One of the lesser known and understood elements of statutory biodiversity net gain (BNG) arises in the case of any planning application that includes a watercourse or ditch within the application site and, even if outside the application site when it is within 10 metres from the top of a bank of a river, stream or canal, or within 5 metres from the top of a bank of a ditch. That requirement captures many rural sites, even where it is only the site access that crosses or runs parallel with a watercourse or ditch for all or part of its length.
Where watercourse BNG applies, the base-line survey and recommendations for enhancements have to be undertaken by an ecologist with suitable training and qualifications. Where there are rivers, streams and canals this means being qualified to undertake river condition assessments. Enhancement can be achieved in a number of ways including removing shading from vegetation, protection from physical damage or planting wetland vegetation along water margins.
Unlike most area based BNG where there is flexibility to select areas and habitat types that are best suited to the site in question, watercourse BNG can only be achieved by enhancing the watercourse itself or, if that is not possible, another watercourse within the applicant’s ownership and control or, as a last resort, by purchasing off-site watercourse BNG units on the open market. The availability of watercourse BNG units to purchase is limited and, in the current market, they are likely to cost between £100,000 and £200,000 per unit.
The above raises two practical issues. The first is where there is a later planning application on the same site – e.g. for additional farm buildings – and the relevant watercourse has already been enhanced. In that case the base-line is the enhanced score and further enhancement may not be possible. The second is where the watercourse is in different ownership and can not be enhanced without the agreement of the owner and a legal planning agreement. In these cases, the purchase of off-site units may be the only available option.
