streamflow
Streamflow is always important and often the only information we can get. To say it is meaningless is obtuse. It is always an advantage to know rivers at different stages, but general rules work almost all the time.
For instance, I check a river flow and trend in the spring and it is consisently above 800 cfs. The trip is a go.
If the flow is “meaningless” how do you make a decision?
You’ve added additional information
"For instance, I check a river flow and trend in the spring and it is consisently above 800 cfs. The trip is a go."
You’ve added two very important additional components: you’re checking it consistently and checking it in the spring. I’d call that a go too.
Ppine, all I’m saying is
that the number alone is meaningless. CFS is significant when one knows the past history of that section and what its characteristics are at different CFS. As Clarion points out, consistency is the key. Let’s say you paddle Creek “A” 5 times a year and each time you checked the CFS and took note of the flow. Was it ripping fast or too low? Then later checking the CFS online will yield some idea of what the flow will be like before planning your trip. Then CFS has some meaning vis-a-vis Creek 'A". Without that history the CFS of a given stream on a given day means nothing to the paddler who is wondering what to expect.
flow
We paddle new rivers all the time. They are remote. There is no one to check with, maybe a remote stilling well with telemetry. That is it.
flow
Compared to no information, flow data are perfect and all you need.
I agree
new rivers never paddled and no local paddlers with info are a “just go and try it”. Flow data is no help without prior history. Some streams have no data. There’s usually some local guage or USGS guage and you can get a good idea from those. Some local might point to a bridge piling and offer that when the water level is up to the third rivet on the bridge the rapids will be big, or river will be too low,or etc. You can usually find out something in the area.
not f&%&% much
78 sounds low or its a tiny river. Think of CFS as = to the amount of water the size of a basketball floating by in 1 second. So 78 would be equal to 78 basketballs to give you a visual reverence.
Not exactly…
You don’t need to know the river and watch it at various flows to get good info from the cfs number alone…IF you have some idea of the river’s characteristics, and can compare those characteristics to those of rivers you do know, or that you can find flow information on.
Like I’ve already pointed out, I can look at gauge info on any river in the Ozarks, and have a pretty good idea of whether it’s floatable or not. I don’t have to have been on that river before, all I need to know is that it’s similar to other streams in the Ozarks in the characteristics of its riffles and rapids. And since nearly all Ozark rivers ARE similar in the characteristics of their riffles and rapids, I can be pretty certain that I need about 100 cfs to comfortably float one, under 75 cfs and it’s going to be bony, over 150 and it will be very pleasant floating with little or no scraping bottom or getting out of the canoe.
Now…can I relate that info to streams outside the Ozarks? Maybe, with a couple other pieces of info. One is median flow, which is also found on the gauge. If the 78 cfs on the river in the original post is somewhere close to the median flow for that date on that river, I can assume that the river is not abnormally low. If it’s not abnormally low at 78 cs, it’s probably not a very wide river, so the riffles shouldn’t be extremely wide and shallow.
The other piece of info I need to get elsewhere, and that’s gradient. Most floatable Ozark streams drop at a rate of 2-10 feet per mile. If a river has less gradient than that, it’s more likely to be floatable at low flows like 78 cfs. If it has much more gradient than that, it’s likely to have rock garden rapids that require quite a bit more volume to be floatable. Anything within that 2-10 fpm range, and it should be similar to the Ozark streams I know.
And…one more thing that will complete my evaluation. Go to
Google Earth, or even just the satellite views on Google Maps, and actually see what the river looks like. I can do that and get a definitive answer on how wide the riffles are, and thus be more sure that my Ozark figures will or will not translate to this stream.
Al
I like your post. Lots of pool and drop rivers in the West, so 250 cfs is a lot more maganeable in a canoe. Many higher gradients also.
It depends on the river
– Last Updated: Sep-16-13 1:37 PM EST –
Knowing the flow without knowing the size of the river is more or less meaningless. To illustrate this... imagine a riverbed 1/4 mile wide vs a creekbed 5 feet wide. 100 cfs would be literally a drop in a bucket in one and probably a raging torrent in the other (depending on gradient).
If you have a full years data then SOMETHING could be gleaned from just the CFS ( say the river varies seasonally from 100-1000 cfs), now you could determine if its at least at high or low flow for the year and make an educated guess as to what to expect, but to really know what a river is doing you need to know 3 things..
Flow
Width
Gradient
If its a whitewater type river then one also needs to know how the gradient is arranged, smoothly or in steps. To take this to extremes... imagine two rivers, both 100 feet per mile gradient, the one with the even gradient is a swift moving river, the other is more or less 2 still pools, with a 100 foot waterfall in the middle. Both might be fun, but it's nice to know what to expect!
If you go to the USGS gauge page
and find the “location” data for a particular gauge, it will tell you the watershed area for that gauge. For a particular area, that is an indication of size.
A map will have appeared, and clicking on the map will allow inspection of the stream gradient on a topo. Also available is a view from space where the more significant rapids are visible, as well as trees in the river.
Louisiana bayous may have plenty of
depth and be clear of obstructions with a regular flow of only 78 cfs. But you’re correct, piedmont and mountain streams are usually not negotiable with a flow that low.
My rule of thumb for GA piedmont streams is at least 200 cfs to get by, but 300 for a really nice flow. There are a few piedmont rivers so large and wide that 300 won’t do it. There are mountain streams with gradients so high that 300 may not cover the drops.
How about a practical example?
If you post the state and town, I’ll pull the actual USGS gauge for you. Using the information provided, I make a recommendation. Can’t do more than that!
Cubic feet per second
CFS can be the best way to determine id a creek is runnable as long as you know the area of the watershed.
Creeks under 25SM (square miles)usually require at least 4CFS per square mile of drainage.
That means a creek draining 25Sm would nedd 100+CFS flow.
When the drainage area gets up to about 70 square miles you would need 2CFS per square mile drained.
At 200 square miles you only need 1.2 to 1.5 CFS per mile drained.
So a river draining 200 square miles would need a flow of 300CFS, possibly a little less.
These drainage areas and CFS flows may be found at the USGS real time web-pages.