Agriculture accounts for a significant proportion of diffuse pollution in the UK, and wetlands can function as an effective nature-based solution to this problem by breaking pollutant pathways and benefitting biodiversity on farms and in water. A major advantage of constructed farm wetlands is that they can be designed to provide a range of benefits in addition to water quality improvements.
Constructed Farm Wetlands and SuDS (Sustainable Drainage Systems) are man-made systems which function by mimicking the water treatment properties of natural wetlands. Wastewater is treated through a complex range of processes which occur within the wetland which include sedimentation, uptake of nutrients by plants and reduction of pathogens through exposure to UV.
Constructed Farm Wetlands range from simple vegetated pond-based systems up to complex, multistage systems treating concentrated point-source effluent. SuDS are water holding structures that are used in the rural landscape to slow the flow of surface water, soil runoff and drainage from fields or farmyards. SuDS include a range of structures such as swales, seepage barriers, check dams, earth banks and soil bunds.
WWT have worked with the Catchment Sensitive Farming Initiative of Natural England to develop guidance on where and how to use and manage wetland solutions in agricultural settings with case studies and training videos.
Along with this guidance, a tool has been created for Catchment Sensitive Farming (CSF) by the Wildfowl and Wetlands Trust to approximate the size of a constructed wetlands treating lightly contaminated yard runoff. This is based on the design of a 3-stage wetland used for the Countryside Stewardship option for a constructed wetland for the treatment of pollution.
The tool is only suitable for approximating simple constructed wetlands to treat lightly contaminated farm yard runoff. It is not suitable for technical constructed wetlands treating high-strength pollution. It is not suitable if any of the following effluents are present in the inflow waters: silage effluent, slurry, dairy washings, septic tank outflow.
The tool is intended to give a rough estimate of the area of wetland required but is not a design tool. The actual design should be carried out through a complete farm water management plan which sizes the wetland based on inflow wastewater composition and volume.