Blaen-Y-Cwm Terrace Storm Overflow
Storm overflow run by Dwr Cymru Welsh Water, discharging into Nant Ystradffernol.
"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 Tynewydd River Station (Rhondda Fawr), 660 m 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
46 discharge periods since 15 Feb 2020. 46 of them come from Dwr Cymru Welsh Water's own event-duration-monitoring records (published by the company, Feb 2020 – Dec 2025); the live feed adds anything after that. The official annual count is the figure to quote.
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Tue 9 Dec 2025, 11:1515 min
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Fri 13 Jun 2025, 23:4530 min
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Mon 12 May 2025, 12:3015 min
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Thu 25 Jan 2024, 20:452 h 45 min
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Sun 21 Jan 2024, 21:4515 min
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Wed 27 Dec 2023, 07:0015 min
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Sun 19 Nov 2023, 10:4515 min
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Fri 13 Oct 2023, 03:3015 min
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Wed 20 Sep 2023, 11:1515 min
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Wed 20 Sep 2023, 09:1545 min
Show 30 earlier (of 46)
| Started (UK time) | Ended | Discharge time |
|---|---|---|
| 13 Mar 2023, 01:15 | 01:30 | 15 min |
| 11 Jan 2023, 23:45 | 00:00 | 15 min |
| 7 Jan 2023, 04:15 | 05:45 | 1 h 15 min |
| 4 Jan 2023, 02:15 | 02:30 | 15 min |
| 4 Jan 2023, 01:00 | 01:15 | 15 min |
| 3 Jan 2023, 17:00 | 17:15 | 15 min |
| 28 Dec 2022, 14:00 | 14:15 | 15 min |
| 28 Dec 2022, 10:30 | 11:45 | 45 min |
| 18 Dec 2022, 22:15 | 22:30 | 15 min |
| 23 Nov 2022, 06:00 | 06:15 | 15 min |
| 21 Nov 2022, 13:30 | 13:45 | 15 min |
| 25 Oct 2022, 00:30 | 01:15 | 30 min |
| 10 Mar 2022, 06:15 | 06:30 | 15 min |
| 20 Feb 2022, 12:15 | 12:45 | 30 min |
| 20 Feb 2022, 11:00 | 11:15 | 15 min |
| 28 Oct 2021, 20:00 | 20:15 | 15 min |
| 27 Sep 2021, 04:45 | 05:00 | 15 min |
| 4 Jul 2021, 07:45 | 08:00 | 15 min |
| 9 May 2021, 02:45 | 03:00 | 15 min |
| 9 May 2021, 01:15 | 01:30 | 15 min |
| 8 May 2021, 22:30 | 23:15 | 30 min |
| 8 May 2021, 21:45 | 22:00 | 15 min |
| 8 May 2021, 20:30 | 21:15 | 30 min |
| 8 May 2021, 19:30 | 19:45 | 15 min |
| 27 Mar 2021, 14:15 | 14:30 | 15 min |
| 20 Feb 2021, 01:00 | 01:15 | 15 min |
| 19 Feb 2021, 19:30 | 22:15 | 2 h 15 min |
| 20 Jan 2021, 13:00 | 13:15 | 15 min |
| 18 Dec 2020, 20:15 | 20:30 | 15 min |
| 18 Dec 2020, 19:30 | 19:45 | 15 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 62 raw blocks were merged into 46 continuous discharge periods (gaps under 15 min joined).
Rain nearby last 30 days
Nearest live rain gauge: Tyn Y Waun Treherbert Raingauge, 0.2 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.