CFS - Not a Dinner at Denny's
Cfs is the measurement by which water flow is determined. It literally means "cubic feet per second." When guides speak of river levels, one often hears "It's at 1,500 cfs," meaning, every second 1,500 cubic feet of water is passing a given point on the river.
Well, that's all well and good, but what does a cubic foot of water look like? A good rule of thumb is to think of a cubic foot of water as a little bigger in size than a basketball. So, let's say you were standing beside the river. If we use the previous example of 1,500 cfs, every second, 1,500 basketballs would whiz past your feet. Pretty mind boggling, huh? Just imagine applying this visual to the floods of 1998 when the South Fork American River peaked at 135,000 cfs! That's a lot of basketballs.
But there's a trick to this cfs stuff. A relatively high cfs doesn't actually mean a particular river is running at high water levels.
You see, every river has a specific, and different, optimal flow which is determined by many factors including its gradient, depth, width and so on. A high cfs measurement on one river might mean it is in flood stage, but on a different river, that same cfs reading could mean the water is exceptionally low. For instance, take the Colorado River flowing through the Grand Canyon. That river canyon is enormous and hence it can handle a higher volume of water. So normal water levels on the Canyon range from 10,000 to 40,000 cfs. Low water on that river is considered anything between 5,000 to 10,000 cfs. Compare that to the Tuolumne where 10,000 cfs is an epic flow!
Now that you've been initiated into the inner circle of understanding water levels, the next time your guide rattles off a number followed by "cfs" and your rafting buddy turns to you with a "huh??", you can just tell 'em it's all about basketball.
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