Afon Ystwyth, from Source to Cardigan Bay

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Towns and villages along the Ystwyth

Cwmystwyth	Pont-Rhyd-y-Groes	Llanilar	Llanfarian	Rhydyfelin
8km	14km	28km	34km	36km	from the source
200m	140m	30m	10m	10m	above MSL

The upland section of the Ystwyth is very remote country, and the first settlement of any size is Cwmystwyth (200m above MSL) at 8km from the source, followed by Pont-rhyd-y-groes (140m) at 14km. Llanilar (30m) is reached after 28km. Llanfarian at 34km and Rhydyfelin at 36km are on the southern outskirts of Aberystwyth, and the river is approaching its tidal limit at about 37km. The town of Aberystwyth itself isn't actually directly on the river.

Geology

Map: Site of the capture of the Teifi by the Ystwyth. The north-south section of the river at Pont-Rhyd-y-Groes follows the original river bed of the then Teifi. The abandoned valley runs southward to the west of Ysbyty Ystwyth. The rock formations along the entire length of the Ystwyth, along with most of the Cambrian Mountains, are Silurian (~430Ma old), despite the name of the hill range. The rivers in the area have swapped beds several times due to glacial activity. The upper Rheidol once was the origin of the Teifi, but was tapped into by the Ystwyth due to glacial erosion at the then head of the Ystwyth valley near Pont-rhyd-y-Groes. Later, the same process happened to the Ystwyth when the Rheidol captured the headwaters of the Ystwyth due to erosion at the Rheidol's head at the time, near Pontarfynach[1]. Both captures resulted in a shorter distance from the source of the Teifi-Ystwyth-Rheidol on Pumlumon to the sea, causing the formation of the Ystwyth and, later, Rheidol gorges due to faster flowing water. The original valleys of the Ystwyth and Rheidol, i.e. today's lowland sections, run along geological fault lines, and the capture points are the points where the fault lines intersect with the original Teifi valley, which can still be seen as a high-level valley (cf. thumbnails) running north to south from Pontarfynach (Rheidol) via Pont-Rhyd-y-Groes (Ystwyth) to Pontrhydfendigaid (Teifi). Fig.:Schematic showing the successive captures of the Teifi (red) by the Ystwyth (blue) and of the Ystwyth by the Rheidol (green). Grey lines indicate abandoned valleys. (after [2]).

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Further downstream, just below (west of) the Ystwyth gorge, the valley opens up and the river meanders among sandy deposits. The exact position of the river moves over time, and it splits into several arms with small islands between them ('braiding'). The ground in this section is polluted due to former lead mining activity, and the resulting lack of vegetation contributes to the continual erosion and change of the channel patterns[3] on a timescale of just months.

Land use in the area

	The source of the Ystwyth is the upland bog of Gors Lwyd. This and the first few kilometres of the head of the valley are used only for rough grazing, if at all.
	At Esgair-wen, where the Nant Troed-y-Rhiw meets the Ystwyth, a small area of level ground has formed between the steep hillsides, which is used for enclosed grazing.
	Below the upland farms, the steep-sided valley is dominated by disused lead mines. Pollution resulting from the mining activity results in very little vegetation growing in this area.
	The valley widens sufficiently at Cwmystwyth to allow farming on enclosed grazing land.
	The Ystwyth gorge between Cwmystwyth and Blaen-y-Ddol is mostly covered in Forestry Commission operated woodland. Much of this area is part of the old Hafod estate and is operated as an accessible outdoor recreation area with waymarked walks at present. The village of Pont-Rhyd-y-Groes is perched on the left bank of the river, above the gorge.
	Below Blaen-y-Ddol, where the valley widens again, past use has been for more lead mining, although the environmental implications are less obvious than further up the valley.
	The coastal plain is reached at Pont Llanafan, from where agricultural use (mostly enclosed sheep and cattle farming) dominates. Trawsgoed farm, on the right bank, and some ancillary enterprises are run by the Institute of Grassland and Environmental Research, now part of Aberystwyth University.
	The section of the river to the east of Llanilar has been straightened when the Caerfyrddin/Carmarthen to Aberystwyth railway line was built in 1867 (closed since 1964). The railway alignment is now used as part of the National Cycle Route network.
	West of Rhydyfelin, the river emerges into what once was a broad tidal estuary, although the land has been reclaimed during the 18th century, when the river mouth was diverted to meet the Afon Rheidol at the seaward end of Aberystwyth harbour. This was achieved by placing large boulders (now making up Tan-y-Bwlch beach) across the estuary and digging a trench through a rocky bar at the foot of Dinas hill.

References

[1] G Higgs, Afon Teifi at Cors Caron, Cardiganshire; in KJ Gregory, A Werritty (Eds.), Fluvial Geomorphology of Great Britain; London: Chapman & Hall, 1997, p.163ff.
[2] GM Howe, P Thomas; Welsh Landforms and Scenery; London: Macmillan, 1963
[3] G Higgs, Afon Ystwyth, Cardiganshire; in KJ Gregory, A Werritty (Eds.), Fluvial Geomorphology of Great Britain; London: Chapman & Hall, 1997, p.148ff.

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