Natural history: Salish Sea tides

While growing up in New England, my family used to vacation in the Bay of Fundy in southeast Canada. The tides in that bay are among the highest in the world. The water level between the low and high tide would differ by over 35 feet. I witnessed a similar tidal range when I lived near Cook Inlet, Alaska for 20 years. The tidal range in the Salish Sea is not as dramatic. On average, in the Salish Sea including areas near Blaine, the difference in height between the highest and lowest tides each day is about 11 feet.

Along most of the U.S. Pacific coastline (excluding Alaska), there are generally two high tides and two low tides each day. The two high tides are of different heights, and there are usually about 11 hours between consecutive high tides. In the Salish Sea, the pattern of islands, inlets and channels modifies the tidal cycle in significant ways. For example, in mid-January this year, there was a couple of days when there was only one high tide each day, with the time interval between consecutive high tides widening to about 24 hours. 

When the water in Birch Bay or Drayton Harbor is calm, I like to stand along the shore when the tide is rising and watch the water line creep shoreward. I find it amazing that I’m seeing the influence of the gravitational pull from the moon and sun on the mass of water in these beautiful estuaries. The rise and fall, day after day, gives me a sense of comfort.

Jonathan Hall resides in Birch Bay. He is a retired biologist who has worked in many regions of the U.S. while employed with the State of New York, the U.S. Fish and Wildlife Service, several environmental consulting firms, and the Tulalip Tribes of Washington.