| Witham Navigable Drains | |
|---|---|
 Cowbridge Aqueduct carries the Stonebridge Drain over the Cowbridge Drain | |
| Specifications | |
| Maximum boat length | 70 ft 0 in (21.34 m) |
| Maximum boat beam | 10 ft 0 in (3.05 m) |
| Locks | 2 (3 other locks are defunct) |
| Status | Navigable in summer |
| Navigation authority | Witham Fourth District IDB |
| History | |
| Original owner | Witham Fourth Drainage District |
| Principal engineer | various |
| Date of act | 1801 |
| Date of first use | 1780s |
| Geography | |
| Start point | Anton's Gowt, Boston |
| End point | various |
The Witham Navigable Drains are located in Lincolnshire, England, and are part of a much larger drainage system managed by the Witham Fourth District Internal Drainage Board. The Witham Fourth District comprises the East Fen and West Fen, to the north of Boston, which together cover an area of 97 square miles (250 km2). In total there are over 438 miles (705 km) of drainage ditches, of which under 60 miles (97 km) are navigable. Navigation is normally only possible in the summer months, as the drains are maintained at a lower level in winter, and are subject to sudden changes in level as a result of their primary drainage function, which can leave boats stranded. Access to the drains is from the River Witham at Anton's Gowt Lock.
The area is bounded by the River Witham to the south and west, and the Steeping River to the north. Since the 11th century, there have been attempts to prevent the fens from flooding, so that they could be used for agriculture. A major advance was made in the seventeenth century, when Adventurers built drains in return for rights to some of the reclaimed land, but the success was short-lived, as Fenmen and Commoners rioted in 1642 and destroyed the works. Further attempts to drain the fens were made in the eighteenth century, and the first proposals to use the drains for navigation were made in 1779.
Most of the drainage ditches that are now evident were constructed under the authority of an Act of Parliament obtained in 1801. The plans for the scheme were drawn up by the civil engineer John Rennie. Better drainage was achieved from the 1860s, with the building of steam pumping stations. The steam engines were later replaced by diesel engines, and now many of them use electric pumps. Sensitive restoration of some of the pumping stations in the 1980s and 1990s resulted in the Witham Fourth District IDB being given a Design Award.
There were originally five locks on the system, including Anton's Gowt Lock. Cowbridge Lock is the only other one still operational. Access by boat to Cowbridge Drain and Hobhole Drain which drain the East Fen is no longer possible, because East Fen Lock, which connected Cowbridge Drain to the rest of the system has been filled in, while the lock chamber at Lade Bank Pumping Station has been reused to house extra pumps. Many of the structures built as part of Rennie's upgrade in the early 1800s survive in near-original condition, and are Grade II listed.