Introduction to Biodiversity Net Gain 

Biodiversity net gain is a way to contribute to the recovery of nature while developing land. It seeks to ensure that the habitat for wildlife is in a better state than it was before development. 

The approach steps away from analysis of individual species, and instead looks at habitat and habitat quality. Biodiversity Net Gain is additional to, and does not replace, protected species legislation that remains in place. 

The relative value of habitats within a proposed development site are quantified through professional standardised survey and assessment, using the published Natural England Biodiversity Net Gain Metric.  

The baseline biodiversity value is the habitat value which is calculated before development starts. The value of each type of habitat that will be created or lost through the development is calculated separately.  

The approach expects the developer to set out in their planning application how they will deliver a minimum of a 10% increase in biodiversity values, above the baseline. This is a requirement for all planning permissions granted in England (with a few exceptions) from January 2024. 

Methodology and Application of Biodiversity Net Gain Metrics

All planning applications are required to specify a development boundary.  The baseline biodiversity value within that boundary is established through a combination of professional field survey and desk-based assessment to understand the area and its importance for wildlife. 

Use of the published metric provides a standardised way of assessing biodiversity value through the number of ‘habitat units’ ‘river units’ and ‘hedgerow units’ within the development boundary.  A ‘habitat unit’ is not an area, but is calculated from a combination of area, relative wildlife value and ecological condition of the various habitats on site.  River and hedgerow units are calculated from a combination of length, relative wildlife value and ecological condition. Habitat, river, and hedgerow units are calculated and reported separately. 

Cannop Ponds 

Ecological survey work was commissioned and undertaken in 2022, covering a defined project area.  The biodiversity net gain assessment has been undertaken based on this area and will be revised to align with the development boundary once this is confirmed during the next stage of design. 

In spring 2023, four options for the future of Cannop Ponds were presented to the public.  Each of those four options has now been analysed to assess the habitat gains and losses that may occur if those options were implemented. 

Cannop Ponds Biodiversity Net Gain Options Appraisal 

The baseline biodiversity value of the Cannop Ponds project area is the same for all options. 

A simple overview of the impact of each option on the biodiversity value is presented below: 

Option One:  Spillway Replacement and Dam Upgrade 

Overall, this option delivers a net loss of habitat units, and no change to the river units against the baseline. 

The primary loss of habitat units comes from the reconstruction / reprofiling of the Upper Cannop Dam embankment.  This will negatively impact the area of wet grassland, wet woodland and lowland mixed deciduous woodland that lies immediately below Upper Cannop Pond.  This habitat is replaced with modified grassland (on the new engineered embankment). 

The replacement spillways at both Upper and Lower Cannop will both result in some further losses of habitat, replaced largely by the enlarged concrete spillways, and modified grassland. 

Option Two: Maximise Storm Water Attenuation 

Overall, this option presents a net gain in habitat units, and a marginal increase in river units above the baseline. 

The primary loss of habitat units come from the loss of open water habitat resulting from the drop in water levels on both Upper and Lower Cannop.  However, this loss is more than compensated for by the creation of the new wetland habitat on the margins of Lower Cannop, and across Upper Cannop more generally.   

The marginal increase in river units comes from the creation of short lengths of new stream as a result of the removal of the Upper Cannop spillway. 

Option Three: Cascade of Ponds 

Option three also delivers a net gain in habitat units, and a modest increase in river units. 

The habitat losses are again driven by the reduction in open water habitat, with the replacement habitats of reedbeds, wetlands, grasslands and deciduous woodland generating sufficient ‘positive’ scores to compensate and deliver a small positive gain. 

The increase in river units flow from the new stretches of stream emerging between the individual ponds. 

Option Four: Naturalise Cannop Brook 

Overall, option four presents a net gain in habitat units, and a significant gain in river units. 

Whilst this option shows a very significant loss of open water habitat, this is compensated for by the new wetlands, grasslands and deciduous woodland that will naturally emerge from this option. 

This option provides a very significant increase in river units with the restoration of Cannop Brook. 

Opportunities to enhance the Biodiversity values to deliver a 10% Gain 

The planning requirement inherent in the Biodiversity Net Gain approach is to deliver a 10% uplift against the baseline.  Further biodiversity enhancements will need to be identified and delivered to achieve this overall requirement. This will be evaluated further once the preferred option is selected and developed in more detail.