Ken Smith/Turnagain Times
The bore tide occurs twice a day on Turnagain Arm, traveling up to 15 mph. Some brazen local surfers ride the tide for miles. It can been seen at various pullouts on the Seward Highway from Beluga Point to Twentymile River. See the bore tide schedule below for arrival times on the Arm at specific locations.
By Brian Stoecker
Turnagain Times correspondent
Turnagain Arm’s tidal range ranks third worldwide and its bore tide follows suit. Cook Inlet’s northern latitude generates greater tides than elsewhere, and the Arm’s topography—a shallow tapering bay—results in a phenomenon known as the “seiche effect” akin to water sloshing in a tub.
Our semidiurnal tides drain the arm, leaving a silty “river” braiding through the mud flats. High tides return as a flash flood, occasionally conveying over 40 feet of water through Bird Point, and generating class III to IV whitewater.
The official Anchorage tide (often attributed to Turnagain Arm) peaks at 38.9 feet, with a record bore cresting at 15. Both are dubious statistics. The bore (cresting to at least 10 feet) has no fixed standard of measure.
The obsolete Anchorage mark only applies loosely to Turnagain Arm. Records show at least a 39.5-foot range for Anchorage, prior to factoring a 4.4-foot correction for Turnagain’s Sunrise District. Still, the arm’s massive tide is dwarfed by Nova Scotia’s 55-footer in the Bay of Fundy.
The highest bores occur after full and new moons, when the gravitational forces of either, supplement that of the sun. These spring tides (from the German word “springen”, meaning “leap”) maximize within weeks of the spring and fall equinoxes when earth is nearest the sun.
To view the bore, obtain a free tide book from a retail outlet like Wal-Mart, fishing license outlets, or gas stations.
Find an Anchorage high tide of 30 feet or more. Note the time of the preceding low tide. The bore reaches Beluga Point on Turnagain Arm about an hour later, Windy Point in another half- hour, and the Hope Highway at nearly two hours after low tide.
The Seward Highway pullouts (the middle three of five) between Bird Point and Girdwood offer premier viewing. Bores generally arrive there, two-and-a-half hours after low tide. Extreme tides may arrive up to 15 minutes early, while moderate tides can be equally late.