Rance water levels: heights and lock times
Updated on 30 July 2026
Upstream of the dam, the maritime Rance does not follow the tide tables: its level depends on the turbining and sluicing of the tidal power station, which fill and empty the estuary to EDF’s generation schedule. The curves and tables below reproduce the official EDF forecast measured at the Saint-Suliac tide gauge — the reference for the boaters, shore fishers and residents of the Rance valley, to be read with its margin of uncertainty (± 30 cm) and its revisable-at-any-time status. In the immediate surroundings of the dam, the currents are violent and a zone is strictly closed to boats and swimmers alike.
Rance water levels: the EDF forecast
Water level of the maritime Rance (upstream of the dam), driven by the tidal power plant — not by the tide tables.
Hover over the curve to read the water height hour by hour.
| Time | Height | |
|---|---|---|
| Low | 5:45 | 6.0 m |
| High | 11:00 | 11.2 m |
| Low | 18:15 | 6.0 m |
Estuary range today: 5.2 m.
Hover over the curve to read the water height hour by hour.
| Time | Height | |
|---|---|---|
| Low | 6:15 | 6.2 m |
| High | 11:30 | 11.4 m |
| Low | 18:30 | 6.4 m |
Estuary range today: 5.6 m.
| Day | Estuary level (m CD) |
|---|---|
| 30 July 2026 | 6.0 to 11.2 m |
| 31 July 2026 | 6.1 to 11.7 m |
| 1 August 2026 | 6.4 to 12.1 m |
| 2 August 2026 | 6.7 to 12.2 m |
| 3 August 2026 | 6.7 to 12.1 m |
| 4 August 2026 | 6.5 to 11.9 m |
| 5 August 2026 | 6.6 to 11.6 m |
| 6 August 2026 | 6.5 to 11.2 m |
| 7 August 2026 | 6.0 to 10.8 m |
| 8 August 2026 | 6.4 to 10.5 m |
| 9 August 2026 | 6.3 to 10.7 m |
| 10 August 2026 | 6.3 to 11.3 m |
| 11 August 2026 | 6.4 to 11.9 m |
| 12 August 2026 | 6.2 to 11.9 m |
| 13 August 2026 | 6.1 to 12.1 m |
| 14 August 2026 | 6.2 to 12.2 m |
| 15 August 2026 | 6.2 to 12.2 m |
| 16 August 2026 | 6.2 to 12.2 m |
Lock openings at the dam
| Day | Lock on the hour | On request | Uncertain |
|---|---|---|---|
| 30 July 2026 | 0:00, 1:00, 5:00, 6:00, 7:00, 8:00, 9:00, 10:00, 11:00, 12:00, 13:00, 18:00, 19:00, 20:00, 21:00, 22:00, 23:00 | — | 17:00 |
| 31 July 2026 | 0:00, 1:00, 6:00, 7:00, 8:00, 9:00, 10:00, 11:00, 12:00, 13:00, 18:00, 19:00, 20:00, 21:00, 22:00, 23:00 | — | 14:00 |
| 1 August 2026 | 0:00, 1:00, 2:00, 7:00, 8:00, 9:00, 10:00, 11:00, 12:00, 13:00, 14:00, 19:00, 20:00, 21:00, 22:00, 23:00 | — | — |
| 2 August 2026 | 0:00, 1:00, 2:00, 7:00, 8:00, 9:00, 10:00, 11:00, 12:00, 13:00, 14:00, 19:00, 20:00, 21:00, 22:00, 23:00 | — | 15:00 |
| 3 August 2026 | 0:00, 1:00, 2:00, 3:00, 8:00, 9:00, 10:00, 11:00, 12:00, 13:00, 14:00, 15:00, 20:00, 21:00, 22:00, 23:00 | — | — |
| 4 August 2026 | 0:00, 1:00, 2:00, 3:00, 8:00, 9:00, 10:00, 11:00, 12:00, 13:00, 14:00, 15:00, 16:00, 20:00, 21:00, 22:00, 23:00 | — | 4:00 |
| 5 August 2026 | 0:00, 1:00, 2:00, 3:00, 4:00, 9:00, 10:00, 11:00, 12:00, 13:00, 14:00, 15:00, 16:00, 17:00, 21:00, 22:00, 23:00 | — | — |
Lock on request from 8:30 pm to 4:30 am, with 30 minutes’ notice to the lock keeper. “Uncertain” lock: sea level close to 4 m above chart datum — the lock keeper confirms passage (VHF 13).
EDF operating forecast at the Saint-Suliac tide gauge, in metres above chart datum (± 30 cm, excluding storm surge effects). These values are indicative and can change at any time: only the official EDF page is authoritative. EDF forecast updated on 23 July 2026. Retrieved by this site on 30 July 2026.
Written and kept up to date by a Saint-Malo local in love with this coast. The story behind this guide
Why doesn't the Rance level follow the tide tables?
Because between the dam and the Châtelier lock, the tidal power station drives the water level: turbining and sluicing fill and empty the estuary to EDF's generation schedule. The range is reduced, the times are shifted, and the water can rise earlier and faster than the tide tables would suggest.
Where do the water heights shown here come from?
From the operating forecast published by EDF: forecast levels at the Saint-Suliac tide gauge, in metres above chart datum, with an uncertainty of about ± 30 cm excluding atmospheric pressure effects. This site reproduces them as published, with their update date — only the official EDF page is authoritative.
How do I read the lock table?
The dam's lock operates on the hour whenever the sea level reaches 4 m above chart datum; from 8:30 pm to 4:30 am it opens on request only, with 30 minutes' notice to the lock keeper. An "uncertain" slot means the level is close to the 4 m mark: the keeper confirms passage on VHF 13. Passenger vessels always have priority.
How often is this data updated?
EDF refreshes its forecast weekly — on Thursdays in practice — and can change it at any time (technical issues, prefectoral orders, rescue operations). This site fetches it twice a day; if fetching fails for more than 24 hours, the page shows "unavailable" rather than stale values.
Can you sail or swim near the dam?
No: on both sides of the dam, a zone marked by red buoys is closed to boats, swimmers and all water sports — the sluice gates can open at any moment and create currents that pull towards the structure. The Rosais and Fours-à-Chaux beaches are inside the zone. Check the area on our map before heading out.