Trecynon Harriet Street Storm Overflow
Storm overflow run by Dwr Cymru Welsh Water, discharging into Nant-y-derlwyn.
"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.
Twin outlet
Dwr Cymru Welsh Water runs another overflow within 300 m that also discharges into Nant-y-derlwyn. They share the sewer and the storm, so one outlet's figures are only part of what reaches the water.
This overflow: 0 spills in 2025. Distances are between the published outlet points.
Downstream of this overflow
The next gauge downstream that the river map places is Aberdare River Station (Cynon), 2.2 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
9 discharge periods since 9 Mar 2020. 9 of them come from Dwr Cymru Welsh Water's own event-duration-monitoring records (published by the company, Mar 2020 – Dec 2024); the live feed adds anything after that. The official annual count is the figure to quote.
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Fri 6 Dec 2024, 18:1515 min
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Sun 27 Oct 2024, 04:3015 min
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Tue 10 Sep 2024, 15:3015 min
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Fri 29 Sep 2023, 00:0015 min
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Fri 19 Feb 2021, 10:3015 min
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Wed 20 Jan 2021, 00:1515 min
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Sun 13 Dec 2020, 20:1515 min
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Sat 21 Nov 2020, 16:3015 min
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Mon 9 Mar 2020, 18:4515 min
The year figures above use the EA's 12/24-hour counting method, so they are comparable with the official figures.
Rain nearby last 30 days
Nearest live rain gauge: Maerdy WTW Raingauge, 5.7 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.