Home › Rivers › River Avan (Afon Afan) › Nant Cwm-clais

Nant Cwm-clais

A stream near Cwmafan, Neath Port Talbot. No gauge of its own: what the river map and the banked data say about it.

Nant Cwm-clais is a stream on Ordnance Survey’s river map near Cwmafan, Neath Port Talbot, with about 1.9 km of mapped channel. On the map it flows into the River Avan (Afon Afan) and out to the sea.

Next gauge downstream

Marcroft Weir River Station on the River Avan (Afon Afan), about 160 m along the river below where Nant Cwm-clais ends on the map.

0.59 m Normal · easing 32 min ago

After that, Greenpark Weir, about 2.2 km along the river.

No gauge measures Nant Cwm-clais 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 Cwm-clais

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

Cwmavon Road Cwmafan Storm Overflow Not discharging
Dwr Cymru Welsh Water · into Nant Cwm - Clais · 2025: 85 spills, 480 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: Cwmafan, Caerhendy, Corlannau, Lletyharri, Velindre.

On the map

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

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

The River Avan (Afon Afan), 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 Cwm-clais 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.