Are the Cwm Elan/Elan Valley dams overflowing?

Here’s a guide to what to expect.

If you have ever found yourself wondering whether the dams at the Elan Valley are overflowing today, you are definitely not the only one. The videos of water thundering down the spillways always catch people’s attention. It is one of those big, dramatic Mid Wales sights that sticks in your mind.

Here at Coety Bach, we are only around half an hour from the Elan Valley, and most of our guests take a day trip over while they stay with us. Even on a calm day with no overflow, the views, the walks, the history and the peace of those valleys are absolutely worth the drive.

But if you are hoping to catch an overflow, here is what you need to know.

What does “overflowing” actually mean

Caban Coch Dam

When people talk about the Elan Valley dams overflowing, they mean the water is running over the main spillway and pouring down the face of the dam. That is the huge sheet of water you see in photos and videos.

There are also times when water is released as part of normal management of reservoir levels, but that does not always create the same dramatic waterfall effect.

What makes the Elan Valley dams overflow

Overflow tends to happen when:

• There has been a run of heavy rain in the catchment

• The ground is already saturated, so more water runs straight into the reservoirs

• Water levels are already high before the rain begins

• Occasionally, rapid snowmelt adds to the inflow

It is all down to how much water is arriving at once, and whether the reservoirs have any spare capacity to hold it.

Which dams are in the Elan Valley?

The Elan Valley is home to a group of striking stone Victorian dams and reservoirs, built as part of the water supply system.

Craig Goch Dam

The main dams you will come across are:

• Caban Coch

• Pen y Garreg

• Craig Goch

• Claerwen

• Garreg Ddu (also known as the submerged dam)

Claerwen Dam

Here are the key stats visitors often look up:

• Caban Coch: 37 metres high, 186 metres long, 35,530 megalitres

• Pen y Garreg: 37 metres high, 161 metres long, 6,055 megalitres

• Craig Goch: 36 metres high, 156 metres long, 9,222 megalitres

• Claerwen: 56 metres high, 355 metres long, around 48,300 megalitres

• Garreg Ddu: 20 metres high and 180 metres long

When do the Elan Valley dams usually overflow

There is no official schedule, but your chances are usually better during:

• Late autumn, winter and early spring

• Periods of long, wet weather

• The day after a big storm, when everything is still draining through

Dry spells mean lower reservoir levels and a much smaller chance of overflow. Wet spells make it far more likely.

How often do the dams overflow

It varies from year to year. Some winters have several overflow days, others only a few. It happens often enough that visitors do get to see it, but not reliably enough to guarantee on a certain day.

Even on quieter days, the Elan Valley has the sort of scenery that makes you slow down a bit and take it all in. Overflow is a bonus, not a requirement.

If you are checking before you set off and wondering things like whether the Elan Valley dams are flowing today, if any of the dams are spilling over, or whether the reservoirs are full, you are not alone. People often search for updates on the Elan Valley dams overflowing, and it is one of the most common questions visitors ask before a day out in the valleys. The weather can be wild in this part of Mid Wales and conditions change quickly, so it is always worth having a look to see if the dams are flowing before you head over.

How to check if the dams are overflowing before you go

If you want to time it just right, these are the easiest ways to check:

• Look at the Elan Valley webcam, when it is active

• Check Elan Valley social media, as they often post when the dams are overflowing

• Contact the Elan Valley Visitor Centre and ask on the day

River level charts in the wider catchment can give a rough idea of how wet things are, but they do not guarantee a spillway overflow.

How likely are you to see an overflow during your stay?

If you are staying with us at Coety Bach and planning a day out at the Elan Valley, your chances depend entirely on the weather. If it has been wet for several days, you have a decent shot. If it has been dry, it is less likely.

Because we are only half an hour away, it is easy to check conditions after breakfast and decide if today is the day to go.

A simple Elan Valley day trip from Coety Bach

Most guests follow this simple route:

1. Start at the Visitor Centre by Caban Coch

2. Drive up through the dams and stop at a couple of viewpoints

3. Take a walk and stop for a picnic midway

4. Head back to the cabin for a peaceful evening with a dip in the private wood fired hot tub.

Whether the dams are overflowing or not, the Elan Valley always feels like a proper breath of fresh air.

To book your stay with us and see the Elan Valley dams for yourself, click here.