What the waterfall flow reading means

The five words

Each named waterfall page says one of five things. In spate, Flowing strongly, Flowing well, Modest flow, or Likely low. There is no verdict on a waterfall page, and there never will be.

The words come from how much rain has fallen near that waterfall in the last 48 hours, plus what is forecast for the next 24. Nothing else goes into it.

Nobody measures this

There is no gauge at a waterfall. The Environment Agency runs river level stations, but they are on rivers, at bridges and abstraction points, and almost none of them are at the falls people visit.

So there is no official flow scale for a waterfall to be right about. The five words are this site's own rule of thumb, worked from a rainfall model, and they are said in plain words rather than borrowed from a scale that means something else. The rainfall itself is modelled rather than measured, on a grid several kilometres across.

A catchment can also behave unlike its rainfall. A waterfall fed by a large upland catchment holds its flow for days after the rain stops; one fed by a small steep one can be spectacular for an afternoon and gone by morning. Snow melting changes it again, and the figure this site reads counts snowfall as precipitation, so a cold week can read as rain that never ran.

In spate is not a good day out

In spate is at the top of the list because a waterfall is at its most impressive on exactly the day it is most dangerous, and that is worth saying rather than leaving somebody to discover.

Water in spate is fast, cold, full of debris, and the rock beside it is wet. The pool under a fall in spate can hold a recirculating current that is very hard to swim out of. People drown at waterfalls in this country most years, and heavy rain is when it happens.

Two of the five words are a reason to go and look. One of them is a reason to stand well back.

Nobody tests the water either

Bathing water sampling covers designated bathing waters. Almost no waterfall is one. So there is no classification, no daily pollution forecast, and no sample behind any waterfall page on this site.

That does not mean the water is clean. Upstream farmland, septic tanks and storm overflows all discharge into rivers that end up going over waterfalls, and nobody is checking what is in the water at the bottom of one. An empty space where a verdict would be is not an all clear — it is nobody looking.

Where the waterfalls came from

The register is built from OpenStreetMap, which is why it covers 2,521 waterfalls across Britain and Ireland rather than the handful a guidebook would list. 645 of them carry a name, and those are the ones with their own page.

It also means the list is only as good as what people have mapped. A waterfall nobody has added is not here, a name may be local or contested, and a few will be barely a trickle over a step in a stream. Corrections are welcome.