Grand Union Canal

Site prior to works no standing waterSite during construction. Note minimal disturbance to surrounding vegetationCompleted site with new wetland plantingGrass snake in canal bank brushwood revetmentsPre-established Coir Pallets with a good mix of wetland plants
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Site during construction. Note minimal disturbance to surrounding vegetation

The project aim was to restore a wetland area on the banks of the Grand Union Canal for the benefit of wildlife and the fishery. The scheme design ensured that no material was taken off site and that particular focus was on creating suitable habitat for Water Voles and amphibian species such as Newts.

Salix tendered for and won the project in competitive tender with contract award in October 2010, with the work being completed by March 2011.

The design provided for newly created islands and on-line ponds of variable depths fringed with native plants. Leaf matter and sediment was removed to create these ponds with the sediment being re-used to create the islands with a shallow area on the eastern side of the canal. This area provided an adult fish spawning habitat with gently sloping sides having emergent vegetation and shallow non-vegetated fry shelves. Rotting vegetation was used to replicate a natural compost bin which is highly attractive to grass snakes.

The new islands were also successful in delivering a high value area for habitat and wetland plants combining to encourage the presence of water voles that have recently declined to only two known sites in the Colne Valley Park area.

Post construction, an ecological survey was carried out in May 2011 by Alder Ecology. This report concluded that the site experienced an increase locally in aquatic associated invertebrates such as damselflies and dragonflies.

Alder’s report showed that the general area had a greater biomass and diversity of invertebrates after completion of the works.

In addition, the newly created islands’ vertically cut banks contained holes that could be used by kingfishers for nesting. Positively, kingfisher passes were observed over the backwater and islands during the survey.

Details

Name: Grand Union Canal Habitat Creation
Client: Groundwork Thames Trust
Location: Grand Union Canal, Springwell Lane, Harefield
Category: Wetland Habitat Creation

Case Study