Participatory analysis identifies six economically viable coastal nourishment scenarios for erosion-prone Ovar coastline, balancing physical protection and economic returns.

The study area encompasses a dynamic and fragile 16.5 kilometre sandy open coast on Portugal's north-west shelf. The wave climate is highly energetic with average significant wave heights of 2-3 metres, increasing to over 8 metres during storms originating from the North Atlantic between October and March. Littoral drift moves approximately 1.1 million cubic metres annually from north to south. Current erosion rates average 1.2 metres per year by 2050 and 1.8 metres per year by 2100 under projected sea level rise conditions. The coastline includes urbanised settlements at Esmoriz, Cortegaça/ Maceda, and Furadouro, requiring protection of inhabited areas while considering opportunities for ecological restoration and relocation where appropriate.

To develop and evaluate climate change adaptation pathways for the Ovar coastline through integrated physical and economic analysis, supporting evidence-based decision-making for coastal management that balances erosion mitigation, economic viability, stakeholder preferences, and ecosystem service values over an 80-year time horizon.

• Unit cost for artificial sand nourishment set at €2.5 per cubic metre covering dredging, transport, and deposition operations based on Portuguese west coast studies. 
• Coastal structure construction costs assumed at €10,000 per metre with demolition costs at 25% of construction value. 
• Annual maintenance and overtopping damages initially estimated at one million euros with 15% annual increase. 
• Discount rate of 3% applied to all economic values. Scenarios tested ranged from 16 million euros (C3.2) to 222.5 million euros in total sediment volumes. 
• Economic viability was achieved in six scenarios over the 80-year period, with break-even years ranging from 2051 to 2077 depending on scenario design.

• Artificial nourishment interventions reduce shoreline retreat rates, prevent territorial losses, and avoid overtopping-related costs. 
• Under the most effective combined scenario (C4.2), up to 190 hectares of territory loss can be avoided by 2100 compared to baseline, with overtopping costs reduced by 153 million euros. 
• Medium-viability scenarios achieve 30-46% reductions in territorial loss and 64-132 million euros in avoided overtopping costs. 
• Benefits include maintained beach width supporting recreational uses, reduced coastal structure maintenance requirements, and preserved ecosystem services valued through meta-analytic function transfer including cultural, regulating, and provisioning services.

Three sequential participatory workshops engaged stakeholders: first workshop selected top ten coastal erosion mitigation measures and validated impacts; second workshop developed shared territorial visions including protection of occupied areas and relocation of at-risk communities; third workshop created comprehensive adaptation pathways mapping. The LTC numerical model simulated shoreline evolution using bathymetry, wave climate data, and sea level rise projections (1.125 cm/year). The COAST tool performed lifecycle cost-benefit analysis calculating net present value, benefit-cost ratios, and break-even years for each scenario. Meta-analytic function transfer estimated local ecosystem service values using global ESV functions calibrated to Portuguese socioeconomic conditions under Shared Socioeconomic Pathways SSP3 and SSP5 scenarios.

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Coastal nourishment scenarios for erosion-prone Ovar coastline

The Ovar Municipality coastal stretch on Portugal's western coast is one of the country's most erosion-prone and vulnerable areas, with historical erosion rates reaching 6 metres per year over the past 50 years. The INCCA research project developed a comprehensive approach to evaluate climate change adaptation pathways for this 16.5 kilometre sandy coastline between Esmoriz and Torraão do Lameiro, integrating participatory stakeholder processes with physical modelling and economic analysis.

Sixteen coastal defence structures, including six groins and seven longitudinal revetments, currently protect the shoreline but require ongoing maintenance. Under a business-as-usual baseline scenario with no additional interventions, the shoreline is projected to retreat approximately 290 metres by 2050 and 500 metres by 2100, corresponding to territorial losses of 60 hectares and 248 hectares respectively. Economic losses from this baseline scenario are anticipated to exceed 150 million euros by the end of the century.

Twelve adaptation pathway scenarios were developed through three participatory workshops involving local stakeholders, then evaluated using the LTC numerical shoreline evolution model and the COAST cost-benefit analysis tool. Scenarios tested various combinations of artificial sand nourishment (adding 1-3 million cubic metres of sediment), structural modifications including groin removal and T-groin implementation, and differing frequencies of nourishment intervention from annual to every five years.

The analysis revealed that while scenarios with larger sediment volumes delivered better physical performance in terms of reducing territorial loss, they did not necessarily achieve the best economic outcomes. Six of twelve scenarios achieved economic viability over the 80-year analysis period, demonstrating that optimal solutions depend on balancing design parameters, land use values, and ecosystem service considerations.