Eddy Lines

Eddies are areas of circular current in a waterway.   They are usually caused by a shear in water currents or by Coriolis Force acting on a water current.

Of major concern to paddler's is the shear eddy.  Fast moving streams or tidal flows are powered by the force of gravity.  Water will move because the energy from the earth, the sun or the moon's gravitational pull.  Shorelines and other solid bathymetry (land structure under water) are immovable and will resist water's motion.  At some point the moving water and the stationary water will shear and eddies will be created.

This can be visually imagined by putting a pencil between two outstretched hands and moving them in opposite direction. 

The pencil will revolve. An eddy would react similarly to two opposing water currents by rotating in the same fashion as the pencil when viewed from its end.

Paddlers wishing to paddle against a river or tidal current can find water moving in the opposite direction or at least moving at less velocity inside an eddy line (note the red arrow in the photograph) adjacent to the shoreline.

The following chart shows the location of the above photograph in the black box. The eddy line in the photograph lies approximately on the boundary of the blue shallow water and the white area in the box on the chart.  Notice the current marking arrows in the bay in the bottom right portion of the chart.

The arrows indicate a large eddy current that takes up the entire bay depending upon the tidal current direction. As mentioned, the tide is flooding and flowing through Active Pass from left to right in the chart. As the current reaches the bay it loops around to the right and down creating a massive eddy.

To paddle through this area against the current, following this eddy would give some progress.  However it is a moot point if one attempted to paddle an OC6 outrigger through Active Pass against an 8 knot current!

The area in the main channel just adjacent to the bay has numerous warnings of "Tide Rip" and "Eddies" in this area. There is also a 262 foot deep hole as the channel narrows while approaching the north (out the top of the chart). This adds the third dimension to predicting the water flow through the narrow part of the Pass. 

The details in the marine chart give some hints to where the name "Active Pass" actually originated. The name actually came from US Survey ship called the USS Active, the first steamer to navigate the pass in 1855. The original inhabitants of the islands surely had a name with a similar meaning for this very active waterway before the white folks showed up.