flow from the sea and freshwater flow from the region's mountains.

Installation of the second ADCP on the Kennewick will be completed later this year.