From NOT A LOT OF PEOPLE KNOW THAT

By Paul Homewood

 There has been some bad flooding in Monmouth, following Storm Claudia:

There has been minor flooding elsewhere, but I am not aware of anything else major.

Rainfall totals were not unusually excessive in South Wales, 71mm in Gwent, for instance, over the day and a half of the storm:

Across SW England & S Wales, an average of 22.09mm fell on Friday, which was when nearly all of the rain fell:

https://www.metoffice.gov.uk/hadobs/hadukp/data/daily/HadSWEP_daily_totals.txt

And it was plainly widespread across the whole of the Southwest, not just South Wales:

Yet 22mm in a day is not in the least bit unusual in the region:

KNMI data ends in 2022, but I have updated it to include Claudia, with the chart below showing all days over 20mm:

On average, it happens four times a year on average.

The highest daily rainfall occurred in July 1969. But the autumn storm in November 1931 is directly comparable with Claudia. On that day, 50.55 mm fell, more than double Friday’s rainfall.

The numbers themselves don’t tell the real story, which the Met Office Monthly Weather report at the time revealed:

Totals of 244mm at Trecastle make Claudia appear just another, run of the mill storm, which of course it was.

Rainfall was almost as bad in 3rd December 1960:

7 inches is 178mm and 5.5 inches in the Rhondda in just 20 hours works out at 140mm.

Floods were widespread and serious in Glamorgan.

So why was flooding so bad in Monmouth this week?

Grok has the answer:

History of Flooding in Monmouth, Wales

Monmouth, located at the confluence of the Rivers Wye, Monnow, and Trothy in Monmouthshire, Wales, has a long history of flooding dating back centuries. The town’s position in a river valley makes it particularly vulnerable to riverine flooding from heavy rainfall, thunderstorms, and storms, often exacerbated by rapid snowmelt or overflow from tributaries like the Norton Brook. Historical records show events ranging from flash floods causing localized damage to widespread inundations affecting homes, businesses, and infrastructure. Below is a chronological summary of key flooding incidents in Monmouth before 2025, drawn from official reports and historical archives. This focuses on major events impacting the town itself, though Monmouthshire-wide context is noted where relevant.

9 June 1754
Severe hailstorm with stones up to six inches in diameter caused the River Monnow to overflow rapidly within an hour, depositing fish on streets.
Damage to crops, windows, and homes in Monmouth and nearby Colford; widespread property destruction.

21 November 1766
Violent thunderstorm led to the River Wye rising several feet higher than previously recorded near Monmouth.
Loss of lives and large quantities of goods; meadows and low-lying areas submerged.

20 June 1839
Intense thunderstorm caused the Rivers Wye and Monnow to overflow.
Premises near Wye Bridge inundated; Monnow Street flooded to several feet deep.

2 April 1848
Prolonged thunderstorm with heavy hail and rain (over 1 hour 20 minutes) overwhelmed drainage.
Many houses in central Monmouth flooded; streets turned into torrents.

31 May 1859
Heavy rains swelled the River Trothy, leading to overflow into Monmouth meadows.
Walls washed away in nearby Skenfrith; houses drenched and stones carried downstream in Rockfield.

22 July 1907
Thunderstorm with marble-sized hail turned streets into rushing rivers.
Significant flash flooding in town center; damage to gardens and minor structures (also severe in nearby Cwmyoy on River Monnow).

10 June 1912
Lightning storm during heavy rain implied widespread waterlogging.
One man killed by lightning; roads and low areas flooded.

27 May 1931
Rapid rise of the River Monnow due to thunderstorms across Monmouthshire.
Floodwaters reached bedrooms in houses; Drybridge Street submerged to several feet (boats used for rescues); cattle and sheep washed away in The Forge district; worst flood in living memory at nearby Skenfrith; racecourse and military huts affected.

April 1947
Nationwide flooding event triggered by heavy snowfall followed by rapid thaw; Rivers Trothy and Monnow overflowed into Monmouth.
Severe inundation in Drybridge Street (water to upper bedrooms, evacuations); widespread damage across town and upstream villages.

December 1979
Rivers Wye, Monnow, and Usk burst banks after prolonged heavy rain.
Significant property flooding in lower Monmouth and Mayhill areas; multiple locations affected along riverbanks.

October 1998
Storm-driven rise in River Wye levels.
Peak level of 17.19 m AOD; homes and roads in low-lying areas flooded.

October 2000
Autumn storms caused River Wye overflow.
Peak level of 17.59 m AOD; internal flooding in several properties.

December 2000
Two separate events from winter storms.
River Wye peaks at 17.58 m and 17.61 m AOD; over 50 residential properties reported flooded in Monmouth (including Blake Street and Wyesham).

February 2002
Multiple storms led to two floods.
River Wye peaks at 17.59 m and 17.67 m AOD (latter was previous record); extensive evacuations and damage in Mayhill and town center.

July 2005
Summer deluge overwhelmed rivers.
River Wye at 16.37 m AOD; localized flooding in meadows and streets.

January 2008
Winter storms caused moderate overflow.
River Wye at 16.42 m AOD; some properties affected in lower town.

Monmouth has always been particularly vulnerable to flooding, because it sits at the confluence of three rivers, the Wye, Monnow, and Trothy. Its history is littered with floods every bit as bad as this week’s.

It might seem a daft place to build a town, but the Normans built the castle and town specifically because of those three rivers, allowing them to exert control over the river crossings. Since then, it continued to thrive because of its communication links.