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Nant Rhydian-ddu

A stream near Porthyrhyd, Carmarthenshire. No gauge of its own: what the river map and the banked data say about it.

Nant Rhydian-ddu is a stream on Ordnance Survey’s river map near Porthyrhyd, Carmarthenshire, with about 2.6 km of mapped channel. On the map it flows into Gwendraeth Fach, which flows on into Gwendraeth Fawr, then Afon Tywi (River Towy), then the River Taf (Afon Taf) and out to the sea.

Next gauge downstream

Llangendeirne River Station on Gwendraeth Fach, about 7.5 km along the river below where Nant Rhydian-ddu ends on the map.

0.50 m Normal · easing 16 min ago

No gauge measures Nant Rhydian-ddu 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 Rhydian-ddu

1 storm overflow is placed on this stream on the river map. Each status is the water company’s own monitor.

Porthyrhyd Storm Overflow Not discharging
Dwr Cymru Welsh Water · into Nant Rhydian Ddu · 2025: 94 spills, 1,336 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: Llanddarog, Porthyrhyd.

Place names: OS Open Names. Contains OS data © Crown copyright and database rights 2026.

On the map

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

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

Gwendraeth Fach, 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 Rhydian-ddu 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.