Watercourse Biodiversity Net Gain (BNG) Explained
What is Watercourse Biodiversity Net Gain (BNG)?
Watercourse Biodiversity Net Gain (BNG) is a way of ensuring that rivers, streams, ditches, and other water-dependent habitats are left in a measurably better state than before development takes place. It is part of the UK’s biodiversity net gain framework, which became mandatory under the Environment Act 2021.
When a new project has an unavoidable impact on a watercourse, BNG requires that the loss or degradation of habitat is more than compensated for through carefully designed restoration and enhancement works. This ensures long-term ecological improvements for wildlife, water quality, and local communities.
How is Watercourse Biodiversity Net Gain (BNG) Calculated?
Calculating Watercourse Biodiversity Net Gain (BNG) is different from measuring terrestrial habitats like woodland or grassland. Rivers and streams are highly dynamic systems, and their condition depends on many interlinked features such as flow, banks, in-channel habitat, and water quality.
Under Natural England’s Statutory BNG Metric, watercourses are assessed separately from other habitat types to ensure their unique ecological value is measured correctly. A baseline River Condition Assessment (RCA) is carried out, as well as mapping and recording in-channel and riparian encroachment. An experienced and accredited surveyor should do this. Condition for ditches are calculated differently, using biodiversity metric condition sheets.
River condition, along with encroachment and other factors are entered into the Biodiversity Metric to give a baseline number of watercourse units.
When do you need to include a watercourse in your BNG assessment?
If a watercourse is within your red line boundary, or the watercourse bank top is within 10m of your red line boundary, you must include it in your baseline assessment. Even if you are not directly impacting the watercourse, you will be required to demonstrate a minimum of 10% watercourse unit gain.
How do we go about delivering 10% watercourse net gain?
We advocate following the mitigation hierarchy. Firstly, can the watercourse be excluded from the project red line boundary, or can any impacts on the waterway be avoided completely? Any development within 10m of the bank top should be avoided. This also aligns with the requirements under the Water Framework Directive.
If impact cannot be avoided, we recommend trying to minimise a development's effect on the watercourse through specialist watercourse input early on in the design process. There may be low-cost interventions that can be implemented on-site to compensate for any loss in watercourse units and deliver a 10% net gain on-site.
As a last resort, impact can be compensated for by off-site watercourse improvements. This could be on your own site, or through units purchased from a Habitat Bank or statutory credits purchased from the government. Off-site compensation should occur as close as possible to the impact, and incentives within the Biodiversity Metric are designed to encourage this.
How Can River Habitat Bank CIC help?
Our specialists can advise on all points listed above:
· Baseline surveys (River Condition Assessment, encroachment survey)
· Biodiversity Net Gain baseline and scenario modelling
· Technical input and design for on-site avoidance and mitigation, including any consenting required
· Strategic development of off-site watercourse units within a Water Framework Directive Waterbody
· Sale of off-site units developed through our Habitat Bank.