Imagining the size of a cubic foot could be difficult if you’ve never done it. You have the equivalent of the Blue River. Blue River below Breckenridge: 50 cfs; South Platte near Lake George (Elevenmile Canyon): 228 cfs; Imagine a box 25 feet wide by 2 feet deep filled with water and traveling at a rate of 1 foot per second. CFS stands for cubic feet per second which is a unit of measurement referring to the volume and speed of water flow. CFS or Cubic Feet per Second is the unit of measurement used for determining the “speed” of a river. This is specific to whitewater or river kayaking and the flow rate on most rivers is measured in cubic feet per second (CFS for short). Now imagine that same box is … The final weather factor that we want to mention for the best weather conditions for kayaking is flow rate. Pay attention to this number when booking your trip as you soon will learn, water levels make a BIG difference on your whitewater rafting experience! The Middle Fork of the Salmon, for example, is best run at 1,500-5,000 cfs, while the Lower Salmon River is best run around 15,000-20,000 cfs. River volume is also sometimes measured in gauge feet. So basically, if a river has a high CFS that means the water is flowing faster resulting in larger rapids.