Buckinghamshire Council Culvert Policy

Environmental mitigation measures may be appropriate if any open watercourse is being removed. We must also consider the key aims of the Water Environment (Water Framework Directive) (England & Wales) Regulations 2017 throughout the consenting processes, overall this Directive aims to:

• prevent further deterioration and protect and enhance the status of aquatic ecosystems and associated wetlands
• promote sustainable water consumption
• progressively reduce or phase out discharges, emissions and losses of priority substances and priority hazardous substances
• progressively reduce the pollution of groundwater, and contribute to mitigating the effect of droughts and floods

Environment mitigation for larger culverts:

• make the culvert slightly larger than that needed to accommodate the design flow and then position the invert of the culvert below the natural bed of the watercourse, to enable some more natural bed features to form
• provide ledges running through the culvert (approximately 500mm wide and 300mm above normal water level) to allow for the passage of mammals - or make provision for appropriately located mammal underpasses close to the culvert
• the height of the invert should not pose an obstruction to fish movement
• provide structures to encourage bat roosting and bird nesting as appropriate

Environmental mitigation for smaller culverts:

• propose suitable environmental enhancements, for example opening up a length of previously culverted watercourse elsewhere on the site, enhancing other lengths of the watercourse, creation of a pond, marshy area, scrub, or hedge planting
• construction headwalls and wingwalls in ‘soft-engineering’ or natural materials in keeping with the natural channel