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Nant y Derlwyn

A stream near Llwydcoed, Rhondda Cynon Taf. No gauge of its own: what the river map and the banked data say about it.

Nant y Derlwyn is a stream on Ordnance Survey’s river map near Llwydcoed, Rhondda Cynon Taf, with about 2.3 km of mapped channel. On the map it flows into Afon Cynon, which flows on into the River Taff (Afon Taf) and out to the sea.

Next gauge downstream

Aberdare River Station on Afon Cynon, about 2.2 km along the river below where Nant y Derlwyn ends on the map.

0.19 m Normal · steady 16 min ago

After that, Mountain Ash River Station, about 8.4 km along the river.

No gauge measures Nant y Derlwyn itself. A gauge downstream shows water that has already passed it, mixed with everything else that has joined on the way, so it says nothing exact about this stream.

Storm overflows on Nant y Derlwyn

2 storm overflows are placed on this stream on the river map. Each status is the water company’s own monitor.

Trecynon Harriet Street Storm Overflow Not discharging
Dwr Cymru Welsh Water · into Nant-Y-Derlwyn · 2025: 0 spills, 0 h
Maes Y Ffion Storm Overflow Not discharging
Dwr Cymru Welsh Water · into Nant-Y-Derlwyn · 2025: 77 spills, 426 h

A status says whether an overflow is discharging now, never how much or why. A monitor that is offline or has not reported is not “not discharging”. Sewage in Britain’s rivers →

Live status: © Dŵr Cymru Welsh Water, from its Storm Overflow Map. Annual spill figures: Environment Agency Event Duration Monitoring return, © Environment Agency copyright and/or database right, Open Government Licence (OGL) v3.0.

Places along it

From its source towards its mouth, the settlements within a kilometre of it on the map: Llwydcoed, Trecynon.

On the map

The map needs JavaScript. Everything it shows is listed on this page.

The blue line is Nant y Derlwyn; grey lines are other mapped watercourses. Lines from OS Open Rivers (edition 2026-04).

Afon Cynon, the river it joins →All rivers with gauges →

What this page can and cannot tell you

Its line, its name and where it flows come from Ordnance Survey’s river map (OS Open Rivers, edition 2026-04), which leaves out many small streams, ditches and culverts. “Flows into” is the map’s word: a channel that is not on the map is not shown here, which does not mean it is not there.
No gauge measures Nant y Derlwyn itself, so its own level is not known here.
Storm overflows are listed only where the river map places them on this stream; an overflow it could not place is not counted.
No water-sampling point with a banked sample is placed on this stream. Only England’s samples are banked, and only where the map can place their sampling point.
Nothing on this page says whether any place floods. For an address, see its postcode page.