Natural measures for flood management show low-carbon promise says consultant

A flood management scheme based solely on nature-based measures has outstripped government environmental requirements and delivered £350,000 to its locality according to a long-term impact assessment by engineering consultancy, Atkins.

Atkins worked in partnership with the Environment Agency (EA) to appraise the Oxfordshire Natural Flood Management (NFM) scheme which had been delivered by the EA and local organisations. Its natural interventions included: tree planting and creating wetlands, on-line ponds, sediment traps and woody dams to reconnect the river and floodplain and to store water during flood events.

Atkins said NFM offers “a potentially lower-carbon alternative, or a complementary approach to hard-engineering, flood-risk management approaches.” The consultant said its assessment found that the scheme had delivered “a biodiversity net gain of almost three times the government requirement for new developments, as well as £350,000 per year in natural capital benefits and by 2100 will have removed more than 8,000 tonnes of carbon dioxide from the atmosphere.”

The findings came from a whole-life carbon assessment undertaken on behalf of the EA of the Littlestock Brook NFM scheme delivered by the EA, Wild Oxfordshire and the Evenlode Catchment Partnership with Bruern Estate and Milton Parish Council.

The scheme is located in the Evenlode catchment - a rural headwater of the River Thames in Oxfordshire. According to Atkins it “represents an example of how NFM can help protect smaller local communities at risk from flooding, where hard-engineering flood risk management approaches may not provide value for money.” It has, according to Atkins, delivered more than 28% in biodiversity net gain, compared to the government minimum of 10% gain. The scheme is estimated to £6m over 25 years in present Value’ terms with the most significant benefits coming from water purification, the reduction in soil erosion and provision of educational opportunities.

Principal consultant at Atkins, Monica Barker, said: “The assessment was a pilot that assisted our understanding of the carbon impact of constructing an NFM scheme, as well as quantifying the scale of carbon sequestration benefits delivered by the different habitats created.

“The aim of this was to inform future design and delivery for other NFM schemes. The carbon assessment was framed within a broader study of the natural capital benefits of the scheme, including a detailed evaluation of the biodiversity net gain delivered, to provide an integrated and holistic view on the benefits of a "typical" NFM scheme.

Key findings from the study included:

• by 2100, the project will have removed a net 8,198t of carbon dioxide from the atmosphere;

• total carbon stocks within the study area are expected to increase by 6% by 2100, from 25,213t of carbon to 26,719t; and

• construction and maintenance of the NFM will contribute the equivalent of only159t of carbon dioxide by 2100 – less than 2% of the predicted 8,358t of carbon dioxide it will remove.