I have been researching flow rates if rivers. I understand how they are measured (cubic feet per second), but I don’t have anything to compare that to. Therefore, if someone said a river is flowing at 700 cfs, I don’t “really” know how fast that is. Make sense? For instance, what is the flow rate of a good class III or IV river?
Flow rate has to be factored with
river volume. For example, I have paddled the Edisto at 700 CFS and 10,000 CFS . Our speed was the same because the river was able to move into a flood plain as it rose.There were spots with bluffs that contained the water and the speeds picked up considerably.
Take that same volume and put it in the Chatooga, which flows through the mountains, and you don't want to go there.
In this case , the Chatooga River, there are rapids up to Class VI. My guess is they are classed at median or average stream flow.I have seen one of the Class III rapids at max CFS(Bull Sluice) and it was completely underwater.
Now maybe someone who really knows what they are talking about will answer.
these factors ‘together’ define the classification of a river. Flow alone doesn’t mean squat.
What you really need to know
is how that flow number relates to that specific river. Some rivers can run at 300cfs and are navigable, others may show 1400 cfs but you will drag your boat downstream and walk.
Just because you read someplace that a flow rate = X cfs, does not in any way indicate that it is too low, too high or just right. You must familiarize yourself with your particular river of interest and monitor the gage and actually view the river levels to understand what that number means at location X.
The USGS has many river gages you can check. Often there are indications on the chart where the mean, low and high levels for the creek. Still, this USGS information is not provided for boating navigation and really has no relation to whether that is a good day or bad for that river.
Best advice, if you are interested in a particular creek, find an outfitter or check their site for recommended flow rates. Then go check the recommended gage.
ask the same question
over on http://www.cboats.net/cforum/, but pick particular rivers and ask for ideal flows. You don’t want to low, but too high will “wash out” a rivers fun features as well.
Lots of paddlers from your neck of the woods, and it’s all WW C’s and OC’s
Picture worth 1000 words
Okay, not a picture, but an example. Picture how the speed of water shooting out of a fire hose far exceeds the most violent Class-V rapid, yet if you spray that water into the average little flatwater creek it won't have any visually apparent affect on the creek's flow rate at all.
Illustrating the same principle, I recently paddled both the Upper Iowa River and the Wisconsin River. Though the actual speed of the current in both rivers was similar, the Upper Iowa River had lots of stretches where the current was considerably faster than even the fastest parts of the Wisconsin River (the Upper Iowa River had numerous riffles and light rapids, while the part of the Wisconsin River I paddled is strictly flatwater). Now as to "flow rate", the Upper Iowa River had a flow rate of about 800 cfs, while the flow rate of the Wisconsin River was more than 50 times that figure. There's a LOT more water in motion on the Wisconsin River, but high current speed isn't what makes it so. As others have said, you need to acquaint yourself with the nature of your particular river at various flow volumes.
I appreciate the responses. So basically, because CFS is a three dimensional measurement, a river that is 100 yards wide and 2 feet deep, and one 100 yards wide and 10 feet deep, will have significantly different flow rates in terms of cubic feet per second. So how do you determine the speed?
there is no constant speed on any river. it’s like asking how deep the river is. where the river narrows or steepens, the current speed will increase. that is why cfs is used to measure a river’s flow - because it is constant no matter what the depth, gradient, or width.
and like mentioned above, you can’t compare two rivers to each other by means of flow, as all rivers are different, but it is a great way of measuring the flow of a river relative to itself at different flows.
I think I am clear now. I just need to familiarize myself with the rivers I will paddle the most and then use the flow rates to determine if the level is good for that particular river. Understood. Thanks everyone!
Flow was a good ole gal
I agree with most of what has been said here. CFS is significant only when being discussed with a group of regulars who paddle those sections of river and can compare CFS reading over time. It means something to them.
I sent a post here once that noted I had paddled a river with 480 million GPS that weekend. Of course it was the Miss. R. and not hard to paddle.
This might be what you’re looking for
Color coded and detailed flow info too:
I’ll add the geek flavor to what’s already been said. One cubic feet of water is equivalent to 7.481 U.S. gallons of water. That still tells you nothing about flow or speed, but for anyone wanting to go to gallons for a better mental picture, there you go . . . .
What a great resource. I’ve not seen this page before, but it’s a boaters friend. Who puts this out? Thanks
Alabama Whitewater, of course
Alabama Whitewater is a great organization, providing plenty of information about runs from their homepage. The descriptors will tell you class, put-ins, minimum and maximum flows and in general, give you an idea of when you want and don’t want to put in to a given river (don’t remember if there are “chicken ratings” on their site anywhere, but those are definitely useful, too!)
American Whitewater has good reference material, too (www.americanwhitewater.org).
While the cfs number tells you very little in itself, when you couple it with the table that’s almost always on the same page showing median flow, 20th percentile, and 80th percentile, you can get some idea of what the river is doing relative to “normal” for that day of the year. The little triangles that are usually on the flow graph correspond to the median flow for that day, and they are a pretty good indication of a river’s normal flow at that point (as long as the gage has been in operation for quite a few years–gages that have only been in operation for 10 years or less will not have a truly reliable indicator of normal flows). So if you know enough about the river to know that it is boatable at normal levels (and doesn’t need to be very high to run it), if the flow is pretty close to those little triangles you can figure it’s runnable. On the other hand, if it’s a river that needs to be high, you can sometimes figure that the 80th percentile figure on the table is approximately the flow where it would be getting pretty high, and maybe high enough to run. Still not good enough in itself to make a hard and fast decision, but at least some indication.
In the Ozarks, where I live, the various rivers, with a few exceptions, are pretty similar in character, and I can look at the flow in cfs plus the flow table and get a real good idea of whether a stream is floatable by canoe at that point. Basically, it takes a normal (median) flow in the summer of about 75 cfs for it to be canoeable. If you have a river with a median flow of 100 cfs but it’s only flowing 50 cfs that day, it’s probably going to be VERY bony. However, a stream with a normal flow of 50 cfs, flowing 75 cfs, will probably be runnable. I’ve floated, with considerable dragging, streams that were flowing as low as 30 cfs. The other thing is, if it’s one of those rivers that are sometimes runnable by jetboat, and you wish to avoid jetboats, look for a flow of less than about 200 cfs.