This is a handy summary to make sure you’ve remembered all the construction details.
Remove topsoil from the site of the wetland area, including beneath the banks if a clay liner is to be used. Stockpile soil close to the work area for reuse later within the system and on the banks.
Mould the subsoil to the specified design for the site. This involves digging out the main basin or cell of the wetland marsh and building the banks around the system. Generally systems are designed with a 1m distance from the bank top to the wetland base.
Build inlet and outlet manholes. These are usually pre-moulded Wavin fittings at the inlet and plastered concrete block in-situ manholes at the outlet.
Lay the liner material to seal the system. Waterproof bitumen tape is used at the outlet to seal between synthetic liners and the outlet sewer pipe. A sand blinding and polypropylene geotextile layer is used to protect the liner both above and below where high percolation exists. In sites of low percolation characteristics, no sand should be needed, but prepare the ground well to avoid puncturing the
liner. Clay subsoil may be suitable as a liner material; check with the site engineer for permeability characteristics.
Cover liner with topsoil layer, level to within 5cm. Cover banks and base to a depth as specified in the designs, usually 200-300mm.
Saturate soil then plant the system with specified wetland plants and seed the banks with grass/clover seed mix to minimise erosion by rainfall.
Install septic tank or other pretreatment system with access points prior to the wetland for sampling and inspection.
Install percolation area, willow filter or discharge point. This should be completed before the constructed wetland is used for sewage treatment.
Connect to sewers when plants are established. Only connect after planting is complete. Maintain water levels for at least 12 months after planting to ensure plant health and survival.
Follow-up maintenance of septic tank or other pretreatment system is important to prevent solids carry-over to the constructed wetland and to maximise treatment efficiency.
See the Permaculture Guide to Reed Beds for plans, materials, checklist and lots more info.