HWTWRP - Biodiversity Net Gain - Market Engagement

The need for the HWTWRP Project is to create a new, resilient and sustainable water supply that will protect and enhance the county’s rare and sensitive chalk streams, while maintaining supplies for communities and the local economy.

Biodiversity Net Gain (BNG) for the Project

Biodiversity Net Gain (BNG) is an approach to development that aims to leave biodiversity in a measurably better state than beforehand. At the point of the Project’s submission, BNG was not a requirement for Nationally Significant Infrastructure Projects (NSIP) and therefore was not a legal requirement for the Project, despite this, the project has committed to the delivery of a 10% net gain. Mandatory BNG for NSIP applications came into force on 2nd November 2026 and applied to NSIP’s submitted from November 2026 onwards.

The National Policy Statement for Water Resources Infrastructure (NPSWRI) states that “Development should contribute to and enhance the natural environment by providing net gains for biodiversity”. As such Southern Water has committed to delivering at least 10% BNG for the Project and has prepared a Biodiversity Gain Plan setting out its approach to the delivery of BNG.

Following the application of the mitigation hierarchy, including the retention, reinstatement, creation and enhancement of habitats within the Order Limits, additional off-site biodiversity units will be required to achieve the Project commitment of at least 10% BNG.

Where practicable, BNG will be delivered within the Order Limits as defined in the Development Consent Order (DCO) Application. However, a significant proportion of the required biodiversity units will need to be secured off-site. As far as practicable, all biodiversity units will be delivered within Hampshire.

The current off-site BNG requirement is 201.77 biodiversity units, comprising:

• 169.94 area habitat units
• 29.69 hedgerow units
• 2.14 watercourse units

The indicative off-site habitats required to deliver these units are:

• Other neutral grassland (93.8 BNG Units)
• Hedgerows (29.7 BNG Units)
• Lowland mixed deciduous woodland (2.6 BNG Units)
• Watercourses (2.1 BNG Units)
• Open mosaic habitat on previously developed land (73.3 BNG Units)

The biodiversity unit requirements and habitat types set out above represent the current estimated position based on the project design and Biodiversity Gain Plan available at the time of issue. These requirements may be refined as the Project progresses through detailed design.

The enhancement and creation of ecologically valuable habitats off site (to achieve the commitment of at least 10% BNG) will substantially increase provision of ecosystem services associated with the Project.

The contractor will be expected to provide a full biodiversity unit solution comprising habitat creation, enhancement and acquisition of registered off-site units. The contractor shall be responsible for identifying suitable delivery sites, securing legal and financial arrangements, establishing habitat management agreements, and demonstrating that all biodiversity units are compliant with statutory requirements and capable of being allocated to the project. Solutions may include direct habitat bank delivery, build-to-order habitat creation, or other innovative nature finance mechanisms that provide measurable and verifiable biodiversity outcomes.

The scope shall extend beyond habitat establishment to include long-term stewardship, monitoring and reporting over a minimum 30-year period). The contractor will be required to prepare and implement habitat management and monitoring plans (HMMP), undertake regular surveys, report biodiversity performance to the Project, and apply adaptive management where required to ensure target habitat conditions are achieved and maintained. Delivery partners shall be capable of providing robust governance, security and assurance, enabling biodiversity gains to be evidenced, maintained and reported throughout the lifecycle of the Project and in support of future compliance obligations.