Solution: Start with a place rather than a peril: bring farmers, water utilities, local authorities and the environmental agency around a single catchment, aligning environmental stewardship payments, flood-risk reduction and water-quality improvement into one Program that no individual participant could have funded or justified alone.

Key challenge: The Severn Valley suffers average annual losses of around GBP 150 million ($205 million) from flooding, the catchment spans two nations (Wales and England) with different regulators and funding regimes, and the scheme envisages up to GBP 1 billion ($1.3 billion) of investment - far beyond public grant funding alone.

Context: The River Severn has recorded some of its highest levels in decades in the past seven years alone. Modelling shows that up to 100 million cubic metres of water will need to be stored during large flood events - equivalent to 11 days of the United Kingdom's water supply - to better protect more than 3,000 homes and businesses at risk. The catchment covers rural areas and all property types across the Severn Valley and Shropshire, crossing the England-Wales border.

Solution in practice: Jointly led by the national Environment Agency, Shropshire and Powys Councils and Oliver Wyman, the scheme is the flagship project of a wider cross-border partnership treating catchment-scale resilience as a driver of regional growth. The emerging design combines more than 25,000 nature-based interventions with engineered water storage, aimed at managing a one-in-100-year flood with an allowance for impacts of future climate change. Early delivery is already under way: more than 140 natural flood management measures - leaky dams, ponds and wetlands - have been installed upstream. The coalition is now working with beneficiaries of the risk reduction, from insurers and developers to farmers and government, to identify channels for funding the scheme. Once completed, it is expected to support up to GBP 5 billion ($6.8 billion) in wider economic impact. The coalition is exploring several routes to close the funding gap: green finance as an established starting point, through carbon credit sales and Biodiversity Net Gain (BNG) units; working with large infrastructure operators across rail, water, energy and highways to jointly shape the scheme around their own resilience needs, capturing the value that catchment-scale risk reduction offers assets that would otherwise be exposed to flooding; and wider mechanisms targeted at businesses and communities in the local economy, explored through the Marches Forward Partnership, a cross-border alliance of four councils seeking trailblazer green growth status, including regulatory freedoms and investment zone status. Together these sit alongside blended public and private finance, with the mix still to be confirmed.

Impact / outcome: More than 140 natural flood management measures installed; designed to protect 3,000+ homes and businesses and support up to GBP 5bn of wider economic impact.

Next steps: The priority now is turning these routes into firm commitments: resolving free-rider risk among beneficiaries, securing insurer participation and confirming which mechanisms and investors will anchor the model. Lessons from this process are intended to inform how similar catchments could be financed elsewhere. The playbook identifies two connected areas where innovation is required.

Making the national security and productivity case: the economic arguments most often cited are insured loss avoidance and property value protection, while others - supply chain protection, fiscal revenue stabilization and maintaining labor productivity - are less quantified in ways that reach central governments and treasury departments, and developing that evidence base would unlock a scale of co-investment currently absent from most coalitions, requiring greater ownership and advocacy from local government actors. Governance frameworks for transboundary coalitions: the hardest design question is how costs, benefits and decision rights are shared across jurisdictions, and the river basin and coastal coalition examples have each had to solve this from scratch - there is an opportunity to develop replicable collaboration templates, drawing on water law, watershed management and municipal finance precedents, to make the structure more straightforward for capital markets and insurers who might want to participate.

Organizations involved Authoring: Marsh Actors: Environment Agency; Shropshire Council; Powys County Council; Oliver Wyman; Marches Forward Partnership Implementation partners Regulators & Policymakers; Local Governments; Investors & Banks; Insurers; Civil Society Organizations; Property value chain stakeholders