Bude Canal regeneration
SWH Civils was extremely pleased to be involved with a scheme as prestigious, interesting and challenging as the Bude Canal Regeneration.
Our works included:
- Dredging and disposal of approximately 20,000m3 of accumulated silt from a 3km length of the canal
- Restoration of two locks to a fully operational condition
- Construction of a pumping station and pumping main to replenish the upstream water levels
- Replacement of a small bridge
- Reinstatement and upgrading of the towpath.
The particular nature of the site presented us with a number of interesting environmental, technical and logistical challenges. There were also some surprises along the way, such as a period of sustained rainfall which led to a surge flow down the river and into the canal.
The masonry in both of the locks was in a state of considerable disrepair with the majority of the walls needing repointing and sections having to be taken down and rebuilt. Before masons could start work we first had to drain the locks and remove a thick layer of silt. We decided to install a pair of fairly low-tech coffer dams, made of stone filled dumpy bags and clay either side of each lock. Because of the limited width of access along the existing towpaths, we first had to build haul roads across the waterlogged flood plains.
With the coffer dams in place, and the locks emptied of silt and water, we discovered the bed of each lock was lined with inverted brick arches in almost pristine condition. With the locks empty, the lock gate fabricators were able to visit site to take measurements for their fabrication drawings and, following the preparation of new concrete foundations, installed the bulk timber cills. A new pumping system was installed with the rising main laid at a very shallow gradient at a level below the top water level of the adjacent canal along extremely narrow paths.
The largest single element of the contract was the dredging of 2.3km of canal. Silt was removed using a mechanical excavator mounted within a floating pontoon which was levelled by a pair of hydraulic rams. The silt was loaded into a number of barges, each with an 8m3 capacity, and taken upstream to a transfer point where the silt was then loaded into a static pump. The silt was first pumped approximately 600m horizontally to where a second pump operated in line to drive the silt a further 1000m to a receiving field where it was spread as a soil improver. This minimised the environmental impact of the works and avoided the need to take the arisings to landfill.