Nutrient Neutrality -Developing detailed design guidance for wetland mitigation solutions to nutrient pollution

The objective of this project is to develop detailed design guidance, based on the best-practice approaches taken by professionals in the feasibility, design and maintenance of treatment wetlands for nutrient mitigation. This will ensure that a set standard for high-quality nature-based solutions is delivered through the Nutrient Mitigation Scheme and other nutrient neutrality mechanisms.

The guidance will be used by design and build contractors, as well as local authorities and consenting bodies to ensure wetland proposals are technically robust and will complement the structure of the wetland mitigation framework, as far as is achievable and logical.

This should focus on integrated constructed wetland, free surface wetland and other viable wetland mitigation proposals, taking into account the degree of certainty that nutrient reductions will be achieved, alongside a range of other considerations including compatibility with wider habitat restoration opportunities.

The guidance must:

Set out the processes, calculations, tools and formatting of wetland design processes from feasibility and concept design stages through to detailed design.

Utilise at least one case study to demonstrate real-world application of the principles and processes within the guidance.

Outline planning, permitting and consenting considerations and signposting to how to carry out these stages effectively.

Specify the tasks involved in implementation, operation and maintenance of treatment wetlands, and their associated infrastructure, including timescales and waste management processes.

Set out how the above stages key into the existing wetland mitigation framework with degrees of confidence assigned to each process where more than one pathway is presented

Provide information on designing wetlands in areas of competing interests; such as where flood management or abstraction pressures exist. (e.g. minimising the impact of abstraction/offtake on depleted reaches of watercourses)

Contain information on opportunities to integrate positive biodiversity outcomes within and adjacent to the wetland proposals.

Be written for an informed audience, including technical designers and engineers, local authorities and other consenting bodies, who can be assumed to have an existing basic understanding of wetland processes and design parameters.

Outline how to deliver high-quality wetlands that are robust to changing climatic variables. (e.g. how to design wetlands where flows may become more variable due to future prolonged drought and rainfall events)

Provide a description of how costs would be determined from a detailed design (i.e. what are the cost items associated with the design and delivery of a treatment wetland solution).

Be based on the best available evidence.

The design approaches should be bespoke and proportional to the types of solutions covered in the guidance and include the parameters used to delineate the selection of one design process over another.