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Seymour Narrows is a 5 km (3 mile) section of the Discovery Passagemarker in British Columbiamarker known for strong tidal currents. Discovery Passage lies between Vancouver Islandmarker at Menzies Bay, British Columbiamarker and Quadra Islandmarker except at its northern end where the eastern shoreline is Sonora Islandmarker. The section known as Seymour Narrows begins about 18 km (11.5 miles) from the south end of Discovery Passage where it enters the Georgia Straitmarker near Campbell Rivermarker. For most of the length of the narrows, the channel is about 750 meters wide. Through this narrow channel, currents can reach 15 kn.

Seymour Narrows was described by Captain George Vancouver as "one of the vilest stretches of water in the world." Even after Ripple Rockmarker was removed, it remains a challenging route. In March 1981, the Star Philippine, a freighter ran aground in the narrows.

Seymour Narrows is notable also because the flowing current can be sufficiently turbulent to realize a Reynolds number of about 10^9, i.e. one billion, which is possibly the largest Reynolds number regularly attained in natural water channels on Earth (the current speed is about 8 m/s, the nominal depth about 100 m). Turbulence develops usually around a Reynolds number of 2000, depending on the geometric structure of the channel.

Ripple Rock

Ripple Rock was a submerged twin-peak mountain that lay just nine feet beneath the surface of Seymour Narrows. It was a serious hazard to shipping, sinking 119 vessels and taking 114 lives. The gunboat USS Saranac was one of the rock's first recorded victims. On April 5 1958, after twenty-seven months of tunneling and engineering work, Ripple Rock was blown up with 1,375 tons of Nitramex 2H explosive making it the largest commercial, non-nuclear blast in North America. The Halifax explosionmarker in 1917 was larger but it was not a deliberate act.

The event was broadcast live on Canadian Television. The footage is also regularly screened at the Campbell River Museum.

Vancouver band The Evaporators wrote a song about the event and released it on their 2004 album Ripple Rock.


  1. B.C.'s deadly Ripple Rock blown up, CBC Broadcast Date: April 5, 1958
Canadian Tide and Current Tables, Vol. 6, 2003

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