The tallest waterfalls in Wales

Which bit is supposed to be measured?

This is not an official list (though it is substantially better than any other lists I have encountered). I do not expect this list to be 100% complete, since I may have missed the odd waterfall. Add to that the fact that most waterfalls have no information available at all, and it becomes quite hard to produce this list. In many cases, careful reading of high scale maps is the only option. If you can offer any details, please get in touch.

Tallest single drop

This lists waterfalls with a single drop of 20 metres or more, and gives the heights of the drops that are tall enough.

To qualify for the list of single drops, a waterfall must fall continuously from top to bottom. While it is allowed to make contact with the bedrock, in cases such as a horsetail fall, cascade, or a nearly-vertical plunge, it must not have any sections that are that are gentle enough to be classed as a stream, river or plunge pool separating parts of that fall into separate distinct falls. It is not always easy obtaining this information for waterfalls, as people sometimes only give total height (or in some cases, nothing at all), in an attempt to make the waterfall seem as tall as possible. This is definitely the case for Pistyll Rhaeadr, for example, for which the only reliable information is the total height, when the waterfall is in three very distinct sections.

Tallest total height

This lists waterfalls with a total height of 40 metres or more (chosen because there are too many waterfalls requiring estimates below that height), and gives their heights.

To qualify for the list of total heights, the sections of the waterfall must fall without significant sections of stream or river between drops. Plunge pools and intermediate cascades are allowed. It can be difficult to decide where to draw the line. Small streams that tumble down mountain scarps in a series of repeated, broken cascades are intentionally discounted, not because they do not deserve recognition, but because there are simply too many of them to discover, and it is too difficult to obtain accurate information for them. If you are looking for these, the tallest I know are the streams in Cwm Idwal, with a few being about 200 metres tall, and one to the southeast of the Devil's Kitchen having 300 metres of height dropped in a series of cascades. There are also some small streams that drop very steeply for over 600 metres down the southwest slopes of Glyder Fawr. Examples in Mid Wales would include Rhaeadr Du and Rhaeadr Wen at Tarren Bwlch Gwyn near Aberhosan, both about 250 metres high, but never breaking into proper waterfalls.

Other records

In terms of highest altitude, the tops of Devil's Appendix and Devil's Kitchen both sit at around 780 metres above sea level, significantly higher than any other waterfalls in my lists. There may be tiny waterfalls (none big or significant enough to make it onto my lists) at higher altitudes. A stream above the Devil's Kitchen seems to fall down a small crag at 810 metres altitude. Two streams on Garnedd Ugain may fall down higher crags, with one on Clogwyn y Person at 900 metres altitude, and one in Cwm Glas just below the Crib y Ddysgl summit in the Parsley-Fern Gully at 950 metres altitude. Although the Afon Eigiau starts at 990 metres on the crags of Carnedd Llewelyn, it doesn't appear to create any waterfalls.

In terms of highest average flow, the details are nearly impossible to obtain, since detailed measurements are not taken at each waterfall. Reservoirs, hydroelectric generators, water abstractions, and fish passes can all randomly affect the results at several waterfalls, so these numbers may be artificially influenced to a significant degree. However, the average flow at Cenarth Falls just scrapes into the top spot with 29 m3/s (taken a little downstream just after the junction with another stream, so the flow at the waterfall might be 25-27 m3/s), and a maximum flow of 456 m3/s. An average of a little under 27 m3/s passes over the canoeing rapids at Llangollen (and an estimated maximum of about 550 m3/s), but these are not a proper waterfall (around half of the flow will have passed over a small waterfall upstream). As with Cenarth Falls, the highest average flows belong to very short waterfalls that may appear as little more than a rapid.

In terms of highest peak flow, the maximum flow over Mill Falls and Spuhler's Foly/Pwll yr Hesg was recorded as 775 m3/s (Spuhler's Foly/Pwll yr Hesg gets an additional unknown quantity of water from a tributary river, so would have been slightly higher) during a flood in 1980. However, subsequent data revisions now give a maximum of 633 m3/s during a flood in 1998. The waterfalls would have been completely invisible, submerged under floodwater. The Conwy experienced a maximum flow of 550 m3/s, but this is spread over three major rivers, so only about half of the flow will have passed over a waterfall. (The Severn, Tywi, Usk and Wye have all experienced flows of around 1000 m3/s or above at their mouths, but these flows do not pass over waterfalls.)