Jean-Luc Demaret G
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Official reference · SPW
Navigable kayak flow rates in Wallonia: the official threshold table
Minimum and maximum flow rates authorised for kayaking and canoeing on every river of the Ardennes, measured at the hydrometric stations of the Public Service of Wallonia. A single reference to prepare your descent safely.
Before every kayak descent, only one question really matters: is the river navigable today? The answer lies in one precise figure — the flow rate, expressed in cubic metres per second (m³/s) — and in two official thresholds: a minimum below which the water is too low, and a maximum above which the flood current becomes dangerous. Between the two, navigation is authorised.
These thresholds are scattered across Walloon regulations and technical appendices, which makes them hard to find. We have centralised them here, river by river, together with the corresponding SPW measuring station. The table below is generated directly from our hydrological data: it always reflects the values in force.
| River | SPW station | Minimum flow | Maximum flow | Profile | Live level |
|---|---|---|---|---|---|
| La Semois | SPW 9434 Membre | 2.2 m³/s | 50 m³/s | Class I — easy, family-friendly | See the live flow → |
| La Lesse | SPW 8221 Gendron | 1.5 m³/s | 52 m³/s | Class I-II — easy to moderate | See the live flow → |
| L'Ourthe | SPW 5921 Tabreux | 2.5 m³/s | 65 m³/s | Class I-II — moderate | See the live flow → |
| L'Amblève | SPW DGH/6621 | 2.5 m³/s | 44 m³/s | Class II-III — sporty (white water) | See the live flow → |
| Le Viroin | SPW 9021 Treignes | 1.6 m³/s | 23 m³/s | Class I-II — unspoilt nature | See the live flow → |
| Le Bocq | SPW 8133 Yvoir | 0.4 m³/s | 20 m³/s | Small watercourse — technical, narrow | See the live flow → |
⚠️ These values are reference thresholds. The actual flow is constantly changing: always check the live level on the very day of your outing. The Meuse (SPW 8078 Waulsort station), a river with very large flows, is the subject of dedicated monitoring distinct from these kayak thresholds.
How to read these thresholds?
The flow rate is not the water level (the height in metres): it is the volume of water passing the station every second. It is the most reliable indicator of navigability, because it combines both the depth and the speed of the current.
🪨
Below the minimum threshold
The water is too low: the rocky bed shows through, craft scrape and get damaged, and some passages become impassable. Navigation is prohibited to protect the riverbed and the craft.
🌊
Within the navigable range
Between the two thresholds, the current carries you along without jolting and the depth is sufficient. Conditions are generally most pleasant in the lower half of the range: clear water, steady current.
⛔
Above the maximum threshold
The flood flow makes the current powerful and unpredictable, the water turns turbid and obstacles become invisible. Navigation is prohibited as a safety measure — often after heavy rain upstream.
Why these thresholds exist
The movement of non-motorised craft on Walloon watercourses is regulated by the Region, with a twofold aim: the safety of paddlers and the protection of natural habitats. Many stretches cross Natura 2000 areas and nature reserves where the wildlife (heron, kingfisher, otter, beaver) is sensitive to disturbance.
The thresholds reflect this logic: they prohibit navigation when the water is too low (harm to the bed and benthic fauna) just as when it is too high (danger to people). Between the two, they open a window where the activity is compatible with the river. Each river has its own values, because its morphology, its gradient and its catchment area differ: the Amblève, a class II-III white-water river, has nothing in common with the Semois, a peaceful, family-friendly class I river.
The role of the SPW stations
Each river in this table is linked to a hydrometric station of the Public Service of Wallonia (e.g. SPW 9434 at Membre for the Semois, SPW 6621 at Martinrive for the Amblève). These stations continuously measure water height and flow, and publish the data under an open licence. It is this raw, official data that we read to feed our real-time dashboards and to compute the navigation status, with no intermediary or interpretation.
Checking the flow in real time
A threshold table is no substitute for the measurement of the day. For each river we publish a real-time dashboard that reads the SPW station, compares the flow with the thresholds above and displays a clear verdict — navigation authorised or prohibited — refreshed every 15 minutes:
- La Semois flow live — navigable from 2.2 to 50 m³/s
- La Lesse flow live — navigable from 1.5 to 52 m³/s
- L'Ourthe flow live — navigable from 2.5 to 65 m³/s
- L'Amblève flow live — navigable from 2.5 to 44 m³/s
- Le Viroin flow live — navigable from 1.6 to 23 m³/s
- Le Bocq flow live — navigable from 0.4 to 20 m³/s
You can also download our open datasets (JSON/CSV) if you wish to reuse these measurements.
The detail river by river
Each river of the Ardennes has its own character, and therefore its own thresholds. Here is what these values mean, watercourse by watercourse.
The Semois — 2.2 to 50 m³/s
The flagship river of the valley, the Semois is the most family-friendly (class I). Its shallow depth (40 to 80 cm over much of the routes) and its gentle current explain a wide navigable range: from 2.2 m³/s the water is enough to float from Alle-sur-Semois or Poupehan, up to 50 m³/s beyond which the floods of the National Park close navigation. The data comes from the SPW 9434 station in Membre-sur-Semois.
The Lesse — 1.5 to 52 m³/s
Between Houyet and Dinant, the Lesse (class I-II) is one of the busiest descents in Belgium. More deeply set than the Semois, it accepts a high maximum flow (52 m³/s) while remaining navigable from 1.5 m³/s. Reference station: SPW 8221 at Gendron. Above the upper threshold, the Lesse rapids become technical and navigation is suspended.
The Ourthe — 2.5 to 65 m³/s
Wider and more powerful, the Ourthe (class I-II) winds around Durbuy and La Roche-en-Ardenne. Its large catchment area gives it the highest maximum flow of our kayak rivers (65 m³/s). It remains navigable from 2.5 m³/s, measured at the SPW 5921 station in Tabreux.
The Amblève — 2.5 to 44 m³/s
The most sporty: the Amblève (class II-III) offers genuine white water, notably around Coo and in the Stavelot gorges. Its navigable range is tighter at the top (44 m³/s): beyond, the current becomes dangerous for leisure craft. Navigable from 2.5 m³/s, SPW 6621 station at Martinrive. A river not recommended for beginners and young children.
The Viroin — 1.6 to 23 m³/s
A small wild tributary of the Meuse, the Viroin (class I-II) flows through the Viroin-Hermeton Nature Park, a haven of unspoilt nature. Its modest size explains low thresholds: navigable from 1.6 to 23 m³/s only (SPW 9021 station at Treignes). A river to watch closely, as its level rises and falls quickly.
The Bocq — 0.4 to 20 m³/s
The Bocq, which joins the Meuse at Yvoir, is a small, narrow and technical watercourse. Its thresholds are the lowest of all (0.4 to 20 m³/s, SPW 8133 station at Yvoir): you need enough water to get through, but the slightest flood makes it impassable. Reserved for experienced paddlers.
When does the flow change?
A river's flow is never fixed: it responds to the rainfall over the whole catchment area, sometimes several days earlier and tens of kilometres upstream. After a storm, a river can double its flow in a few hours and cross its maximum threshold; conversely, during a dry summer, it can drop below its minimum threshold and become non-navigable, even in glorious sunshine.
This is why a threshold table, however precise, must always be cross-checked against the measurement of the day. The golden rule of the prudent paddler: check the live flow on the very morning of the outing, and give up without hesitation if the river is outside its navigable range. No descent is worth a risk taken against a flood.
Methodology & source
The thresholds presented here are aligned with the official data of the hydrometric network of the Public Service of Wallonia and the regional regulations governing traffic on the waterways. They are kept up to date in our hydrological engine and synchronised with our real-time dashboards — this table is generated from that same source, guaranteeing its consistency.
This work of centralisation and monitoring is carried out by Quentin Deligne, creator of the platform's real-time hydrological forecasting algorithm and a specialist in navigation in the Belgian Ardennes. In the event of any discrepancy with an official communication from the Region, it is always the SPW data and decrees that prevail.
A final word on the freshness of the data. The thresholds in the table above are not copied by hand: they are read live from the configuration of our hydrological engine, the same one that powers the real-time dashboards. Any update to a threshold — for example following a regulatory revision or a station recalibration — is therefore reflected instantly and everywhere, with no risk of inconsistency between this reference page and the live measurement pages. We also publish all of these measurements as open data (JSON and CSV formats), freely reusable by paddlers, clubs, researchers or developers who wish to build their own tools for monitoring navigability in Wallonia.
Frequently asked questions about navigability
What is a navigable flow rate?
The navigable flow rate is the flow range (in m³/s) within which kayak or canoe navigation is authorised and safe. Below the minimum threshold the water is too low (exposed rocky bed); above the maximum the flood flow makes navigation dangerous and prohibited.
Who sets the navigability thresholds in Wallonia?
The thresholds are based on data from the hydrometric network of the Public Service of Wallonia (SPW) and the regional regulations governing traffic on watercourses. Each river has an official measuring station that publishes the flow in real time.
What is the navigable flow rate of the Semois?
The Semois is navigable between 2.2 and 50 m³/s, measured at the SPW 9434 station in Membre-sur-Semois.
What is the navigable flow rate of the Amblève?
The Amblève, a more technical white-water river, is navigable between 2.5 and 44 m³/s (SPW 6621 Martinrive station). Beyond that, the flow becomes dangerous.
Where can I check the flow in real time before setting off?
Each river has a real-time dashboard on our site, which reads the corresponding SPW station and indicates whether navigation is authorised or prohibited, updated every 15 minutes.
What happens after heavy rain?
After heavy rainfall the flow rises quickly and can exceed the maximum threshold: navigation is then prohibited for safety. You must always check the live flow on the day itself, and not rely on the previous day's figures.
Are these thresholds the same for kayak and canoe?
Yes, the navigability thresholds apply to non-motorised craft (kayak, canoe). The perceived difficulty nonetheless varies according to the craft, the paddler's experience and the river's class (I to III).
Why is navigation sometimes prohibited even in fine weather?
A river's level depends on the rain that has fallen upstream, sometimes several days earlier and tens of kilometres away. A river can therefore be in flood under a blue sky. Only the flow measured at the station is authoritative.
Ready to paddle safely?
Check the flow of the day, then book your descent on the river at the right level.
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