Sustainable drainage (SuDS) and biodiversity net gain

min read time
2022-12-22 11:04:01

Biodiversity net gain was introduced in the Environment Act 2021 which received royal assent on 9th November 2021. It is likely to become law and mandatory for all TCPA (Town & Country Planning Act) developments in January 2023. In this post we take a look at what biodiversity net gain is and what it could mean for Sustainable Drainage Systems (SuDS) and surface water management.

What is biodiversity net gain?

Quite simply, biodiversity net gain is the increase in biodiversity when measured before and after a development. Developers can work to increase the ‘biodiversity score’ when designing the development by incorporating natural spaces and using sound ecological principles including providing habitats for a range of species and providing corridors for the movement of wildlife.

There key components of mandatory BNG include a 10% gain required, calculated using the latest version of the Biodiversity Metric, approval of a biodiversity gain plan, habitat secured for at least 30 years via planning obligations or conservation covenants, delievered on-site, off-site or via a new statutory bio-diversity credit scheme and national register for net gain delivery sites.

How is biodiversity net gain measured?

The Defra Biodiversity Metric which has been developed by Natural England for measuring biodiversity net gain. It is a habitat based approach to determining a proxy biodiversity value. To apply the metric, a site will need to be surveyed and mapped and divided into parcels of distinct habitat types using a recognised habitat classification system. The biodiversity value of a habitat parcel is then evaluated based on area and quality which includes distinctiveness, condition, strategic significance and habitat connectivity. The metric was piloted by Defra in 2012 and has been recently improved by incorporating some of the features requested by industry experts including improved consideration of ecological connectivity, consideration of an extended range of habitats including green infrastructures and rivers and a spreadsheet-based tool to support the application of the metric in practice. The current version is biodiversity metric 4.

Why is biodiversity net gain so relevant now?

The UN reports that nature is declining globally at rates unprecedented in human history with the rate of species extinction accelerating. The UK has an average of only 53% of its biodiversity left and ranks in the bottom 10% of countries in the world. At the COP15 Convention of Biological Diversity in Montreal Canada on 7-19th December 2022 nearly 200 countries worked to agree a path to restoring nature. Biodiversity and climate change are closely linked and without a good outcome on fighter for nature, it will be far more difficult to fight climate change. The UK was among countries agreeing to a new deal to protect nature with a key goal of reversing biodiversity loss and protecting 30% of land and sea by 2030. With the Word Economic Forum highlighting that 50% of our economy is directly linked to nature, it is clear that nature matters to business.

What could biodiversity net gain mean for sustainable drainage (SuDS) systems?

When created inline with the four pillars of SuDS (water, quantity, water quality, biodiversity and amenity), SuDS provide an effective way of both managing surface water and creating diverse habitats for wildlife. Up until now uptake of SuDS has been slow due to a lack of effective legislation and planning policy. However, a requirement for a biodiversity net gain could make incorporating SuDS into new developments a more attractive option for developers.

What additional benefits could biodiversity net gain have?

It is well recognised that incorporating natural open spaces into developments can also play an important part in building thriving communities that contribute to the positive health and well being of the people that live there. The benefits of nature are known to include reduced stress and anxiety, improved physical health and opportunities to connect with others.

BNG whitepaper 900x450px 6

To help you get ahead of the new changes, this guide covers:

• Why the UK needs a new approach to biodiversity
• The key principles for maximising BNG
• New legal requirements relating to BNG
• How to achieve a 10% net gain through onsite improvements
• How BNG can boost a development’s bottom line

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Further information

Biodiversity net gain - the construction industry's promise - Biodiversity net gain: updating planning requirements

Nature England - Biodiversity net gain brochure

RSPB – Sustainable Drainage Systems – maximising the potential for people and wildlife