As much as CFS has been discussed in this forum, I am surprised at the continued lack of understanding and misuse. Cubic feet per second is a measure of the volume of water flowing past a certain point along the stream at a given time. It is not constant along the length of the stream. CFS can vary widely at many points along a stream. To say a stream is running at 100 CFS is useless, without designating the section in question. For instance one can say Stream X is running 100 CFS from point A to point B, 125 CFS from, point B to point C, and etc. Streams virtually never run at a single CFS throughout their length. To say that any and all streams are runnable at a certain CFS, let’s say 100 CFS, is just incorrect. A stream section may be at 2000 CFS and cannot be paddled in any craft because it’s a virtual rock garden. CFS is not a function of gradient alone. It is more a function of cross section shape and size and the coefficient of roughness of bottom and sides.

In summary, CFS is a measure of the cubic feet per second flowing passed a given point along a stream. Different streams can have the same CFS and one be almost flat and the other a raging rapid. CFS as a measure of paddling difficulty is valid only if a paddler has measured the CFS at a given section over time and noted how paddle-able the stream was a certain CFS’s.

Please no lectures, I’ve professionally done many stream flow design studies and am very familiar with how it is done and for what reasons. I do sincerely hope this helps people understand this topic.


You won’t get a lecture from me
The only time the flow means anything to me is if it a river that I have paddled before.

The flow along with the height is what tells us what the conditions will be like, but only if we have paddled that particular river before and have kept a record of the various heights and flows.

Jack L

All true, but if I’m discussing mountain
streams within a particular geological region, with comparable gradients, CFS is essential because gauge readings from stream to stream can’t be quickly compared.

There is nothing incorrect about comparing CFS over streams. You just have to know how to do it. Having CFS derivatives available on the USGS and AW websites has been a godsend. I have no idea how we mountaineers ever got by without them.

It is amusing to paddle a slow bayou and realize that while CFS of 45 would be totally inadequate on a mountain stream, it is a copious day’s cruise in the swamp.

Obviously you do not
need my comments. Your approach is entirely correct and you understand the use of CFS. Good on ya.