What cubic feet per second means on a river

A cubic foot per second means one cubic foot of water passes a reference point in one second. It is commonly abbreviated cfs and used as a discharge or streamflow unit. Picture a cross section drawn from bank to bank: discharge reflects the amount of water moving through that whole cross section, rather than the depth or speed at a single spot. More water depth, a wider wetted channel, faster average velocity, or a combination of those changes can increase the reported cfs.

At many streamgages, water level, called stage or gage height, is measured continuously and converted to discharge using a site-specific stage-discharge relation known as a rating curve. Hydrologists develop and maintain that relation with direct flow measurements. This is why a cfs value is useful information, while still being an estimate tied to that gage and its channel conditions. Some complex locations use other methods to monitor flow, so read the station details when they are available.

The same cfs number can look dramatically different from one river or reach to another. A broad channel may spread water over a wide area, while a confined channel can focus it into deeper, faster runs. Slope, bends, bed material, vegetation, constrictions, tributaries, debris, and floodplain shape all affect how a given discharge is expressed on the water. A number that is routine at one gage can be unusually low, high, or operationally difficult at another.

Cfs is also not interchangeable with stage. Stage is water-surface height relative to a local gage reference, while cfs is the amount of water moving past the site. Their relationship is unique to the station and may not change in a simple one-to-one pattern. Channel erosion, deposited sediment, seasonal vegetation, ice, and debris can alter the relationship over time. Read stage when it helps describe local impacts, but avoid converting a stage or flow number from one river into a judgment about another.

Treat the current cfs as the end point of a story, not the whole story. Review the hydrograph over the last several hours, day, and several days, then compare it with longer seasonal history if the data page provides it. A stable pattern can make conditions easier to interpret than a sharp change, but stable does not automatically mean safe. A rising river can cover access routes, increase current, carry debris, and alter shoreline features before conditions look obviously different from shore.

A falling graph also requires caution. Water may be receding while current remains forceful in the main channel, exits stay cut off, or newly exposed banks and approaches remain unstable. Recent rain upstream can matter even if skies are clear at the fishing location. Note whether the gage is above or below tributaries, dams, or reservoir outlets relative to your planned reach. The closest gage is not always the most representative one if important water sources enter between it and your destination.

An observed cfs value reports conditions measured or calculated for a recent time at the gage. Check its timestamp before treating it as current at your arrival time, especially after rain or during rapid change. Streamflow data can be marked provisional and may be reviewed or revised as measurements and channel information are evaluated. An observation is valuable for knowing what the gage recently indicated; it cannot confirm every condition at an access point, bend, side channel, or crossing farther away.

A forecast is an estimate of future river conditions, not a promise. National Weather Service river pages may show recent observations and, at forecast locations, official forecasts on the same hydrograph. Forecast confidence can be affected by where and how much rain falls, runoff timing, snowmelt, upstream inflows, and managed water operations. When a forecast indicates a rise or precipitation could change the river during the outing, build time and route margin into the plan rather than assuming the displayed peak and timing will be exact.

Start by matching the gage to the actual reach: identify whether it is upstream or downstream of your access, whether tributaries or dam-controlled flows intervene, and when the latest value was posted. Compare today’s cfs and stage, where available, with past visits you know and with the recent graph. Then check rain and river forecasts, official flood products, road or access closures, and credible recent public observations about debris, submerged paths, launch conditions, or changed banks. Official warnings and local restrictions outrank any general reading of flow data.

Make the decision about exposure, not about whether the number looks favorable for fishing. GO fits a familiar local range, a stable or expected trend, open access, a dependable exit, and no official or on-site concern. MAYBE fits unfamiliar flow, incomplete local information, expected rain, a changing graph, or an option to remain on a low-exposure shore area. SKIP fits flood alerts, closures, rapidly rising water, debris, compromised access, flooded routes, uncertain crossings, or any situation where the group cannot confidently retreat. Never drive or walk through floodwater, and do not enter moving water simply to test conditions.

These references were consulted when this guide was generated. Check current official alerts and local rules before every trip.

• forecast.weather.gov (forecast.weather.gov)
• preview.weather.gov (preview.weather.gov)
• pubs.usgs.gov (pubs.usgs.gov)
• pubs.usgs.gov (pubs.usgs.gov)
• pubs.usgs.gov (pubs.usgs.gov)
• pubs.usgs.gov (pubs.usgs.gov)