While neither\u00a0of these would seem to have much applicability to Kootenay Lake, we do have rips, and they behave in a similar manner\u00a0to the oceanographer’s rip tide.<\/p>\n
The residency time for water on the West Arm of Kootenay Lake is three to\u00a0four days, which means that this is\u00a0the average time it takes water to travel westward along the arm from Balfour to Nelson. This corresponds to an average westerly drift of a stately third of a kilometre an hour. A feature of\u00a0this arm\u00a0is that it is occasionally\u00a0constricted by creek deltas to produce what are known as the narrows. Through these, the flow is more like that of a river than a lake. So, while not being driven by a tide, the flow can reach the magnitude of the oceanographer’s rip tide.\u00a0<\/p>\n
However, a rip involves more than a fast current: it requires the water to be rough. For that we need the\u00a0interesting aspect of wave behaviour that occurs when waves move in the opposite direction\u00a0of the\u00a0current.<\/p>\n
Start with a brisk westerly wind in one of the lakelets between the narrows. The wind causes waves to\u00a0propagate against the easterly current, but in the broad\u00a0lakelet, the current is light and this is of little account. However,\u00a0if\u00a0the current moving against the waves is greater than the speed at which the waves are moving, the waves are brought to a stop. Consequently, waves may not be able to\u00a0enter the narrows with its faster current.<\/p>\n
What is particularly interesting\u00a0is what happens as the waves move towards the progressively faster counter current in the narrows. As waves approach the narrows and the current increases, the wavelength shortens and the wave amplitude increases: the waters become quite rough.<\/p>\n
When there is a west wind, the western entrance of the narrows has not only a strong current but really rough water. This is the rip. However, within the narrows where the waves generated in the lakelet haven’t been able to penetrate, it is much calmer and the current is strong.<\/p>\n
Here\u00a0is a view looking west though the Nine-mile Narrows. The nine-mile dolphin is on the left and the distant seven-mile dolphin is on the right. There is a west wind (out of picture) that is building waves in the lakelet between them. But, as the waves approach the narrows, the water becomes quite rough: this is the rip. Closer, at the bottom of the picture, the water in the narrows is much calmer. (The darker water near the bottom of the picture is a cat’s paw print<\/a>.) A rip is stretch of fast-flowing and rough water. Much confusion arises from that simple definition: In the public’s mind, the only rip is the\u00a0particular\u00a0one that is often called a rip current, but, given its provenance, really should really … Continue reading ![\"\"](\"https:\/\/blog.kootenay-lake.ca\/wp-content\/uploads\/2014\/05\/rip140428s.jpg\")
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