Llansannan Storm Overflow
Storm overflow run by Dwr Cymru Welsh Water, discharging into River Aled.
"Not discharging" means the company's monitor reports no discharge right now — not that the water is clean. The feed publishes status only; no discharge volume is measured.
Year by year
Dŵr Cymru Welsh Water's annual Event Duration Monitoring return to Natural Resources Wales (12/24-hour spill count), as compiled by The Rivers Trust. 2026 is our own running count, the same way, from the live feed since 28 February (when we began keeping every discharge it reports) — so it can only be lower than the full year. The official figure is published next spring.
"No data" means the monitor was not working or not required to report that year — not zero.
Downstream of this overflow
The next gauge downstream that the river map places is Pont Y Gwyddel River Station (Elwy), 8.2 km along the river.
A river gauge measures the level of the river; it does not measure this overflow's discharge, and a spill does not by itself explain a change there. Traced on OS Open Rivers (edition 2026-04), which leaves out many small channels.
Contains OS data © Crown copyright and database rights 2026.
Discharges we have recorded
27 discharge periods since 9 Feb 2020. 27 of them come from Dwr Cymru Welsh Water's own event-duration-monitoring records (published by the company, Feb 2020 – Nov 2025); the live feed adds anything after that. The official annual count is the figure to quote.
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Fri 28 Nov 2025, 11:1515 min
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Fri 14 Nov 2025, 21:4515 min
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Fri 14 Nov 2025, 17:151 h 30 min
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Wed 12 Nov 2025, 15:4515 min
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Sun 20 Jul 2025, 23:1530 min
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Sun 20 Jul 2025, 21:4545 min
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Wed 1 Jan 2025, 04:0015 min
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Sat 7 Dec 2024, 10:301 h 30 min
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Sat 7 Dec 2024, 05:4515 min
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Sat 7 Dec 2024, 04:4515 min
Show 17 earlier
| Started (UK time) | Ended | Discharge time |
|---|---|---|
| 6 Nov 2024, 17:30 | 22:15 | 4 h 45 min |
| 2 Sep 2024, 07:45 | 08:30 | 30 min |
| 20 Jul 2024, 17:15 | 17:30 | 15 min |
| 9 Jul 2024, 18:45 | 19:00 | 15 min |
| 20 Oct 2023, 10:00 | 04:30 | 18 h 30 min |
| 20 Oct 2023, 08:30 | 09:15 | 30 min |
| 18 Jun 2023, 16:30 | 16:45 | 15 min |
| 11 Jun 2023, 15:15 | 15:30 | 15 min |
| 8 Sep 2022, 16:15 | 16:45 | 30 min |
| 30 Mar 2022, 10:15 | 10:30 | 15 min |
| 20 Feb 2022, 14:30 | 14:45 | 15 min |
| 20 Jan 2021, 14:15 | 14:45 | 30 min |
| 20 Jan 2021, 13:15 | 13:30 | 15 min |
| 10 Aug 2020, 23:15 | 23:30 | 15 min |
| 16 Feb 2020, 01:15 | 06:00 | 4 h 45 min |
| 9 Feb 2020, 12:45 | 13:00 | 15 min |
| 9 Feb 2020, 07:00 | 07:45 | 45 min |
The year figures above use the EA's 12/24-hour counting method, so they are comparable with the official figures; the monitor log's 34 raw blocks were merged into 27 continuous discharge periods (gaps under 15 min joined).
Rain nearby last 30 days
Nearest live rain gauge: Plas Pigot Raingauge, 2.1 km away. Brown shading = when this overflow was discharging; ▼ = a discharge start.
Overflow shading is a timing match, not proof of cause — heavy rain and spills share a trigger. Times come from the water company’s event-duration monitor (site status only; no discharge volume is published).
Where it is
Concerned about this overflow?
Report pollution you can see or smell to the regulator straight away; the company handles complaints about the overflow itself.
Live status: © Dŵr Cymru Welsh Water, from its Storm Overflow Map. Spill-event history: © Dŵr Cymru Welsh Water's published EDM start/stop records. Annual figures: The Rivers Trust EDM compilation, © Dŵr Cymru/Welsh Water, Open Government Licence. Times are shown in UK local time. FloodRadar republishes the monitor's status; it does not measure discharges itself.