Participatory multi-criteria decision making for optimal siting of dams

The impacts of increasing water scarcity as a consequence of climate change determine an urgent demandfor enhanced management of water resources. The construction of new artificial reservoirs to expandwater storage capacity represents a pivotal strategy to address these pressing concerns and fulfil thecommunity's needs for drinking water, irrigation, energy generation, and flood risk mitigation. Theselection of sites for new reservoirs can be merely based on topographic and hydrologic assessments.However, the identification of optimal locations requires a comprehensive evaluation that considers amultitude of often-competing factors that encompass bio-physical, socio-economic, regulatory, andenvironmental aspects. The involvement of communities and citizens in the initial stages of the decision-making process is crucial. This study introduces a methodology based on multi-criteria decision making(MCDM), to identify optimal reservoir locations, simultaneously addressing all the aforementioned aspectsthrough community engagement. This methodology employs an automated algorithm to analyse a largepool of potential sites, through a Digital Elevation Model (DEM) integrated with hydrologic simulations. Foreach site the algorithm optimizes the location and orientation of the dam and calculate the geometricalcharacteristics, such as the dam length, dam volume and the water storage volume. In a subsequent step, aMCDM analysis is conducted to rank the sites based on quantitative selection criteria established through acomprehensive territorial analysis and hydrological modelling. These criteria include geometric andmorphological aspects (e.g., reservoir volume), hydrological indicators (e.g., water balance, floodmitigation), anthropization (e.g., population density, infrastructures), landscape, archaeological heritage,ecology, environmental components, and potential natural hazards. To foster community engagement, wedeveloped a web-based survey platform that enables the collection of diverse perspectives from variousstakeholders, communities and citizens, allowing them to express their opinions on the relative importanceof each individual criterion. The application of this methodology is demonstrated through a case study inthe Arno river basin, Italy, showcasing its effectiveness in identifying the most suitable reservoir locationswhile targeting the highest environmental preservation and community well-being.