Tides

TIDES are the alternate rising and falling of sea levels along the COAST. They are caused by the gravitational pull of the moon and, to a lesser degree, the sun. Much activity along the coast, both human and animal, responds to the rhythm of the tides. There are 3 tidal cycles: daily, monthly and annual. During the daily cycle—actually 24 hrs, 50 mins—the tide fluctuates twice between high and low. One of the fluctuations is usually smaller than the other. Every day tidal peaks occur about an hour later than the previous day. The monthly cycle is affected by the waxing and waning of the moon. At times of the new and full moons, when the gravitational effect of sun and moon are combined, tides are at their highest, the so-called spring tides. The smallest fluctuations—neap tides—occur at the first and last quarter of the moon when it and the sun are pulling different ways. During the year, tides have their greatest fluctuations near the summer and winter solstices (June and Dec). Tides create brisk currents in the many channels along the coast as water piles up at the ends of narrow passes, waiting to surge through. Some of the best known of these constrictions are ACTIVE PASS and PORLIER PASS in the GULF ISLANDS, SEYMOUR NARROWS at QUADRA ISLAND and the YUCULTA Rapids between STUART and SONORA islands. The currents at NAKWAKTO RAPIDS and the SKOOKUMCHUCK RAPIDS reach 16 knots and are the swiftest tidal currents in the world. See chart listing some of BC's strongest tidal rapids.