Water from the Cotswolds

Much of the rainwater falling in the Cotswolds disappears into the ground, soaking into the permeable limestone rock. It may eventually emerge lower down the hillside at a spring…


…or maybe not, as in here at what was once the source of the Thames.

Water that has trickled through limestone usually comes out pretty clean and carrying various dissolved minerals, particularly calcium. This usually results in a pleasant taste and gives the water health benefits, calcium being needed for strong bones. Thus it is excellent as drinking water.

But you don’t have to live in the Cotswolds to taste it for yourself. Several companies sell spring water that is bottled at its Cotswold source. These enterprises vary in size, with one company having a licence to remove 73 million litres of water per year from its borehole drilled into the limestone rock.

And then there are the water supply companies. They need to source enough water to keep it flowing down the pipes direct into our homes. Thames Water supplies 15 million customers. It gets around 40% of its water from groundwater and some of that comes from the Cotswolds.

So if the water is taken directly out of the rock and at a faster rate than rainwater puts it back, the spring may dry up.

The river may eventually appear from a different spring at a lower level. Compare this…


…with this.


But in the area of the source of the Thames, water was not just needed for drinking. A major project needed a water supply and it turned out to need much more than was anticipated. Find out all about it next week.

Springs in the Cotswolds

The River Thames once began as a spring, in this field, on the lower slopes of the Cotswold Hills.

The Cotswolds are made of limestone, the same type of rock that we encountered in Wharfedale, where the river Wharfe disappears into the ground. On the Cotswolds you won’t find much in the way of rivers for the same reason. Limestone is full of cracks, enabling rainwater to sink into the ground. It is a permeable rock.


The water flows down through the permeable limestone until it can’t go any further, either because the rock has changed and no longer has holes, or because the holes are already full. The water will then flow sideways, out of the hillside, forming a spring, the source of a surface stream.

So if there hasn’t been rain in a while, water stops flowing out and the spring dries up.

But where the Thames is concerned, that is only part of the story. Find out more next week.

Where is the source of the Thames?

The village of Tarlton, in Gloucestershire, lies on the south-east side of the Cotswolds, near the head of a valley.   A valley with no water in it.  Not far from Tarlton, there is a less distinct valley, but clearly labelled on the map it says “source of the River Thames”.

And here it is.


Not a drop of water in sight!


The marker stone shows that we were definitely in the right place.

This happens to also be the start of the Thames Path, a 184 mile waymarked route that basically follows the river from source to sea. So we set off to find the river.

About a mile down the path, we came across the first bridge over the river, built to keep vehicles high and dry on the A429.


Two tunnels allow for a sizeable volume of water.

The dry river bed would have made an even better path than the path, had it not been for the branches lying across it.


It wasn’t even boggy at this point.

Eventually a few puddles appeared.


These got bigger and the in-between bits got boggier…


…until eventually we got to a weir with a trickle of water actually flowing.


We were now nearly 2 miles from the official source, near the village of Ewen.  Between these points, the wide, dry channel and substantial bridge clearly indicate that the Thames has been flowing here in the past. In the next 3 posts in this series, I’m going to look at what has happened to the source of the Thames and why. Join me for the first of these next week.

Bladud’s City – Part 2

In last week’s episode we left Prince Bladud looking for his pigs.

As he stood there deliberating, a fat sow, which was still unwell, came idling down from the top of the meadow.
They’re over there! Now he remembered, there was a copse of trees up there, where the pigs liked to sleep.
Bladud ran to the copse, and pushed open the branches. No pigs in sight.

He headed back down to the main flock. There was that sow, just joining the others in the spring. She inserted her trotters into the water and lowered her head, drinking the fresh, pure liquid. Liking the taste, she headed further in. And…what? Before Bladud’s owl-like eyes, the leprosy vanished from all the parts that touched the water.

He suddenly started out of his stupor, and dashed towards the water like a wild animal, flinging off his clothes as he went. He plunged in, pushing the sow out of the way so hard she fell over, scooping up the water and rubbing it all over himself. Yes, yes! He was cured!

Joy welled up in him. He fell to his knees, crying like a baby, thanking everyone he could think of for this magic water.

At sunset, Bladud returned home with all the pigs, now all cured, and gave his notice to the farmer. When his term of employment was up, he returned to his family and home, where he was reinstated as his father’s heir. Not long after he returned, his father died, and Bladud became king. He ordered the beginnings of a city at the point where the healing spring issued from the hillside, so that others could benefit from its powers.

Bladud ruled for twenty years, and never before had a king been so humble or so in touch with his subjects. He would often think of his time as a leper and swineherd, and be grateful that his life had gone the way it did, for it made him see that he was not a jot above the common people. He could see that rich people had no reason to puff themselves up. For anyone’s fortunes could change completely, in the blink of an eye.

This city we now call Bath, and the city was actually started by the Romans in the first century A.D. when a temple and Roman baths were built there. The waters are only good for you in that it is mineral water, with good minerals such as calcium and iron, but for many years it was fashionable to go to Bath and, “take the waters,” in the hope of a cure. The hot springs are still there to be seen today, although you have to pay £15.50 to go in.

A Canal through Limestone?

Limestone is a permeable rock, since it has cracks through which water can pass.

The Sapperton Tunnel, on the Thames and Severn Canal, tunnels through the limestone rock so that the canal can pass through the Cotswold Hills.


The 3½ km tunnel took 5½ years to build. Along the line of the route, 25 shafts were dug down from the ground surface and the tunnel was excavated from the bottom of these, until they were all connected together. Once the alignment had been checked, the tunnel was enlarged to the correct size.

Before water could be allowed in, the channel had to be made watertight. This was done by lining it with clay, an impermeable rock that doesn’t let water through. The channel was then finished with brick and the sections that were not through solid limestone were also given a brick roof.


Water could then be pumped in to this section of canal, enabling it to be used by boats.

The problem was that the rainwater soaking down into the permeable Cotswold Hills was leaking into the tunnel. This provided an additional water supply in winter, but in summer the springs dried up. Where the spring had pushed a hole through the clay canal lining, the canal water could then leak out through the same hole.

More water was needed to make up for leakage than to transport boats through the locks. The wind pump, by the Thames source, was replaced by a steam engine pump, which was used in the drier summer months, typically from June to October, and could deliver 3 million gallons a day into the canal.

There was a constant need for repairs to deal with the holes. Sections were eventually lined with concrete, but that was over 100 years after the canal first opened. Meanwhile loads of water had been taken from the ground near the source of the Thames. It had leaked back into the ground but not at the same place.

The Thames and Severn canal was closed in 1933, due to the need for repairs, and the Sapperton Tunnel is now impassable as the roof has collapsed in a number of places. You can find lots more information, including diagrams and pictures, on this page of the Cotswold Canals website.

Water shortages caused problems for boats both in the canal and in the river. Join me next Friday to find out more about travel on the Thames.