In 1789 the Thames and Severn Canal was completed, allowing cargo to be transported from Gloucester, through the countryside, to London, by boat. Via a series of locks, it climbed the western side of the Cotswolds to Sapperton, where it entered what was then the longest tunnel in Britain, at 3½ km.
This emerged from the hillside near the source of the Thames.
The canal then descended, via more locks to meet the Thames at Inglesham, near Lechlade…
…from where the river was navigable to London.
To pass through the Cotswolds in either direction, boats had to use a series of locks, to reach the highest level of the canal.
This lock is in Shropshire but illustrates the point. Coming from the lower level, the boat enters the lock, the gates are closed and then water is allowed in from the higher level to fill the lock and raise the boat. Each time the lock is used, water moves down to the lower level. With this happening at both ends of the tunnel section, this top part of the canal needed a water supply.
Water was taken from the River Churn at Cirencester to feed the canal but this alone wasn’t enough. The solution was found in the area near the source of the Thames, where the meadow was described as having “numerous little fountains” – presumably lots of springs. A borehole was dug and a wind pump was used to transfer several tons of water per minute to the canal.
It’s a controversial point, but this is likely to have lowered the level of the water in the limestone and contributed to the drying up of the spring at the Thames source.
But water wasn’t just leaving the canal via the locks. Next week we will be looking more closely at Sapperton tunnel and what was happening to the water inside.