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Seymour Narrows is a long, slender, dangerous stretch of water north of Campbell River, B.C.. Like many sites in this part of the world, vast amounts of water are forced by ocean tides through narrow passages, which creates high water currents and dangerous conditions: whirlpools, overfalls, and other boat-busting conditions.
Seymour Narrows is a 5 km section of the Discovery Passage in British Columbia known for strong tidal currents. Discovery Passage lies between Vancouver Island at Menzies Bay, British Columbia and Quadra Island except at its northern end where the eastern shoreline is Sonora Island. The section known as Seymour Narrows begins about 18 km from the south end of Discovery Passage where it enters the Georgia Strait near Campbell River. For most of the length of the narrows, the channel is about 750 meters wide.
Through this narrow channel, currents can reach 16 knots. It is remarkable that the flowing current of Seymour Narrows can be sufficiently turbulent to realize a Reynolds number of about 109, 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. (For those of you unfamiliar with Reynolds numbers: Re is a dimensionless number that gives a measure of the ratio of inertial forces to viscous forces and consequently quantifies the relative importance of these two types of forces for given flow conditions.)
This stretch of water was worse before 1958. Seymour Narrows was described by Captain George Vancouver as "one of the vilest stretches of water in the world." Before 1958, a dangerous submerged twin-peak mountain named "Ripple Rock" reached within 3 m of the surface of the narrows, creating
dangerous whirlpools as well as gouging out the bottoms of many passing vessels and sending them to the bottom. 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.
Known among sailors and locals as "Old Rip", the rock posed such a hazard to maritime traffic that a public works project was undertaken to demolish it. After several unsuccessful attempts to drill the rock from above, a tunnel was built from a nearby island, under the Passage, and up into the rock. The rock was packed with 1,274 tonnes of explosives, which were detonated on April 5, 1958.
The blast destroyed the peaks in one of the largest ever man-made non-nuclear explosions. Since the demolition, the highest point of Ripple Rock lies 14 m below the surface.
Even with Ripple Rock removed, it remains a challenging route. Mariners should be cognisant and cautious of the strong currents in the passage; the rapids have claimed over a hundred lives and are regarded by many sailors as the worst hazard to marine navigation on the British Columbia coast. In March 1981, the Star Philippine, a freighter ran aground in the narrows. At times of high current, whirlpools form that can draw a boat or a man to the bottom. There also exists a special, rather risky water condition that arises in places like Seymour Narrows. It is described by sailors in everyday language as "opposing wind and current." In this condition, current flows in one direction and wind blows in the opposite direction. This can result in dangerous wave heights and very rough conditions, for a reason that is neither obvious nor commonly understood by sailors. Many sailors believe this condition results
simply from adding wind velocity to current velocity, since they are in opposition. If this were true, it would mean a wind of twenty knots and an opposing current of five knots would produce wave heights typical of a wind velocity of 25 knots and no current. But in fact, in many cases wave heights are much higher than this simple addition of velocities would predict. The reason? Water current passing across irregularities on the bottom (or being
deflected by the sides of a narrow channel) can create ripples in
the surface of the water anyone who has watched water flowing in a stream has seen this effect. But the opposing wind prevents the waves created in this way, and the energy they represent, from moving away from the point of their creation, and this confinement effect causes the waves to become much larger. To say it another way, the wind concentrates and confines wave energy
in a way that builds huge waves out of what might have been small ripples if the wind was not blowing. Technically, it is a positive feedback system in which wind energy is expended to build large waves out of small ones, and in some cases, the result can be waves of stupendous heights that appear not to be moving across the water very much if at all. These abnormally large waves are called "standing waves" or "solitons."
To log this Cache, email us the answers to the following:
1. At the listed coordinates, you can find the following information:
a. Who first charted the Narrows, and in what year?
b. How many attempts were made to remove Ripple Rock in 1943?
c. What other year was an attempt made, before the successful 1958 attempt?
2. Which way does the flood tide flow? The ebb tide?
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