Bridging field surveys and expert consensus: a delphi approach to developing site-specific KPIs for estuary restoration

Measuring the success of a nature conservation project, especially one involving multiple habitats and species, requires selecting effective Key Performance Indicators (KPIs). This study is part of the EU REST-COAST estuary restoration initiative, which includes nine pilot projects aimed at developing a precise, repeatable methodology for large-scale coastal restoration. In Israel, the Dalia Stream, a degraded estuarine system on the Mediterranean coast, was chosen as a pilot site for ecological restoration actions focused on two aquatic nature reserves located within the site. The aim is to rehabilitate these reserves, which have been affected by commercial fisheries, and to restore their ecological and hydrological connectivity to the sea. To evaluate project success, we used the Delphi method, a structured expert-consensus approach that integrated field survey data with professional insights to develop actionable KPIs. The process produced ten KPIs aligned with the project's ecological goals. Uniquely, the same experts who conducted field surveys also participated in the Delphi rounds, ensuring strong continuity between empirical data and expert judgment. This design enabled rapid consensus, whereas previous unstructured discussions had failed to achieve it. We recommend adopting this integrated field–Delphi approach in similar initiatives to improve transparency, comparability, and efficiency in evaluating ecological success.