Morrison Construction/British Waterways Omnibus Partnership.
Client: British Waterways (West Midlands Business Unit)
Morrison Construction/British Waterways Omnibus Partnership is currently involved in a seven-year framework contract to undertake a backlog of mainly safety-related works on the canal infrastructure network throughout England and Wales.
The Rushall Canal was built in 1802 and subsequently suffered from subsidence due to mining at the nearby Walsall Wood colliery, an issue addressed in the past by the building up of embankments. An inspection in 2000 confirmed that they were leaking and this, combined with the low freeboard, led to the need for embankment improvements.
The CEEQUAL award is in recognition of environmental best practice demonstrated on the Omnibus’s £2.35m contract to stabilise the embankment of, and refurbish two bridges over, the Daw End Branch of the Rushall Canal near to Brownhills, West Midlands.
The works were located on the Daw End Branch of the Rushall Canal between Aldridge Wharf Bridge at the southern extent and to a point approximately 1 km beyond Anchor Bridge on the northern extent and took place from March 2003 to May 2004.
The scope of works included:
- 5.3 km of new Breedon gravel towpath between Aldridge Wharf Bridge and a point 1km to the north of Anchor Bridge.
- Freeboard raising to 3 km of towpath side brick wash wall.
- Freeboard raising to 300 m of offside, including earth bund construction.
- Lowering of water level to allow inspection of the wash wall and repair of the brickwork as necessary.
- 535 m of sheet piling within the line of the towpath to stabilise the embankment.
- Strengthening to two brick retaining walls to the north and south of Black Cock Bridge.
- Palisade fencing to the boundary with commercial properties immediately to the north of Walsall Wood Bridge.
- Installation of artificial reed margins to the front of the offside sheet-piled wall between Lathams Bridge and Hollanders Bridge.
- Northywood Bridge: grit-blast and repaint the existing cast iron beams, replacement of existing wrought iron jack arches, and refurbishment of the existing masonry abutments and wing walls.
- Hollanders Bridge: fabrication of a new steel bridge and refurbishment of the existing masonry abutments and wing walls.
Key environmental considerations
An ecological survey in advance of the works revealed 42 white-clawed crayfish (a protected species) at 25 sites along the length of the Daw End Branch. They were living in crevices created by dilapidated brickwork that was to be replaced. To compensate for the loss of habitat, the Omnibus incorporated 3- and 10-hole perforated engineering bricks within the repaired canal walls, together with short lengths of 40-60mm ducts to accommodate the crayfish through the various stages of their lifecycle.
Water voles (another protected species) were evident at seven locations along the offside canal bank. In one area, the Omnibus needed to raise a 300-metre-length of offside freeboard, work which was undertaken under the close supervision of the team’s ecologist.
In another area the Omnibus had stabilised the bank by sheet piling a length of the offside. The team then improved water vole access and restored their natural habitat through an innovative design incorporating prefabricated reed margins that were fixed to the front of the sheet piles just above water level. The margins took the form of coir rolls containing a mix of hazel faggots and soil, pre-planted with reeds and bound by wire mesh matting.
Lurionium natans (a protected plant species) was recorded in the canal bed throughout the length of the Daw End Branch. It was important, therefore, that the canal bed silt was not disturbed during the course of the works. To this end, piling was carried out from a rig located on a pontoon in the canal. In addition, the piling sub-contractor used a Movax vibro-impact piling rig which uses vegetable-based oil and is quieter than other rigs.
Scheduling & Training
The programme for the contract was governed by environmental considerations. For instance:
- Work on offside freeboard raising was deferred until September when the vole population was at its most resilient.
- Vegetation clearance took place between September and March to ensure it did not coincide with the bird nesting season.
All site staff attended training courses led by a British Waterways ecologist on the subjects of water voles and crayfish.