Canada Farm Meadows Rewetting

Tender description

Canada Farm Meadows are part of Shapwick Heath SSSI. They are an area of species-rich floodplain meadows on deep peat. It is designated for its species-rich grassland, breeding waders, and ditch fauna and flora. The ditches are in Unfavourable Condition as they are dry throughout the year except during winter flooding. They have become isolated from the rest of the catchment as they no longer convey water because they are heavily silted and in parts covered in scrub; water control structures no longer function due to lack of management. This inability to convey water into this site during the spring and summer months causes the deep peat soils (averaging 2.00 meters) to dry out, oxidise and release carbon, increasing atmospheric CO₂ levels and contributing to climate change. Restoring the Canada Farm Meadow ditches and replacing defunct culverts will allow water to reach throughout the site all year round. This site will become wetter benefiting wet grassland species and breeding waders, and the high ground-water table will create more favourable anaerobic conditions for peat soils to reduce oxidisation rates and CO₂ emissions. This scheme shall contribute to government targets to reduce CO₂ emissions from peat and improve habitat conditions for the biodiversity of this wetland landscape. Requirement Replace four defunct culverts and restore 700 metres of ditches across 10.6 hectares of floodplain grazing marsh on deep peat soils. Culverts are to allow cattle and agricultural machinery to cross ditches. Replacing Culverts • Working method to follow: Somerset IDB Gateway Construction Culvert Sequence Guide - using Galvanised Steel Motorway Barrier Headwalls • Somerset Internal Drainage Board Consent has been granted provided compliance with the following Culvert Details: a. Depth of existing channel: 900mm b. Rigid twin-walled plastic pipe: 600mm diameter, 6000mm length c. Back fill material: Clean crushed locally sourced quarried natural stone compacted with road-roller d. Cover to over top of pipe: 400mm depth e. Ditch width: 2700mm • Dry working area • Solid, stable structures upon completion • Stock-proof upon completion Restoring Ditches • Woody vegetation removal • Silt removal and disposal • Disposal of vegetation matter General Considerations • Working on peat soils • Working within wetland • Working within Shapwick Heath Site of Special Scientific Interest • Protected species - where applicable • Additional Environmental Considerations • Livestock The main outputs for this project will be: 1. Installation of 4x culverts. 2. Restore 700-meter ditch system