Thames and Severn canal walk Part 2

Описание: Information from Wikipedia.
This is further information but there is more to find.
Looking east from Upper Walbridge Lock
The tunnel was constructed from many workfaces, with 25 shafts sunk along its course to provide access. After completion there were problems, and the tunnel was shut for two and a half months during 1790 for further work to be carried out. The summit level and the branch to Cirencester were completed in 1787, and became operational as soon as the tunnel opened. The final section to the junction with the Thames at Inglesham, which descends through 16 locks, was finished in November 1789. The canal was completed at a cost of £250,000. With the Stroudwater Navigation, which had been completed in 1779, it completed a link between the River Severn in the west and the River Thames in the east.

As built, the main line was just under 28.7 miles (46.2 km) long and had 44 locks. The branch to Cirencester added a further 1.5 miles (2.4 km). The first 2.5 miles (4 km) from Wallbridge to Brimscombe, where there was a transhipment basin, was built with locks 69 by 16 feet (21.0 by 4.9 m), enabling Severn trows to use it. Beyond that, the locks were 90 by 12.7 feet (27.4 by 3.9 m) and the boats used were Thames barges. The canal's summit, which is 362 feet (110 m) above sea level and 8.1 miles (13.0 km) long, includes the 3,817-yard (3,490 m) Sapperton Tunnel, at the time, the longest in England. Its length has only been exceeded by two other canal tunnels, at Standedge in the Pennines and at Strood in Kent.

Operation
Until the summit level was completed, little thought seems to have been given to water supply. It was assumed that the River Frome, to the west of the tunnel, the River Churn which flows through Cirencester, and the River Coln, together with springs at Boxwell and a well near the source of the River Thames at Thames Head, would be sufficient. The original horse pump at Thames Head was replaced by a windmill, but Clowes found that he could not stop the summit pound from leaking. The flow on the River Churn was 1.7 million imperial gallons per day (7.7 Ml/d), whereas the calculated flow at the start of the project had been more than ten times this value. The summit level was losing around 1.1 million imperial gallons per day (5.0 Ml/d), largely because the underlying rock was porous limestone, and it was estimated that around half of the daily requirement could actually be supplied. The wells at Thames Head were extended and a Boulton & Watt steam engine was installed in 1792 to pump the water into the canal. An extra, shallow lock was built at Boxwell, which allowed the level of the canal to be dropped beyond it, and more water to be taken from Boxwell springs. The new arrangements were adequate, although some of the reason was the failure of traffic to develop to the levels anticipated.

Leakage was affected by springs breaking through the clay lining of the canal bed. In summer, when the springs receded, water was lost through these holes at a rate greater than the available supply. In one of the attempts to conserve water, the length of the locks was reduced by 20 feet (6.1 m), giving them an unusual double-headed appearance. In a further attempt to prevent water loss, at King's Reach, the section immediately east of Sapperton Tunnel, the canal was lined with concrete rather than puddle clay. The concrete invert was 18 inches (46 cm) thick, and A. Brome Wilson, the canal's engineer, used pipes to feed water from the underlying springs into the canal, but at a level above the waterline.

Neither of the river navigations to which the canal connected were satisfactory. In the west, the situation was remedied in 1827, on completion of the Gloucester and Sharpness Canal. On the Thames, there had been a proposal for a canal from Lechlade to Abingdon in 1784, and for a cut from Inglesham to Buscot in 1788, but neither had been built. Some improvements were made to the river after 1786, but the canal company encouraged the building of bypasses. The Wilts & Berks Canal was one Thames bypass, providing a link to the river at Abingdon, but did not initially connect to the Thames & Severn Canal. Although it was proposed in 1793, it was not opened until 1810, and the North Wilts Canal, which eventually provided the connecting link from Latton to Swindon for Thames & Severn traffic to bypass the upper river, was not completed until 1819. Even after this, vessels were restricted by the narrow 7ft width of the North Wilts, which was considerably smaller than the rest of the link between the Thames and the Severn, limiting income from cargo.
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