How do you find a river's flow in real time?

Use apps like RiverApp, the eauxvives.org website or official hydrological stations, which publish gauge height and flow almost live. The graduated scales painted on bridges also give an immediate reading on site. Ideally cross-check an official source with feedback from a local club.

What's the difference between flow and water level?

The flow is the volume of water passing through per second, in m³/s: it measures the river's power and can be compared between runs. The level (or gauge height) is the depth of water read at a specific station, in cm: it's specific to that station and can't be directly compared from one river to another.

What water level is too dangerous?

It depends on each river and section: above the maximum given by guidebooks or clubs, the current becomes too powerful, the hydraulics hold and the obstacles drown. In flood, you never put in, even on an easy section. Fast-rising water is a stop signal even below the maximum.

Why does the level rise so fast?

Heavy rain and snowmelt quickly swell rivers, sometimes within a few hours on small mountain catchments. A storm upstream can raise the level while the sky stays clear where you are, which is why it matters to check the weather over the whole catchment.

What does a flow expressed in m³/s mean?

It's the volume of water passing through per second at a point on the river. Each run has an ideal range between a minimum and a maximum; compare the day's figure to these markers rather than to an average. The same figure can be low on a big river and high on a small torrent.

Does the measuring station match my run?

Not always. The station may be upstream or downstream of your section, and a tributary can add water in between. Check the station's position relative to the stretch and rely on the markers that local clubs have calibrated to that specific station.

Is the water's colour a reliable indicator?

It's a useful additional signal, not a measurement. Water turning brown and silt-laden, along with an unusual roar, often indicates a rise in progress after rain upstream. Always check the flow figure and the trend before deciding.

Water level & flow: is the river runnable?

Flow and level: what we're talking about

Two different quantities describe a river's water. The flow is the volume passing through, expressed in cubic metres per second (m³/s); it's the most objective measure of the river's power. The level (or gauge height) is the depth of water read at a given station, in metres or centimetres; it's specific to each station and can't be compared from one river to another.

Every section has an "ideal" range between a minimum (below which it doesn't go, you drag) and a maximum (above which it's too strong and dangerous). Guidebooks and local clubs often list these markers for a specific run: it's this bracket, more than the raw figure, that tells you whether the trip is on.

How to read the figures

A figure on its own means nothing until you put it in context. Three reading reflexes:

Compare it to the section's bracket, not to an average: 15 m³/s can be "low" on a big river and "high" on a small torrent.
Look at the trend, not just the current instant: a curve rising fast is a warning sign, even if the current figure is still fine.
Mind the station/run offset: the station may be upstream or downstream of your section, and a tributary can add water in between.

On the same river, the difference between "perfect" and "do not put in" can come down to a few dozen centimetres on the gauge.

Where to check flow and level

Several sources give the flow and level in near real time:

RiverApp — an app that aggregates stations and shows levels by river, with runnability markers.
eauxvives.org — a French-speaking community with level markers by run and feedback from paddlers.
Official hydrological stations — public gauge-height and flow data, often available online and continuously updated.
Staff gauges — the graduated scales painted on bridge piers or riverbanks, read directly on site before you go.

Ideally cross-check two sources: an official figure for the value, and feedback from a club or paddler for the local interpretation. BeachFinder lists whitewater spots and, when the data exists, shows condition markers to complement these sources.

Too low or too high: the two traps

A level that's too low makes the descent a chore: you scrape the bottom, catch the rocks, get stuck on ledges and sometimes have to carry the boat. It's usually not dangerous, but it's unpleasant, slow and hard on the gear (hulls, raft floors).

A level that's too high is the real risk. Here's what changes when the river swells:

Far more powerful current — less time to manoeuvre, hard to break out of the flow.
Holding hydraulics — normally harmless stoppers become capable of holding a boat or a swimmer.
Drowned obstacles — rocks and ledges disappear under the surface and form invisible hydraulics.
Driftwood and log jams — branches and trees swept along, sometimes right across the current.
Vanished eddies — fewer calm spots to stop and regroup.

In flood, you don't put in, even on a normally easy section.

The effect of weather and season

A river's level isn't fixed: it climbs fast after heavy rain and during the spring snowmelt. A river that's calm in the morning can turn dangerous in the afternoon after a storm upstream, even while the sky is blue above you.

The behaviour depends a lot on the catchment:

Small mountain catchments — react within hours to a storm; sudden rise, rapid fall.
Alpine meltwater rivers — in spring, the flow follows the day/night cycle: stronger in the late afternoon once the snow has melted all day.
Large catchments — slower to react, but a flood can last longer.

Deciding before you put in

The level check is done just before the trip, not the day before. Systematic reflexes:

Check the weather over the whole catchment, not just the put-in point.
Beware of storms upstream even if the sky is clear where you are.
In spring, factor in the snowmelt that swells mountain rivers, especially in warm weather.
Look at the trend (rising / falling), not just the current figure.
When in doubt about a rising level, call it off: the river will still be there tomorrow.

One last useful marker: colour and sound. Water turning muddy (brown) and an unusual roar often signal a rise in progress.

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Water level and flow: how do you know if a river is runnable?