WTF is CFS (1)

WTF is CFS?!

Understanding CFS and Water Levels

The most important and often overlooked acronym in the fly fishing dictionary is CFS, Cubic Feet per Second. This term is used to measure flow or discharge of rivers and streams. Many say they understand, but it can sometimes be tricky to wrap your head around. I know it was for me when I was first starting out. Water levels/flow, or CFS can give insight into how the fishing will be, but most importantly, it will help us stay safe. Here in the southeast, we have had some large tropical storms roll through this past fall. I have witnessed novice anglers taking big risks wading in water they had no business being in. I get it, we all love to fish! I never want to let a little rain ruin my Saturday; the only day some of us get to fish each week. With both safety and big fish in mind, we will discuss when it’s good to hit the water and when it is time to throw in the towel.

So what is Cubic Feet per Second?

To understand CFS, we need to understand that we are measuring the speed a specific amount of water is passing by a fixed point. To break it down a little more, picture a 1ft x 1ft box filled with water. That is one cubit foot. Now, draw a line across the river. The amount of square foot boxes that cross this line per second gives you the CFS measurement. In some streams, that number can be low, in the hundreds and even double digits. In large western rivers, measurements can reach tens of thousands. That is some powerful water. Each river is unique. For example, 1000 cfs here in North Carolina is considered to be high water whereas out west, that would just be a trickle compared to their mighty waters. If you showed me a CFS flow chart to a random stream in a state I was unfamiliar with, it would be difficult to have an understanding of the river. As anglers, it is a good practice to do a little research on streams we have never fished. Let’s check out this flow chart below.

What we are looking for.

Here we see a flow chart from water data. usgs.gov for the Davidson River in North Carolina. The “D” as it’s named is one of the most challenging and technical streams in the state due to the constant fishing pressure and picky fish. I would never claim to be a master of the Davidson (few are), but I have a pretty good understanding of the river because I can read and understand its flows. 
First, take a look at the little gold triangles on the chart. You’ll see the average flow for the past 97 years. That should give you good insight as to whether the current flow is running high or low. With this simple knowledge, you can look at most any stream and know if it’s worth packing the car and hitting the river or if it’s best to play it safe and let the fish off the hook. Looking back at the chart, January 1st and even the morning of the 2nd are a no go; because I know from fishing the Davidson that anything over 600 CFS makes for tough conditions. But get ready, as the river gradually falls from 600 CFS, that is the time to be out there fishing big streamers and heavy nymphs. Think about it. The fish have been in high and most likely dirty water. They are expending energy battling the current and not focused on eating. As the tinted water falls, the fish get fearless and THAT is your time to catch those spooky and selective trophy fish. 
After any rain, I find myself looking at flow charts of rivers all around the state. I like to see how fast they rise, and how fast they fall as I’m trying to pinpoint my ideal time to be fishing the water. It is important as anglers to keep an eye on CFS levels. The main reason being safety, but also looking for the prime time to be on the water. Do your research, talk to other anglers, stop in fly shops, and check Facebook groups; whatever it takes to be knowledgeable on unfamiliar streams. 
In future articles, we will be diving pretty deep into the different scenarios we can find ourselves in with water flows and how to prep our fly boxes for success.

As always, stay safe and stay smooth!

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