Geograph - photograph every grid square

This square includes a classic section of the Nedd Fechan gorge, hiding its three finest waterfalls. Uppermost ie the furthest upstream is Sgwd Ddwli (named as Scwd Ddwli by Ordnance Survey) and often referred to as Sgwd Ddwli Uchaf to distinguish it from a further set of falls a few hundred yards downstream referred to as Sgwd Ddwli Isaf. Sgwd Ddwli is usually translated as ‘gushing falls’, with ‘uchaf’ and ‘isaf’, signifying ‘upper’ and ‘lower’ respectively. The third set of falls is that at Sgwd y Bedol, translated as ‘horseshoe falls’ on account of the shape of the uppermost of three distinct drops. Two further falls are indicated on the Ordnance Survey 25,000 scale mapping downstream of these but neither is given a name and indeed they are less spectacular than the named falls. The lower of the two is in an inaccessible part of the gorge and can only be glimpsed from high above through the tree canopy.

Sgwd Ddwli (Uchaf) is found at SN 9056 0991 - it lies at the left hand side (when looking downstream) of a large area of eastwards sloping slabs of gritstone. This is the top surface of the Twrch Sandstone (a.k.a Basal Grit) A now dry and vegetated embayment to the west of the present-day falls represents the site of the falls in the past; they have effectively migrated eastwards down the ‘dip’ of the rock, in similar fashion to the down-dip migration of Sgwd Gwladus in the nearby square SN 8909.

Sgwd Ddwli Isaf at SN 9040 0979 is of quite a different character to its upstream sibling, confined as it is to a relatively narrow slot in the Twrch Sandstone bedrock. An extensive gently sloping rock platform downstream of this fall extends all the way to Sgwd y Bedol with the river flowing down its eastern edge. The fossils of roots of the Carboniferous plant Lepidodendron can be made out in places in the smoothed rock surface. Beware though – this surface is treacherously slippery!

Sgwd y Bedol interrupts the flow of the Nedd Fechan at the point where the right-bank tributary Nant y Llechau enters at SN 9026 0970. The name of this stream is almost certainly a reference to the slabs (‘llechau’) referred to above. It has carved out a gully in the valley side along a line of weakness caused by a couple of geological faults, the same faults which can be seen forming features stretching across the river below the arcuate falls. The ‘down-throw’ on these faults is to the southwest.