Establishing a strategic blueprint for the design and evaluation of flood control infrastructure in extensive watersheds

Triggered by the need for developing a comprehensive flood protection strategy (referred to as the Master Plan) for Western Thessaly in Central Greece, we demonstrate a strategic approach for large-scale hydrosystems, where the need for design accuracy is contrasted to extreme computational burden. The area of interest occupies approximately 6,400 km2, thus constituting a mega-scale hydrological, hydraulic and water management system, which poses multiple conceptual and computational challenges. The overall question is to provide a synthesis of flood protection solutions and prioritize them under a multipurpose prism. The core methodological framework comprises two axes: (i) a semi-distributed representation of the rainfall-runoff transformations and flood routing processes across the entire study area, and (ii) a coupled 1D/2D hydrodynamic simulation, targeted only over the flood prone riverine system and the highly complex network of main artificial channels. Key results show reductions in flood extents by up to 15% in high-risk areas and significant attenuation of peak flows (averaging to 56% across all dam sites). The final planning prioritizes the strengthening of flood protection through the combined influence of a set of large-scale projects, i.e., dikes, multi-purpose dams and retention basins of controlled inundation. The cornerstone objective is to sketch a framework for facing similar studies in a holistic manner, while maintaining a high level of computational efficiency and explainability.