River Rhondda

The River Rhondda (Welsh: Afon Rhondda) is a river in the Rhondda Valley, South Wales which has two major tributaries; the Rhondda Fawr (English: Large Rhondda) and the Rhondda Fach (English: Little Rhondda).

The river has two major tributaries: the Rhondda Fawr and the Rhondda Fach (respectively, the "big" and "little" Rhondda). Despite these names, both tributaries are of similar length. Both valleys display the U-shape cross-sections typical of glaciated valleys, having been eroded during successive ice ages. They cut deeply into the thick South Wales Coal measures which comprise sandstones and mudstones and coal seams of Carboniferous age. The whole form of the river and its surrounding urbanisation has been dominated by coal mining and the communities that grew up to exploit the rich coal seams. Much of the valley has suffered severe subsidence because of the removal of coal from beneath the valley floor. The houses and streets have subsided with the result that river levels are, in parts, higher than the surrounding houses. In order to contain the river and prevent flooding, walls have been built, sometimes across the ends of streets - these are known as The Rhondda walls.

The Rhondda Fawr has its source on the eastern side of Craig y Llyn south of Llyn Fawr in a spring called Ffynnon y Gwalciau at an elevation of about 544m OD. The main head stream, Nant Carn Moesen (or Nant Carfoesen) runs down a plateau slope for about a mile and drops steeply, joining with the Nant Garreg-lwyd and the Nant Melyn to form the Rhondda. The combined waters then continue descending sharply through a mountain gorge to the foot of Pen Pych. The river runs through Blaenrhondda where it is joined by the Nant y Gwair via a classic example of a hanging valley, and runs down the Rhondda Valley, (Welsh: Cwm Rhondda). The river then passes through a string of mining towns and villages including Treherbert, Treorchy, Pentre, Ton Pentre, Ystrad Rhondda, Llwynypia, Tonypandy, Dinas, Porth and Trehafod before finally reaching its confluence with the River Taff at Pontypridd.

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