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 demand
for enhanced management of water resources. The construction of new artificial reservoirs to expand
water storage capacity represents a pivotal strategy to address these pressing concerns and fulfil the
community's needs for drinking water, irrigation, energy generation, and flood risk mitigation. The
selection 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 a
multitude of often-competing factors that encompass bio-physical, socio-economic, regulatory, and
environmental 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 aspects
through community engagement. This methodology employs an automated algorithm to analyse a large
pool of potential sites, through a Digital Elevation Model (DEM) integrated with hydrologic simulations. For
each site the algorithm optimizes the location and orientation of the dam and calculate the geometrical
characteristics, such as the dam length, dam volume and the water storage volume. In a subsequent step, a
MCDM analysis is conducted to rank the sites based on quantitative selection criteria established through a
comprehensive territorial analysis and hydrological modelling. These criteria include geometric and
morphological aspects (e.g., reservoir volume), hydrological indicators (e.g., water balance, flood
mitigation), anthropization (e.g., population density, infrastructures), landscape, archaeological heritage,
ecology, environmental components, and potential natural hazards. To foster community engagement, we
developed a web-based survey platform that enables the collection of diverse perspectives from various
stakeholders, communities and citizens, allowing them to express their opinions on the relative importance
of each individual criterion. The application of this methodology is demonstrated through a case study in
the Arno river basin, Italy, showcasing its effectiveness in identifying the most suitable reservoir locations
while targeting the highest environmental preservation and community well-being.